Low temperature hybrid micro-channel/micro-jet impingement cooling

Myung Ki Sung, Purdue University

Abstract

This study proposes a new hybrid cooling scheme for high-flux thermal management of electronic and power devices. This scheme combines the cooling benefits of micro-channel flow and micro-jet impingement with those of indirect refrigeration cooling. Experiments were performed to assess single-phase cooling performance using HFE 7100 as a working fluid. Excellent numerical predictions of this performance was achieved using the standard k-&egr; model. The proposed cooling scheme is shown to involve complex interactions of impinging jets with micro-channel flow. Increasing jet velocity allows jets to penetrate the micro-channel flow toward the surface, especially in shallow micro-channels, greatly decreasing wall temperature. In addition to the numerical predictions, a superpositioning technique is introduced that partitions the heat transfer surface into zones that are each dominated by a different heat transfer mechanism, and assigning a different heat transfer coefficient value to each zone. This study also examined the two-phase cooling performance of the hybrid cooling scheme. Vapor layer development along the micro-channel is shown to be fundamentally different from that encountered in conventional micro-channels. In the hybrid scheme, subcooled jet fluid produces repeated regions of bubble growth followed by collapse, rather than the continuous growth common to conventional micro-channel flow. By reducing void fraction along the micro-channel, the hybrid scheme contributes greater wall temperature uniformity. Increasing subcooling and/or flow rate delay the onset of boiling to higher heat fluxes and higher wall temperatures, but also increase critical heat flux considerably. By dividing the test surface into a portion that is dominated by jet impingement and another by micro-channel flow, and applying the appropriate CHF correlation for each portion, the CHF data for this hybrid cooling configuration is predicted with a mean absolute error of 15.2%. This study also explores the single-phase and two-phase cooling performance of a hybrid cooling module in which a series of micro-jets deposit coolant into each channel of a micro-channel heat sink. This creates symmetrical flow in each micro-channel, and the coolant is expelled through both ends of the micro-channel. Three micro-jet patterns are examined, decreasing-jet-size (relative to center of channel), equal-jet-size and increasing-jet-size.

Degree

Ph.D.

Advisors

Mudawar, Purdue University.

Subject Area

Mechanical engineering

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