FALLING FILM ABSORPTION ON A CYLINDRICAL TUBE

The falling liquid film has become a popular means of transferring heat and mass from a vapor to a binary liquid film; applications include heat pump systems, desalination, and gas-liquid contactors. In the heat pump application, in particular, the length of the liquid film is a crucial factor because of size and weight limitations. Consequently, it is desirable to be able to predict the amount of mass absorbed in a given length of tube. In this work the absorption of water vapor into a Lithium-Bromide Water mixture is considered. It is shown that mass transfer takes place in a thin layer of fluid near the liquid-vapor interface which is indicative of a very high level of liquid-side mass-transfer resistance. Closed form solutions for the velocity field may be used to derive a simple closed form solution for the mass fraction. For very thin films the temperature distribution may be obtained analytically in Laplace transform space; however, due to the complexity of the solution, numerical techniques are employed to obtain quantitative results. For thicker films a closed form solution for the temperature may be obtained as well. The principal objective of this work is to develop a design procedure not requiring a significant amount of numerical work whereby the absorption capacity of a given tube may be predicted as a function of the governing geometrical and physical parameters. The analytical/numerical results are presented for parameters corresponding to those of recent experiments and the agreement between theory and experiment is good.