Although radiation is important in heat transfer, an analogous model can be used in the design of photochemical reactors. The modeling of these reactors requires that the radiation intensity be tracked in the reactor as a function of position and coupled to the kinetics of chemical reaction. The RTE becomes an important sub-model for such reactors.

The book by Cassano and Alfabo (1991) is the most valuable source for photochemical reactor modeling. Study this paper or related papers, and set up and solve a case-study example of the light-intensity distribution in a photochemical reactor.