ABRASION - The wearing away of a surface by rubbing, as with sandpaper on wood.

ABRASION RESISTANCE - The ability of a material to resist surface wear.

ABRASIVE EROSION - Erosive wear caused by the relative motion of solid particles which are entrained in a fluid, moving nearly parallel to a solid surface.

ABSOLUTE HUMIDITY - Amount of moisture in the air, indicated in kg/kg of dry air.

ABSOLUTE PRESSURE - Total pressure measured from an absolute vacuum. It equals the sum of the gauge pressure and the atmospheric pressure corresponding to the barometer.

ABSOLUTE PRESSURE - Air at standard conditions (70°F air at sea level with a barometric pressure of 29.92 in Hg) exerts a pressure of 14.696 psi. This is the pressure in a system when the pressure gauge reads zero. So the absolute pressure of a system is the gauge pressure in pounds per square inch added to the atmospheric pressure of 14.696 psi (use 14.7 psi in environmental system work) and the symbol is "psia".

ABSOLUTE TEMPERATURE SCALE - A scale of temperature measurement in which zero degrees is absolute zero.

ABSOLUTE ZERO - A hypothetical temperature at which there is total absence of heat. Since heat is a result of energy caused by molecular motion, there is no motion of molecules with respect to each other at absolute zero. It is theoretically the coldest possible temperature.

ABSOLUTE ZERO TEMPERATURE - Temperature measured from absolute zero (-459.67°F, or -273.16°C).

ABSORBENT - A material which, due to an affinity for certain substances, extracts one or more such substances from a liquid or gaseous medium with which it contacts and which changes physically or chemically, or both, during the process. Calcium chloride is an example of a solid absorbent, while solutions of lithium chloride, lithium bromide, and ethylene glycols are liquid absorbents.

ABSORBER - That part of the low side of an absorption system, used for absorbing vapor refrigerant.

ABSORPTION - A process whereby a material extracts one or more substances present in an atmosphere or mixture of gases or liquids accompanied by the material's physical and/or chemical changes.

ABSORPTION REFRIGERATION SYSTEM - One in which the refrigerant, as it is absorbed in another liquid, maintains the pressure difference needed for successful operation of the system.

ABSORPTION REFRIGERATOR - Refrigerator that creates low temperatures by using the cooling effect formed when a refrigerant is absorbed by chemical substance.

ABSORPTION SYSTEM - A refrigeration system in which the refrigerant gas evolved in the evaporator is taken up in an absorber and released in a generator upon the application of heat.

ABSORPTION TOWER - A tower or column, which effects contact between a rising gas and a falling liquid, so that part of the gas may be taken up by the liquid.

ACCELERATION - The rate of change of velocity, as a function of time. Expressed in m/s.

ACCELERATION DUE TO GRAVITY - The rate of increase in velocity of a body falling freely in a vacuum. Its value varies with latitude and elevation. The International Standard is 32.174 ft. per second per second.

ACCELERATION PERIOD - In cavitation and liquid impingement erosion, the stage following the incubation period, during which the erosion rate increases from near zero to a maximum value.

ACCELRATION - The time rate of change of velocity; i.e., the derivative of velocity; with respect to time.

ACCEPTABLE WELD - A weld that meets all of the requirements and the acceptance criteria prescribed by the welding specifications.

ACCESSIBLE HERMETIC - An assembly of motor and compressor, inside a single bolted housing unit.

ACCUMULATOR - Storage tank which receives liquid refrigerant from evaporator and prevents it from flowing into suction line before vaporizing.

ACETONE - A filler added to acetylene cylinders, capable of absorbing 25 times its own volume of acetylene.

ACID - Literally hitter, but chemically the state of a water solution containing a high concentration of hydrogen ions.

ACID ATTACK - Caused by an incomplete flushing after an acid cleaning process of boilers or similar equipment.

ACID CLEANING - The process of cleaning the interior surfaces of steam generating units by filling the unit with dilute acid accompanied by an inhibitor to prevent corrosion and by subsequently draining, washing, and neutralizing the acid by a further wash of alkaline water.

ACID CONDITION IN SYSTEM - Condition in which refrigerant or oil in a system, is mixed with vapor and fluids that are acidic in nature.

ACID EMBRITTLEMENT - A form of hydrogen embrittlement that may be induced in some metals by an acid.

ACID GAS - A gas that that forms an acid when mixed with water. In petroleum processing, the most common acid gases are hydrogen sulfide and carbon dioxide.

ACID RAIN - Atmospheric precipitation with an pH below 5.6 to 5.7.

ACID SOAK - A method of acid cleaning, in which the acid is pumped into the boiler and rests there for a period of time.

ACIDIC - The reaction of a substance with water resulting in an increase in concentration of hydrogen ions in solution (see acid).

ACIDIFIED - The addition of an acid (usually nitric or sulfuric) to a sample to lower the pH below 2.0. The purpose of the acidification is to "fix" a sample so it will not change until it is analyzed.

ACIDITY - Represents the amount of free carbon dioxide, mineral acids, and salts (especially sulfates of iron and aluminum) which hydrolyze to give hydrogen ions in the water. The acidity is reported as millie equivalents per liter of acid, or ppm acidity as calcium carbonate, or pH, the measure of hydrogen ion concentration.

ACOUSTIC - A term pertaining to sound, or the science of sound.

ACROSS THE LINE - A method of motor starting, which connects the motor directly to the supply line on starting or running.

ACTION - Refers to the action of a controller. It defines what is done to regulate the final control element to effect control.

ACTIVATED ALUMINA - Chemical which is a form of aluminum oxide. It is used as a drier or desiccant.

ACTIVATED CARBON - Is a specially processed carbon, used as a filter drier. Commonly used to clean air.

ACTIVATED SLUDGE - An aerobic biological process for conversion of soluble organic matter to solid biomass, removable by gravity or filtration.

ACTIVE STORAGE PILE - A method of stockpiling coal, sometimes called live storage. The pile is located outside the plant but adjacent to it, and usually contains four or five days of operating supply. The pile is not compacted, as it is not stored long enough to be exposed to the hazard of spontaneous combustion.

ACTUATOR - The portion of a regulating valve, which converts mechanical, fluid, thermal, or electrical energy; into mechanical motion to open or close the valve seats or other such devices.

ADIABATIC - Occurring with no addition or loss of heat from the system under consideration.

ADIABATIC CHANGE - A change in the volume, pressure, or temperature of a gas, occurring without a gain of heat or loss of heat.

ADIABATIC COMPRESSION - Compressing a gas without removing or adding heat.

ADIABATIC COOLING - A method in which paramagnetic salts are pre-cooled, and then demagnetized, thereby producing further cooling.

ADIABATIC EFFICIENCY -The ratio of actual work output of a heat engine to the ideal output.

ADIABATIC EXPANSION - The expansion of a gas, vapor, or liquid stream from a higher pressure to a lower pressure, with no change in enthalpy.

ADIABATIC PROCESS - A thermo-dynamic process in which no heat is extracted from or added to the system of the process.

ADIABATIC SATURATION PROCESS - A process to determine absolute or relative humidity.

ADJUSTABLE DIFFERENTIAL - A means of changing the difference between the control cut-in and cutout points.

ADJUSTABLE RESISTOR - A resistor whose value can be mechanically changed, usually by the use of a sliding contact.

ADSORBENT - A material which has the ability to cause molecules of gases, liquids or solids to adhere to its internal surfaces without changing the adsorbent physically or chemically. In water treatment, a synthetic resin possessing the ability to attract and to hold charged particles.

ADSORPTION - The adhesion of the molecules of gases, dissolved substances, or liquids in more or less concentrated form, to the surface of solids or liquids with which they are in contact. Commercial adsorbent materials have enormous internal surfaces.

ADSORPTION INHIBITORS - They are materials which caused them to be adsorbed on to the metal surface due to their polar properties.

ADVECTION - The transfer of heat by horizontal movement of air.

AERATION - Exposing to the action of air, like blowing air through water before discharging to a river.

AEROBIC - A condition in which "free" or dissolved oxygen is present in water.

AERODYNAMIC NOISE - Also called generated noise, self-generated noise; is noise of aerodynamic origin in a moving fluid arising from flow instabilities. In duct systems, aerodynamic noise is caused by airflow through elbows, dampers, branch wyes, pressure reduction devices, silencers and other duct components.

AGGLOMERATE - The clustering together of a few or many particles into a larger solid mass.

AGITATOR - A device used to cause motion in confined fluids.

AIR - A substance containing by volume approximately 78 - 79% nitrogen; 20.95% oxygen, .94% argon, traces of carbon dioxide, helium, etc.

AIR BLAST TRANSFORMER - A transformer cooled by forcing a circulation of air around its windings.

AIR CAPACITOR - Is a capacitor, which uses air as the dielectric between the plates.

AIR CHANGES - A method of expressing the amount of air leakage into or out of a building or room in terms of the number of building volumes or room volumes exchanged.

AIR CLEANER - A devise used to remove air borne impurities.

AIR COIL - Coil on some types of heat pumps used either as an evaporator or a condenser.

AIR CONDITIONER - They are basically refrigeration devices cooling air and rooms rather then food compartments.

AIR CONDITIONER, UNITARY - An evaporator, compressor, and condenser combination; designed in one or more assemblies, the separate parts designed to be assembled together.

AIR CONDITIONING -The process of treating air to simultaneously control its temperature, humidity, cleanliness, and distribution to meet the requirements of the conditioned space.

AIR CONDITIONING UNIT - An assembly of equipment for the treatment of air so as to control, simultaneously, its temperature, humidity, cleanliness and distribution to meet the requirements of a conditioned space.

AIR CONDITIONING, COMFORT - The process of treating air so as to control simultaneously its temperature, humidity, cleanliness and distribution to meet the comfort requirements of the occupants of the conditioned space.

AIR COOLER - A factory-encased assembly of elements whereby the temperature of air passing through the device is reduced.

AIR DIFFUSER - A circular, square, or rectangular air distribution outlet, generally located in the ceiling and comprised of deflecting members discharging supply air in various directions and planes, and arranged to promote mixing of primary air with secondary room air.

AIR DIFFUSION AERATORS - They are aerators into which air is pumped into the water through perforated pipes, plates, or any other method.

