HEAT-TRANSFER IN INTERMITTENT AIR-WATER FLOWS - PART I - HORIZONTAL TUBE

This paper presents a study on the heat transfer in intermittent air-w ater flows in a horizontal tube. The experimental technique is based a n infrared thermography of an electrically heated wall of the tube, pr oviding 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 fluc tuations and heat transfer coefficient. The water and air Froude numbe rs 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 foll ows. 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 c oefficient does not depend on the gas Froude number. (C) 1998 Elsevier Science Ltd. All rights reserved.