Measurements have been made of heat transfer near atmospheric pressure in the post dryout region of air-water dispersed flow in an electrically heated 12.95 mm i.d. vertical stainless steel tube with a length of 889 mm. The mass velocity ranges from 30 to 83 kg/m2·s, and the average wall heat flux is varied from 6.4 to 36.2 kW/m2 in the experiments. Correlation of a theoretical analysis with the measured wall temperatures suggests that the effectiveness of wall-to-drop heat transfer depends mainly on the wall superheat for surface temperatures below the minimum film boiling temperature. The local two-phase heat transfer coefficient decreases with increasing wall temperature. It is also found that the thermal entrance length for two-phase dispersed flow exceeds that of the single-phase gas flow, and that it decreases with an increase in wall temperature.

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