Numerical modelling of ceria undergoing reduction in a particle-gas counter-flow: Effects of chemical kinetics under isothermal conditions
- Authors: Li, Sha , Wheeler, Vincent , Kumar, Apurv , Lipinski, Wojciech
- Date: 2020
- Type: Text , Journal article
- Relation: Chemical Engineering Science Vol. 218, no. (Jun 2020), p. 14
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- Description: A numerical model is employed to simulate a single tube reactor featuring a downward particle flow counter to an upward inert gas flow for ceria reduction in the dilute flow regime. The coupled phenomena of mass and momentum transfer as well as chemical kinetics are simulated assuming isothermal operation for the reactor. The model predicts the reduction extent under varying reaction kinetics as well as design and operational choices. The reduction extent is found to increase with the reaction rate constant until achieving the thermodynamic upper limit at a certain critical value. This critical rate constant signifies a transition from a chemical kinetics limited conversion to a gas advection limited conversion. The effect of the reactor length and the particle size on reaction extent is studied for a range of realistic cases. An empirical correlation is developed to quantify the effects of particle and gas flow rates on reduction extent at both slow and fast kinetics. The present work offers insights to help guide reactor design and operation towards achieving the maximum reduction extent. (C) 2020 Elsevier Ltd. All rights reserved.
Numerical modelling of radiation absorption in a novel multi-stage free-falling particle receiver
- Authors: Kumar, Apurv , Lipinski, Wojciech , Kim, Jin-Soo
- Date: 2020
- Type: Text , Journal article
- Relation: International Journal of Heat and Mass Transfer Vol. 146, no. (Jan 2020), p. 11
- Full Text: false
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- Description: A novel multi-stage free-falling particle receiver design is proposed to improve the simple free-falling concept by enhancing the hydrodynamic stability and improving the radiation absorption of the particle curtain. The multi-stage design arising from repeated re-initialisation of the particle curtain by using intermediate troughs in the receiver results in an increased average volume fraction and residence time of the particles. The present work numerically solves the mass, momentum and radiative transfer equation for an isothermal two dimensional Eulerian-Eulerian particle-gas multiphase flow equations to estimate the absorption characteristics of the particle curtain. The multi-stage receiver concept significantly improves the absorptance of the curtain and reduces the reflection losses by over 50%. The reflection losses are seen to be insensitive to increase in size of the receiver making the multi-stage concept highly scalable. (C) 2019 Elsevier Ltd. All rights reserved.
Radiation analysis of a particle curtain using polydisperse particel size eulerian granular CFD modelling
- Authors: Patel, Smitkumar , Chen, Jingling , Coventry, Joe , Lipinski, Wojciech , Kumar, Apurv
- Date: 2022
- Type: Text , Conference paper
- Relation: 7th Thermal and Fluids Engineering Conference, TFEC 2022, Las Vegas USA, 15-18 May 2022, Proceedings of the Thermal and Fluids Engineering Summer Conference Vol. 2022-May, p. 969-981
- Full Text: false
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- Description: A solid particle receiver is a principal element in concentrated solar power technology in which falling ceramic particles in a cavity are exposed to extremely concentrated solar irradiation. Such particle receiver holds great promise in achieving high thermal efficiencies due to the possibility of reaching temperatures as high as 1000° C. To accurately model the hydrodynamics and the radiation heat transfer, it is imperative to simulate particle-gas interactions more realistically. All the particle receiver modelling till date has used only monodisperse size assumption to simplify the simulation. However, the radiation interaction with the particle curtain is greatly dependent on the size-dependent radiation properties. In the present work, we aim to model the two-dimensional mass, momentum and radiative transfer equations using a Eulerian-Eulerian multiphase granular model and the discrete ordinates model with a particle size distribution in the falling particles. Gaussian distribution is assumed as a representative size distribution spread around a mean particle size of magnitudes generally used in particle receivers (~100-500 µm). The distribution is then split into n size bands and the Eulerian granular flow is modelled for n secondary phases (up to 3 in this study) with a corresponding concentration to simulate the particle size distribution. Each particle size band was prescribed unique size dependent radiation absorption and scattering coefficient for solving the discrete ordinates radiative transfer equation. Finally, a parametric study is carried out to understand the effect of different particle sizes and their concentration on the volume fraction distribution, particle velocities and radiation absorption by the curtain inside the receiver. © 2022 Begell House Inc.. All rights reserved.