Document qmXD6w756X7bVxOo5KnDYG8qK

954 CHAPTER 67 sooner then it would be without such means, to produce a smaller differential of the controlled property. control, dual effect: one responsive' to temperatures of two cones, or to two variable conditions. .'/ control, high pressure: pressure-responsive device (usually, an electric switch), actuated directly by the refrigerant vapor pressure on the high side of a refrigerating system (usually com pressor head pressure). control, low-pressure: a pressure-responsive device (usuaQy 'an electric switch), actuated directly by refrigerant vapor pressure in the low side of a refrigerating system. ^ convection: transfer of heat by movement of fluid. - 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 convector: an agency of convection. In heat transfer, a'surface designed to transfer its heat to a surrounding fluid largely''or wholly by convection. The heated fluid may be removed mechan ically or by gravity (Gravity Convector). Such a surface may dr may not be enclosed or concealed. (See also definition of radiator.) (See also Chapter 55.) cooler, cold storage: an insulated room maintained at 30 F or above. cooling, direct method of refrigeration: a system in which the evaporator is in direct contact with the material or space'refrig erated or is located in air circulating passages communicating with such spaces. cooling, indirect method of refrigeration: a system in which a Squid, such as brine or water, cooled by the refrigerant, is circu lated to the material or space refrigerated or is used to cool air so circulated. .copper plating: a film of copper deposited by electrical, im mersion, or other means on the surface of another material such as iron or steel. In refrigeration, usually occurs on'compressor walls, pistons, discharge valves, and shaft or seal. core area: the total plane area of the portion of a grille bounded by a line tangent to the outer edges of toe outer openings through which air can pass. corresponding values: simultaneous values of various properties of a fluid, such as pressure, volume, temperature, etc., for a given condition of fluid. corrosive: having chemically destructive effect on'metals (occa sionally on other materials). . counterblow: in heat exchange between two fluids, opposite direction of flow, coldest portion of one meeting coldest portion of the other. critical point: of a substance, state point at which liquid and vapor have identical properties; critical temperature, critical pressure and critical volume are the terms given to the tempera ture, pressure and volume at the critical point. Above the critical temperature or pressure there is no line of demarcation between liquid and gaseous phases. cryohydrate: a frozen mixture of water and a salt; a brine in eutectic proportions to give the lowest freezing point. - - cutting room: cold room in which animal carcasses are cut up into commercial sizes such as rib roast, legs, etc. ' >- cycle: a complete course of operation of working fluid back to a starting point, measured in thermodynamic terms (functions). Also used in general for any repeated process on any system.' cycle, binary vapor: a refrigerating cycle in which two separate refrigerants are used, one superimposed upon and augmenting the cycle of the other '' cycle, Carnot: a sequence of reversible processes forming the reversible working cycle of an ideal beat engine of maximum ther mal efficiency. It consists of isothermal expansion,' adiahAtie ex pansion, isothermal compression and adiabatic compression to the initial state. ;:q cycle, dosed: any cycle in which the primary murfrnm is always enclosed and repeats the same sequence of events. . cycle, 'defrosting: the portion of a refrigeration operation which permits the cooling unit to defrost. . ... cyde, refrigeration: complete course of operation of refrigerant back to a starting point; evidenced'by: a repeated-senes of thermodynamic processes, or flow through a series of apparatus, or a reputed senes of mechanical operations. . cyde, reverpbfo: theoretical thermodynMaic cyde, compose^ 1965 Guide And .Data: Book of a series of reverable processes, which can be completely re versed; e.g., Carnot cyde. 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 pnaajnr through an air outlet, inlet, or duct decibel: a unit used to express the relation between two amounts of power. By. definition the difference in decibels be tween twopowers P, and Pi, Pt being the larger, is: db difference " 10 logt*/VPi. Used in acoustics. declination of son: the.angle above or .below the equatorial plane. It is phis if north of the plane, and minus' if below. objects are located by declination. decomposition: process of.chemical change, breaking up of structures, spoilage. * defrosting: removal of accumulated tee from cooling element. Thawing frozen foods. . degree day:`a unit, based upon temperature differeoce.