Measurement of boiling behaviour in a horizontal heat circular tube with a transparent heating model for low GWP refrigerant

As part of a study to improve the efficiency of two-phase flow systems using HFO refrigerants, a correlating equation for predicting heat transfer coefficient has been proposed. In particular, the separation angle, which is the boundary between the liquid and gas phases, is an important parameter in the equation for separated flow in a horizontal tube, and it is expected that a more accurate prediction model for the wetting boundary angle can be verified by measuring the temperature distribution using an infrared camera. In this study, a horizontal tube heating apparatus was constructed with a heating test section and a transparent heating apparatus as visible sections to conduct the temperature measurement of the boiling flow of refrigerant R1336mzz(E) by a high-speed infrared camera and visualize the boiling flow pattern by high-speed camera. In the experiments, heat transfer coefficient and frictional pressure drop were measured using horizontal circular tube with an inner diameter of 10.0 mm and the flow pattern was observed at mass fluxes of 100 to 300 kg/(m2∙s) and inlet heat fluxes of 2.1 to 19.3 kW/m2. Wavy flow and transition flow to dry-out were observed at low mass fluxes, and slug-wavy, intermittent, and annular flow were observed at high mass fluxes. The heat transfer coefficient and frictional pressure drop gradient were close to the values of the previously correlated equations for the flow pattern stabilized with increasing quality, and these results were reasonable. In the spatial-temporal temperature fluctuation measured by a high-speed infrared camera, the maximum value of the temperature fluctuation was confirmed in the circumferential direction. The temperature fluctuation measurement using a high-speed infrared camera is considered to be a new method to evaluate the separation angle with high accuracy.