Abstract
The heat transfer and pressure drop performance of three 4-in nominal bore tubes internally roughened with Whitworth thread forms of 11, 24 and 60 threads per inch (t.p.i.) has been measured with the tubes empty and with a concentrically mounted smooth cylinder of 2·012-in diameter. The tube with the 24-t.p.i. roughness form was also tested with a concentric cylinder of 2·00-in diameter having the same geometric roughness. The measured Stanton number and friction factors of the annuli with the smooth inner walls have been transformed using a method suggested by Hall (1)†, and compared to the empty channel and completely roughened annulus data.

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