Heat transfer in intermittent air-water flows - Part I Horizontal tube

This paper presents a study on the heat transfer in intermittent air-water flows in a horizontal tube. The experimental technique is based an infrared thermography of an electrically heated wall of the tube, providing both visualization of the temperature held and measurements of the local wall temperature. Measurements of bubble size and frequency are correlated to the measurements of the local wall temperature fluctuations and heat transfer coefficient. The water and air Froude numbers varied from 0.9 to 2.0 and from 0.03 to 0.43, respectively. On the upper part of the tube, the;effect df the gas Froude number is as follows. In the range Fr-G<0.13 heat transfer decreases with increasing Fr-G, while in the range 0.13 < Fr-G < 0.43 the heat transfer increases when Fr-G increases. On the lower part of the tube the heat transfer coefficient does not depend on the gas Froude number. (C) 1998 Elsevier Science Ltd. All rights reserved.