HEAT TRANSFER DURING POOL BOILING OF WATER, METHANOL, AND R141B ON POROUS COATED HORIZONTAL TUBE BUNDLES (original) (raw)
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Experimental thermal and fluid …, 2000
An experimental study of convective boiling of refrigerants R-22, R-134a and R-404A in a 12.7 mm internal diameter, 2 m long, horizontal copper tube has been performed. Experiments involved a relatively wide range of operational conditions. Experiments were performed at the evaporating temperatures of 8°C and 15°C. Quality, mass velocity and heat¯ux varied in the following ranges: 5% to saturated vapor, 50±500 kgas m 2 ); and 5±20 kWam 2 . Eects of these physical parameters over the heat transfer coecient have been investigated. High quality experiments were also performed up to the point of the tube surface dryout, a mechanism which was investigated from the qualitative point of view. Two heat transfer coecient correlations from the literature have been evaluated through comparisons with experimental data. Deviations varied in the range from À25% to 42%. Ó 2000 Elsevier Science Inc. All rights reserved.
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Enhancement of Pool Boiling Heat Transfer over Plain and Rough Cylindrical Tubes
International Journal of Heat and Technology, 2021
Received: 21 May 2020 Accepted: 15 March 2021 This study investigates the pool boiling heat transfer of water over cylindrical heating tubes for different orientations and surface roughness of the tubes. First, two orientations of a smooth heating tube, horizontal and vertical, were used in the boiling chamber. For a given heat flux, the heat transfer coefficient achieved with the horizontal tube was always higher than that for the vertical tube. To investigate the influence of surface roughness, a rough heating tube with a fully rough outer surface was developed through a metal etching process. Under the same range of wall superheat, the rough tube enhanced the heat transfer rate significantly compared to the smooth tube. Finally, a modified heating tube (MHT) was developed by axially roughening half of the surface of an originally smooth tube. The orientation angle of the rough surface of this MHT was varied from 0° (horizontal-upward) to 180° (horizontal-downward) in the chamber....