AIR DUCT - A tube or conduit for conveying air from one place to another.

AIR FLOTATION - A process of accelerating sedimentation, by introducing air into the water, this lowers the density of the water, and increases the differences in the densities of the water and the suspended particles. (DAF), Dissolved Air Flotation.

AIR GAP -The space between magnetic poles, or between the rotating and stationary assemblies in a motor or generator.

AIR HANDLER - The fan blower, heat transfer coil, filter, and housing parts, of a system.

AIR INFILTRATION – The leakage of air into a room through cracks in doors, windows, and other openings.

AIR PURGE - The removal of undesired matter by replacement with air.

AIR SATURATED - Moist air in which the partial pressure of the water vapor is equal to the vapor pressure of water at the existing temperature. This occurs when dry air and saturated water vapor coexist at the same dry-bulb temperature.

AIR SENSING THERMOSTAT - A thermostat unit, in which the sensing element is located in the refrigerated space.

AIR STANDARD - Air having a temperature of (20°C), a relative humidity of 36 percent, and under a pressure of 14.70 PSIA. The gas industry usually considers (16°C) as the temperature of standard air.

AIR VENT - Valve, either manual or automatic, to remove air from the highest point of a coil or piping assembly.

AIR WASHER - A water spray system or device for cleaning, humidifying, or dehumidifying the air.

AIR, AMBIENT - Generally the air surrounding the object.

AIR, DRY - Air without contained water vapor.

AIR, OUTDOOR - Air taken from outdoors and, therefore, not previously circulated through the system.

AIR, RECIRCULATED - Return air passed through the conditioner before being again supplied to the conditioned space.

AIR, REHEATING - In an air conditioning system, the final step in treatment, in the event the temperature is too low.

AIR, RETURN - Air returned from conditioned or refrigerated space.

AIRBORNE SOUND - Sound which reaches the point of interest by radiation through the air.

AIR-COOLED CONDENSER - Heat of compression is transferred from condensing coils to surrounding air. This may be done either by convection or by a fan or blower.

AIR-SENSING THERMOSTAT – A thermostat unit, in which the sensing element is located in the refrigerated space.

ALCOHOL BRINE - A water and alcohol solution, which remains as a liquid below 0°C.

ALGAE - A minute fresh water plant growth which forms a scum on the surfaces of recirculated water apparatus, interfering with fluid flow and heat transfer. Lower form of plant life, usually green and blue green algae appear in cooling water systems. They are responsible for copious amounts of stringy green slime masses.

ALIVE - A term referring to a circuit in which a current is flowing. Also referred to as live.

ALKALI - A substance having marked basic properties. Applying to hydroxides of potassium, sodium, lithium, and ammonium. They turn red litmus to blue. Includes hydroxides of the alkaline earth metals of barium, strontium, and calcium.

ALKALINE - Having a pH greater than 7.

ALKALINE BOIL-OUT - Employed to remove oil and grease deposits from heating surfaces.

ALKALINITY - An expression of the total basic anions (hydroxyl groups) present in a solution. It also represents, particularly in water analysis, the bi-carbonate, carbonate, and occasionally, the borate, silicate, and phosphate salts which will react with water to produce the hydroxyl groups.

ALLEN TYPE SCREW - A screw with a recessed hex shaped head.

ALLOY - A substance having metal properties and being composed of two or more chemical elements of which at least one is a metal.

ALLOY STEEL - Steel containing specific quantities of alloying elements (other than carbon)and commonly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus).

ALTERNATING CURRENT (AC) - Electric current in which the direction of the current alternates or reverses. In a 60 Hertz (cycle) current, the direction of current flow reverses in 1/120th of a second; most commonly used current.

ALTERNATOR - A device which converts mechanical energy, into alternating current.

ALTIMETER - An instrument used to measure the height above a reference point, such as ground or sea level.

ALUM - Is an aluminum sulfate or filter alum. Acts in the range of 5.0 to 8.0 pH.

ALUMINA - Aluminum oxide occasionally found as an impurity in water in very small amounts.

AMBIENT AIR TEMPERATURE - Temperature of fluid (usually air) which surrounds object on all sides.

AMBIENT CONDITIONS - The conditions of temperature, pressure, and humidity, existing around an instrument.

AMBIENT NOISE -The normal sound in a room or other location.

AMERICAN STANDARD PIPE THREAD - A type of screw or thread, commonly used on pipe fittings to assure a tight seal.

AMERICAN WIRE GAUGE (AWG) - A system used in the United States for measuring the size of solid wires.

AMINE - A chemical use in water treatment as a filming or neutralizing agent to protect the metal parts.

AMMETER - An instrument for measuring the magnitude of electric current flow.

AMMETER SHUNT - A low-resistance conductor, placed in parallel (shunt) with an ammeter movement, so that most of the current flows through the shunt, and only a small portion flows through the ammeter. This extends the useful range of the meter.

AMMONIA - Chemical combination of nitrogen and hydrogen (NH₃). Ammonia is a very efficient refrigerant and identified as R-117.

AMORPHOUS - A solid not having a repetitive three-dimensional pattern of atoms.

AMPACITY - A wire's ability to carry current safely, without undue heating. The term formerly used to describe this characteristic was current capacity of the wire.

AMPERAGE - An electron or current flow of one coulomb per second, past a given point in a circuit.

AMPERE - The unit used for measuring the quantity of an electrical current flow. One ampere represent a flow of one coulomb per second.

AMPERE HOUR - A term used for rating battery capacity. As stated, an ampere for an hour; ex: 5 amperes for 20 hours = 100 amp hour on a 20 hr rating.

AMPERE TURNS - A term used to measure magnetic force. It represents the product of amperes, times the number of turns of the coil, in an electromagnet.

AMPLIFICATION - The process of obtaining an output signal greater than the input signal, through auxiliary power controlled by the input signal. The process of increasing the strength, current, power, or voltage, of the signal.

AMPLITUDE - The maximum instantaneous value of alternating current or voltage. It can be in either a positive or negative direction. The greatest distance through which an oscillating body moves from the mid point.

ANAEROBIC - A condition in which "free" or dissolved oxygen is not present in the water.

ANALYSIS - The process of determining the composition of a substance, by chemical or physical methods.

ANEMOMETER - An instrument for measuring the velocity of a fluid.

ANGLE OF LAG OR LEAD - The phase angle difference, between two sinusoidal wave forms having the same frequency.

ANGLE VALVE - A type of globe valve design, having pipe openings at right angles to each other. Usually one opening on the horizontal plane and one on the vertical plane.

ANGSTROM UNITS - A unit of wave length, equal in length to one ten billionth.

ANHYDROUS CALCIUM SULFATE - A dry chemical, made of calcium, sulfur, and oxygen.

ANION - A negatively charged ion such as the chloride ion (Cl^-).

ANION INTERCHANGE - The displacement of one negatively charged particle by another on an anion-exchange material. This principle is used with water treatment.

ANNEAL - To soften by heating and allowing to cool slowly.

ANNEALING - A process of heat treating metal, to get the desired properties of softness and ductility, (easy to form).

ANODE - In electrolysis or electrochemical corrosion, a site where metal goes into solution as a cation leaving behind an equivalent of electrons to be transferred to the opposite electron, called the cathode.

ANODIZING - The treatment of a metal surface whereby the metal is made anodic.

ANSI - American National Standard Institute, which is an organization defining standards for computer language.

ANSI-B.31.1 - Power Piping.

ANSI-B.31.5 - Refrigeration Piping.

ANTI KNOCK VALUE - A premature explosive combustion, as the detonation of the fuel air mixture in an internal combustion engine, produces a characteristic knock. The Anti Knock Value is the measure of its resistance to the condition which tends to produce this knock.

ANTICIPATING CONTROL - One which, by artificial means, is activated sooner than it would be without such means, to produce a smaller differential of the controlled property. Heat and cool anticipators are commonly used in thermostats.

ANTICIPATORS - A small heater element in two-position temperature controllers which deliberately cause false indications of temperature in the controller in an at tempt to minimize the override of the differential and smooth out the temperature variation in the controlled space.

ANTI-CORROSIVE ADDITIVE - A lubricant additive to reduce corrosion.

ANTI-FOAM ADDITIVE (FOAM INHIBITOR) An additive used to reduce or prevent foaming.

ANTIFOAM AGENTS - The reduction of carry over by the addition of polymerized esters, alcohol’s, and amides. The antifoam agent is absorbed on the steam generating surface resulting in a hydrophobic condition, causing fewer but larger steam bubbles, which readily coalesce. These agents also weaken the wall of the bubble formed, causing them to quickly burst on the water surface.

ANTIFOULANTS - Are materials which prevent fouling from depositing on heat transfer equipment. Materials that prevent deposits forming; include anti- oxidants, metal coordinators, and corrosion inhibitors. Compounds that prevent deposition are surfactants. They act as detergents or dispersants.

ANTIFREEZE - Compounds of glycol’s or alcohol’s, that lower the freezing point of cooling water systems.

ANTIOXIDANT - A substance which when added in small amounts to petroleum products, will delay or inhibit undesirable changes; such as the formation of gum, sludge, and acidity, which are brought about by oxidation.

ANTI-OXIDANT - An additive for the purpose of reducing the rate of oxidation and subsequent deterioration of the material.

ANTI-SCUFFING LUBRICANT - A lubricant that is formulated to avoid scuffing.

ANTI-SEIZURE PROPERTY - The ability of the bearing material to resist seizure during momentary lubrication failure.

ANTI-WEAR ADDITIVE - A lubricant additive to reduce wear.

API - American Petroleum Institute.

API GRAVITY (API DEGREE) - A measure of density used in the US petroleum industry.

APPARENT (EMF) - The apparent voltage, as measured by the drop in pressure due to a current flowing through a resistance.

APPARENT WATTS - The product of volts times amperes, in an alternating current circuit.

AQUEOUS - Watery. A substance containing water.

AQUIFER - A porous, subsurface geological structure carrying or holding water.

ARC - A flash, caused by an electric current ionizing a gas or vapor.

ARC BRAZING - A brazing process in which the heat required is obtained from an electric arc.

ARC FURNACE - An electric furnace, in which heat is produced by an arc between two electrodes.

ARC WELDING - A group of welding processes which produce coalescence of metals by heating them with an arc, with or without the application of pressure, and with or without the use of a filler metal.

