Heat transfer in intermittent air–water flows—Part II: Upward inclined tube

This paper presents a study on the heat transfer in intermittent air–water flows in an upward inclined tube. The experimental technique is based on infrared thermography of an electrically heated wall of the tube, providing both visualization of the temperature field and measurements of the local wall temperature. Local heat transfer coefficients and flow parameters have been measured for air–water flow in a pipe of 49.2 mm inner diameter at inclination angles of 2° and 5°. The water and air Froude numbers varied from 0.59 to 2.0 and from 0.03 to 0.57, respectively. Experimental correlations of the heat transfer coefficient indicate that the liquid and gas Froude numbers and dimensionless frequency of bubble appearance are good correlating parameters. A simple physical model was developed to correlate between the flow parameters and the heat transfer.