A Transient Nucleate Boiling Model Including Microscale Effects and Wall Heat Transfer

Abstract

A new model is presented to compute nucleate boiling heat and mass transfer. It is based on a previous one (Kern, J., and Stephan, P., 2003, ASME J. Heat Transfer, 125, pp. 1106–1115) for quasi-stationary heat transfer to single vapor bubbles. In contrast to the preceding model, fully transient heat and fluid flow is computed with a free surface of the rising bubble and a periodic calculation of repeated cycles of bubble growth, detachment, and rise, requiring only specification of the waiting time between successive bubbles. Additionally, microscopic effects at the foot of the bubble are considered. The model is verified by comparing computed with measured heat transfer coefficients. Typical results for heat and mass transfer to a single vapor bubble are shown at all time steps of the bubble cycle. By means of the model the transient heat flow through different interfaces, e.g., wall/liquid or liquid/vapor, is computed for the whole bubble cycle. Thus, it was possible to evaluate the influence of transient heat conduction, heat storage, and convection in liquid as well as heat transfer in the wall on overall heat transfer performance.