Experimental study on the grid-enhanced heat transfer at supercritical pressures in rod bundle

Abstract Experimental results of spacer grid effect on the heat transfer under supercritical pressure conditions are investigated. The experiments are carried out in an electrically heated 19-rod bundle cooled with supercritical Freon R134a. Standard spacer grids with blockage ratio of 0.29 are equipped into the bundle. The local wall temperatures and heat transfer coefficients along the flow direction of the bundle are measured. An interpolation method to determine the fully developed Nusselt number at supercritical conditions is reported. The results indicate that the enhanced heat transfer is limited within 30 bundle diameters downstream of the spacer grids. A peak heat transfer enhancement is observed near the pseudo critical region, which cannot be captured by the subcritical correlations. Considering the maximum heat transfer enhancement as a function of dimensionless temperature ratio, an original approach for deriving the grid-enhanced heat transfer correlation for supercritical applications is presented and the corresponding correlation has been established.