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Abstract: 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. [Copyright &y& Elsevier]

Abstract: Falling films on horizontal tube banks are widely used in absorption heat pumps. Liquid film heat and mass transfer models in the literature are based on simplistic assumptions about such flows. Droplets forming under the tubes fall on subsequent tubes, and the ensuing waviness and mixing on the liquid film affect absorption. High-speed flow visualization, image analysis, and computations are used to understand the effect of hydrodynamics on local absorption phenomena. Image analysis mathematically describes the interface, and the surface area and volume of the droplets. These flows are also numerically analyzed using the volume-of-fluid method for the liquid–vapor interface. The 3-D model corroborates with high fidelity the droplet formation, detachment and impact observed in experiments. Fully resolved 3-D computations of the coupled fluid flow and heat and mass transfer reveal the local gradients and transfer rates, and their spatial and temporal variations in the falling-film and inter-tube regions. [Copyright &y& Elsevier]