ESDU 83037
Pressure losses in curved ducts: single bends.
Abstract:
ESDU 83037 gives comprehensive data for the estimation of pressure loss in circulararc bends taking account of the effects of bend radius ratio and angle, upstream and downstream duct lengths, surface roughness, crosssectional shape and Reynolds number. The data are in the form of a general equation for which a graphical solution is also provided. For the common case of a 90 degree, smooth bend of circular or square section a direct graphical presentation of pressure loss coefficient is given. Reanalysis of the available information for single and 90 degree composite mitre bends has shown that, contrary to the usual assumption, surface roughness has a significant effect on pressure losses. These data are given graphically in terms of a reference pressure loss coefficient and correction factors for Reynolds number and roughness effect. Approximate data are provided for "standard pipe bends" for use where little detail of the bend geometry is available and sources of data for other bend types (for example, bends where the inner and outer walls are not concentric) are referenced. The effect of guide vanes or splitters in bends is considered and a simple design for use in mitre bends is given. All the information results from correlations of experimental data drawn from a wide range of sources. A practical worked example is included, and data on straight pipe friction factors and effective surface roughness of various pipe materials are given. The method for circulararc bends is provided as a computer program, ESDUpac A8337.Indexed under:
 Bends
 Cascades of Guide Vanes
 Curved Ducts
 Curved Pipes
 Curved Tubes
 Elbows
 Guide Vanes
 Pipe Bends
 Pressure Drop in Internal Flow
 Roughness
 Splitters
 Vanes
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Data Item ESDU 83037  

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ESDUpac A8337 
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This Data Item contains 22 interactive graph(s) as listed below.
Graph  Title 

Figure 1  Friction factor for straight pipes 
Figure 2  Boundary layer between long and short circulararc bends 
Figure 3a  Transition region for flow in long circulararc bends 
Figure 3b  K'_{s,G} for long, smooth circulararc bends 
Figure 3c  Surface roughness correction factor phi_{4} for long circulararc bends 
Figure 4a  K_{s,G} for short, 90 degree circulararc bends in laminar flow 
Figure 4b  K_{s,G} for smooth, short circulararc bends in turbulent flow 
Figure 5a  K_{b} for short circulararc bends in turbulent flow 
Figure 5b  K_{C} for short, 90 degree circulararc bends in turbulent flow 
Figure 5c  K_{d} for short, 90 degree circulararc bends in turbulent flow 
Figure 5d  Part 1  Downstream tangent length correction to K'_{d} for short, 90 degree circulararc bends 
Figure 5d  Part 2  Downstream tangent length correction to K'_{d} for short, 90 degree circulararc bends 
Figure 5e  Bend angle correction to K'_{d} for short circulararc bends 
Figure 6a  Basic pressure loss coefficient for single mitre bends 
Figure 6b  Basic pressure loss coefficient for composite mitre bends, theta = 90 degrees 
Figure 7a  Reynolds number correction for mitre bends (for rough bends use factor Phi_{4} also) 
Figure 7b  Roughness correction for mitre bends (use factor Phi_{1} also) 
Figure 7c  Roughness correction for mitre bends (use factor Phi_{1} also) 
Figure 8a  Part 1  Guide vanes or splitters in circularsectioned circulararc bends. Optimum location for one guide vane 
Figure 8a  Part 2  Guide vanes or splitters in circularsectioned circulararc bends. Optimum location for two guide vanes 
Figure 8b  Guide vanes or splitters in circularsectioned circulararc bends. Reduction in loss coefficient for vanes at optimum location K_{s,G} (with vanes) = K_{s,G} (without vanes) x Phi_{6} 
Figure 9  Approximate K_{s,G} values for 90 degree standard pipe bend fittings 