Document ga14aG7brg8naJejz40opMVKL

8 CHAPTER 1 1950 Guide ; Refrigerant: A substance which produces a refrigeratingeffeot by its absorption of heat while expanding or vaporizing. Refrigeration, Ton of: The removal of heat at a rate of 200 Btu per min, 12,000 Btu per hr, or 288,000 Btu per 24 hr. Resistance, Thermal : The reciprocal of thermal conductance. Symbol R. Resistor, Electric: A material used to produce heat by passing an electric current through it. Resistivity, Thermal: The reciprocal of thermal conductivity. Symbol r. Return, Dry: A return pipe in a steam heating system which carries both water of condensation and air. The dry return is above the level of the water line in the boiler in a gravity system. (See Return, Wet.) Return, Wet: That part of a return main of a steam heating system which is filled with water of condensation. The wet return usually is below the level of the water line in the boiler, although not necessarily so. (See Return, Dry.) Return Mains: Pipes or conduits which return the heating or cooling medium from the heat transfer unit to the source of heat or refrigeration. Reversed-Retum System: A system in which the heating or cooling medium fms several heat transfer units is returned along paths arranged so that all circuits 3c:.:a nosing the system or composing a major sub-division of it are of practically length. Sabin: A unit of equivalent sound absorption equal to the equivalent absorption of one square foot of a surface of unit absorptivity (i.e., of one square foot of surface which absorbs all incident sound energy). Saturation: The condition for co-existence in stable equilibrium of a vapor and liquid or a vapor and solid phase of the same substance. Example: Steam over the water from which it is being generated. Saturation, Degree of: The ratio of the weight of water vapor associated with a pound of dry air to the weight of Water vapor associated with a pound of dry air saturated at the same temperature. Smoke: An air suspension (aerosol) of particles, usually but not necessarily solid, often originating in a solid nucleus, formed from combustion or sublimation. Also defined as carbon or soot particles less than 0.1 micron in size which result from the incomplete combustion of carbonaceous materials such as coal, oil, tar, and tobacco. Smokeless Arch: An inverted baffle placed in an up-draft furnace toward the rear to aid in mixing the gases of combustion, and thereby to reduce the smoke produced. Solar Constant: The solar intensity incident on a normal surface located outside the earth's atmosphere at a distance from the sun equal to the mean distance between the earth and the sun. Its value is 415,445, or 430 Btu per (hr) (sq ft) as the July, January, or mean value, respectively. At sea level in July the solar intensity value is about 300 Btu per (sq ft) (hr) since about 28 per cent is absorbed in the earth's atmosphere. Sorbent: A material which extracts one or more substances present in an atmos phere or mixture of gases or liquids with which it is in contact, due to an affinity for such substances. Sorption: Adsorption or absorption. Split System: A system in which the heating is accomplished by means of radiators or convectors supplemented by mechanical circulation of air (heated or. uhheated) from a central point. Ventilation may be provided by the same system. - Square Foot of Heating Surface (Equivalent): This term is synonymous with Equivalent Direct Radiation (EDR). ' Stack Height: The height of a gravity convector between the bottom of the heating unit and the top of the outlet opening. - Steam: Water in the vapor phase. Dry Saturated Steam is steam at the saturation temperature corresponding to the pressure, and containing no water in suspension. WetSaturated Steam is steam at the saturation temperature corresponding to the pres sure, and containing water particles in suspension. Superheated Steam is steam at a temperature higher than the saturation temperature corresponding to the pressure. Steam Heating System: A heating system in which heat is transferred from the boiler or other source of heat to the heating units by means of steam at, above, or below atmospheric pressure. Steam Trap: A device for allowing the passage of condensate, or air and con densate,and preventing the passage of steam. Supply Mains: The pipes through which the heating medium flows from the boiler or source of supply to the run-outs and risers leading to the heatinir units. 