Gradual Expansion and Contraction : If the expansion or contraction is gradual, the losses are quite different. A gradual expansion situation is encountered in the case of a diffuser as shown in Fig. 5.6.6. A diffuser is intended to raise the static pressure of the flow and the extent to which the pressure is recovered, is defined by the parameter pressure-recovery coefficient . The loss coefficient is then related to this parameter . For a given area ratio, the higher value of implies lower loss coefficient .

(5.6.10)

When the contraction is gradual, the loss coefficients based on downstream velocities are very small. The typical values of range from 0.02 – 0.07 when the included angle changes from 30º to 60º. Thus, it is relatively easy to accelerate the fluid efficiently.

 

Fig. 5.6.6: Loss coefficients for gradual expansion and contraction.

 

Minor losses due to pipe fittings : A piping system components normally consists of various types of fitting such as valves, elbows, tees, bends, joints etc. The loss coefficients in these cases strongly depend on the shape of the components. Many a times, the value of is generally supplied by the manufacturers. The typical values may be found in any reference books.