Numerical Evaluation for Spacer Vane Effects on Flow and Heat Transfer of Water at Supercritical Pressure in Annular Channel

In the nuclear fuel structure, most spacers are constructed with vanes that increase turbulence flow mixing downstream of the spacer and therefore enhance the heat transfer rate. The objective of this work is numerical evaluation of the effects of a spacer without a vane and a spacer with a vane (hereinafter referred to as spacer/spacer with vane) on the flow and heat transfer of water at supercritical pressure downstream to the spacer of the annular channel. In this study, computational fluid dynamics (CFD) models of the annular channel have been developed considering spacer/spacer with vane. Experimental data for the heated annular channel have been used to validate the same CFD model (as the geometry used for the experiment) using the CFD code ANSYS Fluent. The CFD results show good agreement with the experimental data used, and hence, the developed CFD models of the annular channel that consider spacer/spacer with vane can be simulated with adequate precision for the flow and heat transfer downstream to the spacer. The effects of spacer/spacer with vane on heat transfer and flow behavior of water have been studied with numerical simulations for the following parameters: mass fluxes of 500 and 1000 kg/m²·s, heat flux of 400 kW/m², pressure of 25 MPa, and inlet water temperature of 350°C. The results obtained through the simulations show that the spacer with vane has a remarkable influence on flow and heat transfer downstream to the spacer vane against spacer without a vane in an annular channel. Raising the flow velocity is an effective approach to reduce wall temperature and enhance the heat transfer in the channel. The range of the spacer effect in the enhancement of heat transfer is observed from X/D = 0 to 45 in the downstream direction. In addition, the simulation results for the Nusselt number ratio of the present CFD models have been compared with correlation data established by several researchers in a downstream direction to the spacer/spacer with vane, and qualitatively proper agreement has been found.