Experimental study of condensation heat transfer on hydrophobic vertical tube

Condensation heat transfer on surfaces can be enhanced by altering the surface topography. Surface modification technology can promote dropwise condensation which can exhibit higher heat transfer rate than filmwise condensation. This paper presents experimental data on the condensation of steam on vertical bare copper tubes and lead coated copper tubes for degree of sub-cooling in the range 0.5 degrees C <= Delta T < 20 degrees C. The chemical texture of the tube surface was altered by coating with lead of thickness 10 mu m and the physical texture of the surface was transformed by providing four grooves each having equal depths 0.10 mm, 0.15 mm and 0.30 mm. The condensation heat transfer characteristics of the tube surface is explained based on contact angle hysteresis and sliding velocity of the droplet. The results of the study reveal that for the tubes tested the average condensation heat transfer coefficient decreases with increase in degree of sub cooling. It is also found that for copper tubes, providing grooves aids condensation heat transfer for the range of sub-cooling. However, for lead coated copper tube with/without grooves the heat transfer performance at Delta T < 2 degrees C shows marked difference in contrast to Delta T > 2 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.