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Research Papers: Micro/Nanoscale Heat Transfer

Experimental Investigation of the Air Flow Behavior and Heat Transfer Characteristics in Microchannels With Different Channel Lengths

[+] Author and Article Information
Zhi Tao, Zhibing Zhu

National Key Laboratory of Science and
Technology on Aero-Engine
Aero-thermodynamics,
The Collaborative Innovation Center for
Advanced Aero-Engine of China,
Beihang University,
Beijing 100191, China;
Aircraft/Engine Integrated System
Safety Beijing Key Laboratory,
Beihang University,
Beijing 100191, China

Haiwang Li

National Key Laboratory of Science and
Technology on Aero-Engine
Aero-thermodynamics,
The Collaborative Innovation Center for
Advanced Aero-Engine of China,
Beihang University,
Beijing 100191, China;
Aircraft/Engine Integrated System
Safety Beijing Key Laboratory,
Beihang University,
Beijing 100191, China
e-mail: 09620@buaa.edu.cn

Presented at the 2016 ASME 5th Micro/Nanoscale Heat & Mass Transfer International Conference. Paper No. MMNHMT2016-6668.Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 14, 2016; final manuscript received December 14, 2016; published online February 14, 2017. Assoc. Editor: Zhuomin Zhang.

J. Heat Transfer 139(5), 052403 (Feb 14, 2017) (7 pages) Paper No: HT-16-1384; doi: 10.1115/1.4035589 History: Received June 14, 2016; Revised December 14, 2016

This paper attempts to experimentally investigate the influence of channel length on the flow behavior and heat transfer characteristics in circular microchannels. The diameters of the channels were 0.4 mm and the length of them were 5 mm, 10 mm, 15 mm, and 20 mm, respectively. All experiments were performed with air and completed with Reynolds number in the range of 300–2700. Results of the experiments show that the length of microchannels has remarkable effects on the performance of flow behavior and heat transfer characteristics. Both the friction factor and Poiseuille number drop with the increase of channel length, and the experimental values are higher than the theoretical ones. Moreover, the channel length does not influence the value of critical Reynolds number. Nusselt number decrease as the increase of channel length. Larger Nusselt numbers are obtained in shorter channels. The results also indicate that in all cases, the friction factor decreases and the Poiseuille number increases with the increase of the Reynolds number. It is also observed that the value of critical Reynolds number is between 1500 and 1700 in this paper, which is lower than the value of theoretical critical Reynolds number of 2300.

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Figures

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Fig. 1

Schematic diagram of experimental device. Compressed air was provided by air compressor and stored in a gas reservoir. Following two valves, the thermal mass flow meter was installed. Then the air flow through test section and the pressure of inlet and outlet manifolds were measured.

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Fig. 2

Schematic diagram of test section. The test pieces were sandwiched between up and down fixture. A pressure hole and a thermocouple hole were set close to the inlet of the channels; a pressure hole and five thermocouple holes were set by the outlet. Two holes in the top fixture were for thermocouples and the wires of the heating films.

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Fig. 3

Structure of the copper block and heat device. Considering that the heat conductivity coefficient of copper is high enough, lumped parameter method is suitable for this model to calculate heat flux. The temperature of the copper plate was regarded as uniform. The heating films were power by current heater. The heating film was bonded with copper plates by thermal conductive adhesive closely and covered by asbestos to decrease the heat dissipation. (a) Structure of the copper plate and (b) structure of the heating device. 1: asbestos, 2: heating film, and 3: copper plate.

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Fig. 4

Diagram of test pieces. There are 44 parallel identical circular microchannels in each test pieces. Diameter of each channel is 0.4 mm, horizontal spacing of channels is 0.9 mm.

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Fig. 5

Variations of pressure gradients with different Reynolds number. The pressure drops at inlet and outlet manifolds.

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Fig. 6

Variations of friction factor at different Reynolds number

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Fig. 7

Variations of Poiseuille number at different Reynolds number

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Fig. 8

Variations of Nusselt number at different Reynolds number. The Nusselt number is an average value.

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