{'fraction_non_alphanumeric': 0.011217049915872126, 'fraction_numerical': 0.004206393718452047, 'mean_word_length': 5.438628158844765, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
ISOTHERMAL FRICTIONAL TWO PHASE PRESSURE DROP CORRELATIONS IN VERTICAL DOWNWARD GAS-LIQUID TWO PHASE FLOW

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 gasliquid 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 airwater 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. INTRODUCTION The pressure drop in gas liquid two phase flow is a key parameter in designing and sizing of industrial equipment and components pertaining to the petroleum, chemical, refrigeration and nuclear industries. The knowledge of two phase flow void fraction and pressure drop is of significant importance in artificial gas lift systems. The understanding of two phase pressure drop is desired in the designing of the direct expansion ground source heat pumps systems and sizing of other refrigeration units. Nuclear engineering safety operations involving natural circulation loops also require a method of determining the two phase pressure drop. The two phase pressure drop consists of the hydrostatic, accelerational and frictional components of the pressure drop. The hydrostatic component of two phase pressure drop comes into picture due to significant density differences between the gas and liquid phase and the influence of gravity potential. The hydrostatic component can be predicted with sufficient accuracy by the accurate prediction of the void fraction. The accelerational component of pressure drop is usually small and can be neglected in comparison to the hydrostatic and frictional component for small pipe lengths. However, it can be of significant magnitude in artificial gas lift systems and pipelines carrying oil and natural gas mixture over long distances. The frictional component of two phase pressure drop has been a subject of research for many years due to complexity involved in its prediction. This complexity is evolved due to dependence of frictional pressure drop on flow patterns, pipe geometry and fluid properties. Literature reports several frictional pressure drop correlations developed for determining frictional pressure drop categorized as those