Analysis Of Heat And Mass Transfer Of LiBr Solution Falling Film Absorption In Absorber With Horizontal Tube

Falling film absorption of lithium bromide solution is one of the fierce study fields of absorption refrigeration. The result of numerical simulation for single tube, will lead to great error, neglecting transverse convection and variable film thickness, being lack of experimental test. In order to establish a more reliable prediction model for the real absorption process, the falling film absorption model is given according to 2D laminar flow and vortex-flow function method, with the consideration of variable thickness, transverse convection and wet ratio. Also, the model in droplet formation, falling and column absorption areas is formulated. The whole model is solved by finite difference method. Heat and mass transfer performance can be enhanced by transverse convection and self-circulation according to field synergy principle. The effect of wet ratio defined is made on falling film absorption performance. The simulation process including the computation of outlet temperature and concentration, thermal load and absorption rate, is established for the tube bundle. The simulation results have a good agreement with Joudi's prediction and test data by Frances. The local properties distribution along the circumference is investigated. The effect of such parameters as wet ratio, spray density, inlet temperature of solution and cooling water and steam, are analyzed. Simulation result shows that the mass absorption rate in droplet formation and falling area is up to 20% and the enhanced mechanism by transverse convection and self-circulation is confirmed. The value according to variable properties is 10% less than that of constant properties. Heat and mass transfer performance is enhanced with the increase of S/D (the optimized range: 1.0-1.5), which reassures the contribution of droplet formation and falling process. Solution outlet temperatures and concentration, heat and mass transfer coefficients decrease with the increment of tube diameter. The results obtained will be helpful to absorber design and improvement of absorption performance.