For extended surfaces used in boiling liquids, the specified fin-base temperature may be such as to result in simultaneous nucleate, transition, and film boiling at adjacent positions on the fins. If the fins are spines of circular cross section, the optimum shape to minimize the volume of metal resembles a turnip, as shown by Haley and Westwater. The object of the new study was to develop easy-to-machine shapes using cones and cylinders. It was shown mathematically that two cones, base-to-base, give an excellent approximation to the turnip shape. Three such fins were constructed of copper and tested in Freon-113 at atmospheric pressure. The measured, peak heat duties were 5 to 70 percent higher than the predicted values, proving that the design method is conservative.

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