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.' dehomidification: the condensation of water vapor from air by cooling below the dew point or removal of water vapor from air by chemical or physical methods. dehomidiffer: an air cooler or washer used for lowering the moisture cootent of the air passing through it. An absorption or adsorption device for removing moisture from the air. dehomidify: to reduce by any process- the quantity of water vapor within a given space. . ., dehamidifying effect: the heat removed in reducing the mois ture content of air, passing through a dehumidifier, from its en tering to its leaving condition. ..i dehydrate:-to remove water.in all forms from matter. Liquid water, hygroscopic water,' and water of crystallization or water of hydration are included. dehydration: the removal of water vapor from air by the use of absorbing or adsorbing materials. The removal of water from stored goods. density: the ratio of the mass of a specimen of a substance to the volume of. the specimen. The 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. 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. desiccation: any process for evaporating water or removing water vapor from a'material. dew point: see temperature, dew point. dew point, apparatus: that temperature which would result if the psychrometnc process occurring in a dehumidifier, humidifier or surface cooler were carried to the saturationcondition of the leaving air while maihtaining'the same ratio of sensible to total heat load in the process. .................... - dew point, room: the dew-point temperature of the conditioned room or space. differential (of a control): the difference between cut-in And cut-out tempratures or pressures. - diffosivity, thermal: thermal conductivity divided by product of density and specific beat. See definition of a in Chapters 5 and 64. ....... direct connected: driver and driven, as motor and compressor, positively connected id line to operate at speed. displacement, actual: the'actual volume, at compressor'inlet conditions, of gas moved per unit of rim* displacement, piston: the volume swept by a'piston per revolu tion. displacement, theoretical: the total volume displaced by all the pistons of a compressor per revolution or per unit of time. distributor: device for dividing flow of liquid fluid between parallel paths in an evaporator, or in other types of beat transfer apparatus. ... '........ 1' " ` down-feed ooe-pipe riser (steam): a pipe which carries steam downward to the heating units and into ,which the condensate from the heating units drains. Terminology draft: a current of air, when referring to the pressure difference which a current of air or gases to flow through a flue, chimney, heater, or space; or to a localized effect caused by one or more factors of high air velocity, low ambient temperature, or direction of air flow, whereby more beat is withdrawn from a person's skin than is normally dissipated. , draft head (gravity heating-convector): 1. (tide outlet en~ cloture): the height of a gravity convector between the bottom of the bearing unit and the bottom of the air outlet opening. 2.-(top outlet endoture): the height of a gravity convector between the bottom of the beating unit and the top of the enclosure. drier: a manufactured device containing a desiccant, placed in the refrigerant circuit, its primary purpose being to collect and hold within the desiccant all water ui the system in excess of the mount which can be tolerated in the'circulating refrigerant. . drift: in a water spray devioe, the entrained unevaporated water carried from the device by air movement through it ' /, HHnfclng water cooler: a factory-made assembly' which'em- filoys a complete refrigerating system and which has the primary unction of cooling potable water and provides for dispensing such water, by either Integral or remote means, or both. . " 1 drip: a pipe, or a steam trap and a pipe considered'as a unit, which conducts condensation from the steam side of a piping system to the water or return-side of the'system. '` drop: the vertical distance that the lower edge of a horizontally projected air stream falls or rises as the combined result of density effect of cool or warm air and the vertical expansion of the air path resulting from entrainment. dry: to separate or remove a liquid or vapor from another substance. Tne liquid may be water, but the term is also used for the removal of liquid or vapor forms of other substances.. , dry ice: solid carbon dioxide, COj (proprietary term), doct: a passageway made of sheet metal or other suitable mate rial, not necessarily leak-tight, used for conveying air or other gas at low pressures. dunnage: strips of wood used in stowing cargo to provide air space between pieces or packages. < <: dost: an air suspension (aerosol) of solid particles of earthy material as differentiated from smoke. . ebullator: a device inserted in flooded evaporator tuba ..to revent the evaporator from becoming oil bound or refrigerant quid becoming quiescent at a. pressure lower, than its boiling point. , effective area: the net area of an outlet or inlet'device through which air can pass; it is equal to the free area of the device times the coefficient of discharge. . efficiency, compression: ratio of hp required to compress adiabaticaUy and reversibly all the vapor delivered by compressor (in single stage) to the indicated horsepower. 