# Calculation Methods - Bends

For all phase states the pressure loss across a bend is calculated from the expression: ΔP = 0.5 K ρ v2 The pressure loss coefficient, K, is independent of fluid properties and so this approach can be used for all fluids and all phase states. For a more detailed discussion and explanation on the universality of loss coefficients see Miller [4]. FluidFlow allows the calculation of the pressure loss coefficient to be made according to 4 different correlations: Idelchik [5] Miller [4] Crane [13] SAE [14] Note, the Crane method assumes that each pipe connection is the same diameter and also assumes a 90 deg angle. Idelchik and Miller allow for unequal pipe diameters and user defined angles. Detailed explanations of the estimation of K can be found in the above sources. When the tee definition is set to "Crane" the K values used are as follows: 90 o Bend/Elbow
r/d | K
1 | 20 ft
1.5 | 14 ft
2 | 12 ft
3 | 12 ft
4 | 14 ft
6 | 17 ft
8 | 24 ft
10 | 30 ft
12 | 34 ft
14 | 38 ft
16 | 42 ft
20 | 50 ft
The K value for standard threaded elbows is calculated from K = 30 ft. where: ft is the turbulent friction factor. Figure 1: Bend/Elbow Illustration.