Research Papers: Two-Phase Flow and Heat Transfer

Mathematical Modeling of Novel Two-Phase Heat Transfer Device for Thermal Management of Light Emitting Diodes

[+] Author and Article Information
Karthik S. Remella

Microscale Heat Transfer Laboratory,
Department of Mechanical
and Materials Engineering,
College of Engineering and Applied Science,
University of Cincinnati,
565 Rhodes Hall,
Cincinnati, OH 45221
e-mail: sivarara@mail.uc.edu

Frank M. Gerner

Microscale Heat Transfer Laboratory,
Department of Mechanical
and Materials Engineering,
College of Engineering and Applied Science,
University of Cincinnati,
565 Rhodes Hall,
Cincinnati, OH 45221
e-mail: Frank.Gerner@uc.edu

Ahmed Shuja

BritePointe, Inc.,
Hayward, CA 94541
e-mail: ahmed@lvlanalytics.com

1Corresponding author.

2Present address: lvl Analytics LLC, Oakland, CA 94612.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 28, 2015; final manuscript received December 15, 2016; published online February 28, 2017. Editor: Portonovo S. Ayyaswamy.

J. Heat Transfer 139(6), 062901 (Feb 28, 2017) (13 pages) Paper No: HT-15-1623; doi: 10.1115/1.4035649 History: Received September 28, 2015; Revised December 15, 2016

The paper introduces a novel two-phase heat transfer device (TPHTD) which is employed in the thermal management of light emitting diodes (LEDs). The heat transfer device structurally resembles a conventional loop heat pipe (LHP) without a compensation chamber, but operates very differently from it. The device is comprised of a central evaporator package and a circular coil that acts as a heat exchanger loop. The working fluid leaving the evaporator has a two-phase mixture quality of approximately 0.2. Having introduced the device, the paper delineates a mathematical model for predicting its thermal performance. The primary objective of the model is to provide a fundamental understanding of the operation of the device. A one-dimensional thermal resistance model (TRM) is utilized in modeling the evaporator. The paper presents a detailed discussion on obtaining these resistances from experiments conducted on the device. A correlation for the external heat transfer coefficient of the heat exchanger loop is proposed based on experiments and is found to be in good agreement with literature. The model predicts performance parameters such as board temperature, two-phase mixture quality, and saturation and subcooled temperatures (Tsat and Tsc) of the working fluid for different input thermal powers (Qtot). Based on experimental evidence, it is concluded that the majority of Qtot (∼75%) is utilized in phase change of the working fluid, and the rest reheats the working fluid from a lower subcooled temperature (Tsc) to the saturation temperature (Tsat) of the evaporator.

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Fig. 1

A detailed schematic of conventional loop heat pipe (LHP) [10]

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Fig. 2

A 2D schematic of the gravity-assisted TPHTD

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Fig. 3

The evaporator package of the two-phase heat transfer device along with its orientation

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Fig. 4

Environmental scanning electron microscope image of wire-mesh screen

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Fig. 5

Thermal resistance model of evaporator package

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Fig. 6

Liquid void fraction versus two-phase mixture quality, comparing two void fraction models

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Fig. 7

Thermocouple locations during experiments on TPHTD

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Fig. 8

Experimental reference heat transfer coefficient (ho-ref) versus saturation temperature (Tsat)

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Fig. 9

Variation of board temperature (Tbrd) with applied thermal power (Qtot)

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Fig. 10

Variation of saturation temperature (Tsat) with applied thermal power (Qtot)

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Fig. 11

Variation of condenser (Lcon) and subcooler (Lsc) lengths with applied thermal energy (Qtot)

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Fig. 12

Variation of subcooler temperature (Tsc) with applied thermal power (Qtot)

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Fig. 13

Variation of two-phase mixture quality (xevp) with applied thermal power (Qtot)

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Fig. 14

Variation of mass flow rate of working fluid with applied thermal energy (Qtot)



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