ARC WELDING - A process where coalescence is obtained by heating with an electric arc.

ARCHIMIDES PRINCIPAL - States that an upward force acting on a body wholly or partly submerged in a fluid, is equal to the weight of the fluid displaced, and acts through the center of gravity of the fluid displaced, or the center of buoyancy.

ARMATURE - the rotating part of an electric motor or generator. The moving part of a relay or vibrator.

ARMATURE AIR GAP - The air space between the stationary and rotating parts of a motor or generator, through which magnetic lines of force pass.

ARMATURE BACK AMPERE TURNS - The magnetic field produced by current flowing in the armature winding, that opposes and reduces the number of magnetic lines of force, produced by the field magnets of a motor or generator.

ARMATURE BAR - Copper bars used in place of wire windings, in large armatures, generators, or motors.

ARMATURE CIRCUIT - The path that the current takes, in flowing through the windings from one brush to another.

ARMATURE COIL - The loop or coil of copper wire, placed on the armature core, and forming part of the winding.

ARMATURE CORE -The laminated iron part of the armature, formed from thin sheets or disks of steel, on which the windings are placed.

ARMATURE CURRENT - The current flowing from the armature of a generator, to the armature of a motor. Not including the current taken by the shunt field.

ARMATURE DEMAGNETIZATION - The reduction in the effective magnetic lines of force, produced by the armature current.

ARMATURE REACTION - The effect, that the magnetic field produced by the current flowing in the armature, has on the magnetic field produced by the field coils.

ARMATURE REGULATING RESISTORS - Are resistors, designed to regulate the speed or torque of a loaded motor, by placing a resistance in the armature or power circuit.

ARMATURE RESISTANCE - The resistance of the wire used in the windings of the armature, measured between the rings or brushes, or from positive to negative terminals.

ARMATURE SLOT -The groove or slot in the armature core, into which the coils or windings are placed.

ARMATURE TESTER - Any device used for locating faults or defects in the armature winding.

ARMATURE VARNISH - Is a liquid put on the field and armature windings, to improve the insulation of the cotton covering on the wires.

ARMATURE WINDING - All of the copper wire placed on the armature, and through which the current flows.

AROMATICS - A group of hydrocarbons of which benzene is the parent. They are called "aromatics" because many of their derivatives have sweet or aromatic odorous.

ARTIFICIAL MAGNET - Is a manufactured magnet, which is distinguished from a natural occurring magnet.

ASHRAE - The American Society of Heating, Refrigeration, and Air Conditioning Engineers.

ASME - American Society of Mechanical Engineers.

ASME APPENDIX SECTION I - Explains matter which is mandatory, unless specifically referred to in the rules of the code, including formulas.

ASME BOILER CODE - The boiler code listing standards, specified by the American Society of Mechanical Engineers, for the construction of boilers.

ASME PART PEB SECTION I - Requirements for electric boilers.

ASME PART PFH SECTION I - Requirements for feedwater heaters.

ASME PART PFT SECTION I - Requirements for firetube boilers.

ASME PART PG SECTION I - General requirements for all methods of construction.

ASME PART PMB SECTION I - Requirements for miniature boilers.

ASME PART PVG SECTION I - Requirements for organic fluid vaporizer generators.

ASME PART PW SECTION I - Requirements for boilers fabricated by welding.

ASME PART PWT SECTION I - Requirements for watertube boilers.

ASME SECTION I - Power Boilers.

ASME SECTION II - Material specifications.

ASME SECTION III - Nuclear Power Plant Components.

ASME SECTION IV - Heating boilers.ASME SECTION IX ASME SECTION V - Nondestructive examination.

ASME SECTION VI - Recommended rules for the care and operation of heating boilers.

ASME SECTION VII - Recommended rules for the care and operation of power boilers.

ASME SECTION VII APPENDIX - Consists of conversion factors for converting Imperial units to SI Units.

ASME SECTION VII SUBSECTION C1 - Rules for routine operation of power boilers.

ASME SECTION VII SUBSECTION C2 - Operating and maintaining boiler appliances.

ASME SECTION VII SUBSECTION C3 - Rules for inspection.

ASME SECTION VII SUBSECTION C4 - Prevention of direct causes of boiler failure.

ASME SECTION VII SUBSECTION C5 - Is partial rules for the design of installations.

ASME SECTION VII SUBSECTION C6 - Operation of boiler auxiliaries.

ASME SECTION VII SUBSECTION C7 - Control of internal chemical conditions.

ASME SECTION VIII - Pressure vessels.

ASME SECTION X - Fiberglass reinforced plastic pressure vessels.

ASME SECTION XI - Rules for inservice inspection of Nuclear Power Plant components.

ASPECT RATIO - The ratio of the length to the width, of a rectangular air grille or duct.

ASPIRATING PSYCHROMETER - A device which draws sample of air through it to measure humidity.

ASPIRATION - Production of movement in a fluid by suction created by fluid velocity.

ASTM - American Society for Testing and Materials.

ASYNCHRONOUS - Not having the same frequency. Out of step, or phase.

ASYNCHRONOUS GENERATOR - An induction generator.

ASYNCHRONOUS MOTOR - An induction motor, whose speed is not synchronous with the frequency of the supply line.

ATMOSPHERE - Is the mixture of gases and water vapor surrounding the earth.

ATMOSPHERIC ELECTRICITY - Is static electricity, produced between cloud fronts in the atmosphere.

ATMOSPHERIC PRESSURE - Pressure exerted by the weight of the atmosphere; standard atmospheric pressure is 101.325 kPa or 1.01325 bars or 14.696 psia or 29.921 inches of mercury at sea level.

ATOM - The smallest complete particle of an element, which can be obtained, yet which retains all physical and chemical properties of the element.

ATOMIC NUMBER - The number of protons found in the nucleus of an atom, of an element.

ATOMIC WEIGHT - The weight of an elementary atom, in relation to the weight of an atom of hydrogen. A hydrogen atom being taken as 1.00g.

ATOMIZE - Process of changing a liquid to minute particles or a fine spray.

ATTEMPERATING WATER IMPURITY - Refers to turbine deposits caused by impurities in the water used for attemperators. (Chemicals used with attemperating water should be of the volatile type).

ATTEMPERATOR - An apparatus for reducing and controlling the temperature of a superheater vapor or a fluid.

ATTENUATION - The sound reduction process in which sound energy is absorbed or diminished in intensity as the result of energy conversion from sound to motion or heat.

ATTRITION - The rubbing of one particle against another in a resin bed; frictional wear that will affect the site of resin particles.

AUTOMATIC - Self-acting. Operating by its own mechanism, when activated by some triggering signal.

AUTOMATIC CONTROL - The process of using the differences, between the actual value, and desired value, of any variable, to take corrective action, without human intervention.

AUTOMATIC CONTROLLER - A device that measures the value of a measured variable, and operates to correct or limit the deviation from a selected reference. Both measuring and control applications.

AUTOMATIC DEFROST - System of removing ice and frost from evaporators automatically.

AUTOMATIC EXPANSION VALVE (AEV) - A type of metering device that senses low-side pressure and modulates in order to maintain low-side pressure constant.

AUTOMATIC EXTRACTION UNIT TURBINE - Bleeds off part of the main steam flow at one, two, or three points. Valved partitions between selected stages control the extracted steam pressure at the desired level. When extracted steam flowing through the unit does not produce enough shaft power to meet the demand, more steam flows through the turbine to exhaust. Located between steam supply and process steam headers.

AUTOMATIC FROST CONTROL - Control which automatically cycles refrigerating system to remove frost formation on evaporator.

AUTOMATIC GOVERNING SYSTEM - A system which correlates steam flow, pressure, shaft speed, and shaft output, for any one turbine unit.

AUTOMATIC ICE CUBE MAKER - Refrigerating mechanism designed to automatically produce ice cubes in quantity.

AUTOMATIC RESET (INTEGRATION) - Is a type of control, in which the controller output, changes at a rate proportional to the deviation or error. The output will continue to change as long as any deviation or error exists.

AUTOMATIC STARTER -

AUTOMATION - The employment of devices, which automatically control one or more functions.

AUTOTRANSFORMER - A transformer in which both primary and secondary coils, have turns in common. The step up or step down of voltage, is accomplished by taps in common windings.

AUXILIARY CONTACTS - A set of contacts that perform a secondary function, usually in relation to the operation of a set of primary contacts.

AVAGADRO'S HYPOTHESIS - States that equal volumes of different gases, at the same temperature and pressure, will contain equal numbers of molecules.

AVAGADRO'S NUMBER (N) - The number of elementary units such as atoms, formula units, molecules, or ions, that constitute one mole of the said particle.

AVERAGING ELEMENT - A thermostat sensing element which will respond to the average duct temperature.

AXIAL FLOW COMPRESSOR - Uses rotor blades shaped like airfoils, to bite into the air, speed it up, and push it into the subsequent stationary blade passages. These passages are shaped to form diffusers, that slow up the incoming air, and make it pressurize itself by catching up with the air ahead of it.

AZEOTROPE - Having constant maximum and minimum boiling points.

AZEOTROPIC MIXTURE - Example of azeotropic mixture - refrigerant R-502 is mixture consisting of 48.8 percent refrigerant R-22 and 51.2% R-115. The refrigerants do not combine chemically, yet azeotropic mixture provides refrigerant characteristics desired.

BACK PRESSURE - Pressure in low side of refrigerating system; also called suction pressure or low-side pressure.

BACK SEATING - Fluid opening/closing such as a gauge opening or to seal the joint where the valve stem goes through the valve body.

BACK WORK RATIO - Is the fraction of the gas turbine work used to drive the compressor.

BACKGROUND NOISE - Sound other than the wanted signal. In room acoustics, the irreducible noise level measured in the absence of any building occupants.

BACKING RING - Backing in a form of a ring, generally used in welding of piping.

BACKWASH - The counter-current flow of water through a resin bed (that is, in at the bottom of the exchange unit, out at the top) to clean and regenerate the bed after exhaustion (water treatment). Also, the process whereby a filtering mechanism is cleaned by reversing the flow through the filter.

BACTERIA - Microscopic unicellular living organisms.

BAFFLE - Plate or vane used to direct or control movement of fluid or air within confined area.

