EFFECT OF LENGTH L BETWEEN TWO BENDS

[5umbzyyr]

How does the effect of a spacer of length L between two bend or elbows affect pressure drop in the bends

 

[siretb]

Refer to internal flow systems, D S Miller, chap 10
ISBN 8-47711-77-5
Neglecting interaction usually results in overpredicting pressure drop.
K12 (K , loss coefficient for 1 and 2 combined) is
K12=(K1 + K2)*C12, C12 intercation coefficient.
C12 is normally less than 1, (0.8-1) if you have less than 4 hydraulic diameters between two bends.

So a spacer between two bends would, usually, increase the pressure drop.