Numerical study of heat and mass transfer in lithium bromide-water falling films and droplets

• Temporally and spatial resolved computational modeling of falling-film absorption.
• Full accounting of propagating waves in film flow and inter-tube droplet mode flow.
• Coupled heat and mass transfer in LiBr-H2O absorption modeled for realistic flow modes.
• Effect of complex wave and drop evolution on absorption demonstrated.

The absorber has the largest impact on the performance of an absorption heat pump. Most models of absorption heat and mass transfer in horizontal tube banks make simplistic assumptions about flow mechanisms. The flow over tube banks actually occurs as wavy films on the tube surface and as droplets in the inter-tube space. The formation and detachment of these droplets, and their impact on the tube affects heat and mass transfer considerably. Absorption models in the literature typically assume the solution to flow as a uniform film. The present study models heat and mass transfer in the absorber while accounting for the realistic drop-wise and wavy film flow patterns. The significant effects of mixing and the waves caused by droplet impact on heat and mass transfer are successfully modeled with full 3-D spatial and temporal resolution using the Volume of Fluid technique.