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• 3D numerical simulation of oil-water droplet flow in a microchannel. • Effect of short and long obstacles and flow rate on heat transfer and pressure. • Improved mixing and heat transfer due to recirculating flow. • Droplet size and liquid film thickness directly and reversely affect the heat transfer, respectively. • Increased heat transfer with slight pressure drop penalty using the obstacles. Droplet-based microfluidics is an emerging technology for thermal management of high heat dissipating systems and electronics cooling. The current work investigates the potential of slug flow for thermal management of mini-sized heat dissipating devices and microchannels. Hydrothermal characteristics of oil-water slug flow including droplet size, liquid film thickness, pressure drop, and heat transfer have been studied in a T-shaped microchannel. Three dimensional numerical simulations have been carried out for two types of ribbed channels with short and long obstacles at different flow rates. Results indicate that droplet size and liquid film thickness directly and reversely affect the heat transfer rate, respectively. The former intensifies the flow recirculation, and the thermal boundary layer disturbance while the latter changes the dominant heat transfer mechanism to conduction. On the whole, a maximum of 55 % heat transfer enhancement has been achieved relative to the single-phase water flow. It is also observed that by using obstacles on the channel surface, the heat transfer enhancement can be further increased with a slight pressure drop penalty. [Display omitted] [ABSTRACT FROM AUTHOR]

• 3D numerical simulation of droplet flow in a microchannel. • Effects of surface tension, wettability and heat flux on droplet size, heat transfer and pressure. • Improved mixing and heat transfer due to recirculating flow. • liquid film thickness and droplet velocity positively affect the heat transfer rate. • Reverse relation between surface tension and heat transfer. Droplet-based microfluidics refers to the production and utilization of micrometer-sized droplets. This technology has found widespread applications in drug delivery, biotechnology, disease prevention, chemical analysis, cell research, and functional material synthesis. Cooling of high heat flux electronic systems and hot spots is another application of the droplet flow which is focused by the current work. In this paper, formation and hydrothermal performance of oil droplets in water flow in a T-junction microchannel is studied by a 3D numerical simulation. Effects of different parameters such as surface tension, wettability and heat flux on the droplet size, heat transfer rate and pressure drop are investigated. It is observed that the shear between the discrete and continuous phases results in recirculating zones in both phases which contribute to improved mixing and heat transfer rates. Liquid film thickness adjacent to the heated surface and the droplet velocity are two other factors that positively affect the heat transfer. Decreasing the surface tension is shown to enhance the heat transfer rate. Moreover, an optimum value is found for the contact angle as 135° at which a 23 % heat transfer enhancement is achieved. Results also indicate that droplet size decreases with increase of contact angle while it slightly increases with increase of the surface tension and negligibly varies with the applied heat flux. [Display omitted] [ABSTRACT FROM AUTHOR]