Validation of fluent software for prediction of flow distribution and pressure gradients in a multi-branch flow header

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. Historically, nuclear safety analysis has been performed using one-dimensional averaged system codes, and as such the distribution headers are cross-sectionally averaged. 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 were 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 inlet flow rate was found to affect the flow distribution especially at low flow rates and the header pressure gradient especially at high flow rates. The aim of this work is to validate FLUENT software in predicting flow distribution and pressure gradients in single phase flow in such a multi-branch geometry. The effects of flow model, grid density,convergence criteria, flow inlet velocity and header size 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. The impact of convergence criteria was studied by tightening the pressure and momentum relaxation factors as well as by decreasing the tolerance. The laminar model provided the best data fit in comparison with the standard and the RNG k-ε models. Vortex formation and flow separation were also studied and compared to the experimentally observed flow behaviour. Agreed with the experiment, largest vortices occur around the first branch pipe of the header.