BAGHOUSE - A chamber containing bags for filtering solids out of gases.

BALLAST GAS - Are the nonflammable portion of the gas, such as carbon dioxide.

BAROMETER - Instrument for measuring atmospheric pressure. It may be calibrated in pounds per square inch, in inches of mercury in a column in millimeters or kPa.

BASE - An alkaline substance.

BASE METAL - The metal present in the largest proportion in an alloy. (Copper is the base metal in brass)

BASE METAL - The substrate metal that is coated or protected by a surface coating.

BASICITY - The ability of a substance to boost the pH after neutralizing all the acid species.

BATCH OPERATION - The utilization of ion-exchange resins to treat a solution in a container wherein the removal of ions is accomplished by agitation of the solution and subsequent decanting of the treated liquid.

BAUDELOT COOLER - Heat exchanger in which water flows by gravity over the outside of the tubes or plates.

BEARING, AIR - A bearing using air as a lubricant.

BEARING, ALIGNING - A bearing with an external spherical seat surface that provides a compensation for shaft or housing deflection or misalignment.

BEARING, ANNULAR - Usually a rolling bearing of short cylindrical form supporting a shaft carrying a radial load.

BEARING, ANTI-FRICTION - A bearing containing a solid lubricant.

BEARING, BABBIT - A bearing metal of non-ferrous material, containing several tin-based alloys, mainly copper, antimony, tin and lead.

BEARING, BALL - A rolling element bearing in which the rolling elements are spherical.

BEARING, BIG END - A bearing at the larger (crankshaft) end of a connecting rod in an engine.

BEARING, BIMETAL - A bearing consisting of two layers.

BEARING, BUSH - A plain bearing in which the lining is closely fitted into the housing in the form of a bush, usually surfaced with a bearing alloy.

BEARING, CIRCULAR STEP - A flat circular hydrostatic bearing with a central circular recess.

BEARING, FIXED PAD - An axial or radial load bearing equipped with fixed pads, the surface of which a are contoured to promote hydrodynamic lubrication.

BEARING, FLOATING - A bearing designed or mounted to permit axial displacement between shaft and housing.

BEARING, FLOATING RING - A type of journal bearing that includes a thin ring between the journal and the bearing. The ring floats and rotates at a fraction of the journal rotational speed.

BEARING, FULL JOURNAL - A journal bearing that surrounds the journal by a full 360°.

BEARING, GAS - A journal or thrust bearing lubricated with gas.

BEARING, HALF JOURNAL - A bearing extending 180° around a journal.

BEARING, JOURNAL - A machine part in which a rotating shaft revolves or slides.

BEARING, MAGNETIC - A type of bearing in which the force that separates the relatively moving surfaces is produced be a magnetic field.

BEARING, MAIN - A bearing supporting the main power-transmitting shaft.

BEARING, NEEDLE - A bearing in which the relatively moving parts are separated by long thin rollers that have a length-to-diameter ratio exceeding 5.0.

BEARING, NONCONTACT - A bearing in which no solid contact occurs between relatively moving surfaces.

BEARING, PEDESTAL - A bearing that is supported on a column or pedestal rather than on the main body of the machine.

BEARING, PIVOT - An axial load bearing, radial-load-type bearing which supports the end of a shaft or pivot.

BEARING, POROUS - Made from porous material, such as compressed metal powders, the pores acting either as reservoirs for holding or passages for supplied lubricant.

BEARING, ROLLER - A bearing in which the relatively moving parts are separated by rollers.

BEARING, RUBBING - A bearing in which the relatively moving parts slide without deliberate lubrication.

BEARING, SELF-ALIGNING - A roller-element bearing with one spherical raceway that automatically provides compensation for shaft or housing deflection or misalignment.

BEARING, SELF-LUBRICATING - A bearing independent of external lubrication. These bearings may be sealed for life after packing with grease or may contain self-lubricating material.

BEARING, SLEEVE - A cylindrical plain bearing used to provide radial location for a shat, which moves axially. Sleeve bearings consist of one or more layers of bearing alloys, bonded to a steel backing.

BEARING, SLIDE - A bearing used or positioning a slide or for axial alignment of a long rotating shaft.

BEARING, STEP - A plane surface bearing that supports the lower end of a vertical shaft.

BEARING, THRUST - A bearing in which the load acts in the direction of the axis of rotation.

BEARING, TILTING PAD - A pad bearing in which the pads are free to take up a position at an angle to the opposing surface according to the hydrodynamic pressure distribution over its surface.

BEARING, TRUNNION - A bearing used as a pivot to swivel or turn an assembly.

BED - A mass of ion-exchange resin particles contained in a column.

BED DEPTH - The height of the resinous material in the column after the ion exchanger has been properly conditioned for effective operation.

BED EXPANSION - The effect produced during backwashing when the resin particles become separated and rise in the column. The expansion of the bed due to the increase in the space between resin particles may be controlled by regulating backwash flow (typical with water treatment).

BELLOWS - Corrugated cylindrical container which moves as pressures change, or provides a seal during movement of parts.

BELLOWS SEAL - A type of mechanical seal that utilizes a bellows for providing secondary sealing.

BENDING MOMENT - The algebraic sum of the couples or the moments of the external forces, or both, to the left or right of any section on a member subjected to bending by couples or transverse forces, or both.

BERNOULLI'S THEOREM - In stream of liquid, the sum of elevation head, pressure head and velocity remains constant along any line of flow provided no work is done by or upon liquid in course of its flow, and decreases in proportion to energy lost in flow.

BICACARBONATE ALKALINITY - The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are produced, and the solution is alkaline.

BICARBONATE - An ion or salt of carbonic acid, containing hydrogen, carbon, and oxygen (HC0₃), such as sodium bicarbonate, NaHC0₃.

BIMETAL STRIP - Temperature regulating or indicating device which works on principle that two dissimilar metals with unequal expansion rates, welded together, will bend as temperatures change.

BIMETALLIC COUPLE - A joint or union of two dissimilar metals.

BIOCIDE - A chemical used to control the population of troublesome microbes.

BLACK LIQUOR - The liquid material remaining from pulpwood cooking in the soda or sulfate papermaking process.

BLADE CLEARANCE (STEAM TURBINE) -

BLADE SEALS -

BLADE VELOCITY -

BLAST FREEZER - Low-temperature evaporator which uses a fan to force air rapidly over the evaporator surface.

BLAST FURNACE GAS - Is the waste product from furnaces used to smelt iron ores.

BLEEDER VALVE - A valve designed to slowly relief a liquid or gas form system.

BLEEDING - Slowly reducing the pressure of liquid or gas from a system or cylinder by slightly opening a valve.

BLEEDOFF - The continuous removal of water from a re-circulating water system.

BLEEDOFF RATE - The rate at which water is continuously removed from a system.

BLOWDOWN - In connection with boilers or cooling towers, the process of discharging a significant portion of the aqueous solution in order to remove accumulated salts, deposits and other impurities.

BOILER - Closed container in which a liquid may be heated and vaporized.

BOILER FEED WATER - The total water fed to a boiler producing steam. This water is the mixture of return steam condensate and makeup water.

BOILER HORSEPOWER - The work required to evaporate 34.5 lb of water per hour into steam from and at 100°C.

BOILER LAY-UP - Storing and protecting the boiler when not in use.

BOILING - (See vaporization)

BOILING OUT - The boiling of high alkaline water in boiler pressure parts for the removal of oil, greases, prior to normal operation or after major repairs.

BOILING POINT - The temperature at which the vapor pressure of a liquid equals the absolute external pressure at the liquid-vapor interface.

BOILING TEMPERATURE - Temperature at which a fluid changes from a liquid to a gas.

BORE - Inside diameter of a cylinder.

BOURDON TUBE - Thin-walled tube of elastic metal flattened and bent into circular shape, which tends to straighten as pressure inside is increased. Used in pressure gauges.

BOYLES' LAW - If the temperature on a gas is constant, the volume is inversely proportional to the pressure. By formula - VP = V₁P₁

BRANCH CIRCUIT - Wiring between the last overcurrent device and the branch circuit outlets.

BRASS - A copper-zinc alloy containing up to 40% zinc and some smaller amounts of other metals.

BRAYTON CYCLE (also referred to as the Joule Cycle) - A rotating machine in which compression and expansion take place. Gas turbine are such an example.

BRAZE - A weld produced by heating an assembly to suitable temperatures and by using a filler metal having a liquidus above 450°C. The filler metal is distributed between the closely fitted facing surface of the joint by capillary action.

BRAZING, BLOCK - A brazing process in which the heat required is obtained from heated blocks applied to the parts to be joined.

BREAKTHROUGH - The first appearance in the solution flowing from an ion-exchange unit of unabsorbed ions similar to those which are depleting the activity of the resin bed. Breakthrough is an indication that regeneration of the resin is necessary.

BRINE - Water saturated with a chemical such as salt.

BRITISH THERMAL UNIT, (BTU) - The Btu is defined as the heat required to raise the temperature of a pound of water from 59° to 60°F.

BRITTLENESS - The tendency of a material to fracture without first undergoing significant plastic deformation.

BRONZE - A copper-rich copper tin alloy with or without small proportions of other elements.

BTU - British Thermal Unit.

BUFFER - A substance used in solution, which accepts hydrogen ions or hydroxyl ions, added to the solution as acids or alkali’s, minimizing a change in pH.

BULB - The name given to the temperature-sensing device located in the fluid for which control or indication is provided. The bulb may be liquid-filled, gas filled, or gas-and-liquid filled. Changes in temperature produce pressure changes within the bulb which are transmitted to the controller.

BULGE - A local distortion or swelling outward caused by internal pressure on a tube wall or boiler shell due to overheating.

BUS BAR - A heavy, rigid metallic conductor which carries a large current and makes a common connection between several circuits. Bus bars are usually uninsulated and located where the electrical service enters a building; that is, in the main distribution cabinet.

BYPASS - A pipe or duct, usually controlled by valve or damper, for conveying a fluid around an element of a system.

BYPASS - Passage at one side of, or around, a regular passage.

BYPASS FEEDER - A closed tank that is installed in a system in "bypass," that is, in a side stream taken off the system and leading back to the system rather than directly in-line.

