Numerical study of microchannel heat transfer with nanofluid based two - phase slug flow

Abstract

Microfluidics has recently gained research attention for its high-end thermal applications, including micro heat exchangers, Lab on a Chip, micro reactors, and MEMS. It has been proven that the addition of suitable nanoparticles to a fluid can enhance the heat transfer efficiency in microchannels, both in single phase and liquid-liquid two-phase flow. In general, slug flow is said to be the most efficient in heat transfer. However, the investigation performed on liquid-liquid slug flow with added nanoparticles was found to be very limited. Hence, this study numerically investigates the heat transfer characteristics in microchannels with liquid-liquid two- phase fluid flow (water and light mineral oil) with added nano particles (AI2O3). The VOF method and phase field equations were solved using ANSYS Fluent and COMSOL Multiphysics to capture two-phase flow interfaces. Adaptive mesh refinement techniques were employed to reduce computational power while maintaining sharp interfaces between fluid phases. The Eulerian mixture model was used to solve the cases containing nanoparticles. Numerical results were validated against published experimental data reported by [1] and [2]. Simulations were conducted for a 3000 micron long microchannel with a diameter of 100 microns for fluid velocity, ranging from 0.1 m/s to 0.5 m/s. First, 1 kW/cm2 of heat flux is introduced to the channel wall after 1000 microns to mimic the microchip heat generation, also allowing flow to be developed. Results have shown that using nanoparticles in either phase significantly increases heat transmission. This can be amplified even more when used in the secondary phase, by 58 percent compared with liquid-liquid two phase slug flow. This was accomplished with a nanoparticle fraction of 0.05 v/v in the secondary fluid phase. The addition of nanoparticles to the primary fluid increased heat transfer by 34%. The findings of this study can be used to improve MEMS and micro-to-macro systems that move heat.