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Research Papers: Heat Exchangers

Cross-Flow Heat Exchanger: Volume-Averaging Formulation of a Unit Cell Model and Thermal Performance Analysis

[+] Author and Article Information
Hengyun Zhang

College of Automotive Engineering,
Shanghai University of Engineering Science,
No. 333 Longteng Road, Songjiang,
Shanghai 201620, China
e-mail: zhanghengyun@sues.edu.cn

Zhaoqiang Wang

College of Automotive Engineering,
Shanghai University of Engineering Science,
No. 333 Longteng Road, Songjiang,
Shanghai 201620, China
e-mail: wangzhaoqiang_2008@zju.edu.cn

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 25, 2016; final manuscript received January 26, 2017; published online March 7, 2017. Assoc. Editor: Chun Yang.

J. Heat Transfer 139(5), 051801 (Mar 07, 2017) (10 pages) Paper No: HT-16-1301; doi: 10.1115/1.4035997 History: Received May 25, 2016; Revised January 26, 2017

A formulation of the unit cell model and the corresponding thermal performance analysis for the cross-flow heat exchanger are carried out, with the design goal of dissipating 175 W from a high-power electronic chip in a compact space. A liquid to liquid heat exchanger in the cross-flow arrangement is preferred due to its compact size and high effectiveness. The unit cell model is formulated based on the volume-averaging method to determine the heat transfer coefficient involving two heat exchanging fluids and a solid. The various factors such as channel shape, channel edge length, channel size, and heat exchanger material can be examined based on the unit cell model. The obtained heat transfer coefficients are used for the estimation of the heat exchanger thermal performance based on the effectiveness–number of transfer units (NTU) correlation. To verify the model formulation, the heat and fluid flow over the cross-flow heat exchangers are investigated through the full-field numerical computation. The amount of heat exchanged from the numerical computation is extracted and compared with the predicted results from the unit cell model. A fairly good agreement is obtained between the two approaches. Based on the unit cell model, an aluminum cross heat exchanger with eight channel layers for the hot and cold fluids, 15 channels in each layer with a channel diameter of 2 mm, is able to meet the design target.

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Figures

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Fig. 1

Typical liquid cooling configuration to transport heat from heat generating chip to the cooling facility, with the heat exchanger to exchange the heat from the hot fluid 1 to the cold fluid 2, with T1i, T1o, T2i, and T2o representing the temperatures of hot fluid inlet, hot fluid outlet, cold fluid inlet, and cold fluid outlet, respectively, and FM denotes the flowmeter

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Fig. 2

Schematic of the cross-flow heat exchanger: (a) a representative unit cell in the heat exchanger, (b) 3D view, (c) the two fluid streams separated by the solid wall in plan view, and (d) A–A cross-sectional view of the representative unit cell with two adjacent stacks, stacks N and N − 1

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Fig. 3

Square channel 2 mm × 2 mm in the domain of three unit cell, each cell of 3 × 3 × 6 mm3 (SS-water) as encircled: cross-sectional view of (a) temperature profile and (b) heat flux and (c) enlarged isometric view of the temperature and heat flux profiles

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Fig. 4

Circular channel of diameter 2.256 mm in the domain of three unit cells, each cell of 3 × 3 × 6 mm (SS–water) as encircled: cross-sectional view of (a) temperature profile and (b) heat flux and (c) enlarged isometric view of the temperature and heat flux profiles

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Fig. 5

The computed cell heat transfer coefficients for different heat exchanger materials: (a) unit cell with square channels and (b) unit cell with circular channels

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Fig. 6

Heat transfer coefficient based on the hydraulic diameters for different heat exchanger materials

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Fig. 7

Exchanged heat based on the unit cell model for the cross-flow heat exchanger

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Fig. 8

The plan view of the temperature profile (upper) and velocity magnitude (lower) in the cold flow channel for the cross-flow heat exchanger

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Fig. 9

Comparison of the heat exchanger performance based on the numerical analysis and the unit cell model at different cold flow conditions but the same inlet flow 24 kg/h

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Fig. 10

The comparison of the full-field numerical results and the unit cell model results at different heat exchanger materials: T1i = 46.25 °C and T2i = 25 °C

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Fig. 11

Photograph of the fabricated liquid to liquid cross-flow heat exchanger

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