Validation of Fluent Software for Prediction of Flow Distribution and Pressure Gradients in a Multi-Branch Flow Header

Abstract

Flow headers are commonly used in nuclear reactors, boilers and heat exchangers to distribute fluid to small branches along the body of the header or to combine flow from the branches along the header. In this paper, flow distribution and pressure gradients along a multi-branch header have been predicted using the three dimensional computational fluid dynamics software FLUENT and was compared to results obtained from experimental data obtained from literature for single phase conditions. Water inlet flow rate through the header was varied and flow rates in the header branches were measured. The aim of this work is to validate FLUENT software in predicting flow distribution and pressure gradients in such a multi-branch geometry. The impact of grid density, convergence criteria and flow model on the computational results were studied. For the impact of grid density, coarse, fine and very fine meshes were used and the mesh size beyond which no change in solution occurred was adopted and used in the rest of the study. The impact of convergence criteria was studied by tightening the pressure and momentum relaxation factors as well as by decreasing the tolerance. Laminar model provided the best data fit in comparison with the standard and the RNG k-ε models. FLUENT computational predictions provided good fit of the experimental data especially at high flow rates. Vortex formation and flow separation were also studied and compared to the experimentally observed flow behavior. Agreed with the experiment, largest vortices occur around the first branch pipe of the header.