Precise metering of the void fraction is one of the important problems in the oil, chemical and petrochemical industries. For void fraction measurement, there are different kinds of sensors with different configurations. In this regard, the capacitance-based sensor and gamma-ray attenuation-based sensor are very well known as two most accurate and widely used sensors. In this paper, we report, to the best of our knowledge, for the first time a comparison between these two sensors in an annular air–oil flow. Simulations were accomplished with benchmarked COMSOL Multiphysics software and MCNPX code. Results show that the general sensitivity of gamma-ray sensor is ~ 90% higher than the general sensitivity of capacitance-based sensor. For a more accurate comparison, momentary sensitivity factors for a variety void fractions in both sensors were obtained. In the low void fraction range, the gamma-ray sensor has much better performance; however, in the high void fraction range, the capacitance-based sensor has a better performance. In the range of 0.9–1 void fractions, the momentary sensitivity of capacitance-based sensor is ~ 67% higher than that of gamma-ray attenuation-based sensor.
