Heat and mass transfer performance analysis of a vertical tubular ammonia/water bubble absorber based on CFD modeling

Abstract

Bubble absorbers are highly efficient in mass transfer processes, but their popularization is limited by the risks associated with too much ammonia charging. In order to reduce the ammonia charge, it is essential to optimize the heat and mass transfer performance in the absorber. Existing models provide in-depth analysis of bubble motion and morphology, but insufficient attention has been paid to the concentration distribution and interfacial heat and mass transfer resistance. In this study, a two-dimensional axisymmetric vertical tubular ammonia/water bubble absorber was modeled based on Fluent and phase equilibrium, absorption heat data based on Aspen was imported. The relative deviations were 9%, 0.45%, and 4.1% in terms of the completely absorbed height, the liquid phase ammonia mass fraction, and the outlet temperature, respectively. The results showed that the mass transfer deterioration point was at the gas column closure and the heat transfer deterioration point was at the gas column contraction. Variable parameter studies have shown that turbulence effects at the gas–liquid interface can lead to enhancement and deterioration of local heat and mass transfer, which in turn cause local oscillations in the concentration and temperature profiles. While increasing the interphase mass transfer driving force promotes the interphase mass transfer process, it hinders the diffusion mass transfer process within the liquid phase. This effect is particularly pronounced in the absence of intense cooling, leading to an increase in the complete absorbed height.