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Journal of Flow Visualization and Image Processing
SJR: 0.161 SNIP: 0.312 CiteScore™: 0.5

ISSN Druckformat: 1065-3090
ISSN Online: 1940-4336

Journal of Flow Visualization and Image Processing

DOI: 10.1615/JFlowVisImageProc.v1.i4.80
pages 359-370

LASER SPECKLE PHOTOGRAPHY TECHNIQUE FOR MEASURING LOCAL AND GLOBAL HEAT TRANSFER CORRELATION COEFFICIENTS

T. E. Walsh
Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123
Kenneth D. Kihm
Texas A&M University College Station, TX; and Micro/Nano-Scale Fluidics and Energy Transport Laboratory, University of Tennessee, Mechanical, Aerospace and Biomedical Engineering Department, Knoxville TN 37996-2210, USA

ABSTRAKT

A laser specklegram technique, or, equivalently, speckle photography, is capable of directly measuring local surface temperature gradients providing an extremely high resolution and a full-field interrogation from a single data taking. A complete specklegram system using a 35 mW power He-Ne laser has been developed at Texas A&M University, and the system has been applied to investigate heat transfer characteristics for a common configuration, but under some dispute in determining the heat transfer correlation. Convective heat transfer from an upward-facing isothermal plate has been studied by measuring the local and global Nusselt numbers. An aspect ratio (AR) of 1.75 has been considered in the present case. The Rayleigh number, based on the length scale equivalent to the ratio of the surface area to the perimeter, has varied from 8.5 × 104 to 2.0 × 105. The results have been compared with several previously published calculations and data that employed classical and conventional techniques. The present result for the global heat transfer shows a 0.234 power law, i.e., Nu = 0.46 Ra0.234, correlates the data more properly, whereas previously published predictions and data for infinite or semi-infinite plate exhibit 0.2 power law. For the aspect ratios of order of unity, published correlations indicate that a 0.25 power law fit the data well. It is suggested that the band between 0.25 and 0.2 power correlations should contain the information for horizontal heated plates of AR ranging from 1.0 to showing a gradual decrease in Nusselt number with increasing aspect ratio.


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