Effect of light-source characteristics on the performance of circular annular photochemical reactor
30 Dec 1972-Journal of Chemical Engineering of Japan (The Society of Chemical Engineers, Japan)-Vol. 5, Iss: 4, pp 385-391
TL;DR: In this paper, the authors compared three light source models, i.e., radial, specular, and diffuse line source, for light intensity profile, overall rate of reaction, and radial scale-up ratio of annular photochemical reactors, with the assumptions of constant absorption coefficient and constant quantum efficiency.
Abstract: Three light source models, i.e., radial, specular, and diffuse line source models, are compared for light intensity profile, overall rate of reaction, and radial scale-up ratio of annular photochemical reactors, with the assumptions of constant absorption coefficient and constant quantum efficiency. The necessary condition for the radial light model to hold is that, when the ratio of inner radius to height of the reactor m, is 0.1, that of outer radius to inner radius ρ should be less than 3, and that when m is larger ρ should be close to 1. Published reaction data are analyzed according to this condition.
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TL;DR: In this paper, a detailed derivation of the radiation transport equation (RTE) has been presented and the path of a photon was traced using a stochastic approach, and a semi-empirical kinetic model was presented to evaluate the rate of reaction and conversion of a photoreactor using the computational fluid dynamics (CFD) approach.
Abstract: In this paper, we have discussed the state of the art on numerical techniques for estimating light intensity distribution in photocatalytic reactors. After giving a brief introduction to various photocatalytic reactor designs, a detailed derivation of the radiation transport equation (RTE) has been presented. The RTE is an integrodifferential equation and needs appropriate boundary conditions and optical properties of the medium. To provide a boundary condition for the light emitted from the radiation sources, a number of lamp source models have been described. Different approaches for the numerical simulation of the RTE have been presented with special emphasis on the Monte Carlo and finite volume (or discrete ordinate) approaches. In the Monte Carlo approach, the reaction space was divided into small cubical cells. The path of a photon was traced using a stochastic approach. A conservative variant of the discrete ordinate model available in FLUENT was used to assess the effect of wall reflectivity, catalyst loading, and phase function parameter on the light intensity distribution. For relatively low catalyst loadings, the wall reflectivity strongly influenced the light intensity distribution. However, for an optically thick medium, the wall reflectivity had very little or no effect. The volume-averaged light intensity distribution decreased rather sharply with the catalyst loading and an opposite trend was obtained for LVREA. Finally, a semiempirical kinetic model was presented to evaluate the rate of reaction and conversion of a photoreactor using the computational fluid dynamics (CFD) approach. Model verification was carried out using experimental data for photodegradation of Bayer liquor. A correlation coefficient of 0.974 between simulated and experimental results indicated that the proposed model was adequate. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
140 citations
TL;DR: In this article, an analysis of the existing models for the description of the radiation field inside photochemical reactors for homogeneous systems is presented, where incidence and emission models are critically analysed and the contributions of the main research groups are presented.
113 citations
TL;DR: The agreement between the new model and the experimental data was excellent and these experiments provide a strong validation of the model, even under conditions in which the fluence rate varied by >1000-fold between extreme sites in the reactor.
Abstract: Thirty-seven Suprasil quartz spheres, each approximately 1 cm in diameter and containing an iodide-iodate actinometric solution, were attached to a metal rack and inserted into a bench-scale UV reactor filled with water. The spheres were located at various distances and heights around a 12.4 W low-pressure Hg lamp housed inside a 3.2 cm-radius quartz sleeve in the middle of an annular batch reactor. UV light exposure at 254 nm was performed with the percent transmittance of the water present in the reactor at either 73% or 100% defined over a 1 cm path length. The spheres were simultaneously exposed to the UV light for a given period of time, after which the solutions were removed from the spheres and the yield of triiodide determined from the increase in absorbance at 352 nm. The resulting fluence rate at each site was then calculated on basis of the yield of triiodide. These results were compared with the predictions of a mathematical model based on the multiple point source summation approximation, including reflection and refraction at the air-quartz-water interface. Initially, the agreement was not satisfactory, especially in regions at an oblique angle to the lamp. The model was modified from a multiple point source model to a multiple cylindrical segment model by incorporating a cosine factor. The agreement between the new model and the experimental data was excellent and these experiments provide a strong validation of the model, even under conditions in which the fluence rate varied by >1000-fold between extreme sites in the reactor.
92 citations
TL;DR: Blue–green algae, Spirulina platensis, is cultivated under photoautotrophic growth conditions designed to have nearly uniform growth rate throughout the fermentor by illumination both sides of a rectangular vessel and results show that growth rate and bioenergetic yield are a function of light intensity.
Abstract: Blue-green algae, Spirulina platensis, is cultivated under photoautotrophic growth conditions designed to have nearly uniform growth rate throughout the fermentor by illumination both sides of a rectangular vessel. The results show that growth rate and bioenergetic yield are a function of light intensity. Several kinetic models are considered to express the relationship between growth rate and light intensity.
88 citations
TL;DR: In this paper, a computational radiation field model for simulating the irradiance in single-phase annular photoreactors was developed and evaluated experimentally, which included the lamp within the computational domain allowing to incorporate important interactions between the UV radiation, the quartz walls, and the Hg vapor inside the lamp.
Abstract: A computational radiation field model for simulating the irradiance in single-phase annular photoreactors was developed and evaluated experimentally. The developed model included the lamp within the computational domain allowing to incorporate important interactions between the UV radiation, the quartz walls, and the Hg vapor inside the lamp. Several lamp emission models were evaluated against far- and near-field experimental data. The models with diffused radiation emission showed better overall irradiance prediction capabilities. In particular, a modification of the extensive source volumetric emission model that incorporates the high photon absorbance/re-emission effect produced by the Hg vapor in the lamp illustrated superior results. This latter model showed excellent agreement with near- and far-field experimental data indicating its suitability for integration in multi-physics models for the simulation of photoreactor performance. The advantages of this model are: it is very easy to set up; it comprises the main physical phenomena occurring in the lamp; and it allows for taking into account important lamp-sleeve interactions. Experimental results reaffirmed the importance of applying proper estimates of the lamp power output under the actual operating conditions to perform accurate simulations of radiation distribution.
59 citations