Study Of Spacer Effects On Heat Transfer Characteristics Of Supercritical Fluid In An Annular Channel

The spacer grid is an important part of the fuel assembly,its main role is to support and locate fuel rods and muddy coolant channels.It has been fully studied about the spacer effects on the heat transfer characteristics of the fluid under subcritical pressure.However,the spacer effects on the heat transfer characteristics of the fluid are still not fully understood under the supercritical pressure.Based on the safety design requirement of supercritical water-cooled reactor(SCWR),this paper carried out experimental and numerical simulation on the effects of spacer grid on the heat transfer characteristics of supercritical fluid.Based on the supercritical model fluid thermal hydraulics test facility(SMOTH)of Shanghai Jiao Tong University with working fluid of Freon R134 a,the experiment of the spacer effects on the heat transfer of supercritical fluid is carried out in an annular channel.Based on computational fluid dynamics(CFD)software,numerical simulation is carried out,and the influence of geometric parameters and flow parameters on spacer effect under supercritical pressure is analyzed.The conclusions are as follows: 1)Under normal heat transfer working conditions,the enthalpy of the end of the spacer has a significant influence on the heat transfer enhancement effect of the spacer.On the left side of the pseudo-critical region,the heat transfer enhancement effect of the spacer increases with the increase of the enthalpy of the end of the spacer.On the right side of the pseudo-critical region,the heat transfer enhancement effect of the spacer decreases with the increase of the enthalpy of the end of the spacer,and the heat transfer enhancement effect of the spacer reaches the peak near the pseudo-critical region;2)Different from the sub-critical pressure,besides equivalent diameter of flow channel,blockage ratio of the spacer and dimensionless distance from the spacer end,the relevant flow parameters have a significant effect on the spacer effect under supercritical pressure;3)The destroy mechanism of the boundary layer is the main reason for the peak value of the heat transfer enhancement near the pseudo-critical zone under the supercritical pressure;4)Under the condition of heat transfer deterioration,the spacer may cause the oscillating distribution of TKE in the near wall region downstream,resulting in the further deterioration of the heat transfer coefficient in some areas and new wall temperature peak appears.