CALCAREOUS COATING OR DEPOSIT - A layer consisting of a mixture of calcium carbonate and magnesium hydroxide deposited on surfaces being cathodically protected against corrosion, because of increased pH adjustment to the protected surface.

CALCIUM - A scale forming element found in boiler feedwater.

CALCIUM CHLORIDE - A substance used to obtain calcium chloride brine.

CALCIUM SULFATE - Chemical compound (CaSO₄) which is used at a drying agent or desiccant in liquid line dryers.

CALIBRATION - A process of dividing and numbering the scale of an instrument; also of correcting or determining the error of an existing scale, or of evaluating one quantity in terms of readings of another.

CALORIE - It is equal to the amount of heat required to raise the temperature of one gram of water one degree Celsius.

CALORIMETER - Device used to measure quantities of heat or determine specific heats.

CANGE OF STATE - Change from one phase, such as solid, liquid or gas, to another.

CAPACITANCE - The property of an electric current that permits the storage of electrical energy in an electrostatic field and the release of that energy at a later time.

CAPACITOR, (CONDENSER) - A device that can store an electric charge when voltage is applied.

CAPACITY - The adsorption activity possessed in varying degrees by ion-exchange materials. This quality may be expressed as kilograins per cubic foot, gram-milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per milliliter, and so on, where the numerators of these ratios represent the weight of the ions adsorbed and the denominators represent the weight or volume of the adsorbent.

CAPILLARY - The name given to the thin tube attached to the bulb which transmits the bulb pressure changes to the controller or indicator. The cross sectional area of the capillary is extremely small compared to the cross section of the bulb so that the capillary, which is usually outside of the controlled fluid, will introduce the smallest possible error in the signal being transmitted from the bulb.

CAPILLARY TUBE - The capillary tube is a metering device made from a thin tube approximately 0.5 to 6 metre long and from 0.025 to 0.090 inches in diameter which feeds liquid directly to the evaporator. Usually limited to systems of 1 ton or less, it performs all of the functions of the thermal expansion valve when properly sized.

CARBON DIOXIDE - Compound of carbon and oxygen (CO₂) which is sometimes used as a refrigerant. Refrigerant number is R-744.

CARBON FILTER - Air filter using activated carbon as air cleansing agent.

CARBON TETRACHLORIDE - Colorless nonflammable and very toxic liquid used as a solvent. It should never be allowed to touch skin and fumes must not be inhaled.

CARBONACEOUS EXCHANGER - Ion-exchange materials of limited capacity prepared by the sulfonation of coal, lignite, peat, and so on.

CARBONATE - An ion or salt of carbonic acid, containing carbon and oxygen such as calcium carbonate. (CaC03)

CARBONATE HARDNESS - That hardness caused in water by bicarbonates and carbonates of calcium, and magnesium.

CARBONATE-POLYMER TREATMENT - A treatment method using synthetic polymers, generally used with high hardness (60-70) ppm and high alkalinity.

CARBOXYLIC - A term describing a specific acidic group (COOH) that contributes cation-exchange ability to some resins.

CARRYOVER - The moisture and entrained solids forming the film of steam bubbles, as a result of foaming in a boiler. This condition is caused by a faulty boiler water condition. See also foaming.

CASCADE - A series of stages in which the output of one stage is the input of the next stage.

CASCADE SYSTEMS - Arrangement in which two or more refrigerating systems are used in series; uses evaporator of one machine to cool condenser of other machine. Produces ultra-low temperatures.

CATHODE - In electrolysis or electrochemical corrosion, a site on a surface where actions in solution are neutralized by electrons to become elements that either plate out on the surface or react with water to produce a secondary reaction.

CATHODIC PROTECTION - A method of preventing corrosion by making the metal a cathode in a conducting medium by means of a direct electrical current that is galvanic.

CATHODIC PROTECTION - Reduction of corrosion rate by shifting the corrosion potential of the electrode towards less oxidizing potential by applying an external electromotive force.

CATION - A positively charged ion that migrates through the electrolyte toward the cathode under the influence of a potential gradient.

CATIONIC - The condition of a polymer, colloid, or large particle having exchangeable anions on its surface and an opposite, positive charge on the substrata.

CAUSTIC CRACKING - A form of stress-corrosion cracking most frequently encountered in carbon steels or iron-chromium-nickel alloys that are exposed to concentrated hydroxide solutions at temperature of 200 to 250°C.

CAUSTIC EMBRITTLEMENT - An obsolete term replaced by caustic cracking.

CAUSTIC SODA - A common water treatment chemical, sodium hydroxide.

CAVITATION - The formation and collapse, within a liquid, of cavities or bubbles that contain vapor or gas or both. In general, cavitation originates from decreases in static pressure in the liquid. In order to erode a solid surface by cavitation, it is necessary for the cavitation bubbles to collapse on or close to that surface.

CAVITATION EROSION - Progressive loss of original material from a solid surface due to continuing exposure to cavitation.

CELSIUS TEMPERATURE SCALE - A thermometric scale in which the freezing point of water is called 0°C and its boiling point 100°C at normal atmospheric pressure.

CENTANE NUMBER - A measure of ignition quality of a fuel or petroleum with reference to normal centane high-ignition quality fuel with an arbitrary number of 100.

CENTRIFUGAL COMPRESSOR - Pump which compresses gaseous fluids by centrifugal force.

CENTRIFUGAL FORCE -On a centrifugal pump, it is that force which throws water from a spinning impeller.

CENTRIFUGAL PUMP - A pump consisting of an impeller fixed on a rotating shaft and enclosed in a casing, having an inlet and a discharge connection. The rotating impeller creates pressure in the liquid by the velocity derived from centrifugal force.

CENTRIFUGAL PUMP - Pump which produces fluid velocity and converts it to pressure head.

CHANGE OF STATE - Condition in which a substance changes from a solid to a liquid or a liquid to a gas caused by the addition of heat. Or the reverse, in which a substance changes from a gas to a liquid, or a liquid to a solid, caused by the removal of heat.

CHANNELING - Cleavage and furrowing of the bed due to faulty operational procedure, in which the solution being treated follows the path of least resistance, runs through these furrows, and fails to contact active groups in other parts of the bed, (water treatment).

CHARGE - Amount of refrigerant placed in a refrigerating unit.

CHARGING BOARD - Specially designed panel or cabinet fitted with gauges, valves and refrigerant cylinders used for charging refrigerant and oil into refrigerating mechanisms.

CHECK VALVE - Device which permits fluid flow in one direction.

CHELATE - Is a molecule, similar to an ion exchanger, capable to withdraw ions from their water solutions into soluble complexes.

CHEMICAL CLEANING - Using a solvent solution to remove mill scale and corrosion products.

CHEMICAL FEEDLINE - The line which feeds the boiler treatment chemicals into the boiler.

CHEMICAL PRECIPITATION - When the chemicals react with the dissolved minerals in the water to produce a relative insoluble reaction product. A typical example of this takes place with the lime-soda softening process.

CHEMICAL REFRIGERATION - System of cooling using a disposable refrigerant. Also called an expendable refrigerant system.

CHEMICAL STABILITY - Resistance to chemical change which ion-exchange resins must possess despite contact with aggressive solutions.

CHILL FACTOR - Calculated number based on temperature and wind velocity.

CHILLED-WATER SYSTEM - A re-circulating water system using water chilled in a refrigeration machine as a source for cooling.

CHILLER/HEATERS - A unit that supplies either chilled water for cooling or hot water for heating, (HVAC).

CHLORIDE - An ion, compound, or salt of chlorine, such as sodium chloride (NaCl) or calcium chloride (CaCl₂).

CHLORINATION - A process in which chlorine gas or other chlorine compounds are added to the water for the purpose of disinfecting.

CHOKE TUBE - Throttling device used to maintain correct pressure difference between high-side and low-side in refrigerating mechanism. Capillary tubes are sometimes called choke tubes.

CHORDAL THERMOCOUPLE - A thermocouple installed in furnace tubes, designed to measure the effectiveness of water treatment within the boiler.

CIRCUIT - An electrical arrangement requiring a source of voltage, a closed loop of wiring, an electric load and some means for opening and closing it.

CIRCUIT BREAKER - A switch-type mechanism that opens automatically when it senses an overload (excess current).

CLAY - Finely suspended earth mineral sometimes found as an impurity in water.

CLEARANCE SPACE - Space between top of piston and the valve plate.

CLEARANCE VAPOR - The vapor remaining in the clearance space at the end of each discharge stroke.

CLOSED CYCLE - is the gas turbine arrangement, in which the exhaust is directed back again to compressor without coming in contact with the atmospheric air.

CLOSED FEEDWATER HEATER - An indirect-contact feedwater heater. Steam and water are separated by tubes.

CLOSED RE-CIRCULATING WATER SYSTEM - A system using as a heat-transfer medium water that continuously circulates through closed piping and heat exchanger without evaporation.

COCOAGULANT - A substance that promotes the clumping of particulate matter in water, forming a larger mass and thus promoting settling of particulates and clarification of the water.

COAGULATION - Is the process whereby finely divided particles of turbidity and color, capable of remaining in suspension indefinitely, are combined by chemical means into masses sufficiently large to effect rapid settling.

COALESCENCE - The gathering together of coagulated colloidal liquids into a single continuous phase.

CODE INSTALLATION - Refrigeration or air conditioning installation which conforms to the local code and/or the national code for safe and efficient installations.

CO-EFFICIENT OF CONDUCTIVITY - Measure of the relative rate at which different materials conduct heat. Copper is a good conductor of heat and, therefore, has a high coefficient of conductivity.

COEFFICIENT OF EXPANSION - A measure of the change in length or volume of an oject, specifically, a change measured by the increase in length or volume of an object per unit length or volume.

COEFFICIENT OF FRICTION - The dimensionless ratio of the friction force (F) between two bodies to the normal force (N) pressing these bodies together - m (f) = (F/N)

COEFFICIENT OF PERFORMANCE (COP) - Ratio of work performed or accomplished as compared to the energy used under designated operating conditions.

COGENERATION - A term used to describe the combination of different thermodynamic cycles for the purpose of increasing all-over cycle efficiency.

CO-GENERATION GENERATION - a term applied to identify the generation of people interested in co-generation.

COLD - The absence of heat; a temperature considerably below normal.

COLD DECK -The cooling section of a mixed air zoning system.

