Experimental studies have shown that the geometric and thermophysical properties of the heater significantly influence the critical heat flux (CHF). While the thermal activity parameter delta sq p_h C_h k_h has been found to correlate this variation very effectively for pool boiling, a physical explanation for its success is only new beginning to emerge. A conceptual CHF model, emphasizing both the role of transient radial conduction within the heater and the relationship between the heater surface temperature and CHF, is proposed to account for this dependence. A finite element analysis is used toinvestigate the effeect of heater and substrate thermal properties on the temperature distribution at CHF. The numerical results show that the thermal activity parameter is associated with radial transent conduction in the the heater and confirm the empirical observation that the presence of a substrate will augment CHF on thin heaters with low thermal activity values. The effects of wettability on CHF are also highlighted.
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