Heat and momentum transfer in smooth and rough tubes at various prandtl numbers

Abstract

Results are presented from an experimental investigation of the relation between heat transfer and friction in smooth and rough tubes. Three rough tubes and one smooth tube were formed from electroplated nickel. The rough tubes contained a close-packed, granular type of surface with roughness-height-to-diameter ratios ranging from 0.0024 to 0.049. Measurements of the heat-transfer coefficients ( C H ) and the friction coefficients ( C F ) were obtained with distilled water flowing through electrically heated tubes. A Prandtl number range of 1.20–5.94 was investigated by adjusting the bulk temperature of the water. Results were obtained for Reynolds numbers from 6 × 10 4 to 5 × 10 6 and from 1.4 × 10 4 to 1.2 × 10 5 at the lowest and highest Prandtl numbers respectively. A similarity rule for heat transfer was used to correlate, interpret, and extend the experimental results. The results were compared with previously existing results, both theoretical and experimental. Increases in C H due to roughness of as high as 270 per cent were obtained. These increases were, in general, accompanied by even larger increases in C F . An exception to this general behavior occurs at high Prandtl number in the region of transition between the “smooth” and the “fully rough” C F characteristic.