Radiation models, photochemical reactors

Incidence Models. First attempts to describe the radiant power distribution in photochemical reactors can be summarized under the heading of the RI model (radial incident model, Figure 25a). This model is based on the hypothesis of a radial radiation field [2, 3], that is, that all the light striking the reactor wall will be directed radially inward. Corresponding profiles of radiant power or of irradiance are strongly dependent on the radius of the cylindrical reactor (Eq. 68). 

Other emission models for photochemical reactors include the extense source with superficial emission (ESSE) model in which the light source is assumed to be a surface [119], and the equivalent extense source with diffuse superficial emission (ESDSE) model which has been developed to calculate the radiant power profile generated by several superficial light sources [120], Radiation field modelling for photochemical reactors has been extensively reviewed by Cassano et al. [121, 122],... 

Beltran FJ, Gonzalez M, Rivas J, Jaramillo J. Application of photochemical reactor models to UV radiation of trichloroethylene in water. Chemosphere 1995 31 2873-2885. 

Stirred solutions of each polymer or copolymer at a concentration of 10 mg./ml. were Irradiated In air at 25°C In a quartz vessel with the light from a low-pressure mercury lamp at an absorbed Intensity of 2.95 x 10 quanta ml sec. . Polymer films, evaporated from DMM or methylene chloride solutions on quartz cuvettes or plates and vacutim dried, were Irradiated In air at about 35°C In a Rayonnet Model RPR-100 Photochemical Reactor containing 12 low-pressure mercury lamps the Incident radiation at the films was 1.3 x 10 quanta cm" sec"l. 

Photochemical reactor design involves simultaneous solution of the mass, energy, and momentum balance equations (as in normal reactors) along with equations for the radiation field and energy source (which are specific to photochemical reactors). Two approaches are possible (1) the intensity of the incident light, irrespective of the source, is used as the inlet boundary condition incidence models)-, (2) the emission from the source itself is part of the mathematical description emission models). The first approach has been extensively used but suffers from the weakness that the incident light is a function of scale, and hence a priori design from laboratory scale data tends to be uncertain. The second approach is formally correct, and involves no such uncertainty. 

Vesicles. A thin film of the phospholipid mixture was hydrated at 60 "C in water or 0.2 M aq. acetate buffer (pH S.6) for 30 min. The total concenuation of phospholipid in each sample was 2 mg/mL. The mixture was vortexed and then sonicated (Branson sonifier. Model 450. cup horn anachmetH) at 60 for 5 min. The dispersion was then allowed to cool to room temperature. The vesicles were then exposed to UV radiation (254 nm, Rayonet Photochemical Reactor. Model RPR-IOD) at 8°C for IS min. Then. 20 fiL of a SO mM aq. Pd(NH 4CU solution in water was added. After S min. the dispersions were dialyzed against water to remove buffer salt and excess Pd(NH3)4Cl2. The size of the vesicles formed was determined by light scattering (Coulter Submicron Particle Analyzer. N4MD). 

A radiation flow rate model can be used to quantitatively calculate UV light intensity within a reactor, ff a photochemical reaction is promoted by polychromatic sources, the rate of absorbed radiation energy for the solution is given by ... 

The main difference between photochemical and thermal reaction is the presence of a radiation-activated step. The rate of reaction of this step is proportional to the local volumetric rate of energy absorption (LVREA). For any emission model, the LVREA is a function of the spatial variables, of the physical properties and geometrical characteristics of the lamp-reactor system, and some physicochemical properties of the reacting mixture. The most important design parameter that is pertinent in photochemical and photocatalytic reactions is the effective attenuation coefficient. 

The latest development is now to combine continuous photochemistry with microstmctured equipment. Only very recenfly photochemical conversions in microreactors have received a considerable amount of attention due to the problem often encountered in conventional photoreactors that the distribution of radiation is inhomogeneous in the reaction zone. During the scale-up process, such inhomogeneities often require intensive modeling and design considerations usually on the basis of photon transport models [66], and such models have been, for example, developed for biomedical and analytical purposes [67]. The problem of the intensity distribution in a reactor is illustrated in Figure 3.10. It is obvious that spatial restriction of the irradiation zone in a microphotoreactor to a... 

---