Heat Transfer and Wall Temperature Distribution during Flow Boiling In Conventional and Mini Channels

The fluctuation of pressure in flow boiling is affected due to liquid-vapor phase interaction, and thus the flow and wall temperature are influenced. The temporal and spatial variation of wall temperature and the heat transfer coefficient are investigated experimentally at atmospheric system pressure. The two mini-tubes of 2×300 and 4×600 mm inner diameter× heated length are used for analysis. The thermal image technology is used to show the wall temperature distribution. The experimental setup is validated by comparing the heat transfer coefficient with Dittus-Boelter and Gnielinski correlations. The boiling heat transfer coefficient in both tubes are compared to get the effect of diameter, mass flux and heat flux. The radially as well as axially variation of wall temperature during flow boiling is represented. The wall temperature during liquid-phase flow is identical in the radial direction and increases linearly in the axial direction. The wall temperature exhibits significant axially as well as radially variation in two-phase flow. The wall temperature fluctuates vigorously in mini-channels. The influence of subatmospheric system pressure on subcooled flow boiling is examined in the conventional channel with a diameter of 11.7 mm. An increase in the subcooled flow boiling heat transfer coefficient is observed when the system pressure is lower than atmospheric pressure. At subatmospheric system pressure, the wall temperature exhibits radial symmetry across all Froude number values. Furthermore, the mass flux does not significantly impact the subcooled boiling heat transfer coefficient, when subjected to constant heat flux.