Effect of adiabatic length on the performance of closed-loop thermosyphon system

This paper reports the effect of different adiabatic lengths on the thermal performance of loop thermosyphon with different filling ratios (FRs) and heat inputs. The carbon steel thermosyphon loop for three different adiabatic lengths is used in this analysis. The loop with plate-type, forced air-cooled condenser, along with two vertical inline evaporators, is filled and tested with distilled water. The transient and steady-state analyses are carried out to understand the thermal behavior of the loop. The thermal resistance is found to be lowest at 800-mm adiabatic length and 60% FR. The geyser boiling phenomenon is also noticed in the present thermosyphon loop. The period of oscillation and temperature fluctuations in the evaporator and condenser increase with the adiabatic length. The geyser boiling phenomenon may disappear at a very small adiabatic length of the loop thermosyphon with forced air-cooled condenser. This paper proposes a mathematical model for the loop thermosyphon in terms of the Nusselt number, the Reynolds number, the Prandtl number, and the adiabatic length-to-diameter ratio, and the comparative study shows that proposed model validates the experimental results. Also, it is found that the adiabatic length-to-diameter ratio inversely varies with the Nusselt number.