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The effect of wall roughness on heat transfer in pipes

University of British Columbia

Heat transfer and friction data were obtained for air flow through seven commercial pipes with equivalent sand roughness ratios varying from 0.020 to 0.00041 in the Reynolds number range 10,000 - 80,000. Heat transfer for a given power loss decreased with increasing roughness ratio except at very high power losses, where this trend was to some extent reversed. The results for the Karbate pipe were somewhat out of line with those for standard pipes. This is attributed to a difference in the nature of the Karbate roughness. In the plots of friction factor and j[subscript H] versus Reynolds number, the experimental data show that j[subscript H] continues to decrease with Reynolds number when friction factor has become constant for a rough pipe. This fact contradicts not only Reynolds' simple turbulence analogy and Colburn's modification thereof, which are in other respects inapplicable, but is also at odds with the more rigorous analogy of Taylor and Prandtl and the similar, semi-empirical equation of Pinkel. It is, however, in agreement with the Karman analogy, which also gives a good absolute prediction of the heat transfer data.

Text

2012-02-08

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http://hdl.handle.net/2429/40549

Chemical and Biological Engineering

University of British Columbia

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