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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Recent Advances in On-Chip Cooling Systems: Experimental Evaluation and Dynamic Modeling

Get access (open in a dialog) DOI: 10.1615/IHTC15.kn.000006
pages 100-134

Abstract

Extensive work on flow boiling in microchannels with the aim of cooling of electronics has been undertaken in the past 15 to 20 years. With this knowledge in hand, the next step is to develop detailed, accurate and validated simulation codes for steady-state and transient operations of (i) the entire thermal package (micro-channel evaporator, its inlet and outlet ports, the thermal interface material and the electronic chip), (ii) the flow distribution to multiple chips to be cooled in parallel, and (ii) the rest of the two-phase cooling system (condenser, accumulator, driver and controller). First of all, an overall summary of experimental investigations developed with different concepts of on-chip cooling systems is presented (liquid pump, vapor compressor and thermosyphon loops). The experimental results reported here have focused on controllability of the cooling systems under conditions of steady-state, transient, balanced and unbalanced heat loads on two parallel pseudo-chips to mimic the real operation of a server blade. An evaluation of these systems' energetic performances is then provided. The results showed that all proposed and experimentally evaluated systems are highly effective cooling solutions, since they were stable, provided significant reductions in cooling energy consumption when compared with current air-cooling systems, and guaranteed high uniformity and low levels of the multiple chips' temperatures. Then, three different scales of simulation codes of the two-phase on-chip liquid pump loop are described: (i) thermal cooling package of one CPU, (ii) grouping of multiple thermal packages operating in parallel, and (iii) the entire two-phase cooling loop with flow controls. These codes are implemented in a local numerical fashion with detailed models of the two-phase flow, heat transfer, conduction and related thermodynamics, not lumpedparameter methods that sacrifice detail for expediency. The simulation codes' validation using the experimental liquid pump loop with two pseudo-chips in parallel showed that 88 pseudo-chips temperatures were predicted within an error band of +/- 10% with balanced and unbalanced heat loads in the pseudo-chips. Finally, the validated code is used to simulate a compact two-phase on-chip cooling system designed for a real datacenter blade server. The system start-up, steady-state and operation under heat load disturbances with different control strategies are analyzed. Detailed behavior of the micro-evaporators and micro-condenser are discussed. Controlling the outlet water coolant temperature was proven to be desirable for both heat recovery and chip temperature control.