Experimental investigation of the void fractions of refrigerants R32 and R1234yf in a 1 mm diameter horizontal channel using a capacitance-based method

Moojoong Kim*, Yuya Uemura, Tetsuya Sato, Kiyoshi Saito

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The void fraction of two-phase flow in the 1 mm of channel is investigated in this study. The small channels, including micro to mini-channel, are widely used for developing miniaturized air conditioning systems. In terms of carbon emission reduction, optimizing the refrigerant charging amount based on sufficient information and understanding of the characteristics of the two-phase flow is a noteworthy challenge. The void fraction is a parameter of the two-phase flow that is essential for determining the heat transfer coefficient, modeling the pressure drop, and predicting the refrigerant charging amount. Therefore, the precise measurement and prediction of void fraction in small channels for various refrigerants are required. However, thus far, the void fraction characteristics of small channels have not been actively investigated because of the limited volume inside a single small channel and the relatively high error of the quick-closing valve (QCV) method for small channels. This study proposes a capacitance-based sensor as an alternative method for void fraction measurement of small channels. The newly designed void fraction sensor was fabricated with 7.8 % uncertainty under compensation for manufacturing limitations. The void fractions of refrigerants R32 and R1234yf flowing through smooth small horizontal channels under adiabatic conditions (inner diameter: 1 mm, mass flux: 300–600 kg m−2 s−1, saturation temperature: 20–30 °C, vapor quality: 0.025–0.900) were measured. The measurement results were compared with ten existing prediction correlations of five classifications, and the correlations that optimally predicted the void fractions of R32 and R1234yf in the small horizontal channel were presented.

Original languageEnglish
Article number122113
JournalApplied Thermal Engineering
Publication statusPublished - 2024 Feb 1


  • R1234yf
  • R32
  • Small channel, capacitance-based sensor
  • Void fraction
  • low-GWP refrigerant

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Mechanical Engineering
  • Fluid Flow and Transfer Processes
  • Industrial and Manufacturing Engineering


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