HEAT TRANSFER IN VERTICAL AND HORIZONTAL ONE-SIDE-HEATED EVAPORATOR TUBES

Abstract

Heat transfer tests were carried out in a high-pressure test loop using a tube of 6.1-m heated length and 19.55-mm inner diameter. For simulation of nonuniform heating, the wall thickness of the electrically heated tube was reduced over half of its circumference. Experiments included not only vertical upward flow, but also horizontal tube installation with side heating and top heating. The temperatures and heat fluxes on the inside of the tube were determined by two-dimensional analysis based on the temperatures measured at the outer tube wall. For the calculation of the critical heat flux in the case of vertical upward flow, it was found that the occurrence of the boiling crisis is evidently governed by local variables. With horizontal flow and top heating, the boiling crisis often moves toward very low steam qualities. In such cases the reduction in heat transfer in the post-CHF region is less than expected. This may be attributed to the occurrence of secondary flow resulting from nonuniform heating.