Enhancement of boiling heat transfer using highly wetting liquids with pressed-on fins at low contact forces

Ahstraet--ln many cooling situations, permanent attachment of fins to heat dissipating devices is undesirable yet htrge mechanical loads, important in reduction of thermal contact resistance, are not permitted. This work considers the interface between a low-force pressed-on fin and a heat source in boiling heat transfer; the thermal contact resistance and how the interface region may be used to promote early nucleation and gradual boiling spread. Tests were run in saturated FC-72 and FC-87 in atmospheric pressure at a range of contact pressures much lower than conventional studies and on the order of those allowable ir electronic cooling. Results showed that the effect of contact pressure on contact resistance, at such low pressures, is small and that significant boiling enhancement is possible using pressed-on fins with small loads. Dissipation of up to 85 W cm -2 of heater surface using a non-optimized cylindrical fin at low force is demonstrated. This heat flux represents about a four-fold increase in critical heat flux (CHF) over that for a bare surface. The pressed contact fin offers the advantage of a small crevice at the fin base. Highly-wetting fluids are able to penetrate this region, superheat and nucleate earlier than with a solderedon fin. A means of numerically modeling the boiling heat transfer from a fin is also presented. Experiments show that tile nucleate boiling heat transfer coefficient is independent of the surface orientation with respect to gravity. © 1997 Elsevier Science Ltd: All right reserved.