Document 9LQv3aDvkpRkmDg13j6ydYXJq

6 CHAPTER 1 1943. Guide light.) .The mass of a body is numerically equal to the ratio of the force required to give the body a given acceleration to the acceleration, m =* F/a. The common units of mass are the gram and the pound. Mechanical Equivalent of Heat: The quantity of mechanical energy equal, to one unit of heat. J " 778.3 ft:lb per Btu = 4.187 X 107 ergs per gram-calorie. Medium, Heating: A substance such as water, steam, air or furnace gas used to convey heat from the boiler, furnace or other souce of heat or energy to the heating unit from which the heat is dissipated. Micron; A unit of length, the thousandth part of 1 mm or the millionth of a meter. - Millimeter of Mercury: A unit of pressure equal to the pressure exerted by a column of mercury 1 mra high at a temperature of 0 C. One millimeter of mercury at OC = 1.934 X 10"* lb per square inch. Mol: A weight of a substance numerically equal to its molecular weight. If the weight is in pounds the-unit is a Pound Mol, in grams the unit is a Gram Mol. For perfect gases the volume of 1 mol is constant for all gases at the same temperature ana pressure. For real gases this is approximately true at moderate pressures. At 32 F and zero-pressure the value of the product, pressure times specific volume, is 359.045 * 0.006 atmosphere cubic feet (atm ft*), for 1 mol of any gas. For dry air at 32 F and standard atmospheric pressure, the specific volume is 358.83 cu ft per mol (ft* per mol). One-Pipe Supply Riser--(Steam): A pipe which carries steam vertically to a heat ing unit and which also carries the condensate from the heating unit. In an upfeed. system steam and condensate flow in opposite directions; in an overhead or down-feed, system they flow in the same direction. One-Pipe System--(Steam): A steam heating system in which a single main serves the dual purpose of supplying steam to the heating unit and conveying condensate from it. Ordinarily to'each heating unit there is but one connection which must serve as .both the supply and the return, although separate supply and return connections may be used. (Hot Water)--A hot water system in which the cooled water from the heating units is returned to the supply main. Consequently, the heating units farthest from the boiler are supplied with cooler water than those near the boiler in the same circuit. Overhead System: Any steam or hot water system in which the supply main is above the heating unit. In a steam system the return must be below the heating units; in a water system the return may be above or below the heating units., . Panel Heating: A heating system in which heat is transmitted by both radiation and convection from panel surfaces to both air and surrounding surfaces. . Panel Radiator: A heating unit placed on or flush with a flat wall surface and in tended to function essentially as a radiator. Plenum Chamber: An air compartment maintained under pressure and connected to one or more distributing ducts. Potentiometer: An instrument for comparing small electromotive forces or for measuring small electromotive forces by comparison with a known electromotive force. Its principal advantage is that during the measurement no current flows through the source of electromotive force. Power: The rate of performing work. Common units are horsepower, Btu per hour, and watts. Pressure: Force per unit area. Common units are pounds per square inch, gram per square centimeter, inch of water, millimeter of mercury. Pressure, Absolute: The sum of the gage pressure and the barometric pressure. Pressure, Gage: Pressure measured from atmospheric pressure as a base. Gage pressure may be indicated by a manometer which has one leg connected to the pressure source and the other exposed to atmospheric pressure. Pressure, Dynamio: Same as Total Pressure. Pressure, Saturation: The saturation pressure for a pure'substance for any given temperature is that pressure at which vapor and liquid or vapor and solid can co-exist in stable equilibrium. Pressure, Static: The normal force per unit area that would be exerted by a moving fluid on a small body immersed in it if the body were carried along with the fluid. Practi' caily, it is the normal force per unit area at a small hole in a wall of the duct through which the fluid flows (piezometer) or on the surface of a stationary tube at a point where the disturbances created by inserting the tube cancel. .It is supposed that the thermodynamic properties of a moving fluid depend on. static pressure in exactly the same manner as those of the same fluid at rest depend upon its uniform hydrostatic pressure. Pressure, Total: In the theory of the flow of fluids; the sum of the static pressure and the velocity pressure at the point of measurement. Terminology 7 Pressure, Vapor: The pressure exerted by a vapor. If a vapor is kept in confine ment over its liquid so that the vapor can accumulate above the liquid, tbe.temperature being held constant, the vapor pressure approaches a fixed limit called the maximum. Or' saturated, vapor pressure, dependent only on the temperature and the liquid. The term vapor pressure is sometimes used as synonymous with saturated vapor pressure. . Pressure, Velocity: In a moving fluid, the pressure capable of causing an equivalent velocity if applied to move the same fluid through an orifice such that all pressure energy expended is converted into kinetic energy. . Psychrometer: An instrument for ascertaining the humidity or hygrometric state of the atmosphere. Psychrometric: Pertaining to psychrometry or the state of the atmosphere with . reference to moisture. Psychrometry: The branch of physics relating to the measurement or determination of atmospheric conditions, particularly regarding the moisture mixed with the air, . Pyrometer: An instrument for measuring high temperatures. Radiant Heating: A heating system in which only the heat radiated from panels is effective in providing the heating requirements. The term Radiant Healing is fre- ' quentlv used to include both Panel and Radiant Heating. Radiation: The transmission of energy by means of electromagnetic, waves. Radiation, Thermal (Heat) Radiation: The transmission of energy by means of electromagnetic waves of very long wave length. Radiant energy of. any wave length may, when absorbed, become thermal energy and result in an increase in the temperature of the absorbing body. Radiation, Equivalent Direct (EDR): A unit of heat delivery of 240 Btu (Steam) or 150 Btu ( Water) per hour. . It does not imply 144 sq in. of surface. Radiator: A heating unit exposed to view within the room or.space to.be heated. A radiator transfers heat by radiation to objects within visible range and by conduction to the surrounding air which in turn is circulated by natural convection; aso-called radiator is also a convector but the term radiator has been established by long usage. Radiator, Concealed: A heating device located within, adjacent to, br.exterior to the room being heated but so covered or enclosed or concealed that the- heat' transfer . surface of the device, which may be either a radiator or a convector, is not visible 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 minute, 12,000 Btu per hour, or 288,000 Btu per 24 hours. . Resistance, Thermal: The reciprocal of thermal conductance, Symbol R. Resistivity, Thermal: The reciprocal of thermal conductivity. Symbol r. 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 line ' 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 so that all circuits com posing the system or composing a major sub-division of it are ofpractically equal length. 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, or Per Cent: The ratio of the weight of a given-volume of water vapor to the weight of an equal volume of saturated water vapor 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