Experimental And Simulation Study On Performance Of Lithium Bromide Solution Falling Film Evaporation In Vertical Tubes

This text presents a new-structure generator, where the solution film flows down in vertical tubes, and it is heated by exhaust gas. The advantage of falling film style generator is that it is propitious to enhance heat transfer and get high performance at low heat flux. So an experiment is designed to test the heat transfer coefficients in different heat fluxes and volume flows.Firstly, a model based on some hypothesis is presented to describe the heat transfer performance for falling film evaporation on the interior wall of a vertical tube. The mass transfer equation is introduced into heat transfer model of falling film evaporation. The radial velocity and mass diffusion coefficient are taken into account. The inner node method and finite difference method are used to discretize the control equations, and the iterative calculation is programmed by Matlab software. The simulated results indicate that the effect of solution volume flow and heat flux have a high influence on heat transfer coefficient of falling film evaporation. The decrease of volume flow is favorable for the heat transfer coefficient, and heat transfer coefficient of falling film evaporation increases with the increase of the heat flux.The heat transfer coefficients in different volume flow and heat flux are tested in the experiment. Volume flow has a significant effect on falling film evaporation, a relation is deduced between Re number and volume flow by dimension analysis. In film laminar flow (Re<500), the heat transfer coefficient decreases with the increase of Re number, but it increases with the increase of Re number in transition flow (around Re>500). The increase of heat flux is favorable for the heat transfer coefficient. The dimensionless heat transfer coefficient in film laminar flow (Re<500) can be deduced by dimensional analysis and linearity regression: h+ = 8.6229Re?0.5373.The experiment and simulation results in different Re numbers are accordant, the maximal discrepancy in experiment and simulation results is about 20%, and the minimal discrepancy is about 10%. And the experimental value is totally bigger than simulation result.