Document 914QkGejkwdKbdnReVRNykzBV

CHAPTER 3 1946' Guide LETTER SYMBOLS (Continued) m = weight of dry air crossing any duct section, pounds per minute. fnit mi = weights of dry air convected across sectiohs Fi, Ft,' Ft respectively, . pounds per minute: M = weight of dry air withdrawn with inside air, pounds per hour. a = mols of dry air. Hw = mols of water vapor., p = total pressure of a mixture of air and water vapor, pounds per square inch or inches Hg. pa = partial pressure of air, pounds per square inch or inches Hg. Ps = saturation pressure of pure water vapor, pounds per square inch or inches Hg. * Pw =-partial pressure of water vapor in mixture of air arid water vapor, * pounds per square inch or inches Hg. P = atmospheric pressure, inches Hg. P0 = standard atmospheric pressure by definition 29.921 in. Hg. PE = potential energy, Btu.per pound dry air. PE average potential energy, 6tu per pound dry air. q = ratio of energy added (or removed) to water added (or removed), Btu per pound. Also called specific enthalpy of water added. \qt = heat added between sections 1 and 2, Btu per pound dry air.- AqB = heat added between sections A' arid B per pourid of dry air, Btu per pound. , kQb = total heat added between sections A and B, Btu per minute. &Q = energy to be removed from or added to conditioned space, Btu per hour. R = universal gas constant. Ra = gas constant for dry air. Rw, = gas constant for water vapor. : ' j t= entropy of moist air per pound of dry air, Btu per (pound) (Fahrenheit degree). , . 5 = correction to be added to entropy of moist air obtained from Equation 6. I = additional correction to be, added to entropy because of "mixing ' entropy" (obtained'from Table 3). Correction to be added to value of s obtained from Equation 6, ~..$a =< specific entropy of-dry air, Btu per-(pound) (Fahrenheit degree, ab solute). f ' / ^ = the difference between the entropy oCmoist air at saturation per pound , of dry air, and the specific entropy of the'dry.air itself, Btu.per (pound of dry air) (Fahrenheit degree, absolute). : j8 = entropy of moist air at saturation per..pound of dry air, Btu per (pound of dry air) (Fahrenheit degree, absolute). sw- = specific entropy of condensed water (liquid or solid) at standard* atmos pheric pressure, Btu per (pound of water) (Fahrenheit degree, absolute). I* = thermodynamic wet-bulb temperature, Fahrenheit degrees. *(F) = temperature, Fahrenheit degrees. r = absolute temperature, Fahrenheit degrees. T0 = standard atmospheric temperature, by definition. 288 Kelvin degrees. v = volume of moist air per pound of dry air, cubic feet per pound. v = correction to be added to volume of moist air per pound of dry air, t above 150 F., na =. specific volume,of dry air, cubic feet per pound. Thermodynamics ________________ . .__________ ______________ - 73 / LETTER SYMBOLS (Continued) Pas ---Ps -- Pa> the difference between volume of moist: air at 'saturation,' per pound of dry air, and the volume of the dry air itself, cubic feet per pound of dry air. Vs = volume of moist air at saturation per pound of dry airj- cubic feet per . pound of dry air.. ' .- , vr = total volume, cubic feet. V -- velocity, feet per minute. V = average velocity, feet per minute. . W = humidity ratio, of moist air, pounds of water.per pound of dry-air. / A IF = water to be removed from (or added to) conditioned space, pounds per hour, r : ', Ws -- humidity ratio, at saturation, weight of water vapor per pound of dry '. air, pound per pound. Ws* = humidity ratio corresponding to thermodynamic'wet-bulb temperature t*, pounds of water per pound of.dry air. ; Z = elevation above any datum,, feet. Z = average elevation, feet. ' REFERENCES . i-Thermodynamlc Properties of Moist Air, by J. A...Goff and S. Gratch (A.S.H.V.E. Journal Section, Heating. Piping and Air Conditioning, June 1945. p. 334). 2--Low Pressure Properties of Water in the Range. --160 to 212 F. by J. A. Goff and S. Gratch (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, February 1946). 2--Thermodynamic Properties of Steam, by J. H. Keenan and F. G. Keyes (John Wiley and Sons. Inc.. New York. 1936). *--Das i. x-Diagramm fur Dampfluftgemische, by R. Mollier (ZVDI, 1929). 5_The Theory of the Psychrometer, by' J. H. Arnold (Physics, Vol, 4. 1933). -* 6-Rational Psychrometric Formulae, by W. H. Carrier (A.S.M.F.. Transactions, Vol. 33, 1911, p. 1005). i--National Advisory Committee for Aeronautics.1 Technical Report No. 538, 1935. .