Minor Losses

Darcys Equation - h1012v3_55

TABLE 1 Typical Values

Thermodynamics Heat Transfer and Fluid Flow Volume 3 of 3
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HEAD LOSS Fluid Flow Minor Losses The losses that occur in pipelines due to bends, elbows, joints, valves, etc. are sometimes called minor losses. This is a misnomer because in many cases these losses are more important than the losses due to pipe friction, considered in the preceding section. For all minor losses in turbulent flow, the head loss varies as the square of the velocity. Thus a convenient method of expressing the minor losses in flow is by means of a loss coefficient (k). Values of the loss coefficient (k) for typical situations and fittings is found in standard handbooks. The form of Darcy’s equation used to calculate minor losses of individual fluid system components is expressed by Equation 3-15. (3-15) H_f k^v 2 2g Equivalent Piping Length Minor losses may be expressed in terms of the equivalent length (L_eq) of pipe that would have the same head loss for the same discharge flow rate. This relationship can be found by setting the two forms of Darcy’s equation equal to each other. f L v² D 2 g k v² 2 g This yields two relationships that are useful. (3-16) L_eq k^D f (3-17) k f L_eq D Typical values of L_eq/D for common piping system components are listed in Table 1. The equivalent length of piping that will cause the same head loss as a particular component can be determined by multiplying the value of L_eq/D for that component by the diameter of the pipe. The higher the value of L_eq/D, the longer the equivalent length of pipe. HT-03 Page 34 Rev. 0

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