Document dQ2zBrmaBXErRgrbdd2zLMe50

8 CHAPTER 1 1948 Guide 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 (hour)'(square foot) as the July, January, or mean value respectively. At sea level in July the solar intensity value is about 300 Btu per (square foot) (hour) 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 unheated) 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 hehting 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. Wet Saturated Steam is steam at the saturation temperature corresponding to the pressure, and containing water particles in suspension. Superheated Steam is steam at a tem perature 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 of 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 heating units. , 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 thd 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, Dry-Bulb: The temperature of a gas or mixture of gases indicated by an accurate thermometer after correction for radiation.- 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, tp saturation (100 per -cent relative humidity) for a given absolute humidity at constant pressure. .. . . 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 numericail value is that of the temperature of still, saturated air which would induce an identical sensation. Temperature, Wet-Bulb: Thermodynamic wet-bulb temperature is the tem perature 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. (A.S.M.E. Power Test Codes, Series .1932, Instru ments and Apparatus, Part 18.) 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 proportional to Terminology 9. the work done. (JouIe)a (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 bbdy 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 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 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 between the two fluids). Sometimes called Over-all Coefficient of Heat Transfer. Common unit is Btu per (hour) (square foot) (Fahrenheit degree). Symbol V. Two-Pi pe 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 of the 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 the beating units which they serve. ' Vacuum Heating System: A two-pipe steam heating system equipped with the nperecsessusraerywahcecnesdseosriyreadp.paratus which will permit operating the system below atmospheric Vane Ratio: In air distributing devices the ratio of depth of vane to shortest opening width between two adjacent grille bars. Vapor: The gaseous form of substances which are normally in the solid or liquid state and which can be changed to these states either by increasing the pressure or decreasing the temperature. Vapors diffuse. (d.S.d. definition.) Vapor Keating System: A steam heating system which operates under pressures at or- near atmospheric and which returns the condensate to the boiler or receiver- by gravity. Vapor systems have thermostatic traps or other means of resistance on the return ends of the heating units for preventing steam from entering the return mains; they also have a pressure-equalizing and air-eliminating device at the end of the dry return. Velocity: A vector quantity which denotes at once the time rate and the direction of a linear motion. V <= . For uniform linear motion V = -7- . Common units are: feet per second. dt t Ventilation: The process of supplying or removing air, by natural or mechanical means, to or from any space. Such air may or may not have been conditioned. (See Air Conditioning.) Volume, Specific: The volume of a substance per unit mass; the reciprocal of density. Units: cubic feet per pound, cubic centimeters per gram, etc. Warm Air Heating System: A warm air heating plant consists of a heating unit, (fuel-burning furnace) enclosed in a casing, from which the heated air is distributed to the various rooms of the building through ducts. Warm Air Heating System, Gravity: A warm air heating system in which the motive head producing flow depends on the difference in weight between the heated air leaving the casing and the cooler air entering the bottom of the casing. Warm Air Heating System, Mechanical: A warm air heating system in which circulation of air is effected by a fan. Such a system may include air meaning devices. bFrol^ aUth0rr3"hofiTM 'aw are given in parentheses. From Glossary of Physics, by LeRoy Dougherty Weld. (McGraw-Hill. 1937).