Correlations to predict heat transfer characteristics of an inclined closed two-phase thermosyphon at normal operating conditions

This paper describes the effect of dimensionless parameters on heat transfer characteristics of an inclined thermosyphon. The parameters studied in this paper are: Bond numbers, Froude numbers, Weber numbers and Kutateladze numbers, and experiments are conducted to find out their effects on the heat transfer rate and on the total thermal resistance. Copper thermosyphons with an ID of 7.5, 11.1 and 25.4 mm are employed with R22, R123, R134a, ethanol, and water as the working fluids. The selected filling ratios are 50, 80, and 100% and the selected aspect ratios are 5, 10, 20, 30 and 40 respectively. Experiments are conducted by varying the inclination angle from the horizontal axis by 5, 10, 20, 30, 40, 50, 60, 70, 80 and 90°, and the controlled vapor temperature ranged from 0 to 30°C. It is found from the experiments that, the filling ratio has no effect on the ratio of heat transfer characteristics at any angle to that of the vertical position (Q/Q₉₀), but the properties of the working fluid affected Q/Q₉₀. Results show that the lower the latent heat of vaporization, the higher the Q/Q₉₀. It is also shown that the modified Kutateladze number can be employed to predict the maximum Q/Q₉₀, or Q_m/Q₉₀. Another modified Kutateladze number can also be used to predict the ratio of minimum total thermal resistance to that at vertical position, or R_m/R₉₀.