The effect of a knurled heat transfer surface upon pool nucleate boiling of normal pentane
"The effect of knurling a nucleate boiling heat transfer surface was studied. The knurling utilized produced regular, four-sided, adjacent pyramids with an apex angle of 90 degrees. Four knurling densities were used ranging from 416 to 2591 pyramids per square inch. The transfer surface was gold-plated copper and the heaters used were electrically heated, ten-inch long, horizontal cylinders of one-inch diameter. The liquid boiled was normal pentane at its saturation temperature and a pressure of 760 millimeters mercury. For some of the knurled surfaces the temperature difference required to produce a given heat flux was found to be less than half that required for an unknurled control surface. For all of the knurled surfaces, values of the heat flux 20 per cent higher than burnout for the control surface were measured, and experimental indications suggest burnout may lie considerably higher. At low heat fluxes, where visual bubble observations could be made, bubble growth was seen to occur only at the corners of the bases of the pyramids. The experimental results can be represented by the form:: Q/n = (3.67-0.738D)ΔT1.88 where Q/n is the rate of heat transferred per pyramid [Btu/(hr)(pyramid)], D is the pyramid density [(pyramids/ft2) X 10-5], and ΔT is the temperature difference (F°)"--Abstract, page ii.
Missouri University of Science and Technology
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