Experimental study of film condensation heat transfer of high pressure steam in inclined tube

Abstract

In-tube film condensation is important in numerous industries such as chemical process industries, refrigeration and air-conditioning systems. Especially, in the case of high pressure steam, film condensation is important in nuclear safety system. Increasing condenser efficiency in these application can reduce the running cost, environmental impact and system size. Furthermore, the safety margin of nuclear safety system can be enhanced. For these reasons, a lot of studies have been reported concerning film condensation in tubes with various test conditions. In previous researches, the two-phase flow pattern can affect to condensation heat transfer coefficient. The gravitational force and vapor-liquid interfacial shear stress are known as two dominant factors controlling the flow pattern and these forces are affected by inclination angle. If the vapor flow rate is quite large, the condensate film flows on the tube wall in annulus-shape and the vapor flows in the core, On the contrary, if the vapor flow is very low, condensate accumulates in the lower part of the pipe and the stratified flow is formed. These condensate film acts as a thermal resistance, the heat transfer coefficient changes depending on the flow pattern. To understand effect of these phenomena, experiments were conducted with various steam mass fluxes (27kg/m2s, 54kg/m2s, 82kg/m2s), pressures (0.5MPa, 2.0MPa) and inclination angles (-37.5°, -15°, 0°, 7.5°, 30°). The results were compared with four previous studies for validation. Similar values and trends were observed as in previous studies, and the correlations predicting the experimental results were different according to the mass flux. The uncertainty analysis of experimental results was also conducted. The maximum and average uncertainty of base case in horizontal tube is measured as 31.1% and 18% each. The range of mass flux and pressure in this experiment did not affect to heat transfer coefficient in horizontal tube. However, the heat transfer coefficient along the inclination angle changes according to test conditions. According to the experimental conditions, the dominant influence on the heat transfer coefficient was predicted based on the previous research results, and hypothetical flow patterns were presented.