Document DGxY1wxbp6y8rgKG8pRmQmxw4

4 CHAPTER 1 1950 Guide Down-Feed System (Steam): A steam heating system in which the supply mains are above the level of the heating units which they serve. Draft: A current of air. Usually refers to the pressure difference which causes a current of air or gases to flow through a flue, chimney, heater or space. Draft Head (Side Outlet Enclosure): The height of a gravity convector between the bottom of the heating unit and the bottom of the air outlet opening. (Top Outlet Enclosure): The height of a gravity convector between the bottom of the heating unit and the top of the enclosure. Drip: A pipe, or a steam trap and a pipe considered as a unit, which conducts com densation from the steam side of a piping system to the water or return side of the system. Dry: To separate or remove a liquid or vapor from another substance. The liquid may be water, but the term is also used for the removal of liquid or vapor forms of other substances. Dust: An air suspension (aerosol) of solid particles of any material. (See also Chapter 8.) ' Electric Heating Element: A unit assembly consisting of a resistor, insulated sup ports, and terminals for connecting the resistor to electric power. Enthalpy : A term used in lieu of total heat or heat content. Expressible in Btu per pound. Mathematically defined as h = u + pv/J. When a change occurs at con stant pressure, as when water is boiled, the change in enthalpy is equal to the heat added, in this case latent heat. 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 avail able energy can occur spontaneously. Enthalpy, Specific: A term sometimes applied to enthalpy per. unit weight, the English unit being Btu per pound. Entropy: The ratio of the heat added to a' Substance to the absolute temperature at which it is added. Mathematically, for a reversible process, dS = dQ/T or S=fdQ/T. These formulas are applicable when temperature is not constant. During a re-. versible adiabatic change, entropy is constant. During1 a. reversible isothermal change, the heat absorbed by the substance is equal to the'product of the absolute temperature of the substance and its change of entropy. Entropy, Specific: A term sometimes applied to entropy per unit weight, the English unit being Btu per (Fahrenheit degree, absolute) (pound). 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. ' Fan Furnace System: SeaWarmAir Beating System. Fog: Suspended liquid droplets generated by condensation from the gaseous to the liquid state, or by breaking up a liquid into a dispersed state, such as oy splashing, foaming, and atomizing. (See also Chapter 8.) Force: The action on; a body which tends to. change its relative condition-as to rest or motion. ... Fumes-: Smoke; aromatic smoke; odor emitted, as of flowers; a smoky or vaporous exhalation, usually odorous, as that from concentrated nitric acid. The word fumes is so broad and inclusive that its usefulness as a.technical term is. very limited. Its principal definitive characteristic is that it implies an odor. The terms vapor, smoke, fog, etc., which can be more strictly defined, should be used whenever, possible. Also defined as solid particles generated by condensation from the gaseous state, generally, after volatilization from molten metals, etc., and often accompanied by a chemical reaction such as oxidation. Fumes flocculate and sometimes coalesce.. (See also Chapter 8.) Furnace: That part of a boiler or warm air heating plant in which combustion" takes place. Also a' complete heating unit for transferring heat from fuel being burned to the air supplied to a heating system. Furnace Volume (Total): The total furnace volume for horizontal-return tubular boilers and water-tube,boilers is the cubical contents of the furnace between the grate and the first plane of entry into or between tubes. It therefore includes the volume behind the bridge wall as in ordinary horizontal-return tubular boiler settings, unless A :.1 i A |4 1: Terminology 5 manifestly ineffective (.e., no gas flow.taking place through it), as in the case of waste-heat boilers with auxiliary coal furnaces, where one part of the furnace is out of action when the other is being used. For Scotch or other internally-fired boilers, it'is the cubical contents of the furnace, flues and combustion chamber, up to the plane of first entry into the tubes. (A JS.U.E. Power Test Codes, Series 1929.) Grate Area: The area of the grate surface, measured in.square feet, to be used in estimating the rate of burning fuel. This area is construed to mean the area meas ured in the plane of the top surface of the grate, except that with special furnaces, such as those having magazine feed, or special shapes, the grate area shall be the mean area of the active part of the fuel bed taken perpendicular to the path of the gases through it. For furnaces having a secondary grate, such as those in double grate down-draft boilers, the effective area shall be taken as the area of the upper grate plus one-eighth of the area of the lower grate, both areas being estimated as previously defined. , Gravity, Specific: The ratio of the mass of a unit volume of a substance to the mua of the same volume of a standard substance at a standard temperature. Water at 39.2 F is the standard substance usually referred to. ;For gases, dry air at the same temperature and pressure as the gas, is often taken as the standard substance. Gravity Warm Air Heating System: See Warm Air Heating System. Head, Dynamic: Same as Total Pressure expressedin height of liquid. Heat: The form of energy that is transferred by virtue of a temperature difference. At constant pressure heat added is equal to enthalpy change. Heat, Humid: Ratio of increase of enthalpy per pound of dry air to rise of tem perature under conditions of constant pressure and constant humidity ratio.. Heat, Latent: A term used to express the energy involved in a change of state. ' Heat, Sensible: A term used in heating and cooling to indicate any portion of heat which changes only the temperature of the substances involved. Heat of the Liquid: The increase in enthalpy per unit weight of a saturated liquid as its temperature increases from a chosen base temperature. For water, the base temperature is usually taken as 32 F. Heat, Specific: The heat absorbed (or given up) by.a unit mass of a substance when its temperature is increased (or decreased) by 1 deg. . Common Units: Btu per (pound) (Fahrenheit degree); calories per (gram) (Centigrade degree). For gases, both specific heat at constant pressure (C,,) and specific heat at constant volume (C,) are frequently used. In air-conditioning, Cp is usually used. Heat, Total: See Enthalpy. Heat Transmission, Coefficient: Any one of a number of coefficients used in the calculation of heat transmission by conduction, convection, and radiation, through various materials and structures. (See thermal conductance, thermal conductivity, thermal resistance, thermal resistivity, thermal transmittance, etc.). . Heater, Electric: A complete assembly of heating elments with their enclosure ready for installation in service. . Hot Water Heating System: A heating system in which water is used as the me dium by which heat is carried from the boiler to the heating units. Humidify: To increase, by any process, the density of water vapor within a given space.' Humldlstat: A regulatory device, actuated by. changes in humidity, used for the automatic controrof relative humidity. Humidity: Water vapor within a given space. . Humidity, Absolute: The weight of water vapor per unit volume, pounds per cubic foot or grams per cubic centimeter. Humidity, Relative: The ratio of the actual partial pressure of the water vapor in a space to thejaaturation pressure of pure water at the same temperature. (See' discussion in Chapter;)!.) . Humidity Ratio: In a mixture of water vapor and air, the weight of water vapor per pound of dry air. Also called Specific Humidity. Humidity Specific: See Humidity Balio. Hygrostat: Same as Humidistal. Inch of Water: A unit of pressure equal to the pressure exerted by a column of liquid water 1 in. high at a standard temperature. The standard temperature is sometimes taken as 0 C and sometimes as 62 F. One inch of water at 62 F = 5.197 lb per sq ft. ' ' .