What is the formula for calculating pressure drop @ a 90 degree or 45 degree pipe bend?

Question

If you have flow rate in GPM(or velocity in ft/s), pipe diameter, friction coefficeint, and fluid density, how do I calculate pressure drop at 90 and 45 degree bends?

Answer 1

This is normally done using empirical (measured) factors. Somebody measured the pressure drop for various fittings and various rates and developed correlations for general use. The easiest to use correlations will estimate the pressure drop for the fitting in "equivalent feet" of pipe. In other words, they give the length of straight pipe that would have the same pressure drop as the fitting.

These are necessarily estimates but are generally pretty good.

This site has a very good article with a table giving equivalent feet of various fittings and some good explanation of how to use the table and how to do piping pressure drop calcs in general

http://www.fluidh.com/WebCalcPumpHead.htm

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fluid mechanics is cool