Faster mass transfer in small channels: Understanding static mixing phenomena

Many processes have rates controlled by mass transfer. One example is ultrafiltration, an attractive process for water purification. In such processes, mass transfer in thin channels can often be enhanced with spacers, which accelerate mass transfer by serving as static mixers.; This thesis focuses on providing a better explanation of how these spacers function. Static mixing phenomena are studied for rigid and non-rigid spacers. Using electrochemical mass transfer experiments and CFD simulations, a model, which successfully predicts the rigid spacer performance, has been developed. This model shows how a new rigid spacer configuration can give four times better mass transfer than an empty channel.; This research also shows that further enhancements in mass transfer can be achieved by using non-rigid spacers. In small channels with these non-rigid spacers, different flow physics arise due to the interaction of stresses in the fluid and the solid giving rise to better mass transfer. Overall, a fivefold increase in the mass transfer can be secured by choosing the appropriate geometry and material of the spacer.