Introducing a hydrostatic similarity criterion for laboratory-scale two-phase flow modeling

• The study is based on the sulfur mining process, where sulfur is melted with hot water and transported to the surface using compressed air, serving as a relevant test case for multiphase flow modeling. • A new hydrostatic similarity criterion was introduced, improving the accuracy of flow pattern predictions and transient behavior replication in scaled-down models. • A CFD model was developed to capture key multiphase interactions, providing verification of the proposed hydrostatic criterion. • Practical guidelines were developed for scaling real two-phase gas–liquid flow systems under laboratory conditions using air and water. • The existing installations can be easily adapted using the proposed similarity criteria, improving model reliability and predictive capability. This paper presents practical guidelines for modelling real two-phase gas–liquid flow systems at a reduced scale under laboratory conditions using air and water. Key similarity criteria, including classical dimensionless numbers and a newly proposed hydrostatic criterion—defined as the ratio of static pressure to hydrostatic pressure—are discussed. The introduction of this criterion significantly improved the accuracy of flow pattern predictions and the replication of real system transient behaviour. Field observations provided data on slug intervals, and laboratory experiments demonstrated improved model fidelity. CFD simulations further confirmed that incorporating the hydrostatic criterion improves model reliability. The study also incorporates the Bøe criterion and flow pattern maps, yielding consistent results across all methods. The developed principles offer a robust framework for designing and optimizing scaled models, enhancing the effectiveness of multiphase flow studies in laboratory settings and enabling the rational design of full-scale technological or metering installations.