Verification and validation of COMSOL for heat transfer in thin rectangular channels using NACA test results [1]

Currently efforts are underway at Oak Ridge National Laboratory to convert the High Flux Isotope Reactor (HFIR) from high-enriched uranium to low-enriched uranium fuel. To provide confidence to the thermal hydraulics calculations, computational fluid dynamics (CFD) simulations—simulated using COMOSOL—have been used to calculate the pressure drop and heat transfer in the coolant. While CFD simulations provide well-resolved results, turbulence models include many assumptions and must be validated for use in any safety-based analysis. In HFIR, long, thin involute fuel plates are separated by coolant channels of equal size. The coolant channels are best described as thin rectangular channels. Unfortunately, there are few studies verifying and validating CFD for use in thin rectangular channels. This study seeks to bridge that gap by verifying, validating, and comparing various CFD models used in thin channels. To verify and validate CFD for use in thin channels, a series of simple analytic test cases are used, and the method of manufactured solutions (MMS) is used to further verify the COMSOL tool and mesh geometry. For the validation, a series of tests conducted at the National Aeronautics and Space Administration were simulated in COMSOL. The results of this study are threefold. First, it verifies the ability of COMSOL to model heat transfer in thin channels. Second, it addresses the various aspects of CFD modeling that are of greatest concern for heat transfer simulations in the geometry. Third, and finally, it discusses the ability of various CFD models used in COMSOL to accurately predict heat transfer in narrow rectangular channels.