Two-phase thermosyphon loop with different working fluids used in data centers.

• Comparative study among CO 2 , R134a and R410A TPTLs was conducted. • Operation state, optimal filling ratio, and thermal performance. • CO 2 TPTL was more energy efficient used in data centers. • CO 2 TPTL has a slightly larger normal working load range than the others. The two-phase thermosyphon loop (TPTL) is an effective cooling technology used in data centers. TPTLs filled with different working fluids typically have various operating characteristics that influence their practical applications. A comparative experiment was conducted on CO 2 , R134a, and R410A TPTLs, and differences in their operating states and thermal performances were analyzed. The optimal filling ratio of the CO 2 TPTL was 45%, while that of the R134a and R410A TPTLs was 35%. At their optimal filling ratios, all the three TPTLs successively underwent the pre-start, oscillatory, and stable operation stages as the heat transfer quantity increased. The oscillations of the CO 2 TPTL were periodic, whereas those of the R134a and R410A TPTLs were irregular. The normal working load ranges of the CO 2 , R134a, and R410A TPTLs were 550–1200, 760–1160, and 790–1300 W, respectively. When the heat transfer quantity was 1000 W, the driving temperature difference of CO 2 TPTL was 2.4 °C lower than that of R410A TPTL and 6.0 °C lower than that of R134a TPTL. [ABSTRACT FROM AUTHOR]