Document DYoJLqdg8ZzQpJzB6M2xzKbo

74 CHAPTER 3 1949 Guide REFERENCES . 1 Thermodynamic Properties of Moist Air, by J. A. Goff and S. Gratch (A.S.H.V.E. Transactions, Vol. 51,1945, p. 125). , T , __ , * 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). ,, ,T u Thermodynamic Properties of Steam, by J. H. Keenan and F. G. Keyes (John Wiley and Sons, Inc., New York, 1936). * 4 Das i, x-Diagramm fur Danipfluftgemische, by R. Mollier (ZVD1, 1929). 8 The Theory of the Psychrometer, by J. H. Arnold (Physics, Vol. 4,1933). Rational Psychrometric Formulae, by W. H. Carrier (A.S.M.E. Transactions, Vol. 33, 1911, p. 1005). 7 National Advisory Committee for Aeronautics, Technical Report No.-538, 1935.. CHAPTER 4 FLUID FLOW Theory; Pressure Loss in Circular and Non-Circular Pipes; Compressible Fluids; Nozzles and Orifices; Steam Flow Measurement; Metering Liquids; Nozzle Coefficients and Expansion Factors; Pitot Tube; Installa tion of Nozzles and Orifices, Variable Area Flow Meters THE flow of fluids is part of the branch of engineering science knownas fluid mechanics, which will be discussed here insofar as it applies to the work of engineers in the fields of heating, ventilating, and air conditioning. Probably air is the most frequently handled fluid, but other gases and liquids are often involved. Compressible fluids (gases) and incompressible fluids (liquids) vary somewhat in behavior, though in cases where pressure and density changes are small, the gases may be treated as incompressible fluids. THEORY OF FLUID FLOW The following energy equation for one dimensional steady flow processes will serve as a basis for the theory of the flow of fluids. This equation is presented in several ways in various texts, but a suitable form is V,* o VP a -------f- Jui -f- piVi + Jq H----- Zi = ---------1- Jut 4* piVt + W -|----- zi 2ffc g 2ffe (1) where V = velocity in feet per second. g = gravitational acceleration, in feet per (second) (second), ff. = gravitational conversion factor'= 32.174 (pounds mass per pound force) X ft per (second) (second). J = mechanical equivalent of heat = 778 foot pounds per Btu. u = internal energy, in Btu per pound of fluid, p <= pressure in pounds per square foot. v = specific volume, in cubic feet per pound. W = mechanical work done by the fluid in foot pounds per pound of fluid. q -- heat transferred to the fluid in Btu per pound of fluid.flowing. . , z = elevation above some arbitrary datum, in feet. Subscript 1 refers to the entrance, subscript 2 to the exit. Introducing the enthalpy h, which by definition is u + y, expressed in Btu per pound of fluid, Equation 1 becomes Vi* q Va* - g ^- + Jhi + Jq + Z-zl=1+Jh, + W+-zt 2ff. gc . . 2g g* (2) The equivalent differential form for. energy Equation 1 is . ' . dv> + Jdu + d(pv) + -- dz -- J dq + dW = 0 . 75 (3)