Void fraction of R32 in microfin tube under condensation conditions using capacitance-based sensor

• Void fraction in microfin tube under condensation was experimentally studied. • Capacitance-based sensor was validated with QCV method for measurement accuracy. • Void fraction decreased up to 22 % compared to smooth tube correlations. • Modified prediction model achieved RMSPE below 2 % across all tested conditions. • Results improve refrigerant charge estimation in heat pump systems. This study investigates the void fraction characteristics of R32 refrigerant under condensation conditions in helical microfin tubes, with a focus on the effects of mass flux and vapor quality on phase distribution. A capacitance-based sensor, validated through cross-verification with the Quick Closing Valve (QCV) method, was employed to ensure measurement reliability. Experiments were conducted at saturation temperatures of 25 °C and 40 °C, mass fluxes ranging from 100 to 400 kg m −2 s −1 , and vapor qualities from 0.025 to 0.800. Results reveal that void fractions in microfin tubes are significantly reduced—by up to 22 %—compared to smooth tube predictions, particularly under low mass flux and low vapor quality conditions. These reductions are attributed to enhanced liquid hold-up and the promotion of annular-like symmetric flow induced by the micro-grooved structure during condensation. A comparative analysis with ten conventional void fraction correlations reveals that correlations incorporating mass flux effects, such as the Steiner correlation, consistently outperform the others. A modified prediction model combining geometric correction and a condensation-specific empirical factor further improved accuracy, yielding RMSPE values below 2 % across all tested conditions with selected conventional correlation. These findings contribute to improving the accuracy of refrigerant charge prediction in system simulations, particularly for advanced air-conditioning and heat pump systems using microfin tube condensers.