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A numerical study of an oil-water Taylor flow is presented in this paper to explore its flow and heat transfer characteristics. Due to the large surface area to volume ratio in narrow channels, using slug flows, high heat and mass transfer rates could be achieved. Sound knowledge of the underlying physics of slug flow is required for the practical design of microfluidic devices. In this study, hydrodynamics and heat transfer characteristics of dispersed oil droplets flowing inside a vertically upward circular microchannel (D = 0.1 mm) with water being the carrier phase have been explored numerically. ANSYS Fluent was employed to capture the liquid-liquid interface using volume of fluid method. Two different boundary conditions were considered in the present study. First, an isothermal wall of 373 K and later a constant wall heat flux (420 kW/m 2 ) were, respectively, prescribed over the wall of the microchannel.The numerical code was validated against the results available in the literature, and the significant results in the form Nomenclature: Ca, capillary number (dimensionless); D, diameter (m); F, body force vector (kg m −2 s −2 ); h, convection heat transfer coefficient (W m −2 K −1 ); k, thermal conductivity (W m −1 K −1 ); L, length (m); Nu, Nusselt number (dimensionless); P, pressure (Pa); Pe, Peclet number (dimensionless); q, heat flux (W m −2 ); R, microhannel radius (m); Re, Reynolds number (dimensionless); S , mass source term (kg/m 3 s); t, time (s); T, temperature (K); U TP , mixture velocity (m/s); u cell , unit cell velocity (m/s); V, velocity vector (m/s)

Liquid–liquid slug flow heat transfer in microchannels has been an interesting topic of research to many researchers. However, the heat transfer studies available in the existing literature deal with stationary walls of the microchannels. In the present work, a modulated motion is prescribed to the walls of the channel in the transverse direction during oil–water slug flow between micro-parallel plates. The influence of frequency and amplification factor of the modulated wall motion as well as capillary number on the droplet shape, film thickness, pressure drop, and heat transfer rate under uniform wall heat flux conditions is investigated computationally. The heat transfer results for the modulated wall motion case show a significant improvement over liquid-only flow and slug flow without any wall motion. Besides, the effect of slug length on the heat transfer has also been discussed for both modulated and unmodulated wall motions of the channel. A mean absolute deviation of 2%–75% in the pressure drop obtained from the numerical studies and existing semi-empirical models for stationary walls for the studied Capillary numbers is observed. This suggests that a better formulation is required for the pressure drop model. In addition, although Nusselt numbers are found to be in reasonable agreement with the existing model for stationary walls, requirement for the formulation of a generalized model considering the effect of wall oscillations is also suggested. This study proposes a new perspective for heat dissipation in micro-scale channels and promotes flow and heat transfer studies, which could bring benefits to relevant applications.

Numerical analysis of a two-dimensional, axisymmetric, incompressible, laminar liquid-liquid Taylor flow inside a vertical circular microchannel is carried out in the present study. The focus is laid on fluid flow characteristics in the slug flow regime. Although many researchers have performed numerical and experimental studies of two-phase flows in narrow channels, their efforts seem to have been fairly successful in explaining the underlying mechanisms of fluid flow phenomena, especially for slug flow regime. Here, an attempt has been made to explore the hydrodynamics of such flows. In the present study, dodecane and Pd5 have been used as the carrier phases and water is used as the discontinuous phase. The internal diameter of the circular microchannel is 1.5 mm with its wall being insulated. The flow and volume fraction equations are solved by the finite volume approach (FVM). The volume of fluid (VOF) method has been adopted for capturing the interface. The effect of Capillary number on film thickness and interfacial pressure drop is explained. The film thickness is found to increase with Capillary number and is also found to be in a close match with the models available in the literature. The pressure drop per unit length obtained from the CFD study is compared with a standard model available in the literature. The pressure drop across the unit cell is found to be following the phenomenological model. It is observed that the pressure drop at the interface has the highest contribution to the total pressure drop in contrast to the other pressure drops in the channel, with ~50-55% in dodecane-water and ~55-62% in Pd5-water systems. Besides, the distribution of the velocity, axial, and wall pressure fields inside the microcapillary are also discussed.