Mechanical Augmentation of Convective Heat Transfer in Air

[+] Author and Article Information
J. K. Hagge, G. H. Junkhan

Department of Mechanical Engineering, Iowa State University, Ames, Iowa

J. Heat Transfer 97(4), 516-520 (Nov 01, 1975) (5 pages) doi:10.1115/1.3450421 History: Received September 19, 1975; Online August 11, 2010


An experimental investigation was conducted into augmentation of forced convection heat transfer in air by mechanical removal of the boundary layer. A rotating blade element passing in close proximity to a flat plate convective surface was found to increase the rate of convective heat transfer by up to eleven times in certain situations. The blade element effectively scrapes away the boundary layer, thus reducing the resistance to heat flow. Parameters investigated include scraping frequency, scraper clearance, and type of boundary layer. Increased coefficients were found for higher scraping frequencies. Significant augmentation was obtained with clearance as large as 0.15 in. (0.0038 m) between the moving blade element and the convective surface. The technique appears most useful for laminar and transitional boundary layers, although some improvement was obtained for the turbulent boundary layers investigated. The simple surface renewal theory developed for scraped surface augmentation in liquids was found to approximately predict the coefficients obtained. A new relation is proposed which gives a better prediction and includes the effect of scraper clearance.

Copyright © 1975 by ASME
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