Experimental study of the self-regulating performance of an R744 two-phase thermosyphon loop

The two-phase thermosyphon loop (TPTL) is an efficient solution for use in air-conditioning systems in data centers. The typical TPTL system pattern in data centers is the multi-evaporator TPTL. When the heat generated from the evaporators varies, the TPTL will self-regulate according to its own rules. In the current study, an experiment on a double-evaporator R744-based TPTL was conducted. Uniform, non-uniform, and variable heating power conditions were investigated, and a theoretical analysis was performed. The experimental results show that the mass flow rate of the high-power evaporator is higher than that of the low-power evaporator, but the self-regulating ability of the TPTL is very limited. The mass flow rate ratio (Mmax/Mmin) was between 1 and 1.5, with the heating power ratio (Qmax/Qmin) changing from 1 to 3; even when Qmax/Qmin is as high as 15, Mmax/Mmin is only 1.67. If the heating power of the two evaporators is different, the operating conditions of the evaporators will be affected. Therefore, when a TPTL is designed, more attention should be paid to the load of each single evaporator and the load of the other evaporators in parallel. In practical applications, significant differences between the heat transfer loads of parallel evaporators should be avoided as much as possible.