The Study Of Marangoni Effect On The Gas-Liquid Mass Transfer Process

The surface tension gradient leads to a surface flow, commonly known as Marangoni effect. This study is focused on the Marangoni effect on the gas-liquid mass transfer systems.Firstly , a series of qualitative experiments were conducted to observe the Marangoni effect by laser Schlieren system. Experimental investigations of the occurrence of Marangoni convection are presented and the typical polygonal patterns and even reaching chaotic interfacial flow are observed. The local surface-tension gradient is the primary reason of the Marangoni convection. The optical experimental results are explained by a combination of Marangoni instability and Marangoni number is proposed to gauge the interfacial convection stability status.Secondly, a gas-liquid falling film system has been used to study the Marangoni effect at the liquid surface. Experiments were conducted to investigate instantaneous hydrodynamic characteristics of laminar falling films using Laser Doppler Anemometer (LDA). Instantaneous velocity profiles across a wavy laminar film and profiles of film thickness were measured simultaneously and analyzed from statistical data. Regularly velocity disturbance were found in the film falling. The small-scale interfacial flow increases the surface renewal rate. Consequently, due to the occurrence of the Marangoni effect, the mass transfer rate can be significantly enhanced. Liquid mass transfer coefficients were measured in a gas-liquid channel for count-current falling flows, and the results were compared with values calculated by penetration theory. The experimental results showed that liquid mass transfer coefficient kL could be enhanced as much as 3 fold when the Marangoni number was increased beyond its critical transition point. The influence of the intensity of Marangoni convection on mass transfer coefficient in the liquid phase is analyzed. The conventional mass transfer correlation was modified by using the Marangoni number, Ma, which combines the surface tension gradient and the driving force of mass transfer to explain Marangoni effects. The average error between predicted values and experimental data can be significantly reduces by such improvement.Thirdly, the onset of Marangoni convection for mass transfer process is analyzed using the linear stability theory. Theoretical considerations confirm the possibility of the occurrence of Marangini convection in the investigated systems. The relationship between the Marangoni stability and Sc and Bi numbers is discussed.Finally, the flow and concentration fields of liquid phase in a gas-liquid system are simulated to show the Marangoni convection by using the CFD method. The surface wave dynamics of vertical falling films is computed by taking Navier–Stokes equations and using the Volume of Fluid (VOF) method to track free surfaces and the Continuum Surface Force (CSF) model to account for the dynamic boundary conditions at free surfaces. The simulated results are presented and compared with the corresponding experimental data, and give analysis and discussion. Simulation result indicates that the mass transfer process is enhanced by small Marangoni convection.