HEAT TRANSFER CHARACTERISTICS IN A LOOPED PARALLEL THERMOSYPHON

摘要

A new type of thermosyphon, two single tube thermosyphons simply connected by two U tubes at the top and bottom ends, which is named Looped Parallel Thermosyphon, is developed to improve heat transfer characteristics utilizing flow fluctuation occurred in the bottom U tube. The purpose of this study is to experimentally examine how it improves the characteristics and show unexpected other favorable and unfavorable effects of the fluctuation on its performance. Experiments are conducted in LPT and also a single tube thermosyphon for comparison. Comparison of the heat transfer characteristics is made between them relating to heat transfer measurements in an evaporator and a condenser sections. Major findings are as follows: The flow fluctuation actuated in the U tube makes the evaporator wall temperature more uniform in the LPT than that in the single thermosyphon. The maximum heat flux in the LPT is much larger, more than twice, than that in the other and the difference of boiling heat transfer coefficient, however, is small between them. The condensation heat transfer on the condition without a non-condensable gas in the LPT is similar to that in the single thermosyphon. But on including the gas the deterioration effect on the condensation heat transfer is not mitigated by the LPT, and further its maximum heat flux is much lower than that of the single thermosyphon.