Research Papers

Thermal Analysis of Cold Plate for Direct Liquid Cooling of High Performance Servers

[+] Author and Article Information
Bharath Ramakrishnan

Department of Mechanical Engineering,
Binghamton University,
Binghamton, NY 13902
e-mail: bramakr1@binghamton.edu

Yaser Hadad

Department of Mechanical Engineering,
Binghamton University,
Binghamton, NY 13902
e-mail: yhadad1@binghamton.edu

Sami Alkharabsheh

Department of Mechanical Engineering,
Binghamton University,
Binghamton, NY 13902
e-mail: salkhar1@binghamton.edu

Paul R. Chiarot

Department of Mechanical Engineering,
Binghamton University,
Binghamton, NY 13902
e-mail: pchiarot@binghamton.edu

Bahgat Sammakia

Fellow ASME
Department of Mechanical Engineering,
Binghamton University,
Binghamton, NY 13902
e-mail: bahgat@binghamton.edu

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received August 16, 2018; final manuscript received June 19, 2019; published online July 12, 2019. Assoc. Editor: Baris Dogruoz.

J. Electron. Packag 141(4), 041005 (Jul 12, 2019) (10 pages) Paper No: EP-18-1069; doi: 10.1115/1.4044130 History: Received August 16, 2018; Revised June 19, 2019

Data center energy usage keeps growing every year and will continue to increase with rising demand for ecommerce, scientific research, social networking, and use of streaming video services. The miniaturization of microelectronic devices and an increasing demand for clock speed result in high heat flux systems. By adopting direct liquid cooling, the high heat flux and high power demands can be met, while the reliability of the electronic devices is greatly improved. Cold plates which are mounted directly on to the chips facilitate a lower thermal resistance path originating from the chip to the incoming coolant. An attempt was made in the current study to characterize a commercially available cold plate which uses warm water in carrying the heat away from the chip. A mock package mimicking a processor chip with an effective heat transfer area of 6.45 cm2 was developed for this study using a copper block heater arrangement. The thermo-hydraulic performance of the cold plates was investigated by conducting experiments at varying chip power, coolant flow rates, and coolant temperature. The pressure drop (ΔP) and the temperature rise (ΔT) across the cold plates were measured, and the results were presented as flow resistance and thermal resistance curves. A maximum heat flux of 31 W/cm2 was dissipated at a flow rate of 13 cm3/s. A resistance network model was used to calculate an effective heat transfer coefficient by revealing different elements contributing to the total resistance. The study extended to different coolant temperatures ranging from 25 °C to 45 °C addresses the effect of coolant viscosity on the overall performance of the cold plate, and the results were presented as coefficient of performance (COP) curves. A numerical model developed using 6SigmaET was validated against the experimental findings for the flow and thermal performance with minimal percentage difference.

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Fig. 1

(a) Cold plate with copper microchannels, (b) zoomed up image of microchannels, (c) opened up top plastic part containing the impinging arrangement, and (d) bottom base metal part containing the microchannels

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Fig. 2

Schematic showing the mock package made of copper block heater with the cold plate mounted on top of it

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Fig. 3

Energy balance comparison between input and output power at different flow rates

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Fig. 4

T-type thermocouples installed in the back of the cold plate to indicate base temperature measurement Tb during thermal tests

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Fig. 5

Schematic of the experimental facility showing the test loop and different components employed

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Fig. 6

Resistance network model used in estimating the average heat transfer coefficient

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Fig. 7

Exploded schematic of the model developed for numerical simulation using 6sigmaET

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Fig. 8

PQ curve for different input powers at constant coolant temperature of 24.3 °C

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Fig. 9

Comparison of experimental pressure drop with numerical simulation

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Fig. 10

Effect of coolant temperature on the pressure drop across the cold plate at different flow rates

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Fig. 11

Schematic of the mock package assembly showing the arrangement of thermocouples and the boundary conditions used in the model

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Fig. 12

Variation of cold plate thermal resistance with respect to the coolant flow rate and input power

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Fig. 13

Variation of coolant outlet temperature with respect to coolant flow rate and input power

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Fig. 14

Cold plate thermal resistance comparison between experiments and numerical model at different flow rates

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Fig. 15

Estimating average heat transfer coefficient following the resistance network model

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Fig. 16

COP comparison at different coolant temperatures, flow rates, and operating power



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