Based on the Greenwood and Williamson theory, an assumption about the contact-area size of asperities on rough surfaces is proposed under the premise that the height of these asperities on rough surfaces is a Gaussian distribution. A formula has been derived to measure the number of asperities on 2D surfaces. The contact stiffness on a unit length of a 1D outline and that on a unit area of 2D surfaces are presented based on a formula for determining the number of asperities. The relationship between macro parameters, such as contact stiffness and micro parameters on the joint surface, is established.

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The present work is to investigate nucleate boiling heat transfer at high heat fluxes, which is characterized by the existence of macrolayer. Two-region equations are proposed to simulate both thermo-capillary driven flow in the liquid layer and heat conduction in the solid wall. The numerical simulation results can clearly describe the activities of several multi vorticies in the macrolayer. These vorticies and evaporation at the vapor-liquid interface constitute a very efficient heat transfer mechanism to explain the high heat transfer coefficient of nucleate boiling heat transfer near CHF. This study also explores the flow pattern of macrolayer with a high conducting solid wall, e.g. copper, and hence the temperature is uniform at the liquid-solid interface, and the heat fluxes and the evaporation coefficient are found to have significant effect on flow pattern in the liquid layer. Furthermore, a parameter``evaporation fraction'' as well as``aspect ratio'' is proposed as an index to investigate the thermo-capillary driven flow system. The model prediction agrees reasonably well with the experimental data in the literature.

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