Spacer effects on thermal-hydraulic performance of fluid flow at supercritical pressure in annular channel - CFD methodology

Abstract

Spacer is a vital component in assembly of nuclear fuel rod bundles. It is used to support and maintain suitable distance between the rods in assembly of nuclear fuel bundle. Spacer promotes the local heat transfer in downstream to the spacer in rod bundle. The objective of present work is to analyse the spacer effects on thermal and hydraulic performance of R-134a at supercritical condition of pressure 4.5 MPa in an annular flow. A Computational Fluid Dynamics (CFD) code ANSYS Fluent has been used for present numerical analysis and SST (Shear Stress Transport) k-ω turbulence model was considered for turbulence flow analysis. Numerical analysis was carried out in an annular channel of 6 mm hydraulic diameter with spacer, located at middle of channel. Hydraulic and thermal performance due to the spacer have been investigated for three different mass flow rates (0.33175, 0.41469 and 0.53909 kg/s) and three different heat fluxes (60, 100 and 160 kW/m2 ). Two blockage ratios of 0.3 and 0.38 have been used in present analysis. Due to the presence of spacer as flow obstruction, it is observed that at spacer location, velocity increased significantly and subsequent decrease in pressure. Also; it is noticed that the wall temperature is decreased and corresponding coefficient of heat transfer enhanced significantly at the location of spacer in annular channel. The observed value of ratio of Nusselt number for the case of spacer and without spacer (Nu/Nu*) shows better agreement with correlations data for flow obstacle at Re=97000.