Simulation Study On Heat And Mass Transfer Characteristics Of LiBr Solution Bubble Absorption In Vertical Tube

The bubble absorption method occupies an important position in the field of refrigeration and air conditioning as well as waste heat recovery due to its high efficiency.When the absorber uses lithium bromide-water（Li Br-H₂O）as the absorption working medium,it needs to work in a vacuum environment.This requirement limits the development of lithium bromide（Li Br）bubble absorption.In this rearch,based on the pressurization technology,using Li Br-H₂O as a working pair,a single-bubble heat and mass transfer model of Li Br solution bubble absorption was established,and a corresponding experimental platform was built.The shape and size of bubbles and the heat and mass transfer characteristics between gas and liquid in the bubble absorption process of Li Br were studied by simulation and preliminary experiment.So as to provide a theoretical reference for the design of the Li Br bubble absorber,and it also has a certain guiding significance for improving the capabilities of the system and the miniaturization of the absorption unit.The main items are as follows:（1）The heat and mass transfer effects of the two absorption methods were compared and analyzed by theoretically calculating the heat and mass transfer coefficients of bubble absorption and falling film absorption of Li Br solution.The results show that the heat and mass transfer capabilities of bubble absorption are more excellent than that of falling film absorption.（2）A single-bubble heat and mass transfer model of Li Br solution bubble absorption was established,and the bubble absorption process of Li Br solution was numerically simulated by COMSOL.The effects and change law of nozzle diameter,solution concentration and bubble velocity on the heat and mass transfer characteristics were studied.A corresponding experimental device was built to verify the feasibility of bubble under negative pressure,and the shape and size of the bubbles and the heat and mass transfer during Li Br solution bubble absorption under negative pressure were preliminarily studied through visual and non-visual experiments.（3）The results intuitively reflected the transient changes of the velocity field,concentration field,and temperature field in the single bubble absorption process;based on the stationary conditions,the single-bubble transfer characteristics of Li Br solution bubble absorption under different working conditions were obtained.The results show that when the nozzle diameter is 2～6mm,the solution concentration is 50%～60%,and the bubble velocity is0.1～0.5m/s,the larger the nozzle diameter and bubble velocity,the smaller the solution concentration,the better the heat and mass transfer effect.