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THE ROLE OF THICKNESS AND THERMAL EFFUSIVITY IN POOL BOILING CHF IN HIGHLY-WETTING LIQUIDS

A. A. Watwe
Department of MeG:hanical Engineering University of Minnesota, Minneapolis

Avram Bar-Cohen
Laboratory of the Thermal Management of Electronics, Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455; and Defense Advanced Research Projects Agency (DARPA), Microsystems Technology Office, University of Maryland, College Park, MD

Abstract

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 δ√(ρcpλ) has been found to correlate this variation very effectively, no physical explanation for its success is as yet available. 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 to investigate the effect 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 transient conduction in the heater and that the presence of a substrate will augment the critical heat flux on thin heaters with low thermal activity values.

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