Effect of working fluid inventory and heat input on transient and steady state behavior of a thermosyphon

Abstract

The effect of working fluid inventory and heat input on the performance of thermosyphon is investigated in this paper. First, a thermosyphon with diameter of 16 mm made of steel with toluene as working fluid and the length of the evaporator, adiabatic and condenser section 10, 23 and 17 cm was considered, respectively. The working fluid inventory was considered 0.1, 0.14, 0.18 and 0.24 of total volume of thermosyphon and in each case 54–235 W of heat input applied to the evaporator area also. In order to evaluate the transient behavior of the thermosyphon, in any amount of working fluid, 28 W of heat input was considered and temperature of the evaporator area were recorded at different times. The results showed that in startup, in the values of the working fluid equal to 0.14, 0.18 and 0.24, the evaporator temperature has fluctuated behavior that is indicative of the occurrence of geyser boiling phenomenon. When the volume of the working fluid was more than 0.24, thermosyphon performance was associated with vibration, indicating a high fluidity and a lack of proper functioning of the thermosyphon. The amount of optimal working fluid with respect to the total thermal resistance of thermosyphon is equal to 0.18 that in this case, the efficiency of thermosyphon at different levels of heat input is between 73 and 78%. In addition, in any amount of working fluid, increase of heat input leads to increment in the evaporator and condenser heat transfer coefficient increases and reduction in the total thermal resistance of thermosyphon.