Non-Newtonian ow on bubble mattresses

In this research non-Newtonian flow over a microfluidic bubble mattress was studied. In a bubble mattress a liquid flows over an array of transverse micro gas bubbles. The research consists of a numerical modeling study and an experimental part using micro particle image velocimetry (muPIV). Since a bubble mattress consists of alternating bubbles and side channel walls, the fluid encounters an alternating pattern of no-shear and no-slip boundaries. The fluid used is a solution of Xanthan gum in a glycerol-water mixture, a fluid that can be characterized as a shear thinning fluid. The viscosity can be described with the Power-Law model. The model shows an increase of the effective slip length beff for low values of the protrusion angle of the bubbles , caused by the higher velocity of a shear thinning fluid at the gas-liquid interface which is a result of the specific velocity profile of a shear thinning fluid. A higher value of the porosity results in larger differences between the non-Newtonian fluid and the Newtonian fluid. The experimental studies were performed with a microfluidic device in which a bubble mattress could be established. The
velocity field was determined for different fluids for various values of the bubble angle. The differences in b_eff between the non-Newtonian fluid and Newtonian fluid were not significant, for which surfactants, elastic effects, inaccuracy in the obtained velocity near the wall and the time required for the flow to reach a developed flow profile can be possible causes.