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Research Papers

The Use of a Nano- and Microporous Surface Layer to Enhance Boiling in a Plate Heat Exchanger

[+] Author and Article Information
Richard Furberg1

School of Industrial Engineering and Management, Department of Applied Thermodynamics and Refrigeration, Royal Institute of Technology, Stockholm 10044, Swedenrichard.furberg@energy.kth.se

Björn Palm

School of Industrial Engineering and Management, Department of Applied Thermodynamics and Refrigeration, Royal Institute of Technology, Stockholm 10044, Sweden

Shanghua Li, Muhammet Toprak, Mamoun Muhammed

School of Information and Communication Technology, Division of Functional Materials, Royal Institute of Technology, Stockholm 10044, Sweden

1

Corresponding author.

J. Heat Transfer 131(10), 101010 (Jul 31, 2009) (8 pages) doi:10.1115/1.3180702 History: Received September 27, 2008; Revised April 15, 2009; Published July 31, 2009

Presented research is an experimental study of the performance of a standard plate heat exchanger evaporator, both with and without a novel nano- and microporous copper structure, used to enhance the boiling heat transfer mechanism in the refrigerant channel. Various distance frames in the refrigerant channel were also employed to study the influence of the refrigerant mass flux on two-phase flow heat transfer. The tests were conducted at heat fluxes ranging between 4.5kW/m2 and 17kW/m2 with 134a as refrigerant. Pool boiling tests of the enhancement structure, under similar conditions and at various surface inclination angles, were also performed for reasons of comparison. The plate heat exchanger with the enhancement structure displayed up to ten times enhanced heat transfer coefficient in the refrigerant channel, resulting in an improvement in the overall heat transfer coefficient with over 100%. This significant boiling enhancement is in agreement with previous pool boiling experiments and confirms that the enhancement structure may be used to enhance the performance of plate heat exchangers. A simple superposition model was used to evaluate the results, and it was found that, primarily, the convective boiling mechanism was affected by the distance frames in the standard heat exchanger. On the other hand, with the enhanced boiling structure, variations in hydraulic diameter in the refrigerant channel caused a significant change in the nucleate boiling mechanism, which accounted for the largest effect on the heat transfer performance.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental set-up for thermal tests of plate heat exchanger

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Figure 2

Plate heat exchanger with gasket seals and distance frame

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Figure 3

(a) Heat exchanger plate with enhanced surface structure fabricated on the refrigerant side. (b) Close-up view of enhanced heat exchanger plate. (c) and (e) SEM picture of the enhancement structure. (d) SEM side-view.

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Figure 4

Overall U-value as a function of heat flux for standard and enhanced heat exchangers

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Figure 5

Heat transfer coefficient on the refrigerant side, href, as a function of heat flux for a standard and an enhanced heat exchanger

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Figure 6

Measured and calculated heat transfer coefficients on the refrigerant side, href, as a function of heat flux standard configurations

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Figure 7

Heat transfer coefficients on the refrigerant side, href, as a function of heat flux for the enhanced configurations including results from pool boiling tests

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Figure 8

Heat transfer coefficient on refrigerant side, href, as a function of refrigerant mass flux, Gref (filled symbols—nμP, white symbols—STD)

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Figure 12

Calculated and measured heat transfer coefficient, href, as a function of heat flux, q″

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Figure 9

Heat transfer coefficient on refrigerant side, href, as a function of the hydraulic diameter of the refrigerant channel, dh_ref (filled symbols—nμP, white symbols—STD)

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Figure 10

Heat transfer coefficient versus heat flux, q″, for evaporator and pool boiling tests with the enhancement structure

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Figure 11

Pictures from enhanced evaporator channel (dh=2.5 mm) in a thermosyphon loop at various heat and refrigerant mass flux

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