Modeling of photocatalytic honeycomb monolith reactors for air purification.

摘要

A mathematical model has been developed from first principles to investigate the performance capabilities and limitations of titania-coated photocatalytic monolith reactors. The model accounts rigorously for the developing flow field and the radiation field within the monolith channels.; The radiation field sub-model is formulated from the basic principles of radiation heat transfer, and accounts for a polychromatic light source and for wavelength-dependent optical properties of the TiO₂ thin film. In the sense that these properties can be independently measured, the model contains no adjustable parameters. Experimental light intensity profiles for square channeled un-coated ceramic monoliths with two different cell densities confirmed the model prediction that dimensionless profiles are not dependent on absolute channel dimensions, but rather are uniquely determined by the channel aspect ratio. Model predictions are in excellent agreement with the experimental light intensity data for titania-coated monoliths. For identical aspect ratio, the light intensity profiles for square and circular channels are quite similar.; The three-dimensional convection-diffusion-reaction model accounts rigorously for entrance effects arising from the developing flow field, and employs the radiation field sub-model. The model requires user-specification of an intrinsic photocatalytic reaction rate dependent on local UV intensity and local reactant concentration. Published reaction rate expressions and independently determined kinetic parameters were employed in the simulation.; Model predictions are in excellent agreement with experimental formaldehyde conversion measurements for a range of inlet concentrations, humidity levels, monolith lengths, and for various monolith/lamp bank configurations. This agreement was realized without any adjustable parameters. The model tends to systematically overpredict toluene conversion data by about 33%. This level of inaccuracy falls within the accepted limits of experimental kinetic parameter accuracy.; For a given UV profile, the fundamental dimensionless parameters (Re, Da) control reactor performance. For fast photocatalytic reactions, the inlet portion of the reactor likely operates in the mass transfer controlled regime. Irradiating the monolith from both the inlet and outlet sides can increase the effective length of the reactor; although the incremental increase in performance does not scale linearly with increased total irradiation flux. With further validation the model could be used in PCO reactor design and optimization.