NUMERICAL VISUALIZATION OF TURBULENT FILM BOILING HEAT TRANSFER AND VAPOR FILM GROWTH ON HORIZONTAL ELLIPTICAL TUBES

摘要

Numerical visualization is conducted to investigate turbulent film boiling heat transfer and vapor film growth on horizontal isothermal elliptical tubes. The effects of both eddy dif-fusivity and thermal radiation are taken into account. Theellipticity, heat capacity parameter, radiation parameter, and wall-to-saturated-vapor temperature ratio are varied to determine their effects on turbulent film boiling heat transfer performance and vapor film growth. It is concluded that the vapor film grows monotonically around the periphery of the elliptic tube from the lower to upper stagnation point. In contrast, the local Nusselt number is enhanced, reaching a maximum value and then diminishing rapidly along the lower to upper stagnation point. The average Nusselt number is augmented with an increase in both the ellipticity and temperature ratio. Results compared satisfactorily well with the existing experimental data obtained using Freon 12 and liquid nitrogen as the boiling media.