Flow hydrodynamics of laminar falling film of aqueous Li Br solution (Li Br - H_2O) on a horizontal elliptical tube has been investigated in this research. The film velocity distribution and film thickness, namely, the flow characteristics are determined by solving analytically simultaneous simplified Navier-Stokes equations and continuity equation in polar and Cartesian coordinates. The analysis is based on steady state laminar flow of falling liquid film of Li Br - H_2O on a horizontal elliptical tube in polar model and Cartesian model (CM), for cases in which traction on the film surface is considered negligible. Models are compared with each other in three cases of aspect ratios (A_r), tube diameters, flow rate, mass concentration and temperature of solution. The flow characteristics values in Cartesian model are over predicted with respect to polar model. The results show that the error in Cartesian model with smaller tube diameter is increased as mass flow rate increases. In Cartesian model, the aspect ratio and tube diameter show no effect on flow characteristics values around the elliptical tube. Therefore, as the eccentricity of ellipse (the ratio of the ellipse focal separation to the major axis) in the elliptical tube increases, the error increases as well. Finally the flow characteristics around horizontal elliptical tube with A_r > 1 are showing better performance with respect to flow characteristics around horizontal elliptical tube with A_r < 1.
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