The Numerical Research On Heat And Mass Transfer Of Two-component Falling Film Evaporation In Vertical Tubes

A lot of disposal heat resource in manufacture industry can't be fully utilized while the energy resources are urgent. So it is a great signification that the refrigeration powered by low-grade energy resources instead of high-grade energy resources. This text presents a new-structure generator, where the solution film in vertical tubes, and it is heated by exhaust gas. Because the coefficient of heat transfer is low, and the heat transfer can't be enhanced if the gas flows in tube, so the heat transfer performance is low and as a result, the generator is very large. So the structure of falling film which gas scours the exterior wall of tubes transversely, it is propitious to enhance heat transfer and get high performance, at the same time, the structure of falling film can reduce the pressure-drop of steam in small temperature difference. Above all, it can improve the efficiency of the refrigeration system.This text focuses on the analysis and numerical simulation of the condition of LiBr/H2O solution film falling down in vertical tube; it also studies the influence of mass transfer on heat transfer.A model based on some hypothesis was presented to describe the heat and mass transfer performance for falling film evaporation on the inside wall of a vertical tube. The mass transfer equation was introduced into heat transfer model of falling film evaporation. The radial velocity, mass diffusion coefficient and variation of film thickness were taken into account. Discrete model is inner node method, the solution was obtained using finite difference method, and the calculation was programmed by Matlab software. The influence of solution feed flow, heat flux, concentration, pressure and length of tube on heat and mass transfer were analyzed.The simulation results indicate that the effect of solution feed flow and heat flux has a high influence on heat and mass transfer coefficient of falling film evaporation. The decrease of feed flow is favorable for the heat and mass transfer coefficient, and heat transfer coefficient of falling film evaporation increases with the increase of the feed flow for the laminar flow mode. It also finds that the heat and mass flux is decided by diffusion part at the gas-liquid interface. A relationship formula was obtained based on the simulation results when Re<400: h⁺ = 1.1161Re^-0.3159...