CFD simulation of water vapor absorption in laminar falling film solution of water-LiBr ─ Drop and jet modes

The rate of absorbed water vapor over a horizontal tube bank in a water-cooled falling film absorber depends on several parameters and working conditions. The flow regime between the tubes in falling film absorbers is one of the most influential parameters in the amount of the absorbed vapor. Among different falling film regimes, in this study, the drop and jet modes are simulated numerically. The full Navier-Stokes equations are solved and the well-known volume of fluid (VOF) method is used to capture the gas/liquid interface. In addition, the energy and diffusion equations are solved in this 3D-simulation with aid of an in-house CFD code. Adaptive mesh refinement, in accordance with the magnitude of volume fraction gradient, has strongly improved the interface capturing and therefore increased the accuracy of simulation. The simulation results reveal that by changing just the regime from drops to jets, the rate of average vapor mass flux decreases one order of magnitude, from 6.3×10-3 to 4.76×10-4kg s-1m-2.