An experimental investigation of heat transfer to water in film flow Part I – non‐boiling runs with and without induced swirl

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Abstract
Local heat transfer coefficients have been measured in the range of Reynolds Numbers 3,000‐20,000 for non‐boiling heat transfer to water flowing down the inside of a copper tube. The tube was 0.948‐in. Inside diameter and 8‐ft long, heated in 15 sections 6‐in. long, by electrical resistance heaters wound on the outside of the tube. Thermocouples measured the wall temperature at the midpoint of each section. Coefficients obtained for downward, non‐swirling, full tube flow were correlated by the Dittus Boelter equation, with a correction for heat flux. An experimental correlation was obtained for the improved coefficients resulting from the use of a swirl generator in full tube flow. Non‐swirling falling film data were correlated by an equation:hLA = 3.9 ReLA0.05It is to be noted that the exponent on ReLS is higher than the value of 0.1‐0.33 found by previous workers. The effect of swirl on falling film heat transfer was complex; increased coefficients were noted at ReL below 10,000 but much reduced coefficients were obtained at RL above 15,000 in the lower parts of the tube.

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