9 Terminology Surface, Heating: The exterior surface of a heating unit. Extended heating surface (or extended surface): Heating surface consisting of fins, pins or ribs which receive heat . by conduction from the prime surface. Prime Surface: Heating surface having the heating medium on one side and air (or extended surface) on the other. (See also BoTileermHpeearatitnugreS: uTrfhaeceth.)ermal state of matter with reference to its tendency to com municate heat to matter in contact with it. If no heat flows upon contact, there is no Tdeiffmerpeenrcaetuirne,teAmbpseorluatteu:reT.emperature expressed in degrees above absolute zero. Temperature, Dew-Point: The temperature at which the condensation of water vapor in a space begins for a given state of humidity and pressure as the temperature of the vapor is reduced. The temperature corresponding to saturation (100 per cent relative humidity) for a given absolute humidity at constant pressure. Temperature, Dry-Bulb: The temperature of a gas or mixture of gases indicated by an accurate thermometer after correction for radiation. Temperature, Effective: An arbitrary index which combines into a single value the effect of temperature, humidity, and air movement on the sensation of warmth or cold felt by the human body. The numerical value is that of the temperature of still, "jlit^rated air which would induce an identical sensation. `ii/p^mperature, Wet-Bulb: Thermodynamic wet-bulb temperature is the tempera'Cu-e at which liquid or solid water, by evaporating into air, can bring the air to saturation adiabatically at the same temperature. Wet-bulb temperature (without qualification) is the temperature indicated by a wet-bulb psychrometer constructed and used according to specifications. (ASMS Power Test Codes, Series 1932, Instruments and Apparatus, Part 18.) Therm: A quantity of heat equivalent to. 100,000 Btu. Thermodynamics, Laws of: Two laws upon which rest the classical theory of thermodynamics. These laws have been stated in many different, but equivalent ways. The First Law: (1) When work is expended in generating heat, the quantity of heat produced is proportional to the work expended; and conversely, when heat is em ployed in the performance of work, the quantity of heat which disappears is propor tional to the work done. (Joule)* (G.P.)"; (2) If a system is caused to change from an initial state to a final state by adiabatic means only, the work done is the same for all adiabatic paths connecting the two states. (Zemansky); (3) In any power cycle or refrigeration cycle the net heat absorbed by the working substance is.exactly equal to the net work done. The Second Law (1) It is impossible for a self-acting machine, un aided by any external agency, to convey heat from a body of lower to one of higher temperature. (Clausius) (U.P.): (2) It is impossible to derive mechanical work from heat taken from a body unless there is available a body of lower temperature into which the residue not so used may be discharged (Kelvin) (G.P.); (3) It is impossible to construct an engine that, operating in a cycle, will produce no effect other than the extraction of heat from a reservoir and the performance of an equivalent amount of woTrkhe(Zrmemosatnast:kyA).n instrument which responds to changes in temperature, and which directly or indirectly controls temperature. Transmittance, Thermal: The time rate of heat flow, from the fluid on the warm side to the fluid on the cold side, per (square foot) (degree temperature difference be tween the two fluids). Sometimes called Overall Coefficient of Heat Transfer. Common unit is Btu per (hour) (square foot) (Fahrenheit degree). Symbol Vm Two-Pipe System (Steam or Water): A heating system in which one pipe is used for the supply of the heating medium to the heating unit, and another for the return of the heating medium to the source of heat supply. The essential feature of a two-pipe system is that each heating unit receives a direct supply ofthe heating medium, which medium cannot have served a preceding heating unit. Up-Feed System: A heating system in which the supply mains are below the level of tVhaecuhuematinHgeautninitgs Swyhsictehmth: eAy tsweorv-ep.ipe steam heating system equipped with the necessary accessory apparatus which will permit operating the system below atmos pheVraicnepRreasstiuor:eIwnhaeirnddiesstriribedu.ting devices the ratio of depth of vane to shortest open ing width between two adjacent grille bars. 1937)- X