Experimental Study on the Heat Flux at the Operating Limit of a Closed Two-Phase Thermosyphon

Abstract

A closed two-phase thermosyphon is an efficient heat transfer device which is expected to be useful for waste heat recovery in high temperature range. In this study flow patterns inside a vertical thermosyphon were visually observed in detail and the relation between the flow pattern and the operating limit was experimentally investigated. The parameters were the inner diameter of thermosyphons, the kind and the amount of fill charge of the working fluid and the system pressure. At the operating limit the boiling of a liquid pool in an evaporator is quite violent so that the condensed liquid in the film cannot flow down into the evaporator. Then the dryout of the cooling liquid takes place on the heating wall of the evaporator. Taking this boiling-affected flooding phenomenon into consideration, a correlation was proposed, which correlates a large amount of critical heat flux data obtained by many kinds of thermosyphons by the height of the liquid pool and the bubble rising velocity. The agreement of the correlation with those data is better than that of Sakhuja's flooding correlation and Imura's.