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Research Papers: Forced Convection

Heat Transfer Investigation of Air Flow in Microtubes—Part I: Effects of Heat Loss, Viscous Heating, and Axial Conduction

[+] 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 25, 2012; published online February 11, 2013. Assoc. Editor: Jose L. Lage.

J. Heat Transfer 135(3), 031703 (Feb 11, 2013) (9 pages) Paper No: HT-11-1434; doi: 10.1115/1.4007876 History: Received September 07, 2011; Revised May 25, 2012

Experiments were conducted to investigate local heat transfer coefficients and flow characteristics of air flow in a 962 μm inner diameter stainless steel microtube (minichannel). The effects of heat loss, axial heat conduction and viscous heating were systematically analyzed. Heat losses during the experiments with gas flow in small diameter tubes vary considerably along the flow length, causing the uncertainties to be very large in the downstream region. Axial heat conduction was found to have a significant effect on heat transfer at low Re. Viscous heating was negligible at low Re, but the effect was found to be significant at higher Re. After accounting for varying heat losses, viscous heating and axial conduction, Nu was found to agree very well with the predictions from conventional heat transfer correlations both in laminar and turbulent flow regions. No early transition to turbulent flow was found in the present study.

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Figures

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Fig. 1

(a) Schematic of the experimental setup for heat transfer and pressure drop investigation in a microtube and (b) 3D drawing of measurement equipment mounting

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Fig. 2

Schematic drawing of test section assembly

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Fig. 3

Test tube cross-section viewed from an optical microscope and the internal surface image obtained from a laser confocal scanning microscope, Ra = 0.8 μm

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Fig. 4

Comparison of heat losses from the test section at different vacuum levels

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Fig. 5

Heat loss versus wall to ambient temperature difference for three test sections with different heating lengths

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Fig. 6

Comparison of heat loss, qloss, normalized by the input heat, qin, as a function of Re at three different heating lengths

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Fig. 7

Comparison of local net heat flux along the test tube with and without considering heat losses for Re = 4700 and Re = 2100

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Fig. 8

The variation of uncertainty in Nu as a function of Re at three heating lengths

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Fig. 9

Comparison of friction factor data with theoretical predictions

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Fig. 10

Comparison of experimental data for Nu for 962 diameter tube with available correlations after accounting for heat losses, viscous heating and axial conduction; inner diameter of microtube = 962 μm and Lh = 25 mm

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Fig. 11

The comparison of viscous heating effect on Nu in turbulent flow region using laminar flow equation, Eq. (8), and turbulent flow equation, Eq. (9)

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Fig. 12

Comparison of Nu/Nuth with different heat loss correction equations, Eq. (8) based on laminar flow, and Eq. (9) based on turbulent flow

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Fig. 13

Effect of axial heat conduction in laminar and turbulent regions and comparison of experimental data with Lin and Kandlikar [28] model

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