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Direct Numerical Simulation of Coupled Heat and Mass Transfer in Dense Gas-Solid Flows with Surface Reactions

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Direct Numerical Simulation of Coupled Heat and Mass Transfer in Dense Gas-Solid Flows with Surface Reactions Direct numerical simulation of coupled heat and mass transfer in dense gas-solid flows with surface reactions Citation for published version (APA): Lu, J. (2018). Direct numerical simulation of coupled heat and mass transfer in dense gas-solid flows with surface reactions. Technische Universiteit Eindhoven. Document status and date: Published: 19/11/2018 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 10. Oct. 2021 Direct Numerical Simulation of Coupled Heat and Mass Transfer in Dense Gas-Solid Flows with Surface Reactions Jiangtao Lu This dissertation was approved by the promotor: Prof.dr.ir. J.A.M. Kuipers and the co-promoter: dr.ir. E.A.J.F. Peters This work was supported by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation programme funded by the Ministry of Education, Culture and Science of the government of the Netherlands. Part of this work was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative. Copyright @ 2018, Jiangtao Lu, Eindhoven, the Netherlands All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of the author. A catalogue record is available from the Eindhoven University of Technology Library ISBN: 978-90-386-4612-1 Direct Numerical Simulation of Coupled Heat and Mass Transfer in Dense Gas-Solid Flows with Surface Reactions PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de rector magnificus, prof.dr.ir. F.P.T. Baaijens, voor een commissie aangewezen door het College voor Promoties, in het openbaar te verdedigen op maandag 19 november 2018 om 13:30 uur door Jiangtao Lu geboren te Jiangsu, China Dit proefschrift is goedgekeurd door de promotoren en de samenstelling van de promotiecommissie is als volgt: voorzitter: prof.dr. C.W.M. van der Geld promotor: prof.dr.ir. J.A.M. Kuipers co-promotor: dr.ir. E.A.J.F. Peters leden: prof.dr.ir. M. van Sint Annaland prof.dr.ir. E.J.M. Hensen prof.dr. J.G.M. Kuerten prof.dr.ir. R.A.W.M. Henkes Technische Universiteit Delft & Royal Dutch Shell Prof. Dr. Rodney O. Fox Iowa State University, United States Het onderzoek of ontwerp dat in dit proefschrift wordt beschreven is uitgevoerd in overeenstemming met de TU/e gedragscode wetenschapsbeoefening. To my family Direct Numerical Simulation of Coupled Heat and Mass Transfer in Dense Gas-Solid Flows with Surface Reactions Summary Fluid-solid flows are frequently encountered in a wide range of processes. A typical example is fixed bed reactors, which are commonly used in chemical industry for catalytic reactions. In such processes, reactions take place at active sites deep inside porous catalyst particles. Therefore, it is important to know how reactants are transported to these particles and how products move out with the fluid flow. The performance of a catalytic process is determined not only by the efficiency of the catalytic reaction, but also by the efficiency of mass transport. In such highly heterogeneous systems, there are two important factors, specifically variable reaction rates and significant heat effects, which introduce additional complexities to the equipment design as well as the process performance. In chemical engineering, most researchers focus on either reaction kinetics or transport processes, but in this thesis the flow of reactants and products around catalytic particles is modelled as well as the reactions that occur there. Using detailed models the performance of a catalytic process can be predicted by computer simulations. The simulations give insights in the interplay among mass transfer, chemical transformations and heat effects. Using the detailed information the models provide, real chemical processes can be improved and in that way technological development is accelerated. In this thesis, an efficient ghost-cell based immersed boundary method (IBM) is developed to perform direct numerical simulation (DNS) of (coupled) mass and heat transfer problems in fluid-particle systems. The fluid-solid coupling is achieved by implicit incorporation of the boundary conditions into the discretized momentum, species and thermal energy conservation equations of the fluid phase. Taking advantage of a second order quadratic interpolation scheme in the reconstruction procedures, the DNS model is capable to handle the Robin boundary condition at the exact position of the particle surface. This is the unique feature of this DNS model. A fixed Eulerian grid is used to solve the conservation equations for the entire computational domain. Several fluid-particle systems, with increasing complexity, are studied in the subsequent chapters with the aim to push forward the frontier of the application of DNS towards more realistic chemical reaction processes. In Chapter 2, the governing equations, the numerical solution method and the IBM are introduced in detail. The newly developed quadratic interpolation scheme is verified by first comparing the numerical results for unsteady mass diffusion around a single sphere with the analytical solutions and, second, by comparing computed Sherwood numbers for convective mass transfer with the empirical values. In both cases, an infinitely fast surface reaction is assumed and excellent agreement is achieved. In Chapter 3, a catalytic surface reaction is introduced into the DNS model. The Damköhler number is used to describe the interplay between chemical reaction and mass transfer processes in fluid-particle systems. First, a detailed verification study of unsteady mass diffusion is performed, where the concentration profile and the instantaneous Sherwood number are compared with the analytical solutions. Next, both single particle and multi-particle dense systems with different reaction rates are considered. It is noted that, the mass transfer performance of the dense particle array is improved to some extent with higher reaction rates. In Chapter 4, mass transfer problems in particle clusters, specifically a nine-sphere cuboid cluster and a randomly-generated spherical cluster consisting of hundred spheres, are studied. The clusters are composed of active catalysts and inert particles, which are realized by the Dirichlet and Neumann boundary condition respectively. Mixed boundary conditions of individual spheres are handled consistently in the DNS model. In case of a cluster, the swarm effect decreases the mass transfer performance dramatically, however, dilution with inert particles can help to counteract this decrease quite a lot. In Chapter 5, the heat transfer problems in fluid flowing through tubular fixed beds are studied. For the classical Graetz-Nusselt problem with both isothermal and isoflux boundary conditions, the DNS results agree well with the analytical results in a wide range of the Péclet number. An advanced Graetz-Nusselt problem with hundreds particles randomly positioned inside a tube with adiabatic wall is then studied. The channeling effect at the wall region is noticed to significantly reduce the performance of the system, nevertheless large and passive particles will increase the heat transfer coefficient. The simulation results are compared with the results obtained by a team from the University of Twente using a different class of IBM, revealing good agreement. In Chapter 6, independently coupled heat and mass transfer is studied in fluid-particle systems. The reaction rate is specified to be first order with a rate coefficient which is independent of temperature. The coupling of heat and mass transfer arises as a consequence of an exothermic reaction where the liberated heat heats up the particle that, subsequently, transfers the thermal energy to the
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