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In this work, we present a thorough reaction engineering analysis on the modeling of a vortex-flow reactor to show that commonly practiced one-plug reactor approach is not sufficient to explain the flow behavior inside the reactor. Our study shows that N-plug flow reactors in series is the best approach in predicting the flow dynamics based on the computational fluid dynamics (CFD) simulations. We have studied the residence time distribution using CFD by two different methods. The residence time distribution characteristics are calculated by approximating the real reactor as N-ideal reactors in series, and then estimated the number of ideal reactors in series for the model. We have validated our CFD model by comparing the simulation results with experimental results. Finally, we have done a parametric study with a different sweeping gas to identify the best screening gas to avoid carbon deposition inside the vortex-flow reactor. Our results have shown that hydrogen is a better screening gas than argon.

Solar reactors, by nature of their high temperature, are nearly experimentally inaccessible. Most instruments capable of measuring fluid flow cannot survive the harsh temperatures inside the reactor. As such, computational fluid dynamics (CFD) has been relied on to provide insight into the flow within the reactor. Because of the size of the computing resources necessary to properly account for all of the physical mechanisms within the solar reactor, the current state of numerical simulations only provide a limited level of insight. The present study provides an analysis of flow behavior and thermal interaction of gas-particle flow for a directly irradiated vortex flow solar reactor. The thermal hydraulics between gas flow and particle has been considered by two way coupled Euler-Lagrange approach. A two band discrete ordinate (DO) model has been considered to solve radiative transport between walls and entrained particles. The effect of main flow, secondary flow, particle loading, particle diameter and residence time are studied to analyze flow physics and heat transfer. Results are presented in terms of static temperature contours, temperature distribution along the center line of the cavity, path lines and particle temperature. It is observed that with the increase in main flow, secondary flow and particle diameter average outlet temperature of the fluid increases, and with the increase in particle loading the outlet temperature decreases. The particle exit temperature is observed to increase with the increase in residence time.

Solar reactors can convert intermittent solar radiation into storable chemical energy in the form of fuels that are transportable. In order to use solar energy as a source of high temperature process heat in a solar reactor, incident radiation needs to be concentrated over a small surface area, the inlet of which is called the aperture. The image of the incoming solar radiation over the aperture can be approximated by a Gaussian distribution where the solar radiation inside the reactor varies by the peak value and aperture size. Due to the transient nature of solar energy, there is a critical need for proper control to maximize system efficiency under field conditions. The objective of this paper is to present numerically proven advantages of having a camera-like variable aperture, one that is sensitive to natural variations in solar flux, and having the ability to shrink or enlarge accordingly in order to maintain quasi-constant radiation inside the reactor. Since the internal temperature has a major impact on reactant to product conversion efficiency, by maintaining the temperature constant, process efficiency is kept high. By maintaining the internal temperature despite transient operating conditions, the system can maintain peak performance through a wider insolation range than fixed aperture systems. Our numerical results from optical, thermodynamic, and flow dynamic simulations led us to develop a computational two dimensional heat transfer distribution model inside the reactor in order to validate our optical results. The combined simulation results show that correctly varying the aperture diameter with respect to transient incoming solar flux densities facilitates the maintenance of quasi-constant temperature distributions inside the reactor.

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