CHF enhancement in flow boiling system with TSP and boric acid solutions under atmospheric pressure

Abstract

The phenomenon which the heat transfer coefficient between a heated wall and fluid with change from the liquid phase to the vapor phase of fluid near the heated wall decreases suddenly is generally called a CHF phenomenon. In case of a heat flux control system, there is a sudden increase of wall temperature. A CHF is a flux at the situation, and this is an important factor in a heat transfer system. The enhancement of CHF means the increase of efficiency of the heat transfer system due to perform normal operation at higher heat flux, and it also means the increase of safety due to increase the safety margin. Therefore, many researchers have studied about methods and applications of the CHF enhancement for 30 years. In this study, the effect of tri-sodium phosphate (TSP) and boric acid on the CHF enhancement was studied. Both TSP and boric acid are used to control pH in nuclear power plants. TSP is a kind of surfactant, and several surfactants, include TSP, have been reported to have an effect on the enhancement of heat transfer. Nothing has been reported in case of boric acid, yet. The CHF experiment was performed with mass flux ranged 100-500 $kg/m^2s$ and two inlet subcooling temperatures of 25, 50℃ under atmospheric pressure. In case of TSP, one inlet subcooling temperature of 50℃ was used. The test section was vertical circular SS316 tube having the inside diameter of 10.98 mm. The heated length is 224 mm, and it was heated by a heat flux control system using electricity. Fluids filled in the test loop were plain water, TSP solutions, and boric acid solutions. TSP solutions had three concentrations (0.2, 0.4, 0.6%), and boric acid solutions had four concentrations (0.2, 0.4, 0.6, 0.8%). In case of TSP, 21.4% enhancement of CHF was observed at inlet subcooling temperature of 50℃ and extremely low mass flux (100 $kg/m^2s$). In case of boric acid, 14% enhancement of CHF was observed at inlet subcooling temperature of 50℃ and extremely low mass flux (1...