Rigorous model and experimental verification of the radiation field in a flat-plate solar collector simulator employed for photocatalytic reactions

In any kinetically controlled photocatalytic process the catalyst activatio n is always a photochemical act that depends upon the local value of the vo lumetric rate of energy absorption (LVREA). In a heterogeneous photocatalyt ic reaction, a precise evaluation of the LVREA can be obtained when the spa tial and directional distributions off radiation intensities are known. Wit h this purpose, a mathematical model of the radiation field inside a flat-p late heterogeneous reactor (a solar simulator) has been developed. The soli d-liquid reactor is irradiated by two tubular UV lamps with the aid of two parabolic reflectors. Since titanium dioxide suspensions absorb and scatter radiation the model accounts for both effects. Resorting to information ab out the lamp and reflector characteristics, the catalyst optical properties and concentration, as well as the reactor dimensions and wall reactor prop erties, the solution of the mathematical model (a two-dimensional-two-direc tional model) provides a detailed description of the spatial and angular di rectional distributions of radiation intensities inside the reactor, Using this information, it is possible to precisely calculate the rate of absorbe d radiation energy at each point inside the: reactor. This is one of the ke y variables for reactor design and/or scale-up purposes. The radiation dist ribution inside the reactor was verified by computing forwardly transmitted and backwardly scattered radiation fluxes coming out of the reaction space through the glass reactor walls. These radiation fluxes were compared with experimental measurements made with a UV radiometer and good agreement was obtained; when no fouling was present and considering low catalyst loading to obtain measurable radiation fluxes, the maximum observed error was 12%. The predicted inlet boundary condition was also verified with actinometry and the error was smaller than 14% For this reactor configuration, when the radiation absorption performance is the only factor under consideration, i t was found that Aldrich titania is more efficient than the Degussa P 25 va riety. (C) 1999 Elsevier Science Ltd. All rights reserved.