Calculating equivalent length of expansion/contraction from K value

[cjc0117]

If you know the resistance coefficient, K, for a sudden expansion or contraction in a pipe, how can you calculate the equivalent length, L_e from the K value?

I know that for fittings, L_e=KD/f, where D is the diameter and f is the Darcy friction factor. But when considering a contraction or expansion with a known K value, should you use the diameter of the larger or smaller pipe when calculating L_e? And which pipe's friction factor should be used? Do you use averages, perhaps? Thanks

 

[Valkarie]

.For a sudden expansion or contraction, the equivalent length is usually calculated using the diameter of the larger pipe and the friction factor of the smaller pipe. This is because the larger pipe's diameter affects the pressure drop more than the smaller one does. The average friction factor can be used if the two pipes have similar properties.