A compact two-phase thermosyphon employing microfabricated boiling enhancement structures

A new compact, two-phase thermosyphon was developed for localized high heat dissipation applications. The thermosyphon employs three-dimensionally stacked enhanced boiling structures that reduce the incipience overshoot and raise the critical heat flux. The effects of reducing the system size on the thermal performance were experimentally evaluated. The results showed performance similar to pool boiling with a very compact evaporator design. Several techniques were investigated to fabricate the enhanced structures in silicon and copper. A parametric study was conducted to understand the effect of geometrical parameters on the thermal performance of the system. The heat dissipation was found to increase with an increase in the channel width, and number of channels per unit length. Adding more layers in the three-dimensional stack resulted in an improvement in the heat dissipation. However, it also increased the volume of the structure. A practical limit will result based on the collective influence of these two factors.; High-speed visualization was carried out to understand the boiling mechanism from these structures. The study confirmed some of the differences in the mechanism compared to boiling from plain surfaces, as outlined by previous authors. Distinct regimes similar to boiling from plain surfaces, at different wall superheats, were observed. Important boiling parameters were measured including the bubble departure diameter, frequency and the nucleation site density. These were used to develop a semianalytical model that simulates the boiling phenomena, for a limited range of the experiments (isolated bubble regime). The model captures the experimentally observed trends fairly accurately. However, it needs further refinement, with the help of fundamental studies, to reduce the errors in prediction.; The unique contributions of this study are---demonstration of the feasibility of extending the knowledge base available for pool boiling to designing compact cooling systems, developing new techniques for fabricating three-dimensional enhanced structures in silicon, providing a better understanding of the boiling mechanism at higher wall superheats and identifying important parameters for developing a semianalytical model for this range.