EFFECT OF SURFACE WETTABILITY AND GAS/LIQUID VELOCITY RATIO ON MICROSCALE TWO-PHASE FLOW PATTERNS Hongxia Li, Charles C. Okaeme, Weilin Yang, TieJun Zhang* Department of Mechanical and Materials Engineering, Masdar Institute of Science and Technology P.O.BOX 54224, Abu Dhabi, UAE Email: tjzhang@masdar.ac.ae ABSTRACT Predicting and controlling the flow regime transition of multiphase fluids in microchannels is essential for various energy applications, such as flow boiling, de-emulsification and oil recovery processes. This in turn requires a better understanding of multiphase flow behaviors in microchannels with various channel surface wettability, fluid interfacial tension and flow rates. In this paper, experiments and Lattice Boltzmann method (LBM) simulations are carried out to study complicated multiphase flow at micro or meso scales. With the Shan-Chen multiphase LBM model, the flow pattern transitions of adiabatic two phase flow in a microchannel were investigated. The effects of surface wettability and liquid/gas velocity ratio on the flow regime transition were further studied. A series of two-phase flow experiments were conducted on a PDMS microfluidic device under different gas/oil velocity ratios. Under various surface wettability conditions, our simulation results agree well with the flow visualization experiments equipped with a high speed camera (HSC). Our finding shows that the cross-section meniscus curve width, corresponding to the shadow in the HSC photo, increases with decreasing contact angle, which was confirmed by the simulated liquid/gas distribution. Besides the influence of surface wettability, the role of gas/liquid velocity ratio on two-phase flow regime transition was discussed in detail. The proposed approach paves the way to probe complicated physics of multiphase flows in microporous media. INTRODUCTION Two phase flows especially at the micro scale are playing a critical role in applications such as electronic cooling, oil/gas processing and chemical reactors [1][2][3][4]. It is essential to flow in porous media study. So a better understanding of the behavior of two phase flow inside microchannels is crucial for successful design and operation of functional multiphase microfluidic systems. The configuration of these two-phase flow patterns depends on several factors including fluid flow rates, fluid properties, channel geometry, surface properties and so on [5][6]. In order to understand how various factors affect the two- phase flow behavior, many researchers [5-10] have performed experimental studies to observe the various flow regimes common in microchannel two-phase flows and analyze the effects of changing flow properties on the flow regimes. Early experimental work by Suo and Griffith [5] identified slug, slug-bubbly, and annular flow patterns in horizontal channels with 0.5 mm and 0.7 mm diameters. Similar work was performed by Kawahara et al [7] using nitrogen gas and de- ionized water in circular microchannels of 100 um. Furthermore, Triplett et al[8] developed flow pattern maps of different flow patterns such as bubbly, churn, slug, slug-annular and annular flow using gas and liquid superficial velocities as coordinates. In another study, Dreyfus [9] showed that the role of the wetting properties of the fluids with respect to the walls crucially determines the two-phase flow pattern. Chung et al [10] investigated the effect of channel geometry on gas-liquid two- phase flow characteristics in horizontal microchannels using water-nitrogen gas mixture in a 96 μm square microchannel and compared the resulting flow patterns with those in a 100 μm circular microchannel. They reported that the flow maps exhibited transition boundaries that were shifted depending on the channel shape. Sur and Liu [11] studied the effects of channel size and superficial phasic velocity on the two-phase flow pattern and pressure drop of air-water flow in circular microchannels with three different diameters (100, 180 and 324 μm). It is known from the literature that many conditions affect the two-phase flow patterns in microchannels. However, no consensus has been reached on the exact conditions for flow regime transition. Especially the effect of surface wettability is Proceedings of the ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer MNHMT2016 January 4-6, 2016, Biopolis, Singapore MNHMT2016-6383 1 Copyright © 2016 by ASME