Effect of pressure on burnout in annuli and a 19-rod cluster cooled by upflow of FREON-12.

Abstract

Burnout tests were conducted in Freon-12 at four different inlet pressures for four uniformly heated annuli, and three different inlet pressures for a 19-rod cluster (the respective inlet to critical pressure ratios being 0.21, 0.26, 0.33, 0.40 and 0.26, 0.32, 0.41). For the rod cluster, the ratio of the heat flux on the outer rods to the heat flux on the inner rods was 1.6. All annulus test sections were internally heated except one whose outer tube (shroud) only was heated. Resistance heating using d.c. power was used. Results show that, in general, for a constant inlet subcooling, increasing inlet pressure caused a non-linear decrease of burnout heat flux for mass velocities up to 4 Mg m-2s-1. An apparent independence of burnout heat flux from inlet pressure was observed for the rod cluster at a very small value of mass velocity (50 kg m-2s-1). At a high mass velocity (4 Mg m-2s-1), the internally heated annulus had a significantly greater burnout heat flux than the corresponding externally heated one. The CISE burnout correlation,modified for the effect of inlet pressure, generally underpredicted the burnout heat flux by up to 40 per cent.