Effects of nanofluid and radiative heat transfer on the double-diffusive forced convection in microreactors

Understanding transport phenomena in microreactors remains challenging owing to the peculiar transfer features of microstructure devices and their interactions with chemistry. This paper, therefore, theoretically investigates heat and mass transfer in microreactors consisting of porous microchannels with thick walls, typical of real microreactors. To analyse the porous section of the microchannel the local thermal non-equilibrium model of thermal transport in porous media is employed. A first order, catalytic chemical reaction is implemented on the internal walls of the microchannel to establish the mass transfer boundary conditions. The effects of thermal radiation and nanofluid flow within the microreactor are then included within the governing equations. Further, the species concentration fields are coupled with that of the nanofluid temperature through considering the Soret effect. A semi-analytical methodology is used to tackle the resultant mathematical model with two different thermal boundary conditions. Temperature and species concentration fields as well as Nusselt number for the hot wall are reported versus various parameters such as porosity, radiation parameter and volumetric concentration of nanoparticles. The results show that radiative heat transfer imparts noticeable effects upon the temperature fields and consequently Nusselt number of the system. Importantly, it is observed that the radiation effects can lead to the development of a bifurcation in the nanofluid and porous solid phases and significantly influence the concentration field. This highlights the importance of including thermal radiation in thermo-chemical simulations of microreactors.