A 2-D numerical analysis of heat and mass transfer in lithium bromide-water falling films and droplets. (October 2021) - Subramaniam, Vishwanath
Highlights: 2-D transient numerical model for horizontal falling-film absorption. Droplet formation, break up and fall, and their impact on liquid film modeled. Flow patterns, hydrodynamics, and heat and mass transfer phenomena elucidated. Effects of different absorber operating parameters discussed. Model provides insights into absorber performance at low computational cost. Abstract: The absorber is the most crucial component of the vapor absorption system and has the largest impact on its performance. The horizontal tube bank geometry is by far the most commonly used absorber geometry, due to the high absorption efficiencies achievable without incurring commensurate pressure drops. The design of these falling film absorbers requires an understanding of the underlying heat and mass transfer mechanisms. A majority of the models proposed in the literature for absorption heat and mass transfer in horizontal tube banks make very simplistic assumptions about the flow profiles in the absorber. The effects on heat and mass transfer due to the mixing in the film caused by droplet impact are successfully modeled by the transient, 2-D spatial model developed in the present study. This 2-D model requires a significantly lower computational overhead compared to the transient, 3-D spatial model developed by the present authors in a previous study. The results from the baseline and parametric analyses are discussed. The key differences between the 2-D and 3-D models are also elucidated. The results obtained from this study will aid in the understanding and design of efficient vapor absorption systems.