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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]

• 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. 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. [ABSTRACT FROM AUTHOR]