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Research Papers: Evaporation, Boiling, and Condensation

Flow Boiling in an In-Line Set of Short Narrow Gap Channels

[+] Author and Article Information
D. Janssen, J. M. Dixon

Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455

S. J. Young

General Dynamics,
Advanced Information Systems,
Minneapolis, MN 55431

F. A. Kulacki

Fellow ASME
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455
e-mail: kulacki@me.umn.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received August 9, 2013; final manuscript received April 10, 2015; published online June 9, 2015. Assoc. Editor: W. Q. Tao. The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Heat Transfer 137(11), 111501 (Jun 09, 2015) (12 pages) Paper No: HT-13-1405; doi: 10.1115/1.4030382 History: Received August 09, 2013

Heat transfer coefficients in a set of three symmetrically heated narrow gap channels arranged in line are reported at power densities of 1 kW/cm3 and wall heat flux of 3–40 W/cm2. This configuration emulates an electronics system wherein power dissipation can vary across an array of processors, memory chips, or other components. Three pairs of parallel ceramic resistance heaters in a nearly adiabatic housing form the flow passage, and length-to-gap ratios for each pair of heaters are 34 at a gap of 0.36 mm. Novec™ 7200 and 7300 are used as the heat transfer fluids. Nonuniform longitudinal power distributions are designed with the center heater pair at 1.5X and 2X the level of the first and third heater pairs. At all levels of inlet subcooling, single-phase heat transfer dominates over the first two heater pairs, while the third pair exhibits significant increases because of the presence of flow boiling. Reynolds numbers range from 250 to 1200, Weber numbers from 2 to 14, and boiling numbers from O(10−4) to O(10−3). Exit quality can reach 30% in some cases. Overall heat transfer coefficients of 40 kW/m2K are obtained. Pressure drops for both Novec™ heat transfer fluids are approximately equal at a given mass flux, and a high ratio of heat transfer to pumping power (coefficient of performance (COP)) is obtained. With a mass flux of 250 kg/m2s, heater temperatures can exceed 95 °C, which is the acceptable limit of steady operation for contemporary high performance electronics. Thus, an optimal operating point involving power density, power distribution, mass flux, and inlet subcooling is suggested by the data set for this benchmark multiheater configuration.

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References

Figures

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Fig. 1

Configuration of in-line chip pairs. Subcooled coolant enters from the right.

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Fig. 2

Design of the in-line chip pairs, offsets and location of thermocouples. Heaters are 12 mm in length, and offset from the wall is 0.6 mm. All dimensions are in mm.

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Fig. 3

Assembly of flow chamber with heaters. The gasket determines the gap between heaters. Inlet plenum is on left side of assembly.

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Fig. 4

Flow loop and flow rate monitoring system

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Fig. 5

Power input calculated from single phase energy balance compared to ideal case (zero losses). Deviations occur in regions of two phase flow.

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Fig. 6

Chip temperatures with uniform power density with Novec 7200. d = 0.36 mm. “First set” is heater pair at flow inlet. (a) G = 250 kg/m2s, Ti = 25 °C; (b) G = 250 kg/m2s, Ti = 55 °C; (c) G = 500 kg/m2s, Ti = 25 °C; and (d) G = 500 kg/m2s, Ti = 55 °C; and (e) G = 250 kg/m2s, Ti = 66 °C.

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Fig. 7

Heat transfer coefficients with uniform power density for Novec 7200. “First set” is the chip pair at inlet. d = 0.36 mm. (a) G = 250 kg/m2s, Ti = 25 °C; (b) G = 500 kg/m2s, Ti = 25 °C; (c) G = 250 kg/m2s, Ti = 55 °C; (d) G = 500 kg/m2s, Ti = 55 °C; and (e) G = 250, Ti = 66 °C.

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Fig. 8

Subcooling effect on local heat transfer coefficients with Novec 7200 and uniform applied power. Each value of the heat transfer coefficient represents an average over power density range of Fig. 6. First chip pair is denoted by “1” on the abscissa. d = 0.36 mm.

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Fig. 9

Chip pair temperatures with second pair at 1.5X the average power density and Novec 7200. d = 0.36 mm. “First set” is chip pair at flow inlet. (a) G = 250 kg/m2s, Ti = 25 °C; (b) G = 250 kg/m2s, Ti = 55 °C; (c) G = 500 kg/m2s, Ti = 25 °C; (d) G = 500 kg/m2s, Ti = 55 °C; and (e) G = 250 kg/m2s, Ti = 66 °C.

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Fig. 10

Heat transfer coefficients with Novec 7200 in terms of power density at second chip pair at 1.5X average power density. d = 0.36 mm. “First set” is the chip pair at inlet. (a) G = 250 kg/m2s, Ti = 25 °C; (b) G = 250 kg/m2s, Ti = 55 °C; (c) G = 500 kg/m2s, Ti = 25 °C; (d) G = 500 kg/m2s, Ti = 55 °C; and (e) G = 250 kg/m2s, Ti = 66 °C.

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Fig. 11

Subcooling effect on local heat transfer coefficients with Novec 7200 and uniform applied power. Each value of the heat transfer coefficient represents an average over power density range of Fig. 9. First chip pair is denoted by “1.” d = 0.36 mm.

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Fig. 12

Exit quality based on Eq. (2) and total input power. Subcooling = 21 °C. d = 0.36 mm.

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Fig. 13

Overall heat transfer coefficient versus empirical quality. Hollow data points are for a single chip pair [1].

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Fig. 14

Overall heat transfer coefficients versus exit quality for Novec 7200. Uniform power density. d = 0.36 mm. (a) G = 250 kg/m2s and (b) G = 500 kg/m2s.

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Fig. 15

Overall heat transfer coefficients versus exit quality for Novec 7300. Uniform power density. d = 0.36 mm. (a) G = 250 kg/m2s and (b) G = 500 kg/m2s.

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Fig. 16

Overall Nusselt number with correlation relations for d = 0.36 mm. Results for a single chip pair [1] are shown for comparison.

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