流体力学与 及传热课件1.5 Pipe Flow Systems.pptVIP

1.5 Pipe Flow Systems ;We will concern two classes of pipe systems: those containing a single pipe and those containing multiple pipes in parallel, series.;Pipe system ; They include : the pipes themselves, the various fittings used to connect the individual pipes to form the desired system, metering devices, and the pumps or turbines that add energy to or remove energy from the fluid.;1.5.1 Single Pipes ;Solution: Since the velocity in the pipe is given by ;And the fluid properties are ρ=999.9kg/m3 and μ=1.12×10-3Pas;Governing equation for either case (a), (b), or (c) is the mechanical balance equation given by;Where z1=0, z2=6.1m, p2=0, and outlet velocity is ;(a) If all losses are neglected, Eq.1 gives;(b) If only losses included are the skin friction losses , the friction loss is ;Relative roughness ε/D=8×10-5;Of this pressure drop, the amount due to skin friction is 71739 Pa;( c) If skin friction losses and minor losses are included, Eq.1 becomes;The loss coefficients of the components (Kf=1.5 for each elbow and 10 for the wide open globe valve) are given. The loss coefficient of the faucet is 2. thus ; Note that we did not include an entrance or exit loss because points (1) and (2) are located within the fluid streams, not within an attaching reservoir where the kinetic energy is zero. Thus, by comparing Eqs.2 and 3 we obtain the entire pressure drop as ;Example 2;Solution : The energy equation can be applied between the surface of the lake (point 1) and the outlet of the pipe as ;The head loss is given by;Thus, Eq.1 can be written as ;1.5.2 Multiple Pipe Systems;The governing ‘mechanisms for the flow in multiple pipe systems are the same as for the single pipe systems. However, because of numerous unknowns involved, additional complexities may arise in solving for the flow in multiple systems.;Parallel pipe system;By writing the mechanical energy balance equation it is found that the energy loss experienced by any fluid particle traveling between the