Effect of valve regulation on the operating state of a CO2 two-phase thermosyphon loop

During the operation of two-phase thermosyphon loops (TPTLs), different types of oscillations may occur, affecting their safety and performance. Although existing research has preliminarily explored the use of valve regulation to eliminate oscillatory operations in TPTLs, the effects of valves on different types of oscillations have not been verified. In this study, valve regulation was applied to two types of oscillation in a CO2 TPTL. The distinct effects of the valve on each type of oscillation were analyzed in conjunction with their respective mechanisms through experiment. For natural circulation oscillations, valve regulation can effectively suppress fluctuations within the loop. When the valve opening (theta) reduced from 100 % to 75 %, the TPTL transitioned from oscillatory to stable operation. However, the thermal performance of the TPTL remained nearly unaffected. For geyser boiling, valve regulation cannot alter the oscillatory operating state within the loop. Even when the theta was reduced from 100 % to 25 %, the TPTL remained in an oscillatory operating state. The results provide a deeper understanding of the influencing mechanisms of valve regulation and offer insights into the active regulation of TPTLs.