Review of coefficient of local resistance for pipe fittings in district cooling systems

The coefficient of local resistance is a hydraulic parameter proposed to simplify the description and analysis of complex hydrodynamic phenomena of pipe fittings，and widely used in the design and analysis of hydraulic pipeline engineering. The accuracy of its value determines the accuracy of pipeline hydraulic engineering analysis. In different references, the value of coefficient of local resistance varies greatly, leading to result deviations of pipe fitting pressure losses in practical application or different conclusions of pipeline hydraulic analysis. This paper reviews the value of coefficient of local resistance of pipe fittings in several typical literatures, including 90° welded elbow, 90° tee, gradual contraction and enlargement and butterfly valve. Among which, the coefficient of local resistance of 90° elbow with large pipe diameter is close to 0.2, while the coefficient of local resistance is dependent on the flow ratio and area ratio for 90° tee, the geometry for gradual contraction and enlargement, and the pipe diameter and opening for butterfly valves, respectively.