C.A. Estrada

Solar photocatalytic degradation of Aldrin

Abstract Photocatalytic degradation of the pesticide Aldrin dissolved in water was carried out, in one case, using concentrated solar radiation and, in another case, using non-concentrated solar radiation. In these experiments, the effects of catalyst concentration, oxidant agent concentration, and solar irradiation were tested. In experiments without irradiation, strong adsorption of the pesticide over titanium dioxide was observed in the first few minutes of contact in the presence of titanium dioxide (TiO 2 ). These results can be explained by means of Coulombic interactions between the catalyst surface and the pesticide molecules. During the photodegradation process, results show a residual degradation (photolysis) in both the cases, when no catalyst was added. In the case of the non-concentrated solar system, the achieved results suggest that the use of H 2 O 2 increased the degradation rate. For concentrated sunlight, an increase of the Aldrin concentration was observed during the first few minutes of irradiation. This can be explained as a desorption process that is triggered by a change in surface charge of the catalyst in the presence of hydrogen peroxide (H 2 O 2 ) during irradiation. When photocatalysis was performed with TiO 2 alone, no Aldrin was detected in the water solutions throughout the entire experiment. This result was unexpected; however, it might be explained by the adsorption of the pesticide on the catalyst surface and by the absence of the oxidant’s effect. Three transformation products (TPs) of the degradation process were identified: dieldrin, chlordene and 12-hydroxy-dieldrin. The results presented here are in agreement with previously reported results for photocatalytic degradation of other chlorinated pesticides using lamps as radiation sources.

Photocatalytic degradation of DBSNa using solar energy

This paper reports experimental results on photocatalytic degradation of sodium dodecylbenzene sulfonate (DBSNa), using the solar energy concentrator for photocatalysis studies (SECPS). The SECPS operation is based on the concentration of ultraviolet solar radiation on a reactor that contains contaminated water and a catalyst where the photocatalytic e!ect occurs. This e!ect produces ruptures in the toxic molecules, until transforming them into harmless compounds. The study focuses on determining how great is the contribution of the catalyst itself and the oxidant agent to the DBSNa photocatalytic degradation. Finally, three conditions were found as optimal for the photocatalytic degradation of DBSNa using the SECPS, which are 0.2 wt% TiO 2 , 3000 ppm H 2 O 2 and 60 min exposure time. ( 2000 Elsevier Science B.V. All rights reserved.

Mathematical simulation of a solar ejector-compression refrigeration system

This paper presents a mathematical simulation for the dynamic thermal behavior of a solar ejector-compression refrigeration system with a capacity production of 100 kg of ice per day. It consists of an evacuated tube solar collector array, a thermal storage unit and an ejector-compression refrigeration unit. Due to the change in climate, the collector efficiency varies and, therefore, so does the system efficiency. This fact makes it necessary to evaluate the design of the system not just for a whole day but also for a whole year. The ejector-compression refrigeration system was designed to work with Freon R142b as the working fluid at condenser temperature (Tc) of 30°C, generation temperature (TG) of 105°C, evaporator temperature (TE) of −10°C, with a required generator heat load (QG) of 5.6 kW and an obtained evaporator heat load (QE) of 2 kW, the corresponding COP was 34%. With these conditions, the ejector geometry was fixed and curves for QG, QE and COP as a function of TC and TG were obtained. A plot of the daily history of system storage tank temperature for two days of the year (one in January and one in June) is presented. Also graphs for the monthly average ice production, COP, collectors and system efficiencies are presented. The annual average values for COP, collector efficiency and system efficiency were 0.21, 0.52 and 0.11, respectively.

Comparison of Solar Collection Geometries for Application to Photocatalytic Degradation of Organic Contaminants

A comparative study between four different solar collectors was carried out using oxalic acid and the pesticide carbaryl as model contaminants. The comparison was performed by means of a figure-of-merit developed for solar driven Advanced Oxidation Technology systems by the International Union of Pure and Applied Chemistry (IUPAC) for standardization purposes. It was found that there is a relationship between the photocatalyst concentration and the overall solar collector performance. Compound parabolic concentrator was the geometry with the highest turnover rate in the photocatalytic process of oxalic acid, followed by the V trough collector, the parabolic concentrator, and, finally, the tubular collector. When a comparative analysis was carried out using the figure of merit (collector area per order, ACO), the parabolic trough concentrator (PTC) showed the highest efficiency (lower ACO values) at low photocatalyst loads. The V trough collector and the compound parabolic collector showed similar ACO values, which decreased as the photocatalyst concentration increased. The tubular collector was the worst in all catalyst concentration ranges, with the higher collection surface by the order of oxalic acid. Photocatalytic degradation of the carbamic pesticide was tested using the same experimental arrangement used for oxalic acid. In this case, the use of the figureof-merit allowed us to observe the same trend as that displayed for oxalic acid, but with slightly higher ACO values. Results of this work demonstrate that a comparison between different reactor geometries for photocatalytic processes is viable using this figure-ofmerit approach and that the generated results can be useful in the standardization of a methodology for solar driven processes comparison and provide important data for the scaling up of the process. DOI: 10.1115/1.2390986

