Experimental investigation of void fraction of R32 refrigerant in horizontal flow configuration using capacitance-based and quick-closing valve-based methods

This study investigates the void fraction of R32 refrigerant flowing through a smooth horizontal macro-tube under adiabatic conditions. Recently, low-global warming potential (GWP) refrigerants have been proposed to replace the existing HFC refrigerants. For the application of a low-GWP refrigerant, its flammability, coefficient of performance (COP), and refrigerant charge amount should be sufficiently reviewed in the design stage. R32 is a low-GWP refrigerant that is a significant component of low-GWP mixed refrigerants, such as R454C and R466A. Therefore, to analyze and understand the characteristics of the low-GWP refrigerants comprising R32, investigating the void fraction of R32 is important. Additionally, void fraction measurement using a capacitance-based sensor, which has recently been attracting attention, has been investigated. The measurement results using the capacitance-based sensor were compared and validated with that obtained via a conventional method involving a quick-closing valve (inner diameter: 7.1 mm, mass flux: 100–400 kg m−2 s−1, saturation temperature: 10–40 °C, vapor quality: 0.025–0.900). Furthermore, the measurement results are compared with the existing void fraction correlations, and the correlation that optimally predicts the void fraction of R32 is presented herein.