Numerical Simulation And Experimental Study On Gas-liquid Mass Transfer In Minichannel

Heterogeneous catalysis process plays an important role in the chemical industry. The traditional multi-phase reactors such as the fixed bed and the slurry bed reactor are widely used in the chemical production, but the problems and challenges they faces can not be ignored. The new type of multi-phase reactors, monolithic reactor with lower pressure drop, high rate of mass transfer, easy to enlarge and the higher production strength is an attractive alternative to the traditional reactor. Despite these advantages, the monolithic reactor is of less application in the chemical production. A very important reason is the lack of basic work. Especially the law of fluid flow and mass transfer of the two core issues are far from perfect and systemic. The law of fluid flow and mass transfer in a minichannel was studied in the present work.With the water-CO₂ system in the monolithic multi-channel, gas-liquid mass transfer experiment was made to determine the liquid side volumetric mass transfer coefficient in the present work. It is found that as the superficial gas velocity and superficial liquid velocity increased, the liquid side volumetric mass transfer coefficient and the pressure drop increased. The liquid side volumetric mass transfer coefficient kLa was determined from CFD simulations of Taylor bubbles in circular tube, using periodic boundary conditions, two-dimensional axisymmetric model, ideal shape of Taylor bubble and laminar flow. The mass transfer from the Taylor bubble is the sum of the contributions of the two bubble caps, and the film surrounding the bubble. The separate influences of the bubble rise velocity, unit cell length, film length, film thickness, liquid diffusivity and tube diameter on kLa were investigated. The separate influences of the bubble rise velocity, unit cell length, film length and film thickness on the liquid film mass transfer coefficient kL,film and (kL,filmafilm)/kLa were focused in the tube of 1.068mm diameter. It will take a unit cell a time t to cross the top surface. The average liquid side volumetric mass transfer coefficient within the initial time t was defined as (kLa)0. A calculation of (kLa)0 was fitted. It was found that (kLa)0 is proportional to the bubble rise velocity of the 0.5-th power, inversely proportional to the unit cell length, proportional to the length of liquid film, inversely proportional to the liquid film thickness of the 0.15-th power and proportional to the liquid phase diffusion coefficient of the 0.5-th power.