Transition Boiling Heat Transfer on a Vertical Surface

Abstract

Transition boiling heat transfer on a vertical surface in a pool of saturated water is investigated experimentally. Local heat transfer rates are obtained on a 6.3-cm-wide and 10.3-cm-high surface which was machined from a large block of copper. Experiments conducted with water show that even for relatively slow transient cooling rates (|dT/dt| < 11 K/s), the transient maximum heat fluxes are as much as 60 percent lower than the maximum steady-state heat fluxes. It is found that transition boiling heat transfer is very sensitive to the surface condition as well as to the history of the process. Two distinct transition boiling curves are observed during transient heating and cooling of clean surfaces. However, the difference between the two curves diminishes as the wettability of the surface increases. A correlation is developed to relate the transient quenching and steady-state peak heat fluxes for the range of temperature transient rates and surface conditions used in this investigation. Although the transient transition boiling curves obtained during heating and cooling are distinct because of different initial conditions, it is found that they possess the same rate of change of heat transfer coefficient with surface temperature when a correction factor equal to the ratio of steady to transient maximum heat fluxes is used.