Document zzBaa0LRM1bqNQ37ex17B9j1g

8 CHAPTER 1 1955 Guide from the room. Such a device transfers its heat to the room largely by convection air currents. . . .. - .. Radiator, Direct: Same as Radiator. * Radiator, Recessed: A heating unit set back into a wall recess, but not enclosed. ; Radiator, Tube or Tubular: A heating unit used as a radiator in which the heat transfer surfaces.are principally tubes. Refrigerant: A substance which produces a refrigerating effect 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. v. Resistance, Thermal: The reciprocal of thermal conductance. Symbol R. ^Resistivity, Thermal: The reciprocal of thermal conductivity. Symbol r. Resistor, Electric: A material used to produce heat by passing an electric currentthrough it. 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 Jine 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-Return System: A system in which the heating or cooling medium from several heat transfer units is returned along paths arranged bo that all circuits com posing the system or composing a major sub-division of it are of practically equal 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 percent is absorbed in the earth's at mosphere. 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 radia tors or convectors supplemented by mechanical circulation of air (heated or urn heated) 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 heat ing unit and the top of the outlet opening. Steam: Water in the vapor phase. Dry Saturated Steam is steam at the satura tion temperature corresponding to the pressure, and containing no water in suspen sion. Wet Saturated Steam is steam at the saturation temperature corresponding to the pressure, and containing water particles in suspension. Superheated Steam is Terminology 9 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 v/hich the heating medium flows from the boiler or source of supply to the run-outs and.risers leading to the heating units. Surface, Heating: The exterior surface of a heating unit. Extended heating sur face (or extended surface): Heating surface consisting of fins, pins or ribs which re ceive 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 Boiler Heating Surface.) Temperature: The thermal 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 difference in temperature. Temperature, Absolute: Temperature 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 percent 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, saturated air which would induce an identical sensation. Temperature, Mean Radiant (MRT): The temperature of a uniform black en closure in which a solid body or occupant would exchange the same amount of radi ant heat as in the existing nonuniform environment. Temperature, Wet-Bulb: Thermodynamic wet-bulb temperature is the tempera ture at which liquid or solid water, by evaporating into air, can bring the air to satu ration 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. . (ASME Power Test Codes, Series 1932, In struments 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 employed in the performance of work, the quantity of heat which disappears is pro portional to the .work done. (Joule)* (G.P.)b; (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, unaided by any external agency, to convey heat from a body of lower to one of higher temperature. (Clausius) (G.P.); (2) It is impossible to derive mechanical work from heat taken from a body- unless there is available a body of 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 pro duce no effect other than the extraction of heat from a reservoir and the performance of an equivalent amount of work (Zemansky). Thermostat : An 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.U. Names of authors who first stated laws are given in parentheses. From Glossary of Physics, by LeRoy Dougherty Weld (McGraw-Hill, 1937).