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The correct prediction of gas-liquid two phase pressure drop is of immense significance for proper sizing of industrial equipment and safety operations involved in chemical, energy and petrochemical applications. The hydrostatic component of the two phase pressure drop is predicted based on the accurate estimation of void fraction. However, there exists a complexity in correct estimation of the frictional component of two phase pressure drop owing to interfacial friction at dynamic gas-liquid interface. The present study is focused on the experimental measurements of gas-liquid two phase frictional pressure drop and the performance evaluation of eleven correlations for its prediction in vertical downward orientation. The experimental determination of two phase frictional pressure drop is carried out for a 0.01252 m I.D. pipe with surface roughness of 0.0000152 m using air-water as the fluid combination. Unlike most of the other studies centered towards annular flow, this experimental study is spanned over different flow patterns and the entire range of the void fraction. In addition to the experimental measurements, the scope of this study also includes the performance analysis of eleven frictional pressure drop correlations available in the literature. These correlations are those based on the separated flow model initially proposed by Lockhart and Martinelli [1].The available frictional pressure drop correlations are compared against the data measured in the present study. Based on the experimental data available in the literature, the influence of the pipe diameter and fluid viscosity on the frictional pressure drop is also analyzed.

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Highlights• This paper focuses on the effect of different build orientations.• An effective model was designed for laser powder bed fusion.• The effect of build orientation on martensite decomposition is emphasized.

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