Research Papers

Flow Boiling Heat Transfer and Pressure Drops of R1234ze(E) in a Silicon Micro-pin Fin Evaporator

[+] Author and Article Information
C. Falsetti

Laboratory of Heat and Mass Transfer (LTCM),
Ecole Polytechnique Fédérale de
Lausanne (EPFL),
Station 9,
Lausanne CH-1015, Switzerland
e-mail: chiara.falsetti@epfl.ch

M. Magnini

Laboratory of Heat and Mass Transfer (LTCM),
Ecole Polytechnique Fédérale de
Lausanne (EPFL),
Station 9,
Lausanne CH-1015, Switzerland
e-mail: mirco.magnini@epfl.ch

J. R. Thome

Laboratory of Heat and Mass Transfer (LTCM),
Ecole Polytechnique Fédérale de
Lausanne (EPFL),
Station 9,
Lausanne CH-1015, Switzerland
e-mail: john.thome@epfl.ch

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received February 27, 2017; final manuscript received June 21, 2017; published online July 10, 2017. Assoc. Editor: Mehdi Asheghi.

J. Electron. Packag 139(3), 031008 (Jul 10, 2017) (8 pages) Paper No: EP-17-1023; doi: 10.1115/1.4037152 History: Received February 27, 2017; Revised June 21, 2017

The development of newer and more efficient cooling techniques to sustain the increasing power density of high-performance computing systems is becoming one of the major challenges in the development of microelectronics. In this framework, two-phase cooling is a promising solution for dissipating the greater amount of generated heat. In the present study, an experimental investigation of two-phase flow boiling in a micro-pin fin evaporator is performed. The micro-evaporator has a heated area of 1 cm2 containing 66 rows of cylindrical in-line micro-pin fins with diameter, height, and pitch of, respectively, 50 μm, 100 μm, and 91.7 μm. The working fluid is R1234ze(E) tested over a wide range of conditions: mass fluxes varying from 750 kg/m2 s to 1750 kg/m2 s and heat fluxes ranging from 20 W/cm2 to 44 W/cm2. The effects of saturation temperature on the heat transfer are investigated by testing three different outlet saturation temperatures: 25 °C, 30 °C, and 35 °C. In order to assess the thermal–hydraulic performance of the current heat sink, the total pressure drops are directly measured, while local values of heat transfer coefficient are evaluated by coupling high-speed flow visualization with infrared temperature measurements. According to the experimental results, the mass flux has the most significant impact on the heat transfer coefficient while heat flux is a less influential parameter. The vapor quality varies in a range between 0 and 0.45. The heat transfer coefficient in the subcooled region reaches a maximum value of about 12 kW/m2 K, whilst in two-phase flow it goes up to 30 kW/m2 K.

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Fig. 1

Schematic of the experimental flow loop

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Fig. 2

Test section top side (a), bottom side (b), micro-pin fins geometry and configuration of the heated area (c and d)

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Fig. 3

Experimental repeatability of the heat transfer coefficient versus vapor quality

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Fig. 4

Total single-phase pressure drops versus mass flux

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Fig. 5

Friction factor versus Reynolds number

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Fig. 6

Average Nusselt number versus Reynolds number. Comparison with existing correlations.

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Fig. 7

Total two-phase pressure drop versus outlet vapor quality varying the test conditions

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Fig. 8

(a) Micro-evaporator base temperature measured with the IR camera, (b) corresponding heat transfer coefficient calculated with the explained data reduction, (c) screenshot from the high-speed camera, and (d) local heat transfer coefficient averaged along the widthwise direction, under the test conditions of G = 1000 kg/m2 s, q = 28 W/cm2, and Tsat = 35 °C. Flow is from the left to the right.

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Fig. 9

Local heat transfer coefficient versus vapor quality. Effects of heat flux when G = 1000 kg/m2 s (a), and G = 1500 kg/m2 s (b). Tsat = 35 °C.

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Fig. 10

Local heat transfer coefficient versus vapor quality. Effects of mass flux when q = 28 W/cm2 (a), and G = 40 W/cm2 (b). Tsat = 35 °C.

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Fig. 11

Local heat transfer coefficient along the streamwise direction, with flow visualization screenshots obtained by means of the high-speed camera. Tsat = 35 °C.

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Fig. 12

Local heat transfer coefficient versus vapor quality. Effects of the outlet saturation temperature. Test conditions: G = 1500 kg/m2 s, q = 40 W/cm2.



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