Experimental design and analysis for film boiling heat transfer in a circular tube

In order to study the heat transfer of water during film boiling, stable film boiling heat transfer experiments are conducted in a circular tube. As the temperature of the heater surface sharply increases in a short period of time when critical heat flux (CHF) occurs, hot-patch technology is adopted to prevent damage to the test section. A complete experimental design, including the experimental facility, test section, experimental procedures, and the measurement of parameters, is developed. Two experimental schemes are used for testing, namely the post-CHF test and the quench test, respectively. These two schemes have been verified to achieve stable film boiling and yield consistent results. The effect of various parameters, including heat flux, pressure, mass flow and inlet subcooling, on the heat transfer coefficient has been analyzed. The experimental parameters range from an inlet subcooling of 10-50 K, a pressure of 0.1-2.5 MPa, and a mass flux of 100-1000kg/m2s. Through the analysis of the distribution of heat transfer coefficient along the axial location, three distinct heat transfer regions can be identified. Combined with heat transfer characteristics, three types of flow are considered: smooth inverted annular flow, rough inverted annular flow and inverted slug flow. Most of the data in this study is concentrated in the first two regions, namely the inversed annular flow. The data obtained in these tests is expected to provide important information for the study of inverted annular flow.