Experimental study on the thermal stratification in a pool boiling with a horizontal heat source

Abstract

Large pools of water near atmospheric pressure have been incorporated into several advanced nuclear reactor designs. These pools provide a heat sink to remove heat from the reactor or containment by natural circulation and are a source of water for core cooling. Thermal stratification is formed in horizontal fluid layers with different temperatures, where the warmer fluid layers are situated above the cooler fluid layers. In the present study, the key thermal hydraulic phenomena within a passive condensate cooling tank (PCCT) of a small-scale pool test rig with a single heater rod are experimentally investigated. The two-dimensional velocity vector fields that occur as the water temperature increases to the saturation temperature are experimentally investigated in a pool that contains a horizontal heater rod. The detailed velocity measurements using the 2D PIV measurement technique were conducted to investigate single- and/or two-phase natural convection flow and thermal stratification in a pool boiling. The experimental results indicate that a large natural convection flow occurs above the heater rod and that thermal stratification occurs below the heater rod. The flow in the opposite directions to each other was shown in the region between the heater rod and the thermal boundary layer. This flow pattern will contribute to maintain the thermal stratification and retard the water temperature rise and the dissipation of the thermal boundary layer in a pool boiling with a horizontal heat source installed asymmetrically. The current experimental data can be directly used to develop and validate turbulence models in a pool boiling. Furthermore, the present experimental results can help characterize the performance of boiling models on heated surfaces and provide benchmark data to validate the calculation performance of a component scale analysis code and CFD code.