Experimental Investigation of the Heat Transfer Performance of a Two-Phase Closed Thermosyphon under Different Inclination Angles and Filling Ratios Using Dimensionless Analysis
Keywords:
Two-Phase Closed Thermosyphon, Heat Transfer Performance, Filling Ratio, Inclination Angle, Dimensionless ParametersAbstract
The primary purpose of this paper is to find the interaction between the inclination angle and filling ratio on the performance of a two-phase closed thermosyphon as both two parameters are rarely studied together in detail so far. The tests were conducted at an inclination angle of 15°, 20° and 25° from horizontal plane and filling ratios of 60%, 70% and 80% of the evaporator volume by ethanol. A copper tube with a diameter of 22 mm and a total length of 450 mm was used in the experiment; the tube was divided into three parts; 150 mm heating section, an adiabatic section, and a cooling section. The hot fluid inlet temperatures were 55, 65 and 85 °C and the cooling water was held at 20 °C constant. The results of the two-phase closed thermosyphon performance were evaluated based on the recovered heat transfer rate, thermal resistance, and by a second evaluation from the heat transfer inside the machine. To understand the figures the Nusselt number, Rayleigh number and Jakob number were used as dimensionless parameters. Based on the experimental results, it is found that the two-phase closed thermosyphon with 70% filling ratio and inclined at 20° gives the highest heat transfer performance. The thermal resistance was the lowest under these conditions, and the heat transfer was the highest amongst other conditions tested and the theory of boiling and natural convection was in good agreement. Clearly from this study, both the inclination angle and the filling ratio influence a lot the heat transfer efficiency within the two-phase closed thermosyphon. The data obtained will be useful for further design and implementation of the waste heat recovery systems.
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