Experimental study on operating characteristics of a controllable CO2 two-phase thermosyphon loop

Abstract

To improve the performance and applicability of the two-phase thermosyphon loops (TPTL) used in data centers, TPTLs with auxiliary devices were widely studied. In the existing literature, the regulating valve on TPTL is mainly used for heat transfer rate regulation or start-stop control. This paper proposes a controllable CO2 TPTL with a valve on its downcomer to improve the practicability of the TPTL under low-heat-load conditions. It was found that valve regulation could widen the normal working load range (NWLR) of a TPTL. When the valve was fully open, the NWLR of the CO2 TPTL was 700–1300 W. By regulating the valve, the NWLR was expanded to 340–1300 W without changing the structure of the TPTL. Increasing the flow resistance could change the operating state of the TPTL by affecting the vapor–liquid distribution. During the oscillatory operating stage, when the valve opening decreased from 90° to 30°, the TPTL changed from an oscillatory to a stable operating state. In practical applications, the valve regulation is required under low load conditions, where the changes in valve opening have minimal impact on the thermal resistance of the TPTL.