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Research Papers: Forced Convection

Heat Transfer Investigation of Air Flow in Microtubes—Part II: Scale and Axial Conduction Effects

[+] Author and Article Information
Ting-Yu Lin

e-mail: rittonylin@gmail.com

Satish G. Kandlikar

Fellow ASME
e-mail: sgkeme@rit.edu
Thermal Analysis,
Microfluidics, and Fuel Cell Laboratory,
Department of Mechanical Engineering,
Rochester Institute of Technology,
76 Lomb Memorial Drive,
Rochester, NY 14623

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 7, 2011; final manuscript received May 24, 2012; published online February 8, 2013. Assoc. Editor: Jose L. Lage.

J. Heat Transfer 135(3), 031704 (Feb 08, 2013) (6 pages) Paper No: HT-11-1435; doi: 10.1115/1.4007877 History: Received September 07, 2011; Revised May 24, 2012

In this paper, the scale effects are specifically addressed by conducting experiments with air flow in different microtubes. Three stainless steel tubes of 962, 308, and 83 μm inner diameter (ID) are investigated for friction factor, and the first two are investigated for heat transfer. Viscous heating effects are studied in the laminar as well as turbulent flow regimes by varying the air flow rate. The axial conduction effects in microtubes are experimentally explored for the first time by comparing the heat transfer in SS304 tube with a 910 μm ID/2005 μm outer diameter nickel tube specifically fabricated using an electrodeposition technique. After carefully accounting for the variable heat losses along the tube length, it is seen that the viscous heating and the axial conduction effects become more important at microscale and the present models are able to predict these effects accurately. It is concluded that neglecting these effects is the main source of discrepancies in the data reported in the earlier literature.

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Figures

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Fig. 1

Schematic of the test section with LCT temperature measurement

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Fig. 2

Cross-sectional views of the microtubes used in the present study, (a) stainless steel 304, di = 962 μm, do = 1260 μm, (b) nickel, di = 910 μm, do = 2005 μm, (c) stainless steel 304, di = 308 μm, do = 579 μm, and (d) stainless steel 304, di = 83 μm, do = 270 μm

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Fig. 3

TLC Thermography images of (a) 962 μm tube and (b) 308 μm tube at different temperatures

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Fig. 4

Calibration curve of TLC hue to temperature

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Fig. 5

Temperature resolution of thermochromic liquid

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Fig. 6

Friction factors for stainless steel 30 tubes of three different diameters

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Fig. 7

Comparison of Nu as a function of Re for 962 μm stainless steel 304 tube with different heat flux and temperature measurement methods

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Fig. 8

Heat transfer comparison for 308 μm and 962 μm inner diameter stainless steel 304 tubes

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Fig. 9

Viscous heating effect in 308 μm and 962 μm inner diameter stainless steel 304 tubes during laminar flow

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Fig. 10

Comparison of heat transfer performance by different wall temperature measurement methods for 308 μm inner diameter tube

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Fig. 11

Comparison of experimental Nu with and without considering axial heat conduction for stainless steel 304 tubes, di = 308 μm, do = 2005 μm

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Fig. 12

Axial conduction effects on heat transfer coefficient for thick walled nickel tube di = 910 μm, do = 2005 μm

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