Radiation absorption and rate constants for carbaryl photocatalytic degradation in a solar collector

Abstract We discuss an analytical model for the evaluation of radiation absorption in a tubular photocatalytic reactor. The model has no adjustable parameters and takes into account scattering in all directions. We compare the results of this model with those of Monte Carlo (MC) simulations and of a Lambert–Beer (LB) approximation, for a reactor illuminated by a parabolic solar concentrator. A good correspondence is found with the MC simulations. In particular, the model displays the correct saturation behavior of absorption for large catalyst particle concentrations, which is not obtained with the LB approximation. We have carried out experiments for the degradation of carbaryl in a solar parabolic collector (PC). The model is used to calculate the rate constant for this degradation from the experimental data. The theoretical model predictions reproduce well, the trends observed in the experiments.

High-heat-flux sensor calibration using calorimetry

This paper demonstrates a calorimetric procedure for calibrating high-heat-flux sensors. The results are in agreement with calibrations obtained using black-body radiation. However, the proposed method has the potential of being more accurate than traditional approaches. This new procedure calibrates sensors to measure correctly under conditions of concentrated solar radiation. At present, the thermal balance calibration technique in the laboratory is limited to solar irradiances of approximately 100 kW m−2. The next step is to demonstrate this methodology to higher irradiances under non-laboratory conditions in the CIEMAT solar furnace at Plataforma Solar de Almeria.

Solar absorptance and thermal emittance of cermets with large particles

We evaluate, theoretically, the solar absorptance and thermal emittance of cermets with large particles. In particular, we consider Co and Ni particles with radii from 0.05 to 0.13 µm, embedded in binders of alumina and silica, respectively. For these particle sizes, it is necessary to consider the effect of the multiple scattering of light in the material for the visible and near infrared parts of the spectrum. The response of the particles is calculated using the Lorenz-Mie theory, and the multiple scattering effects are taken into account through a four-flux radiative transfer model. In the medium infrared, the Lorenz-Mie theory cannot be used because of the high absorption of the binder. The reflectance of the cermets in this regime is calculated using the Maxwell-Garnett effective medium approximation. In general, moderate values of the absorptance-to-emittance ratio are found.

Three-Dimensional Analysis of a Concentrated Solar Flux

In order to improve the durability of receivers used in solar concentrating systems, it is necessary to minimize thermal stress during their operation. A possible way to do that is to design receivers in which the radiative flux density is homogeneous at the surface. For this reason, a detailed 3D study has been carried out for the distribution of concentrated solar radiation in the focal zone of a parabolic concentrator. A computer program has been developed to obtain isosurfaces of solar irradiance and achieve a homogeneous radiation flux on the receiver surface. The algorithm of the program proposes a methodology to obtain flux iso-surfaces for a great variety of optical configurations. The effect of the optical errors on the mirror surface has been studied, as well as the effect of the shape of the mirror, e.g., round, square, or faceted. The numerical calculations were made using the convolution ray tracing technique.

Radiative heat transfer analysis of a directly irradiated cavity-type solar thermochemical reactor by Monte-Carlo ray tracing

Radiative heat transfer in a 1 kW cavity-type solar reactor devoted to the thermal reduction of compressed ZnO and SnO2 powders is analyzed by a Monte Carlo ray tracing simulation. The developed model takes into account the radiative properties of the reactant particles and of the ceramic cavity walls, as well as the angular intensity distribution of the incoming concentrated solar irradiation. The model also includes the conduction heat losses through the lateral walls and the energy consumed by the endothermic chemical reaction. It is used to predict the temperature and the absorbed flux density profiles on the inner cavity walls for different main features of the reactor, concerning the dimensions of the cavity and the type of reactant. Results show that the absorbed flux density profile and the theoretical thermochemical efficiency change with the cavity aspect ratio and with the oxide reactant. The cavity with an aspect ratio of 3 and a SnO2 pellet undergoing dissociation presents the highest thermoc...

Thermal performance of solar control coatings: a mathematical model and its experimental verification

The experimental validation of a mathematical model that predicts the shading coefficient (SC) and the solar rejection factor (SRF) of various types of solar control coatings is presented. The model allows us to input the solar absorptance and predict the temperature of the solar control glazing as a function of the thermal emittance and exterior temperature for typically AM2-solar radiation. With the additional knowledge of the solar reflectance, the SC and SRF are calculated. The model is tested using a chemically ZnS- solar control coating deposited on a 6 mm clear glass and the results are compared with those for commercial glasses.