COLD JUNCTION - That part of a thermoelectric system which absorbs heat as the system operates.

COLD PROCESS - A water treatment process carried out at room temperature.

COLD WALL - Refrigerator construction which has the inner lining of refrigerator serving as the cooling surface.

COLLOIDAL - A state of suspension in a liquid medium in which extremely small particles are suspended and dispersed but not dissolved.

COLLOIDS - Organic matter of very fine particle size, usually in the range of 10^-5 to 10^-7 cm in diameter. It tends to inhibit the formation of dense scale and results in the deposition of sludge, or causes it to remain in suspension, so that it may be blown from the boiler.

COLUMN OPERATION - Conventional utilization of ion-exchange resins in columns through which pass, either upflow or downflow, the solution to be treated.

COMBINED FEEDER CUTOFF - A device that regulates makeup water to a boiler in combination with a low-water fuel cutoff.

COMBINED STEAM-GAS PLANT - where a gas turbine is combined with steam plant in order to utilize the waste heat.

COMBINED TREATMENT - A method of physical treatment , followed by the addition of chemicals to remove oxygen.

COMBUSTION - The act or process of burning.

COMFORT CHART - A chart showing effective temperatures with dry-bulb temperatures and humidities (and sometimes air motion) by which the effects of various air conditions on human comfort may be compared.

COMFORT COOLER - System used to reduce the temperature in the living space in homes. These systems are not complete air conditioners as they do not provide complete control of heating, humidifying, dehumidification, and air circulation.

COMFORT COOLING - Refrigeration for comfort as opposed to refrigeration for storage or manufacture.

COMFORT ZONE - (Average) the range of effective temperatures over which the majority (50 percent or more) of adults feels comfortable; (extreme) the range of effective temperatures over which one or more adults feel comfortable. An area on the psychrometric chart which shows conditions of temperature, humidity and sometimes air movement in which most people are comfortable.

COMMON NEUTRAL - A neutral conductor that is common to, or serves, more than one circuit.

COMPOSITION - The elements or chemical components that make up a material and their relative proportions.

COMPOUND - They are chemically combined elements with definite proportions of the component elements.

COMPOUND GAUGE - Instrument for measuring pressures both above and below atmospheric pressure.

COMPOUND REFRIGERATING SYSTEMS - System which has several compressors or compressor cylinders in series. The system is used to pump low pressure vapors to condensing pressures.

COMPRESSION - Term used to denote increase of pressure on a fluid by using mechanical energy.

COMPRESSION RATIO - Ratio of the volume of the clearance space to the total volume of the cylinder. In refrigeration it is also used as the ratio of the absolute low-side pressure to the absolute high-side pressure.

COMPRESSION, ADIABATIC - Is compressing a gas without removing or adding heat.

COMPRESSOR - Pump of a refrigerating mechanism which draws a low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high-pressure or condensing side of the cycle.

COMPRESSOR - The pump which provides the pressure differential to cause fluid to flow and in the pumping process increases pressure of the refrigerant to the high side condition. The compressor is the separation between low side and high side.

COMPRESSOR DISPLACEMENT - Volume, in cubic inches, represented by the area of the compressor piston head or heads multiplied by the length of the stroke.

COMPRESSOR SEAL - Leak proof seal between crankshaft and compressor body in open type compressors.

COMPRESSOR SURGING - An instability of air flow with axial compressor on the first stages of these compressors. Air flow might even be reversed that point.

COMPRESSOR TURBINE - in terms of a gas turbine arrangement, it is the turbine which drives the compressor only.

COMPRESSOR, CLEARANCE POCKET - Small space in a cylinder from which compressed gas is not completely expelled. This space is called the compressor clearance space or pocket. For effective operation, compressors are designed to have as small a clearance space as possible.

COMPRESSOR, ROTARY BLADE - Mechanism for pumping fluid by revolving blades inside cylindrical housing.

COMPRESSOR, SINGLE-STAGE - Compressor having only one compressive step between low-side pressure and high-side pressure.

COMRESSIBILITY - The ease which a fluid may be reduced in volume by the application of pressure, depends upon the state of the fluid as well as the type of fluid itself.

CONDENSATE - The liquid formed by condensation of a vapor. In steam heating, water condensed from steam; in air conditioning, water extracted from air, as by condensation on the cooling coil of a refrigeration machine.

CONDENSATE POLISHER - A device used to clean the returning condensate to the boiler feedwater system.

CONDENSATE PUMP - Device to remove water condensate that collects beneath an evaporator.

CONDENSATION - Process of changing a vapor into liquid by extracting heat. Condensation of steam or water vapor is effected in either steam condensers or dehumidifying coils, and the resulting water is called condensate.

CONDENSE - Action of changing a gas or vapor to a liquid.

CONDENSER - An apparatus used to transfer heat from a hot gas, simultaneously reducing that gas to a liquid.

CONDENSER TUBE - The heat transfer surface in a condenser.

CONDENSER-WATER SYSTEM - A re-circulating cooling water used as a heat transfer fluid for the condensation of a gas.

CONDENSING TEMPERATURE - The temperature at which the condensing gas is returned to a liquid at the same pressure.

CONDENSING UNIT - Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control.

CONDENSING UNIT SERVICE VALVES - Shutoff valves mounted on condensing unit to enable service technicians to install and/or service unit.

CONDENSING UNIT, REFRIGERANT - An assembly of refrigerating components designed to compress and liquefy a specific refrigerant, consisting of one or more refrigerant compressors, refrigerant condensers, liquid receivers (when required) and regularly furnished accessories.

CONDUCTANCE, ELECTRICAL - The reciprocal (opposite) of resistance and is the current carrying ability of any wire or electrical component. Resistance is the ability to oppose the flow of current.

CONDUCTANCE, SURFACE FILM - Time rate of heat flow per unit area under steady conditions between a surface and a fluid for unit temperature difference between the surface and fluid.

CONDUCTION - Transfer of heat by direct contact.

CONDUCTIVITY (ELECTRICAL) - The ability of a liquid to conduct an electrical current and indicating the presence of cations and anions. Conductivity is usually expressed in Micromohs per cm.

CONDUCTIVITY (THERMAL) - The time rate of heat flow through unit thickness of an infinite slab of homogeneous material in a direction perpendicular to the surface, induced by unit temperature difference. (W/m · K)

CONDUCTIVITY METER - An electric instrument used to measure the conductivity of water to determine its content of dissolved solids.

CONDUCTIVITY, THERMAL - The time rate of heat flow through unit area and unit thickness of a homogeneous material under steady conditions when a unit temperature gradient is maintained in the direction perpendicular to area. Materials are considered homogeneous when the value of the thermal conductivity is not affected by variation in thickness or in size

CONDUCTOR - Substance or body capable of transmitting electricity or heat.

CONDUIT - A round cross-section electrical raceway, of metal or plastic.

CONGEALER - Also known as freezer.

CONGRUENT PHOSPHATE CONTROL - Similar as a coordinated phosphate control but more restrictive where the equilibrium is based on maintaining a ratio of 2.6 Na/1.0 PO₄, instead of 3.0/1.0 PO₄.

CONNECTED LOAD - The sum of all loads on a circuit. (1) Connection in Parallel: System whereby flow is divided among two or more channels from a common starting point or header. (2) Connection in Series: System whereby flow through two or more channels is in a single path entering each succeeding channel only after leaving the first or previous channel.

CONSTRICTOR - Tube or orifice used to restrict flow of a gas or a liquid.

CONTAMINATION - The introduction into water of microorganisms, chemicals, toxic materials, waste water in a concentration that makes the water unfit for its next intended use.

CONTROL - A device for regulation of a system or component in normal operation, manual or automatic. If automatic, the implication is that it is responsive to changes of pressure, temperature or other property whose magnitude is to be regulated.

CONTROL POINT - The value of the controlled variable which the controller operates to maintain.

CONTROL VALVE - Valve which regulates the flow or pressure of a medium which affects a controlled process. Control valves are operated by remote signals from independent devices using any of a number of control media such as pneumatic, electric or electrohydraulic.

CONTROLLED DEVICE - One which receives the converted signal from the transmission system and translates it into the appropriate action in the environmental system. For example: a valve opens or closes to regulate fluid flow in the system.

CONTROLLER - A device capable of measuring and regulating by receiving a signal from a sensing device, comparing this data with a desired value and issuing signals for corrective action.

CONVECTION - The movement of a mass of fluid (liquid or gas) caused by differences in density in different parts of the fluid; the differences in density are caused by differences in temperature. As the fluid moves, it carries with it its contained heat energy, which is then transferred from one part of the fluid to another and from the fluid to the surroundings.

CONVECTION, FORCED - Convection resulting from forced circulation of a fluid, as by a fan, jet or pump.

CONVECTION, NATURAL - Circulation of gas or liquid (usually air or water) due to differences in density resulting from temperature changes.

COOLER - Heat exchanger which removes heat from a substance.

COOLING EFFECT, SENSIBLE - The difference between the total cooling effect and the dehumidifying effect, usually in watts.

COOLING EFFECT, TOTAL - Difference between the total enthalpy of the dry air and water vapor mixture entering the cooler per hour and the total enthalpy of the dry air and water vapor mixture leavir~ the cooler per hour, expressed in watts.

COOLING TOWER - Device for lowering the temperature of water by evaporative cooling, in which water is showered through a space through which outside air circulates. A portion of the water evaporates, its latent heat of vaporization cooling that portion of the water which does not evaporate.

COOLING, EVAPORATIVE - Involves the adiabatic exchange of heat between air and water spray or wetted surface. The water assumes the wet-bulb temperature of the air, which remains constant during its traverse of the exchanger.

COOLING, REGENERATIVE - Process of utilizing heat which must be rejected or absorbed in one part of the cycle to function usefully in another part of the cycle by heat transfer.

COORDINATED PHOSPHATE CONTROL A treatment to prevent caustic gauging. Free caustic is eliminated by maintaining an equilibrium between the sodium and phosphate. Control is based on maintaining a ratio of 3.0 Na to/1.0 PO₄.

CORRATOR - A device or probe employed to measure current flow in a process flow. It consists of two identical electrodes, to which a small current is applied and measured, from which corrosion rates can be calculated.

CORROSION - The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties.

CORROSION, ANODE - The dissolution of an metal acting as an anode.

