Numerical and experimental study of local heat mass transfer characteristics of horizontal falling films of CaCl_2 solution absorbing vapor from humid air

摘要

The local heat and mass transfer characteristics of the falling film over horizontal tubes in the presence of humid air are investigated thoroughly by numerical simulation method and experimental method. To improve the accuracy of the model, a laminar model or a k-ε turbulence model is employed depending on the film Reynolds number (Re). And the consideration of the heat transfer in the gas phase made the model can effectively reflect the complex flow behavior and adopt more practical boundaries. The simulation results were validated by the experimental data. The simulations demonstrate that the film Re effects on the outlet parameters and the inner solution temperature distribution are consistent with the experimental data. The temporal variations in all the average solution and gas parameters finally undergo periodic cycles in the droplet flow mode, whereas a constant trend is observed in the sheet flow mode. The average absorption rate in the falling-film regions in the droplet and sheet flow mode may be almost 6 and 10 times the average absorption rate in the inter-tube regions. The inter-tube absorption rates in the sheet flow mode show a distinct saw-tooth pattern. The solution parameters variations in the droplet mode are greater than those in the sheet mode, while the gas parameters variations are less apparent.