Hydraulic losses in pipes Politechnika （在管道 Politechnika水力损失）.pdf

Hydraulic losses in pipes Henryk Kudela Contents 1 Viscous flows in pipes 1 1.1 Moody Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Types of Fluid Flow Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Minor losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1 Viscous flows in pipes Our intension here is generalized the one-dimensional Bernoulli equation for viscous flow. When 2 the viscosity of the fluid is taken into account total energy head H = v + p +z is no longer 2g ρg constant along the pipe. In direction of flow, due to friction cause by viscosity of the fluid we 2 2 have v1 + p 1 +z 1 v2 + p 2 +z2 . So to restore the equality we must add some scalar quantity to 2g ρg 2g ρg the right side of this inequality 2 2 v1 p 1 v2 p 2 + +z 1 = + +z2 +∆hls (1) 2g ρg 2g ρg This scalar quantity ∆ls is called as hydraulic loss. The hydraulic loss between two different cross section along the pipe is equal to the difference of total energy for this cross section: ∆hls = H 1 −H2 (2) We must remember tha