A high-frequency electromagnetic experimental setup for measuring the cross-sectional void fraction of slug flow

Gas–liquid two-phase flow is prevalent in industrial processes such as nuclear power, chemical engineering, and energy transportation. Cross-sectional void fraction is a critical parameter characterizing the dynamic features of two-phase flow, and its real-time measurement is essential for operational monitoring and process control. In this study, a cross-sectional 160 MHz high-frequency electromagnetic antenna sensing system was developed for slug flow in vertical pipes. The system utilizes the propagation phase shift induced by the dielectric contrast between the gas and liquid phases as its sensing mechanism. Voltage signals are captured via phase-detection demodulation to characterize the equivalent dielectric properties and invert the void fraction. Validation was conducted on a DN50 vertical two-phase flow experimental platform under 36 operating conditions. The results demonstrate that the measured void fraction trends align well with the typical evolution patterns of two-phase flow. To examine model consistency, the Drift Flux and Nicklin models were modified by introducing dynamic distribution parameters. The modified models yielded mean absolute percentage error (MAPE) values of approximately 2.61%, with a root mean square error of 0.0335 and a coefficient of determination (R2) of 0.867. These comparisons are used to assess consistency between the sensor-derived void fraction and empirical model trends, rather than to provide an independent absolute validation. The results indicate that the proposed sensing system provides a stable event-level response for vertical slug flow in a DN50 pipe under the tested conditions.