Void fraction measurement of gas–liquid two-phase flow from differential pressure

• Mean gas void fraction in gas–liquid flow is derived from the differential pressure.
• Tomographic modalities of Electrical Resistance Tomography and Wire-mesh sensor are employed to validate the results from differential pressure model.
• The importance of frictional pressure loss in the differential pressure model is investigated.
• Additional results added in the revised manuscript to indicate the precision of void fraction measurement from ERT and WMS in terms of standard deviation.
• More analysis added in the revised manuscript to discuss the process of computing Fanning friction factor Cf.
• All the comments from the reviewer are addressed in the revised manuscript.

Void fraction is an important process variable for the volume and mass computation required for transportation of gas–liquid mixture in pipelines, storage in tanks, metering and custody transfer. Inaccurate measurement would introduce errors in product measurement with potentials for loss of revenue. Accurate measurement is often constrained by invasive and expensive online measurement techniques. This work focuses on the use of cost effective and non-invasive pressure sensors to calculate the gas void fraction of gas–liquid flow. The differential pressure readings from the vertical upward bubbly and slug air–water flow are substituted into classical mathematical models based on energy conservation to derive the void fraction. Electrical Resistance Tomography (ERT) and Wire-mesh Sensor (WMS) are used as benchmark to validate the void fraction obtained from the differential pressure. Consequently the model is able to produce reasonable agreement with ERT and WMS on the void fraction measurement. The effect of the friction loss on the mathematical models is also investigated and discussed. It is concluded the friction loss cannot be neglected, particularly when gas void fraction is less than 0.2.