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Ebook Heating, ventilating, and air conditioning analysis and design (6/E): Part 2

(BQ) Part 2 book “Heating, ventilating, and air conditioning analysis and design” has contents: Flow, pumps, and piping design; space air diffusion, fans and building air distribution; direct contact heat and mass transfer; extended surface heat exchangers, and other contents. | Chapter10.qxd 6/15/04 2:32 PM Page 299 Chapter 10 Flow, Pumps, and Piping Design The distribution of fluids by pipes, ducts, and conduits is essential to all heating and cooling systems. The fluids encountered are gases, vapors, liquids, and mixtures of liquid and vapor (two-phase flow). From the standpoint of overall design of the building system, water, vapor, and air are of greatest importance. This chapter deals with the fundamentals of incompressible flow of fluids such as air and water in conduits, considers the basics of centrifugal pumps, and develops simple design procedures for water and steam piping systems. Basic principles of the control of fluid-circulating systems—including variable flow, secondary pumping, and the relationship between thermal and hydraulic performance of the system—are covered. 10-1 FLUID FLOW BASICS The adiabatic, steady flow of a fluid in a pipe or conduit is governed by the first law of thermodynamics, which leads to the equation P1 V2 gz P V2 gz g l + 1 + 1 = 2 + 2 + 2 +w+ gc gc gc f ρ1 2 gc ρ2 2 gc (10-1a) where: P = static pressure, lbf/ft2 or N/m2 ρ = mass density at a cross section, lbm/ft3 or kg/m3 V = average velocity at a cross section, ft/sec or m/s g = local acceleration of gravity, ft/sec2 or m/s2 gc = constant = 32.17 (lbm-ft)/(lbf-sec2) = 1.0 (kg-m)/(N-s2) z = elevation, ft or m w = work, (ft-lbf)/lbm or J/kg lf = lost head, ft or m Each term of Eq. 10-1a has the units of energy per unit mass, or specific energy. The last term on the right in Eq. 10-1a is the internal conversion of energy due to friction. The first three terms on each side of the equality are the pressure energy, kinetic energy, and potential energy, respectively. A sign convention has been selected such that work done on the fluid is negative. Another governing relation for steady flow in a conduit is the conservation of mass. For one-dimensional flow along a single conduit the mass rate of flow at any two cross sections 1 and 2 is given by m˙