- 2:35 PM

Mixing Size Control and Mass Transfer Performance in a Microfluidic Device

Jianhong Xu, Guangsheng Luo, Jing Tan, and Shaowei Li. Department of Chemical Engineering, The State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China, Tsinghua University, Beijing 100084, China, Beijing, 100084, China

Today's microchemical system is no longer in its infancy. Some microfabricated reactors have been proven to provide excellent mass and heat transfer properties because of uniform flow patterns and residence time distributions in these reactors. Some of these devices even are available commercially. Most of them are for chemical reaction. But we still can find numerous investigations in microsepration processes.

In this work, we used the crossflowing rupture technique to prepare monodisperse droplets in a T-junction microfluidic device, and successfully prepared monodisperse droplets ranged from 50 to 500 Ám with the polydispersity index (ˇ) values of less than 2%. Two kinds of flow patterns of plugs flow and drops flow in the T-junction microchannels could be formed. With the change of surfactant concentration, interfacial tension and wetting ability, the disordered or ordered two-phase flow patterns could be controllable. The increase of two phase flow rates and viscosity resulted in the decrease of the droplet size, and the droplet size was correlated with capillary number Ca.

Furthermore, a simple acid-base reaction was used to study the mass transfer performance of the micromixing process when the two-phase flow was in plugs and drops flow patterns respectively. The influences of two phase flow rates, acid and NaOH concentrations on the droplet size and mass transfer time were investigated. The results show that the mass transfer in the micromixing process can be finished from 0.1 s-5.0 s with the droplet size from 100Ám to 1000 Ám. Circulation within the slugs/drops and the Marangoni effects at two-phase interface provide enough enhancements to the mass transfer. Finally, a mathematical model is introduced to expect the enhancement of the reaction and mass transfer performance.

Key words: Micromixing, Monodisperse droplets, Microfluidic device, Mass transfer