Abstract
This study deals with heat transfer in vertical, horizontal, and inclined tubes with water-air mixture flowing in them. We obtain and analyze a thermal pattern on the heated wall, which makes it possible to establish the connection between the flow parameters and heat transfer. The experimental technique is based on the infrared thermography of an electrically heated wall of the tube, providing both visualization of the temperature field and measurements of the local wall temperature. We consider first the results concerning a horizontal tube only. These results serve as a reference basis for the studies on inclined and vertical tubes. The heat transfer coefficient in inclined tubes is drastically enhanced, as compared to that in a horizontal one. In a vertical tube, it is observed that the streaky thermal pattern on the wall is destroyed by the bubbles. This pattern was partially recovered with slug flow. The heat transfer coefficient was observed to increase substantially.
