Research Papers

Two-Phase Flow Control of Electronics Cooling With Pseudo-CPUs in Parallel Flow Circuits: Dynamic Modeling and Experimental Evaluation

[+] Author and Article Information
Nicolas Lamaison

e-mail: nicolas.lamaison@epfl.ch

John Richard Thome

Heat and Mass Transfer Laboratory (LTCM),
Ecole Polytechnique Fédérale de Lausanne (EPFL),
EPFL STI IGM LTCM/EL H0 094/Station 9 CH-1015 Lausanne, Switzerland

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received October 1, 2012; final manuscript received May 16, 2013; published online July 24, 2013. Assoc. Editor: Yogendra Joshi.

J. Electron. Packag 135(3), 030908 (Jul 24, 2013) (12 pages) Paper No: EP-12-1088; doi: 10.1115/1.4024590 History: Received October 01, 2012; Revised May 16, 2013

On-chip two-phase cooling of parallel pseudo-CPUs integrated into a liquid pumped cooling cycle is modeled and experimentally verified versus a prototype test loop. The system's dynamic operation is studied since the heat dissipated by microprocessors is continuously changing during their operation and critical heat flux (CHF) conditions in the microevaporator must be avoided by flow control of the pump speed during heat load disturbances. The purpose here is to cool down multiple microprocessors in parallel and their auxiliary electronics (memories, dc/dc converters, etc.) to emulate datacenter servers with multiple CPUs. The dynamic simulation code was benchmarked using the test results obtained in an experimental facility consisting of a liquid pumped cooling cycle assembled in a test loop with two parallel microevaporators, which were evaluated under steady-state and transient conditions of balanced and unbalanced heat fluxes on the two pseudochips. The errors in the model's predictions of mean chip temperature and mixed exit vapor quality at steady state remained within ±10%. Transient comparisons showed that the trends and the time constants were satisfactorily respected. A case study considering four microprocessors cooled in parallel flow was then simulated for different levels of heat flux in the microprocessors (40, 30, 20, and 10 W cm−2), which showed the robustness of the predictive-corrective solver used. For a desired mixed vapor exit quality of 30%, at an inlet pressure and subcooling of 1600 kPa and 3 K, the resulting distribution of mass flow rate in the microevaporators was, respectively, 2.6, 2.9, 4.2, and 6.4 kg h−1 (mass fluxes of 47, 53, 76 and 116 kg m−2 s−1) and yielded approximately uniform chip temperatures (maximum variation of 2.6, 2, 1.7, and 0.7 K). The vapor quality and maximum chip temperature remained below the critical limits during both transient and steady-state regimes.

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Fig. 5

Microevaporator/pseudochip package model (close up of Fig. 4)

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Fig. 4

Microevaporators in parallel flow without thermal insulation on the experimental two-phase cooling loop

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Fig. 3

Schematic of the experimental liquid pumping cycle for cooling of two microprocessors in parallel

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Fig. 2

Blade/cabinet architecture with two-phase on-chip cooling driven by a liquid pump

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Fig 1

Shortening the heat path to increase the cooling efficiency

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Fig. 6

Flow diagram of the simulation code

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Fig. 7

Experimental versus predicted vapor quality at point 3 of CV1-4

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Fig. 8

Experimental versus predicted mean chip temperature for chip 1

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Fig. 9

Experimental versus predicted mean chip temperature for chip 2

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Fig. 12

Experimental/predicted comparison of transient 1

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Fig. 13

Experimental/predicted comparison of transient 2

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Fig. 10

Experimental results for transient 1

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Fig. 11

Experimental results for transient 2

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Fig. 14

Case study of two-phase cooling of four microprocessors in parallel

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Fig. 15

Mass flow rate distribution per branch (steady-state regime)

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Fig. 16

Time profiles of the mass flow rate per branch

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Fig. 17

Vapor quality profiles in the CV1-4 (left) and in the ME (right) at 0.35 (a), 1.35 (b), and 10 s (c) after time t0

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Fig. 18

Footprint heat transfer coefficient (left) and chip surface temperature (right) profiles in the ME at, respectively, 0.35 (a), 1.35 (b), and 10 s (c) after time t0




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