Analytical and numerical investigation of heat and mass transport in catalytic microreactors

Hunt, Graeme Robert (2020) Analytical and numerical investigation of heat and mass transport in catalytic microreactors. PhD thesis, University of Glasgow.

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Microreactors for chemical synthesis and combustion have attracted increased attention in recent years. Due to the high degree of thermal control exhibited by microreactors, exothermic catalytic activity features heavily in these devices and thus advective-diffusive transport is of key importance in their analyses.
An analytical study of the transport phenomena in a single microchannel microreactor filled with a porous medium is presented, first as a one-dimensional, then expanded to a two-dimensional model with catalytic activity. The systems under investigation include fluid and porous solid phases inside the microchannel under local thermal non-equilibrium (LTNE), in addition to the enclosing structure of thick walls subject to distinct thermal loads. The thermal diffusion of mass, viscous dissipation of the fluid flow is examined for both a heterogeneous catalyst placed on the channel wall and for a homogeneous reaction process. The axial and transverse variations of heat and mass transfer processes are considered to provide two-dimensional solutions of both the temperature and concentration fields. These are then used to calculate the local and total entropy generation within the system. A novel extension of an existing LTNE model capable of taking into account the enclosing structure as well as the porous solid and fluid phases is presented. The thickness of this enclosing structure is shown to have a major influence on heat and mass transport within the system, particularly the Nusselt number. Irreversibilities in the system are found to be dominated by the mass transfer contributions and the influence of the Soret effect as well as the Damköhler number.
A numerical investigation is undertaken to examine the effect of hydrodynamics upon the activity of a heterogeneous catalyst. Three corrugated wall channel configurations with varying phase difference between upper and lower walls were generated. Low Reynolds number flows of fuel lean methane in air were catalytically combusted over platinum in the numerical model. Hydrodynamic reflux features were observed in the out of phase cases. Coinciding with these zones, the site surface concentration of carbon dioxide was observed to vary significantly as compared to the base case.
The extension of the LTNE model significantly increases the capability of modelling the interface between thick walls and a porous medium under thermal load, permitting more accurate modelling of microreactors. The effect of the reflux feature on the surface site fraction of product for the corrugated channels reveals the complex interaction between hydrodynamics and catalytic activity.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Heat and mass transfer, computational fluid dynamics, non-equilibrium thermodynamics, heterogeneous catalysis, homogeneous catalysis, mathematical modelling, analytical modelling, catalytic activity, microreactors.
Colleges/Schools: College of Science and Engineering > School of Engineering > Systems Power and Energy
Funder's Name: Engineering and Physical Sciences Research Council (EPSRC), Engineering and Physical Sciences Research Council (EPSRC)
Supervisor's Name: Karimi, Dr. Nader
Date of Award: 2020
Depositing User: Mr Graeme Hunt
Unique ID: glathesis:2020-80276
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 13 Mar 2020 14:33
Last Modified: 27 Apr 2022 08:49
Thesis DOI: 10.5525/gla.thesis.80276
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