Heat transfer characteristics of closed-end thermosyphon (CE-TPCT)

Abstract

This study investigated the heat transfer characteristics of a Closed-End Thermosyphon (CE-TPCT) made of copper tubes with 5.5 mm diameter. The experiments were conducted with working substance filling rates of 0%, 30%, 50%, and 70% of the volumetric evaporator section, the evaporator temperatures of 50, 70, and 90 °C and inclination angle of 90°. The lengths of the evaporator section, adiabatic section and condenser section used in the experiments were 60 mm, the distance between the compartments was 5Di. Water was the working substance used in the experiments with the mass flow rate of the water inlet at the condenser section of 0.25 L/min. The water inlet temperature at the condenser was 20 °C. Obtained results were compared with convectional Thermosyphon (TPCT) which was tested under the same conditions. The results showed that CE-TPCT at the filling rate of 70% at the evaporator section volume had an average heat transfer rate and average heat flux of 140.72 ± 4.92 W and 33.41 ± 1.16 kW/m2, respectively, throughout the experiment. These results were higher than the other tested parameters. The highest heat transfer rate of 220.32 ± 7.71 W and average heat flux of 52.31 ± 1.83 kW/m2 were recorded at the evaporator temperatures of 90 °C. The experiment also showed a lower average total thermal resistance throughout when it was compared with other test parameters which was equal to 0.547 °C/W. This resulted in high heat transfer coefficients and relative thermal efficiency of 625.11 W/m2·°C and 1 respectively, the highest value of all studied experimental variables. When the maximum heat flux results between CE-TPCT and TPCT under the same condition parameters were compared, CE-TPCT demonstrated a higher heat flux value of 18.24%. The heat transfer characteristics of the CE-TPCT obtained from this study provides an alternative application choice for various types of heat exchanger that can reduce energy consumption in the future.