Chapter 4 - Mass transfer mechanisms in nanofluids

Abstract

This chapter tries to explain the mass transfer mechanisms in the presence of nanofluids in the simplest and most understandable way possible. For this purpose, the latest findings and reports will be reviewed on the use of nanofluids in various fields of engineering in which the mass transfer is of major importance. Also, the existing theories will be carefully examined to provide a relatively complete solution to the problem of the mass transfer mechanism in the nanofluids. In this review, the mechanism of increasing mass transfer in the presence of nanoparticles due to diffusion and convection has been investigated, which can be considered as the main source of increased mass transfer in the nanofluids. Increased mass transfer in the presence of nanoparticles in fluids depends on factors such as the concentration of particles in the fluid and the particle size. According to the literature, increasing Brownian motion in the presence of nanoparticles is one of the most important tools to explain the mechanism of improving mass transfer. However, two main phenomena for relation between nanofluidand improved mass transfer have been generally accepted and proven: diffusive and convective mass transfer. At the same time, more research is underway to understand the precise functional nature of the nanofluids in the mass transfer, in which more and more details are provided. Although the effects and mechanisms of heat transfer in the presence of nanofluids are more quantitatively and qualitatively known, statistically, the improvement in the performance of the nanofluid-containing system in terms of the mass transfer has been significantly greater than the improvement in the heat transfer. However, these experimental results must be explained by theoretical principles to accurately understand the mechanisms, thereby completing the loop of effective presence of the nanofluids in the mass transfer. In this way, heat transfer mechanisms can be very helpful. Thermal conductivity enhancement in nanofluids, which are liquids containing suspended nanoparticles, has been attributed to localized convection arising from the nanoparticles’ Brownian motion. Because convection and mass transfer are similar processes, the objective here is diffusion enhancement with the nanofluids.