A Numerical Study Of LiBr-H₂O Falling Film Absorption On A Spirally Fluted Horizontal Tube

The absorber is one of the most important parties in absorption refrigeration system and its characteristics have significant effect on the machines'performance. Falling liquid film on the surface of a internally cooled horizontal tube are widely used in the absorbers of absorption heat pumps. In this work, falling film and heat and mass transfer on the surface of a horizontal spirally fluted tube is considered. The absorption performance of solution on the surface of spiral fluted horizontal tubes is studied theoretically, which conclusion provides a theoretical and technological basis in the design of an absorber.The numerical falling film absorption model of the LiBr-H2O is established using Navier-Stocks equations for low Reynolds number with considerations of the surface-tension effects and action of gravity. Analytical solutions of film velocity distribution and the liquid film thickness are abtained. The influence of the surface geometry of the fluted tube on the solution film thickness distribution is discussed.Furthmore,the heat and mass transfer behavior of the falling film are also studied. The result shows that the solution tends to flow down the crest region and accumulates in the trough region. The curvature of the tube surface and the number of spirally trough has little influence on the distribution of the solution film thickness due to the special surface tension characteristics of the LiBr-H2O solution. However,the depth of the spiral trough influences a lot. The deeper of the channel,the thinner of the film thickness at the begaining,and the film becomes more uniform. The comparable analysis shows that the absorption performance of spiral fluted tubes is better than that of bare tubes. This is because the spiral fluted tubes provide a good wettability leading to a high heat transfer between the coolant and the solution and a high mass transfer area between the liquid and the vapor.