Thermal performance of a compact two-phase thermosyphon: Response to evaporator confinement and transient loads

This study investigates the effect of evaporator confinement on the perform ance of an enhanced microstructure based thermosyphon, that has shown very high heat transfer rates (upto 100W/cm(2)). The enhanced structure used dem onstrates almost 2.5 times increase in the heat transfer compared to a soli d block of the same size. The top spacing between the microstructure and th e cover of the evaporator was varied and its effect on heat transfer was st udied. The results for the effect of sidewall spacing show that the influen ce of confinement on the boiling performance of the microstructure is negli gible. Total blockage does deteriorate the performance at very high heat fl uxes (40-70W/cm(2)). However, a minute gap of the order 1.5-3 mm is suffici ent to get to performance levels close to boiling in a large enclosure. The response of the confined setup was then studied under, suddenly applied lo ads. This is of particular importance to practical applications where a sud den temperature excursion could be detrimental to electronics. The results show a very smooth transition from startup to steady state. No incipience e xcursion was observed in any of the runs.