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 (Lu, Ld) 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, Lu are Ld 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.

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