A Comparison of Finite Element and Lumped Modeling Techniques to Analyze Flow Boiling in Microchannels

This study quantitatively compares the finite element (FE) and lumped modeling techniques to analyze phase-change and multiphase flow in a microchannel evaporator. We compare the one- and two-zone models in the lumped modeling approach by considering both pressure drop and phase change in the evaporator. The study investigates the deviation in results from the lumped model relative to the FE model for various evaporator heat loads. For the one-zone model, the relative errors in predicting the average density, pressure, temperature, and vapor quality increase with the evaporator heat load. This increase is mainly due to the nonlinear variation in the heat transfer coefficient and pressure drop, which are calculated with higher inaccuracies at larger evaporator heat loads. On the other hand, the liquid-phase region and the exit vapor quality are predicted more accurately. The overall errors using one- and two-zone lumped models were less than 30% when the exit qualities do not exceed 0.5. Since strategies involving flow boiling in evaporators typically avoid high exit vapor qualities to circumvent dry-out and critical heat flux, the use of lumped models under these conditions is favorable. This approach also avoids the computational costs associated with FE models while achieving sufficient accuracy to predict the evaporator’s performance.