Performance Assessment of Void Fraction Correlations in Large Diameter Vertical Pipe Up Flow

Recently, due the to increase in the production demand in many industries such as Nuclear, Oil & Gas and process industries, the requirement to migrate toward larger pipe sizes has become essential. However it is interesting to note that almost all of the earlier two phase flow research is based on small diameter pipes (D≤100mm) and experimental work on predicting the two phase flow behaviour in large diameter (D>100mm) pipes is rare. Thus, the application of methodologies/correlations/equations for predicting flow pattern, void fraction, and pressure gradient based on small diameter poses severe challenges in terms of accuracy. Specifically, the prediction of void fraction in two phase flows, as it plays a fundamental role in characterizing the distribution of the phases within the system. With large number of the void fraction correlations available in the different fields of multiphase flows, the choice for the selection of any void fraction correlation existing in the literature is bewildering. This paper presents an assessment of the predictive capabilities of forty (40) void fraction correlations belonging to different multiphase flow industries. The assessment is performed by comparing the independent experimental data obtained from a 254mm diameter and a 12.2m high vertical pipe upflow loop using air-water as working fluid. The final assessment indicated that most of the void fraction correlations are flow regime dependent as none of the correlations successfully predicted all the four regimes (bubbly, agitated bubbly, unstable slug and churn turbulent) encountered in large diameter vertical upflow experiments.