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ISSN Online: 2377-424X

International Heat Transfer Conference 12
August, 18-23, 2002, Grenoble, France

Impingement Heat Transfer with Meso-scale Fluid Jets

Get access (open in a dialog) DOI: 10.1615/IHTC12.3310
11 pages

Resumo

Experimental and theoretical research is summarized of convective heat transfer with meso-scale impinging fluid jets. Experiments were performed with circular jets of nozzle diameter between 500 micrometers and 1000 micrometers, as well as with slot jets of nozzle width between 90 micrometers and 540 micrometers. The test fluids include air, nitrogen gas, CO2 gas, water, R113, FC72, kerosene, ethylene glycol, transformer oil and L12378 with Prandtl number ranging from 0.7 to 450. Local heat transfer coefficient distribution was measured and correlated at various velocities. Prandtl number dependence was clarified both analytically and experimentally in the wide range of Prandtl number. Influence of Reynolds number was studied in detail for all the nine fluids. Effect of jet inclination was studied with transformer oil as working fluid. Flow transition from laminar to turbulent was investigated. It was found that the completion of transition from laminar to turbulent flow, symbolized by the appearance of second peaks, was finished within several hundred micrometers. Significance of recovery effect with large Prandtl number liquid jets was revealed both by experimental and numerical studies. Distribution of recovery factors was measured. Maximum values up to twenty were recorded in the experimental study. Heat transfer enhancement was explored with impinging free surface jets of transformer oil flowing over heated wall coated by a nano-ferrofluid. Large enhancement of heat transfer was recorded with this new augmentation technique. Besides single phase jet impingement, jet impingement boiling was also studied. Partial and fully developed nucleate boiling was investigated. The effects of jet velocity and fluid subcooling were examined experimentally. Boiling hysteresis with impinging circular jets of highly wetting liquid was studied in experimental details. Analytical results for local laminar heat transfer were obtained with both impinging circular and slot jets of free surface. Using an integral technique, laminar solutions were presented for impinging jets on horizontal surface at arbitrary-heat-flux conditions. For meso-scale jets, very good agreement was observed between the prediction and the data of single phase jets.