Experimental study on the effect of fill ratio on an R744 two-phase thermosyphon loop

• Published in: Applied thermal engineering 2016-04, Vol.99, p.302-312
• Main Authors: Tong, Zhen, Liu, Xiao-Hua, Li, Zhen, Jiang, Yi
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Circulation; Driving temperature difference; Fill ratio; Fluctuation; Fluids; Heat transfer; Heat transfer ability; Liquids; R744 two-phase thermosyphon loop; Thermal engineering; Thermosyphons
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2016.01.065

•Performance of R744 two-phase thermosyphon loop is experimentally analyzed.•There are usually some fluids that circulate in the loop without changing phase.•Maximum heat transfer ability is achieved at the fill ratio around 100%.•Lowest driving temperature difference is achieved at the fill ratio around 62%.•Thermosyphon loop with a lower fill ratio is more likely to fluctuate at small heat loads. As a natural, environmentally friendly fluid with excellent thermodynamic and transport properties, carbon dioxide is an effective alternative refrigerant. This paper describes an experiment conducted on an R744-based two-phase thermosyphon loop (TPTL). With different fill ratios of 45~151%, the effect of fill ratio on the working performance of the R744 TPTL is investigated. To maintain the conservation of momentum, part of the fluid circulates in the loop without changing phase; this part of the fluid may be liquid, vapor, or both liquid and vapor depending on the fill ratio. This is how the R744 TPTL self-adjusts among different heat loads. The experimental results show that the working state of the R744 TPTL has a lot to do with the fill ratio. With a low fill ratio, the TPTL is more likely to fluctuate under small heat loads. When the fill ratio is around 100%, the TPTL reaches its maximum heat transfer ability, and when the fill ratio is around 62%, the lowest driving temperature difference is achieved. Considering that the fill ratio's effect on the driving temperature difference is not very significant and that pursuing maximum heat transfer ability is more meaningful, a fill ratio of around 100% is recommended.