Experimental study of post-dryout with R-134a upward flow in smooth tube and rifled tubes

Abstract

A study of post-dryout heat transfer was performed with a directed heated smooth tube and rifled tubes using vertical R-134a up-flow to investigate the heat transfer characteristics in the post-dryout region. Three types of rifled tube having different rib height and width were used to examine the effects of rib geometry and compare with the smooth tube, using a mass flux of 70-800 kg/m(2) s and a pressure of 13-24 bar (corresponding to an approximate water pressure of 80-140 bar). Wall temperature distribution in all tubes was strongly dependent oil pressure and mass flux. Wall temperatures of the rifled tubes in the post-dryout region were much lower than for the smooth tube at same conditions. This was attributed to swirl flow caused by the rib. Thus, the thermal non-equilibrium, which is usually present in the post-dryout region, was lowered. The empirical correlation of heat transfer in the smooth tube of the post-dryout region was obtained. The heat transfer correlation for rifled tubes was also obtained as a function of rib height and width with the modification of the smooth tube correlation. (c) 2007 Elsevier Ltd. All rights reserved.