Abstract:

ESDU 77009 gives graphs for a factor that can be applied to loss data for individual bends (taken from ESDU 83037) to obtain the combined loss of two bends placed closer together than 50 diameters. The graphs were obtained by correlating the available experimental information drawn from the literature. They deal only with two right angle bends. Cases covered are two identical circular-arc or single mitre bends turning the flow through any angle, and two dissimilar radius circular-arc bends, a combination of a circular-arc and a single mitre bend, or two composite mitre bends turning the flow in the plane of, or at right angles to, the entry flow. Some data are also given for two single mitre bends in a square cross-section duct. For the case of two circular-arc bends the effect of a downstream pipe of less than 50 diameters is also shown, while for other combinations the minimum length of downstream pipe for no modification to the loss data is tabulated. A practical worked example illustrates the use of the graphs.