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Fluid Mechanics: Head Loss



Head Loss

Head loss is a loss in pressure head due to the viscosity of a fluid and obstructions to a fluid such as pipe elbows, valves, etc. By knowing the head loss, you can successfully modify Bernoulli's energy equation accordingly; refer to equation 1. Bernoull's energy equation is Bernoulli's equation divided by the fluid's specific weight.

Modified Bernoulli's energy equation (1)

P = Pressure

γ = Specific Weight

α = Energy Coefficient

v = Velocity

g = Gravitational Constant

z = Fluid Height

HL = Head Loss


In equation 1 α represents the energy coefficient. The energy coefficient is 1 when the flow is developed. However, if the flow is undeveloped the energy coefficient will be less than 1. Finally, hl represents the head loss.

There are two different types of head losses that make up the total head loss seen in equation 2. These head losses are the major head loss and the minor head loss.

Head loss equation (2)




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