Abstract
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.
Highlights
Over the last two decays there has been an increasing interest in miniaturisation in process and energy industries [1,2]
In all of the temperature and local entropy generation plots provided in this investigation, the solid line is the specification of the system for the solid phase in that point, and the dashed line is the specification of the system for the fluid phase
A thermal model was established for microreactors accommodating highly exothermic/endothermic reactions
Summary
Over the last two decays there has been an increasing interest in miniaturisation in process and energy industries [1,2]. The recent advancements in the field of heat convection in partially-filled porous conduits have revealed the strong effects of exothermicity on the temperature profiles and heat transfer rates within the system In their recent theoretical studies, Karimi et al [22] and Torabi et al [23,24] considered internal heat sources in partially-filled porous channels with varying configurations. It has been already demonstrated that in exothermic reactive systems the thermal irreversibility is the most significant source of the entropy generation [23,24,39] Given these points, the current study aims to provide an analytical view of the first and second law behaviours of a simple, yet representative, model of a microreactor with highly exothermic or endothermic reactions. The composite system, including a partial porous insert and thick asymmetric walls, is analysed theoretically through a local non-equilibrium approach
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