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Journal of Enhanced Heat Transfer
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ISSN Imprimir: 1065-5131
ISSN En Línea: 1026-5511

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Journal of Enhanced Heat Transfer

DOI: 10.1615/JEnhHeatTransf.v1.i2.70
pages 179-190

An Insertion Technique Using the Transient Method with Liquid Crystals For Enhanced Heat Transfer Measurements in Ducts

James W. Baughn
Department of Mechanical and Aeronautical Engineering, University of California Davis, CA 95616
Xiaojun Terry Yan
Department of Mechanical and Industrial Engineering Southern Illinois University Edwardsville Edwardsville, Illinois, 62026-1805 U.S.A
Jon L. Roby
Department of Mechanical and Aeronautical Engineering, University of California Davis, CA 95616


A technique for measuring local heat transfer coefficients in ducts is described. The technique involves the sudden insertion or attachment of a preheated section of duct on the end of another duct with the same cross section which has an established flow at ambient temperature. The transient surface temperature of the inserted section is measured using thermochromic liquid crystals and the color change is recorded with a video system. This technique, which is a variation on the transient method, allows control of the hydrodynamic and thermal boundary conditions in the upstream duct.
The technique is used for measurements of turbulent (Re = 15,000 to 80,000) heat transfer on smooth and ribbed, circular and square ducts (ribbed on two sides). For the smooth ducts, the results compare well with the existing correlations for circular and square ducts, respectively. The results for both ribbed ducts show rapid thermal development and high heat transfer coefficients on the top of the ribs and in a region approximately 4 ∼ 6 rib heights downstream of the ribs. For the ribbed square ducts, contour and three-dimensional plots are presented showing the detailed local heat transfer distribution within a rib segment.