A Standard Method to Determine Loss Coefficients of Conduit Components Based on the Second Law of Thermodynamics

Losses in conduit components of a pipe system can be accounted for by using component specific loss coefficients K. Especially in mini- and micro-systems an exact knowledge of these loss coefficients (which in laminar flow strongly depend on the Reynolds number) is important. Limited space will generally lead to a high loss-contribution of single components compared to the contribution of the straight channels. The determination of K-values of single components based on a numerical simulation using the Second Law Analysis (SLA) has turned out to be a very attractive method. The simulation of the flow field shows the distribution of losses and upstream and downstream lengths of impact (L_u, L_d) where the otherwise fully developed flow is affected by the component. The numerical SLA-Method is introduced as a standard method, illustrated and validated with highly accurate measurements in a 90 deg bend with a square cross section. The local entropy generation rates based on the numerical simulation of the flow field are computed and carefully interpreted. Component specific values of K, L_u are L_d are collected in a table and illustrated by plots of the entropy generation rate distribution along the bend’s centerline. Validation is achieved with experimental results from a test facility exclusively built for this purpose: Laminar flow in a 90 deg bend is induced by a controlled gear pump with polydimethylsiloxanes of different viscosities as working fluids.