CORROSION, ATMOSPHERIC - The gradual degradation or alteration of a material by contact with substances present in the atmosphere, such as oxygen, carbon dioxide, water vapor, and sulfur and chlorine compounds.

CORROSION, BIOLOGICAL - Deterioration of metals as a result of the metabolic action of microorganisms. Also often named fouling.

CORROSION, CATHODIC - Corrosion resulting resulting from a cathodic condition of a structure usually caused by the reaction of an amphoteric metal with the alkaline products of electrolysis.

CORROSION, CAVITATION - A process involving conjoint corrosion and cavitation.

CORROSION, CONCENTRATION ATTACK - A form of corrosion caused by the concentration of caustic or phosphate salts under porous deposits, generally iron oxide. Sometimes found at welded tubes and due to steam blanketing.

CORROSION, CONCENTRATION-CELL - Pitting type of corrosion caused by an electrical potential differential between surfaces of a metal as a result of deposits or differences in the solution concentration in contact with the metal.

CORROSION, COUPONS - Pre-weighed metal strips installed into fluid systems for the purpose of monitoring metal losses.

CORROSION, CREVICE - Localized corrosion of a metal surface at, or immediately adjacent to an area that is shielded from full exposure to the environment because of close proximity between metal and the surface of another metal.

CORROSION, DEACTIVASION - The process of prior removal of the active corrosive constituents, usually oxygen, from a corrosive liquid by controlled corrosion of expendable metal or by other chemical means, therby making the liquids less corrosive.

CORROSION, DEPOSIT (also called poultice corrosion) - Corrosion occuring under or around a discontinous deposit on a metallic surface.

CORROSION, EFFECT - A change in any part of the corrosion system caused by corrosion.

CORROSION, ELECTROCHEMICAL - Corrosion that is accompanied by a low of electrons between cathodic and anodic areas on metallic surfaces.

CORROSION, EMBRITTLEMENT - The severe loss of ductility of a metal resulting from corrosive attack, usually intergranular and often not visible.

CORROSION, EXTERNAL - A chemical deterioration of the metal on the fireside of boiler heating surfaces.

CORROSION, FATIGUE - The process in which a metal fractures prematurely under conditions of simultaneous corrosion and repeated cyclic loading at lower stress levels or fewer cycles than would be required in the absence of the corrosive environment.

CORROSION, FILIFORM - Corrosion that occurs under organic coatings on metals as fine wavy hairlines.

CORROSION, FRETTING - A type of corrosion which occurs where metals slide over each other. Long tubes in heat exchangers often vibrate, causing metal to metal contact, tube supports etc.. The metal to metal rubbing causes mechanical damage to the protective oxide coating.

CORROSION, GALVANIC - Corrosion of a metal caused by its contact with a metal of lower activity; this contact results in an electron flow or current and dissolution of one of the metals.

CORROSION, GASEOUS - Corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal. Also called dry corrosion.

CORROSION, GENERAL - A form of deterioration that is distributed more or less uniformly over a surface.

CORROSION, GRAPHITIC - Corrosion of grey iron in which the iron matrix is selectively leached away, leaving a porous mass of graphite behind. This type of corrosion occurs in relativel mild aquous solutions and on buried piping.

CORROSION, HOT - An accelerated corrosion of metal surfaces that results from the combined effect of oxidation and ractions with sulfur compounds or other contminants such as chlorides, to form a molten salt on a metal surface that fluxes, destroys or disrupts the normal protective oxide. (commonly found in pulp mills)

CORROSION, IMPINGEMENT - A form of erosion-corrosion generally associated with local impingement of a high velocity, flowing fluid against a solid surface.

CORROSION, INFLUENCED - The corrosion cause by organisms due to their discharge containing sulfur compounds and the depolarization with other types of discharge due to the presence of the microorganisms.

CORROSION, INHIBITORS - Substances that slow the rate of corrosion.

CORROSION, INTERGRANULAR - Localized attack occurring on the metal grain boundaries. This is commonly found with stainless steels which have been improperly heat treated.

CORROSION, INTERNAL - Usually refers to the internal corrosion and is considered an electrochemical deterioration of the boiler surface at or below the water surface.

CORROSION, LOCALIZED - Corrosion at discrete sites, for example, crevice corrosion, pitting, and stress-corrosion cracking.

CORROSION, LOCALIZED - Non-uniform corrosion of a metal surface highlighted by spotty or pitting-type corrosion.

CORROSION, MICROBIAL - (see biological corrosion).

CORROSION, OXYGEN DEFICIENCY - A form of crevice corrosion in which galvanic corrosion proceeds because oxygen is prevented from diffusing into the crevice.

CORROSION, POTENTIAL - The voltage between a corroding metal and a reference electrode.

CORROSION, POULTICE - A term used in the automotive industry to describe the corrosion of vehicle body parts due to the collection of road salts and debries on ledges and in pockets that are kept moist by weather and washing.

CORROSION, PROTECTION - Modification of a corrosion system so that corrosion damage is mitigated.

CORROSION, RESISTANCE - The ability of a material to resist deterioration by chemical or electrochemical reaction with its environment.

CORROSION, STRAY CURRENT - A form of attack caused by electrical currents going through unintentional path.

CORROSION, STRESS - Preferential attack of areas under stress in a corrosive environment, where such a environment alone would not have caused corrosion.

CORROSION, STRESS CORROSION CRACKING - Material deterioration due to cracking, by being under static stress either applied or residual.

CORROSION, SWEET - The deterioration of metal caused by contact with carbon dioxide in water.

CORROSION, THERMO-GALVANIC - Corrosion resulting from an electrochemical cell caused by a thermal gradient.

CORROSION, UNIFORM - The simplest form of corrosion. It attacks all surfaces exposed to a corrodent.

CORROSIVE WEAR - A material deterioration due to the co-joint action of corrosion and mechanical action.

CORROSIVITY - An indication of the corrosiveness of the water of material. The corrosivity of a water as described by the water’s pH, alkalinity, hardness, temperature, total dissolved solids, dissolved oxygen concentration and the Langerier Index.

COUNTER-FLOW HEAT EXCHANGER - When the fluid to be cooled flows against the direction of the coolant. In heat exchange between two fluids, opposite direction of flow, coldest portion of one meeting coldest portion of the other.

COVALENT BOND - A bond in which two atoms share pair of electrons.

CRANKSHAFT SEAL - Leak proof joint between crankshaft and compressor body.

CRAZE CRACKING (OR CHECKING) - Irregular surface cracking of metal associated with thermal cycling.

CREEP - Time dependent permanent strain under stress. This is used to rate the resistance of a material to plastic deformation under sustained load.

CREEP STRENGTH - The constant nominal stress that will cause a specified quantity of creep in a given time at constant temperature. Creep strength is expressed as the stress necessary to produce 0.1% strain in 1000 hours.

CREEP, DYNAMIC - Creep that occurs under conditions of fluctuating load or fluctuating temperatures.

CRISPER - Drawer or compartment in refrigerator designed to provide high humidity along with low temperature to keep vegetables, especially leafy vegetables - cold and crisp.

CRITICAL HUMIDITY - The relative humidity above which the atmospheric corrosion rate of some metals increase sharply.

CRITICAL POINT - A point at which the saturated liquid and saturated vapor states are identical. Also, the latent heat of evaporization is zero at this point.

CRITICAL PRESSURE - The pressure at the critical temperature above which the fluid no longer has the properties of a liquid, regardless of further increase of pressure.

CRITICAL TEMPERATURE - That temperature above which the vapor phase cannot be condensed to liquid by an increase in pressure.

CRITICAL VELOCITY - The velocity above which fluid flow is turbulent.

CRT - Cathode ray tube terminal.

CRYOGENIC FLUID - Substance which exists as a liquid or gas at ultra-low temperatures - 157°C.

CRYOGENIC SUPERCONDUCTOR SYSTEM - Uses helium to cool conductors to within few degrees of absolute zero where they offer no electric resistance.

CRYOGENICS - Refrigeration which deals with producing temperatures of -157°C below zero and lower.

Crystal Formation, Zone of Maximum: Temperature range in freezing in which most freezing takes place, i.e., about 25¡F to 30¡F for water.

CRYSTALLITES - Atoms arranged in a repeating and definite structure.

CRYSTALLIZATION - The separation, usually from a liquid phase on cooling, of a solid crystalline phase.

CURRENT (I) - The electric flow in an electric circuit, which is expressed in amperes (amps).

CURRENT DENSITY - The current flowing to or from a unit area of an electrode surface.

CYCLE - A series of thermodynamic processes during which the working fluid can be made to undergo changes involving energy transition and is subsequently returned to its original state.

CYCLE, REVERSIBLE - Theoretical thermodynamic cycle, composed of a series of reversible processes, which can be completely reversed.

CYCLE, WATER TREATMENT - A complete course of ion-exchange operation. For instance, a complete cycle of cation exchange would involve regeneration of the resin with acid, rinse to remove excess acid, exhaustion, backwash, and finally regeneration.

CYCLES - A system that undergoes a series of processes and always returns to its initial state.

CYCLES OF CONCENTRATION - The number of times the soluble mineral salts in a water supply have been concentrated in, a system.

CYLINDER HEAD - Plate or cap which encloses compression end of compressor cylinder.

DALTON'S LAW OF PARTIAL PRESSURE - Each constituent of a mixture of gases behaves thermodynamically as if it alone occupied the space. The sum of the individual pressures of the constituents equals the total pressure of the mixture.

DAMPER - A device used to vary the volume of air passing through an air outlet, air inlet or duct.

DASHPOT - A damping device, usually consisting of a cylinder and a piston in which relative motion of either displaces a fluid such as air or oil, resulting in friction.

DEADBAND - In HVAC, a temperature range in which neither heating nor cooling is turned on; in load management, a kilowatt range in which loads are neither shed nor restored.

DE-AERATING HEATERS - Mechanical device using steam to strip dissolve gases from the boiler feedwater and heating the feedwater.

DE-AERATION - Act of separating air from substances.

DE-AERATOR - An apparatus or device which is used to remove dissolved air or oxygen from water.

DE-ALKALIZATION - The removal of alkalinity from a water supply by neutralization or ion exchange.

