Heat transfer to two-phase flow in inclined tubes

Experiments were performed to study the flow regimes and heat transfer in air–water flow in 8° inclined tubes of inner diameter of 49.2 and 25 mm. The flow regimes were investigated by using high-speed video technique and conductive tomography. The thermal patterns on the heated wall and local heat transfer coefficients were obtained by infrared thermography. Under the conditions studied, disturbance waves of different forms were observed. The analysis of the behavior of the heat transfer coefficients, together with flow visualization and conductive tomography showed that dryout took place in the open annular flow regimes with motionless or slowly moving droplets. Even under these conditions, the heat transfer coefficient is about 10 times higher than that for single-phase airflow.