Analytical investigation of heat transfer and classical entropy generation in microreactors - The influences of exothermicity and asymmetry

Heat transfer and entropy generation are analysed theoretically in a thermal model of microreactors accommodating processes with large heat of reaction. This includes an asymmetric, thick wall, partially-filled porous microchannel under local thermal non-equilibrium. The system features exothermicity/endothermicity within the solid and fluid phases to represent heat of chemical reactions and absorption of microwaves by the microstructure. For constant but uneven temperature boundary condition, analytical solutions are developed for the temperature profiles, Nusselt number (Nu) and local and total entropy generation. The influences of the system configuration and thermal specifications upon the heat transfer and irreversibilities are, subsequently, examined. This reveals the strong effects of the wall thicknesses and thermal asymmetry on the heat transfer and entropy generation of the microreactor. Most importantly, it is shown that for given exothermicities in the system there exist optimal wall and porous insert thicknesses that result in the maximum Nu and minimum total entropy generation. The presented analyses are therefore of practical significance and demonstrate the possibility of developing thermal and entropic optimal designs of the microstructure of microreactors.