Performance study of a pulsated two-phase loop thermosyphon

Abstract

Thermoloop, a kind of pulsated two-phase thermosyphon (PTPT), is a device with a promise of dealing with very high heat flux requirements for electronics cooling. It comprises of three main components: evaporator, condenser and a liquid reservoir. In the present study, the thermal performance of the thermo loop has been studied to address some issues on design and heat transfer performance both experimentally and analytically. These issues include variations in thermal load, evaporator fill ratio and condenser convection condition of thermo Ioop. Outside dimension of the two evaporators employed in the test were 72.5 mm x 60 mm x 20 mm for Prototype-I and 77 mm x 65 mm x 8 mm for Prototype-2 with inside volumes of 75 cm3 and 30 cm3 , respectively. Same reservoir was used for the two prototypes with a liquid storage capacity of 80 cm3• Most of the studies were conducted with prototype- I using water as the working fluid. For thermal load variation from 100 W to 250 W, the maximum temperature of the evaporator wall increased from 106°C to 1120C and minimum temperature of evaporator wall increased from 730C to 950C at an evaporator fill ratio of 30%. The values of other functional parameter such as cycle time, height of liquid column in the reservoir and condenser temperature also increased with an increase in thermal load. At a constant heat load and for the same working fluid, the effect of liquid fill ratio on the maximum temperature of the evaporator wall and on cycle time appeared to be insignificant. The addition offan to cool the condenser increased the operational limit of the device from 125 W to 275 W. Further, the various functional parameters of the thermoloop attained a steady value after 5 to 6 heat transport cycles. In the analytical part, a simple mathematical model on the thermo loop heat transfer concept is developed based on the hydrodynamics and heat transfer to have a better understanding of the physics involved, which needs to be tested or verified by the experimental data.