Head Loss

Head loss is combined of two major components: friction losses and minor losses. Friction losses are head losses due to the friction that the walls of the pipe imposes on a liquid. Friction losses are dependent on the viscosity of the fluid and the turbulence of the flow. Head loss due to friction (hf) can be calculated using the Darcy-Weisbach equation:

The friction factor, f, can be determined if you know the relative roughness of the pipe, E/d, and by solving for the Reynolds number, Re, and using the Moody Chart, which can be found in any fluid mechanics book. The Reynolds number can be found using the following equation:

Minor losses are losses due to the change in flow patterns of the liquid, i.e. bends, valves, sudden changes in pipe diameter, etc. Minor losses are usually negligible compared to friction losses in larger pipe systems. Minor losses, hm, can be determined by the following equation:

The coefficient of minor head loss can also be determined from tables in your fluids mechanics book. There are values for every type of valve, elbows, tees, bends, and sudden and gradual expansions and contractions.

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