Light intensity distribution in heterogenous photocatalytic reactors

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.

Coupling the Six Flux Absorption–Scattering Model to the Henyey–Greenstein scattering phase function: Evaluation and optimization of radiation absorption in solar heterogeneous photoreactors

“…The approach consists in establishing a statistically representative sample of photons and recording the history of each photon, from the moment it enters the system until its extinction (by absorption or scattering outside the system) including every interaction along the path. In order to make decisions about photons fates and trajectories, ii) The mean free path-length l, where the photon is neither absorbed nor scattered, is related to the extinction coefficient of the suspension β according to the equation [12]:…”

“…34 incorporate the scattering nature through the SFM/SFM-HG scattering probabilities (see Eqs. (12)(13)(14)). …”

“…Despite the modeling power of the previous methods, these are often mathematically and computationally demanding when applied at the solar dimension scale, which is invariably characterized by atmospheric fluctuations of the boundary conditions (i.e., photon flux), in turn increasing the complexity of the models. Hence these methods are generally limited to modeling systems with constant-flux artificial radiation sources (e.g., UV lamps) [12].…”

“…Despite the modeling power of the previous methods, these are often mathematically and computationally demanding when applied at the solar dimension scale, which is invariably characterized by atmospheric fluctuations of the boundary conditions (i.e., photon flux), in turn increasing the complexity of the models. Hence these methods are generally limited to modeling systems with constant-flux artificial radiation sources (e.g., UV lamps) [12].In contrast, the Six Flux Absorption-Scattering Model (SFM) has been proposed as a practical and simplified approach for solving the RTE. It is based on geometric optics but retains the key aspects of radiation field modeling characteristic of a rigorous approach.…”

Mixing regime simulation and cellulose particle tracing in a stacked frame photocatalytic reactor

“…In addition to the conventional reactor design parameters such as reactor geometry, mixer configuration, mode of operation (continuous or batch), separation efficiency, residence time, reaction selectivity, materials of construction and cost, the following parameters with respect to illumination needs to be considered while designing a photocatalytic reactor [5] shown in Figure 1. As previously reported in the literature, photocatalytic reactor designs can potentially fulfil the following objectives: [6][7][8] (i) Improve the catalyst to reactant ratio and residence time, Recently, however, 12 different photocatalytic reactors for wastewater treatment were compared using a benchmark ratio proposed as the photocatalytic space time yield (PSTY) [6]. According to Leblebici et al PSTY is defined as "the volume of water treated for each kW lamp power per volume of reactor per unit of time" [6].…”