Document 6wwpndmaEmOVwrOpE7Gwz8G19

4 CHAPTER I 1948 Guide Dust: An air suspension (aerosol) of solid particles of any material. (See also Chapter 10, p. 166.) 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 constant 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 available 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 5 = / dQ/T. These formulas are applicable when temperature is not constant. During a reversible adiabatic change entropy is constant. During a reversible isothermal change the heat absorbed by the.substance is equal to the product of the absolute temperature of thet 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: 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, foaming, and atomizing. (See also Chapter 10, p. 167.) 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 sobroadand inclusive that its usefulness as a technical term is very limited. Itsprinapal 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 10, p. 166.) 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 beating system. Furnace Volume {Total): The total furnace volume for horizontal-return tubular boilers arid 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 (*.., no gas flow taking place through it), as in the case of wasteheat 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 .S.M.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 measured 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 mass 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. Terminology 5 Head, Dynamic: Same as Total Pressure expressed-in 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 theenergy 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 tem perature 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 (Cv) 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.). Hot Water Heating System: A heating system-in which water is used as-the medium 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. Humidistat: A regulatory device, actuated by changes, in humidity, used for the automatic control of relative humidity. Humidity:. Water vapor within a given space. ' -Humidity, Absolute: The weight of water vapor per unit volume,'pounds per cubic foot or gramri per cubic centimeter. Humidity, Relative: The ratio ofthe actual partial pressure of the water vapor m a space to the saturation pressure of pure water`at the same temperature. (See' dis cussion in Chapter 3.), i 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 Ratio. Hygrostat: " Same as Humidistat... . Ioch 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 some times taken as 0 C and sometimes as 62 F. One, inch of water at 62 F = 5.197 lb per square foot. Insulation (Thermal): A material having,a relatively high resistance to heat.flow, and used principally to retard the flow of heat. . Isobaric: . An adjective used to indicate a change taking.place at-constant.pressure. Isothermal: An. adjective used to indicate a.-change .taking place at-.constant temperature. Load, Estimated Design: In a heating'or cooling-system, the'sum'-of the useful heat 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 hour or, in heating,, equivalent direct radiation (EDR) which-is becoming obsolete. Load, Estimated Maximum: In a heating or cooling system, the calculated maxi mum heat transfer that the system, will be.called upon to provide.. Manometer: An instrument for measuring pressures; essentially a U-tube partially . filled with a liquid, usually water, mercury, or a light oil, so constructed that the amount of displacement of the liquid indicates the pressure being exerted on the instrument. Mass: A measure of the inertia of a body. It also measures the quantify of matter in a body. Since the only general property of a given portion of matter that cannot be changed is its inertia, it is this property by which quantities of matter are defined. Two bodies which have equal inertias are said to have equal masses or to contain equal quantities of matter. (This definition fails at velocities approaching-the velocity of