Commonly Used Formula in Hydraulics

Darcy Weisbach formula
Darcy Weisbach formula which is valid for laminar or turbulent flow in all fluids is one of the most commonly used formula for determining the head loss.


hf=head loss due to friction, ft (m)

f= friction factor

L =length of pipe, ft (m)

D= diameter of pipe, ft (m)

V =velocity of fluid, ft/s (m/s)

g =acceleration due to gravity, 32.2 ft/s2 (9.81 m/s2)

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Fluid flow in pipes

Laminar Flow

Its is a flow in which the fluid particles move in parallel layers in a single direction.Due to the parabolic velocity distribution in laminar flow, a shearing stress is developed. As this shearing stress increases, the viscous forces become unable to damp out disturbances, and turbulent flow results. The region of change is dependent on the fluid velocity, density, and viscosity and the size of the conduit.

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Similitude for physical models

A physical model is a system whose operation can be used to predict the characteristics of a similar system, or prototype, usually more complex or built to a much larger scale.”A model can be either smaller or bigger than the real construction.It is believed that model is always smaller but that is not true always for example if we want to make a very small computer chip then to illustrate its function properly the model is made bigger as compared to the original chip. Continue Reading »

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Bernoulli Equation

For fluid energy, the law of conservation of energy is represented by the Bernoulli equation(for ideal fluid only):


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Viscosity of a fluid, also called the coefficient of viscosity, absolute viscosity, or dynamic viscosity, is a measure of its resistance to flow. It is expressed as the ratio of the tangential shearing stresses between flow layers to the rate of change of velocity with depth

Facts About Viscosity are:-

1)Viscosity decreases as temperature increases.

2)The pressure effect is neglected in various engineering applications.
Water at 70°F (21.1°C) has a viscosity of 0.00002050 lb s/ft2 (0.00098 N s/m2).

3)Viscosity divided by density is called kinematic viscosity.

4)In hydraulics, viscosity is most frequently encountered in the calculation of Reynolds number to determine whether laminar, transitional, or completely turbulent flow exists.

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