Document Rp9EbX96Q75qwkk59qvbGnNzX

CHAPTER 1 1957 Guide Terminology 5 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 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. other substances. Dust: An air suspension (aerosol) of solid particles of any material. (See also Chapter 8.) Enthalpy: A term used in lieu of total heal 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 Head, Dynamic: Same as Total Pressure expressed in height of liquid. Heat: That form of energy which transfers from one system to another, by virtue of the temperature difference which exists between the two systems, when they a^e placed in communication. - 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. 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 = fdQIT. These formulas are applicable when temperature is not constant. During a re versible adiabatic change, entropy is constant. During a reversible isothermal change, the heat absorbed by the substance is equal to the product of the absolute 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 (cp) and specific heat at constant volume (c,) are frequently used. In air conditioning, cp is usually used. Heat, Total: See Enthalpy. temperature of the substance and its change of entropy. Heat Transmission, Coefficient: Any one of a number of coefficients used in the Entropy, Specific: A term sometimes applied to entropy per unit weight, the calculation of heat transmission by conduction, convection, and radiation, through English unit being Btu per (Fahrenheit degree, absolute) (pound). Equivalent Evaporation: The amount of water a boiler would evaporate, in pounds various materials and structures. (See thermal conductance, thermal conductivity, thermal resistance, thermal resistivity, thermal transmittance, etc.) per hour, if it received feed water at 212 F and vaporized it at the same temperature Heating Element, Electric: A unit assembly consisting of a resistor,insulated sup and corresponding atmospheric pressure. ports, and terminals for connecting the resistor to electric power. Ifit Fan Furnace System: See Warm Air Heating 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 by splashing Heating Unit, Electric: A structure containing one or more heating elements, electrical terminals or leads, electric insulation, and a frame or casing, all assembled together in one unit. foaming, and atomizing. (See also Chapter 8.) Force: The action on a body which tends to change its relative condition as to 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. rest or motion. Fumes: Smoke; aromatic smoke; odor emitted, as of flowers; a smoky or vaporous Humidify: To increase, by any process, the density of water vapor within a given space. 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 Humldlstat: A regulatory device, actuated by changes in humidity, used for the automatic control of relative humidity. principal definitive characteristic is that it implies an odor. The terms vapor, smoke, Humidity: Water vapor within a given space. 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, Humidity, Absolute: The weight of water vapor per unit volume, pounds per cubic foot or grams per cubic centimeter. generally, after volatilization from molten metals, etc., and often accompanied by a chemical reaction such as oxidation. Fumes flocculate and sometimes coalesce. Humidity, Relative: The ratio of the mol fraction of water vapor in a mixture to the mol fraction of water vapor in saturated air at the same dry-bulb temperature (See also Chapter 8.) Furnace: That part of a boiler or warm air heating plant in which combustion and barometric pressure. (See discussion in Chapter 3.) Also defined in various texts as the ratio of the actual partial pressure of the water vapor in a space to the takes place. Also a complete heating unit for transferring heat from fuel being saturation pressure of pure water at the same temperature. burned to the air supplied to a heating system. Humidity Ratio: In a mixture of water vapor and air, the weight of water vapor Furnace Volume (Total): The total furnace volume for horizontal-return tubular per pound of dry air. Symbol, W. Also called Specific Humidity. 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 manifestly ineffective (t.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. (ASMS 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 Humidity, Specific: See Humidity Ratio. Hygrostat: Same as Humidistat. 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 psoemr seqtimfte.s taken as 0 C and sometimes as 62 F. One inch of water at 62 F = 5.197 lb Insulation (Thermal) : A material having a relatively high resistance to heat flow, and used principally to retard the flow of heat. Isobarlc: An adjective used to indicate a change taking place at constant pressure. 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 Isothermal: An adjective used to indicate a change taking place at constant temperature. 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 tie 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 mass of the same volume of a standard substance at a standard temperature. Water Load, Estimated Design: In a heating or cooling system, the sum of the useful neat transfer, plus heat transfer from or to the connected piping, plus heat transfer occurring in any auxiliary apparatus connected to the system. The units are Btu per nour or, in heating, equivalent direct radiation (EDR). Load, Estimated Maximum: In a heating or cooling system, the calculated maxi mum heat transfer that the Bystem will be called upon to provide.