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Experimental studies on heat transfer and flow structure in confined impingement jets were performed. The objective of this study was to investigate the detailed heat transfer coefficient distribution on the jet impingement target surface and flow structure in the confined cavity. The distribution of heat transfer coefficients on the target surface was obtained by employing the transient liquid crystal method coupled with a 3-D inverse transient conduction scheme under Reynolds number ranging from 1039 to 5175. The results show that the average heat transfer coefficients increased linearly with the Reynolds number as Nu = 0.00304 Pr0.42Re. The effects of cross flow on heat transfer were investigated. The flow structure were analyzed to gain insight into convective heat transfer behavior.

Various transient liquid crystal methods have been widely and routinely employed to measure surface heat transfer coefficients. Typically, the heat transfer surface was modeled as a one-dimensional, transient heat conduction over a semi-infinite surface to retrieve information of the surface heat transfer coefficients. To satisfy the theoretical initial and boundary conditions, inconvenient and/or complex designs are required. Frequently, the conditions are not exactly satisfied. To resolve these issues, an approach of measuring heat transfer coefficients coupling the transient liquid crystal method with a 3-D inverse transient conduction scheme was developed and was applied to a nonuniform heat transfer surface produced by arrays of impinging jets. The present method utilized the hue-angle method to process the color images captured from the liquid crystal color play. Instantaneous temperature readings from embedded thermocouples were utilized for in-situ calibration of hue angle for each data set. The convective heat transfer coefficient results were obtained by performing a 3-D inverse transient conduction calculation over the entire jet impingement target surface and the substrate. The results of average heat transfer coefficients agreed well with previous experimental results of point measurements by thermocouples.