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Research Papers: Evaporation, Boiling, and Condensation

Enhanced Flow Boiling of Ethanol in Open Microchannels With Tapered Manifolds in a Gravity-Driven Flow

[+] Author and Article Information
Philipp Buchling

Mechanical Engineering Department,
Rochester Institute of Technology,
Lomb Memorial Drive,
Rochester, NY 14623

Satish Kandlikar

Fellow ASME
Mechanical Engineering Department,
Rochester Institute of Technology,
Lomb Memorial Drive,
Rochester, NY 14623
e-mail: sgkeme@rit.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 20, 2015; final manuscript received September 23, 2015; published online November 17, 2015. Assoc. Editor: Amitabh Narain.

J. Heat Transfer 138(3), 031503 (Nov 17, 2015) (10 pages) Paper No: HT-15-1289; doi: 10.1115/1.4031884 History: Received April 20, 2015; Revised September 23, 2015

There is a clear need for cooling high heat flux generating electronic devices using a dielectric fluid without using a pump. This paper explores the feasibility of employing ethanol as a dielectric fluid in a horizontal, open microchannel heat sink configuration with a tapered gap manifold to yield very low pressure head requirements. The paper presents experimental results for such a system utilizing ethanol as a working fluid under gravity-driven flow. A heat flux of 217 W/cm2 was dissipated with a pressure drop of only 9 kPa. The paper further presents parametric trends regarding flow rate and pressure drop characteristics that provide basic insight into designing high heat flux systems under a given gravity head requirement. Based on the results, interrelationships and design guidelines are developed for the taper, ethanol flow rate and imposed heat flux on heat transfer coefficient and gravity head requirement for electronics cooling. Reducing flow instability, reducing pressure drop, and enhancing heat transfer performance for a dielectric fluid will enable the development of pumpless cooling solutions in a variety of electronics cooling applications.

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Figures

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Fig. 1

Experimental setup

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Fig. 2

Volume concentration of oxygen in liquid (redrawn in different units using data from Imura et al. [20])

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Fig. 3

Schematic of (a) tapered manifold and open microchannel chip and (b) chip surface details

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Fig. 4

Plots showing effect of manifold taper for plain chip at 60 mL/min: (a) boiling curve, (b) heat transfer coefficient as a function of vapor quality, and (c) pressure drop as a function of heat flux

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Fig. 5

Plots showing effect of manifold taper for microchannel chips at 60 mL/min: (a) boiling curve, (b) heat transfer coefficient as a function of vapor quality, and (c) pressure drop as a function of heat flux

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Fig. 6

Plots showing effect of flow rate on (a) plain and (b) microchannel chips with 6% manifold taper

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Fig. 7

Plots showing effect of chip at 80 mL/min with 6% manifold taper: (a) boiling curve, (b) heat transfer coefficient as a function of vapor quality, and (c) pressure drop as a function of heat flux

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Fig. 8

High-speed video frames of growing and coalescing bubbles in chip MC1. Test conditions: 2% manifold taper, 60 mL/min flow rate, heat flux 63.7 W/cm2, and wall superheat 23.3 °C. Frames: (a) 0.00 ms, (b) 3.50 ms, (c) 6.70 ms, (d) 8.00 ms, (e) 10.00 ms, and (f) 12.70 ms.

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Fig. 9

(a) Pressure drop model [30] versus experimental data for microchannel chip with 4% manifold taper at 80 mL/min and (b) two-phase pressure drop components from the model by Kalani and Kandlikar [30]

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