Solution for the coupled heat and mass transfer in falling film absorption using partial discretization via orthogonal collocation

Falling films are a key technology for highly exothermic absorption with high absorption or reaction heats. The textbook literature on falling films is typically limited to either the concentration or the temperature profiles, thereby ignoring the effects of one on the other. The literature on the coupled heat and mass transfer in falling films often relies on significant assumptions and simplifications to solve the coupled system of partial differential equations (PDEs). We derive a numerical scheme using orthogonal collocation on finite elements (OCFE) to solve the PDE system efficiently. The polynomial approximation in the OCFE scheme enables the accurate representation of gradients at the film interface, allowing us to compute accurate absorption rates even for short film lengths. We investigate cases of physical absorption with flow profiles and reactive absorption in comparison to a baseline flux balance model. Our results generally show increased absorption rates for both cases and a typical film flow length. However, a key novel insight from this work is that the absorption rate for very short film flow lengths with reactive absorption is reduced in the case of high heat of reaction. • Solution to coupled heat and mass transport using orthogonal collocation on finite elements. • Solution of first-order reaction diffusion model. • Reduced absorbate mass flow resulting from excess heat of reaction.