DE-ALKALIZER - An apparatus or device used to remove the alkaline carbonate and bicarbonate ions from a water supply.

DE-ALLOYING - This is a corrosion process whereby one constituent of a metal alloy is preferentially removed from the alloy, leaving an altered residual microstructure.

DEASHING - The removal from a solution of inorganic salts by means of adsorption by ion-exchange resins of both the cations and the anions that comprise the salts. See deionization.

DE-CARBONATION - Refers to the removal of carbon dioxide from the boiler feedwater.

DECIBEL (dB) - A decibel is a division of a logarithmic scale for expressing the ratio of two quantities proportional to power or energy. The number of decibels denoting such a ratio is ten times the logarithm of the

DECONCENTRATOR - This is a cylindrical tank connected before the boiler to receive the boiler feedwater before entering the boiler. It is designed to promote settling of suspended solids, which then could be removed via its own blowdown device. Was used for operation with very high suspended solids.

DE-FLOCCULANT - An electrolyte adsorbed on colloidal particles in suspension that charges the particles to create repulsion forces which maintain the particles in a dispersed state, thus reducing the viscocity of the suspension.

DEFROST CYCLE - Refrigerating cycle in which evaporator frost and ice accumulation is melted.

DEFROST TIMER - Device connected into electrical circuit which shuts unit off long enough to permit ice and frost accumulation on evaporator to melt.

DEFROSTING - Process of removing frost accumulation from evaporators.

DEFROSTING CONTROL - Device to automatically defrost evaporator. It may operate by means of a clock, door cycling mechanism or during "off" portion of refrigerating cycle.

DEFROSTING TYPE EVAPORATOR - Evaporator operating at such temperatures that ice and frost on surface melts during off part of operating cycle.

DEGREE DAY - A unit, based upon temperature difference and time, used in estimating fuel consumption and specifying nominal heating load of a building in winter. For any one day, when the mean temperature is less than 65°F there exist as many degree days as there are Fahrenheit degrees difference in temperature between the mean temperature for the day and 65°F.

DEGREES OF SUPERHEAT - The amount by which the temperature of a superheated vapor exceeds the temperature of the saturated vapor at the same pressure.

DEHUMIDIFICATION - The condensation of water vapor from air by cooling below the dewpoint or removal of water vapor from air by chemical or physical methods.

DEHUMIDIFIER -(1) An air cooler or washer used for lowering the moisture content of the air passing through it; (2) An absorption or adsorption device for removing moisture from air.

DEHUMIDIFYING - Removal of moisture from the air.

DEHYDRATION - The removal of water vapor from air, stored goods or refrigerants.

Deionization - Deionization, a more general term than deashing, embraces the removal of all charged constituents or ionizable salts (both inorganic and organic) from solution.

DE-IONIZER - An apparatus or device used to remove the ions of dissolved salts from water.

DEMAND - The probable maximum rate of water flow as determined by the number of water supply fixture units.

DEMAND CHARGE - That part of an electric bill based on kW demand and the demand interval, expressed in dollars per kilowatt. Demand charges offset construction and maintenance of a utility's need for a large generating capacity.

DEMAND CONTROL - A device which controls the kW demand level by shedding loads when the kW demand exceeds a predetermined set point.

DEMAND INTERVAL - The period of time during which kW demand is monitored by a utility service, usually 15 or 30 minutes long.

DEMAND LOAD - The actual amount of load on a circuit at any time. The sum of all the loads which are ON. Equal to the connected load minus the loads that are OFF.

DEMAND READING - Highest or maximum demand for electricity an individual customer registers in a given interval, example, 15 minute interval. The metered demand reading sets the demand charge for the month.

DEMINERALIZER - A process to remove dissolved matter from boiler pretreated water by contacting the water with ion-exchange resins.

DENSITY - The ratio of the mass of a specimen of a substance to the volume of the specimen. The mass of a unit volume of a substance. When weight can be used without confusion, as synonymous with mass, density is the weight per unit volume.

DENSITY, ABSOLUTE - Mass per unit volume of a solid material, expressed usually in kg/m³.

DESALINATION - The removal of inorganic dissolved solids from water.

DESICANT, LIQUID - A hygroscopic liquid, such as glycol, used to remove water from other fluids.

DESICCANT - Any absorbent or adsorbent, liquid or solid, that will remove water or water vapor from a material. In a refrigeration circuit, the desiccant should be insoluble in the refrigerant.

DESIGN PRESSURE - Highest or most severe pressure expected during operation. Sometimes used as the calculated operating pressure plus an allowance for safety.

DESIGN PRESSURE - Highest or most severe pressure expected during operation. Sometimes used as the calculated operating pressure plus an allowance for safety.

DESIGN WORKING PRESSURE - The maximum allowable working pressure for which a specific part of a system is designed.

DESILICIZER - An apparatus or device used to remove silica from a water supply.

DESSERT BAG - A canvas bag which permits seepage of its liquid. The liquid will evaporate and obtains the to evaporate partly from the content of the bag and thus cooling its content.

DESSERT BAG - A canvas bag which permits seepage of its liquid. The liquid will evaporate and obtains the to evaporate partly from the content of the bag and thus cooling its content.

DETERGENT ADDITIVE - In lubrication technology, a surface active additive that helps to keep solid particles suspended in an oil

DETERGENT CLEANING - A boiler cleaning process using an alkaline solution, primarily to remove oil and grease.

DETERGENT OIL - A heavy duty oil containing a detergent additive. These oils are mainly used in combustion engines.

DETERGENT-DISPERSANT - A compound mixture of cleaning agents that have both surface-active properties and suspending properties.

DEW POINT - Temperature at which vapor (at 100 percent humidity) begins to condense and deposit as liquid.

DEW POINT DEPRESSION - The difference between dry bulb and dew point temperatures.

DEW POINT TEMPERATURE - The temperature at which condensation begins, if air is cooled at constant pressure.

DIAPHRAGM - Flexible material usually made of thin metal, rubber or plastic.

DIATOMACEOUS EARTH FILTRATION - Is a process in which a filter cake or precoat of diatomaceous earth is used as a filter medium.

DIELECTRIC - A nonconductor of electricity.

DIELECTRIC FITTING - A non conductive substance such as plastic that is placed between two dissimilar metals to prevent galvanic current flow.

DIELECTRIC STRENGTH - A measure of the ability of a dielectric (insulator) to withstand a potential difference across it without electric discharge.

DIFFERENTIAL - The temperature or pressure difference between cut-in and cut-out temperature or pressure of a control.

DIFFERENTIAL AERATION CELL - An electrolytic cell, the electomagnetic force of which is due to a difference in air (oxygen) concentration at one electrode as compared with that at another electrode of the same material. (see concentration cell)

DIFFERENTIAL SOLUTE CONCENTRATION - A potential difference between an anode and cathode on metal, because of a concentration cell due to dissolved metals.

DIFFUSER - A circular, square, or rectangular air distribution outlet, generally located in the ceiling and com prised of deflecting members discharging supply air in various directions and planes, and arranged to promote mixing of primary air with secondary room air.

DIRECT ACTING - Instruments that increase control pressure as the controlled variable (such as temperature or pressure) increases; while reverse acting instruments increase control pressure as the controlled variable decreases.

DIRECT CURRENT - A source of power for an electrical circuit which does not reverse the polarity of its charge.

DIRECT-EXPANSION EVAPORATOR - One that contains only enough liquid to continue boiling as heat is absorbed by it.

DISPERSANT - A chemical which causes particulates in a water system to remain in suspension.

DISPERSANT OIL - A heavy duty oil containing a dispersant additive.

DISPLACEMENT VOLUME - The volume displaced by the piston between top dead center and bottom dead center.

Dissociation - Ionization.

DISSOLVED GASES - Gases soluble in water.

DISSOLVED SOLIDS (TDS) - The measure of the total amount of dissolved matter.

DISTILLATION - Involves boiling water and condensing the vapor.

DMA - Direct memory access. A process where block of data can be transferred between main memory and secondary memory without processor intervention.

DOMESTIC HOT WATER - Potable hot water as distinguished from hot water used for house heating.

Downflow - Conventional direction of solutions to be processed in ion-exchange column operation, that is, in at the top, out at the bottom of the column.

DOWNSTREAM - The outlet side of an instrument, a pump, valve, etc..

DRAFT GAUGE - Instrument used to measure air movement by measuring air pressure differences.

DRIER - Substance or device used to remove moisture from a refrigeration system.

DRIERITE - Desiccant which operates by chemical action.

DRIFT - Entrained water in the stack discharge of a cooling tower.

DRIFT - Term used to describe the difference between the set point and the actual operating or control point.

DROOP - Terms used to describe the difference between the set point and the actual operating or control point.

DRUM WATER LEVEL LINE - The water level in the drum during the normal operating mode.

DRY BULB - An instrument with a sensitive element to measure ambient air temperature.

DRY BULB TEMPERATURE - The temperature registered by an ordinary thermometer. The dry bulb temperature represents the measure of sensible heat, or the intensity of heat.

DRY COMPRESSION - The compression of vapor, in a vapor-liquid vapor-compression refrigeration cycle.

DRY ICE - Refrigerating substance made of solid carbon dioxide which changes directly from a solid to a gas (sublimates). Its subliming temperature is -78°C.

DRY PIPE - A perforated or slotted pipe or box inside the drum and connected to the steam outlet.

DRY STANDBY - A method of sealing al water and steam connections and placing a desiccant in the unit and applying an airtight seal.

DRY SYSTEM - Refrigeration system which has the evaporator liquid refrigerant mainly in the atomized or droplet condition.

DRYNESS FRACTION OR QUALITY - Weight fraction of the vapor in a vapor-liquid mixture.

DUAL SHAFT GAS TURBINE - a gas turbine which has one turbine on one shaft driving the compressor and when the gas discharged from this turbine is directed to another turbine on a separate shaft to drive a load.

DUAL-TEMPERATURE RE-CIRCULATING WATER SYSTEM - A closed re-circulating water system that uses water either for cooling, by circulating it through a chiller, or for heating, by circulating it through a boiler or heat-exchanger depending upon need.

DUCTILE GOUGING - Referring to irregular wasting of the tube metal beneath a porous deposit The micro structure of the metal does not change with this process and the ductility remains, but the thinning leads to rapture.

DUCTILITY - T