1 V efficiency, mechanical: ratio of the compression energy or work of a compressor to the energy or work input. efficiency, volumetric, apparent: ratio of length of suction line, on indicator card,'to stroke. ` ' . efficiency, volumetric, due to cylinder beating: ratio of .the total to tiie apparent volumetric.efficiency. `Also railed real dr wk clearance volumetric efficiency. '. . '' efficiency, volumetric, total: ratio of the actual volume of gas moved by the compressor or pump.to the actual displacement'of the compressor or pump. ' , .. ejector: a device which builds up a high fluid velocity in a re stricted area to obtain a lower static pressure at.that pointso that fluid from another.source may.be drawn in.. ....... electric precipitator: device for removing dust from the air by means ofelectnc charges induced on the dust particles!- , element, bimetallic: one formed of two metals having different coefficients of thermal expansion such as are used in temperature indicating and controlling devices. , .i - dement, electric heating: a unit assembly consisting of a'resis tor, mtmUtjwl supports, and terminals for connecting the resistor to electric power. -'i;-: emissivity: the ratio of the total radiant flux emitted by a surface to that emitted by an ideal black body at the. same.tem- perature. ., .. emulsion: a relatively stable suspension-of small but oot-cbl? bidal particles of a substance in a liquid, the suspended particles being undissolved.. .> 955 energy, available: the portion of the total energy which-can be converted to work in a perfect engine. energy, internal (Intrinsic): the sum of all the kinetic and- potential energies contained in a substance due to tiie states ofmotion and separation of its several molecules, atoms, and elec trons..It includes sensible heat (vibration energy) and that part' of the latent heat that is represented by the increase in energy during evaporation. engine: prime mover; device for transforming fuel or heat en ergy into mechanical energy. enthalpy: thermodynamic property of a substance defined as tho sum of its internal energy phis the quantity Pv/J, where P - pressure of tiie. substance,-1> -- its volume, and J =* the mechanical equivalent of heat. Formerly called by the obsolescent names total heal and heat content. . enthalpy, free: a thermodynamic property which serves as a' measure of the available energy of a system with respect to surroundings at the same temperature and same pressure as that of the system. No process involving an increase in available en ergy can occur spontaneously. enthalpy, specific: a term sometimes applied to enthalpy per unit weight. entrainment: the induced flow of room air by the primary air from an outlet, creating a mixed air path (commonly called sec-; ondary air motion). entropy: the ratio of the heat added to a substance to the absolute temperature at which it is added. . . entropy, specific: a term sometimes applied to entropy per. unit weight. enzyme: a complex organic substance such as diastase, pepsin, ; etc., capable of transforming by catalytic action some other, compound; a soluble ferment. Equivalent Direct Radiation (EDR): a unit of beat delivery of 240 Btu per hr. equivalent evaporation: the amount of water a boiler would' evaporate, in pounds per hour, if it received feed water at 212 F and vaporized it at the same temperature, and corresponding atmospheric pressure. , . !- eutectic mixture (solution): a mixture which melts or freezes at constant temperature and with constant composition. Its melt ing point is usually the lowest possible fra mixtures of the. given substances. evaporation: change of state from liquid to vapor, evaporative cooling: the adiabatic exchange of heat between air and and a water spray or wetted surface. The water approaches the wet bulb temperature of the air, which remains'constant dur ing its traverse of the exchanger. evaporative equilibrium (of a wet-bulb instrument): the condi tion attained' When the wetted wick has reached a stable and constant temperature (when the instrument is exposed to air at velocities over 900 fpm, thw temperature may be considered to approach the true wet-bulb temperature). evaporator: that part of a refrigerating system in which re frigerant b vaporized to produce refrigeration. evaporator, dry-type: an evaporator of the continuous tube type where refrigerant from a pressure-reducing device is fed into the inlet end and the suction fine connects to the outlet endr-j - evaporator, flooded: a refrigerant evaporator in which: (1). the heat transfer surface b iminersed in the refrigerant being evap orated, or (2). an excess of. refrigerant over that which cam be,- evaporated b circulated through the surface. exfiltration: air flow outward through a wall;*.leak; .mem brane, etc. -. V - I 5- opening: any opening through which air is removed from a space which b being heated or cooled, or humidified or;de- humidined, or ventilated. ....... . exhauster: a fan used to withdraw air under suction. , expassion, dry: a process of heat removal by a refrigerant.-in an evaporator fed by a flow control, responsive to temperature,, or pressure or both at some point in the evaporator, or to.the dif ference between high and low side pressures, And hot to the liquid level in the evaporator; all entering refrigerant is evaporated be^ fore being recirculated. . . expansion, multi-stage: passing volatile refrigerant. through two or more pressure reducing devices, connected in series, usually with an evaporator between them operating at one pressure,and a second evaporator fed through both devices, at_a,lower pressure., expansion;coil: an evaporator constructed .of pipe or, tubing,