Flow Resistance For Fittings

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Flow Resistance for Fittings

There are a number of general formulas for determination of steady flow pressure drop available. One preferred by many is expressed as follows:


Where:

In order to determine the friction factor, f, for use with this formula, it is necessary to first calculate the appropriate Reynolds number, R, and then to select it from the graph below.

The formula for calculating R is:

Where:

Values for þ and u for different liquids and gases are available in various engineering handbooks.

As an example, if water at 70ºF is flowing through the 6" assembly of the previous page at an average velocity of 20ft/sec. the pressure drop due to flow friction (only) may be calculated as follows:

For water

and

then

ƒ = .015

(From graph below)

and

Therefore, the approximate pressure drop from flange to flange, due only to flow friction, is 4 psi. Calculation of total pressure drop would have to also take into account any change in elevation.

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