Effect Of Wall Structure Of Microchannel On Motion Characteristics Of Gas-liquid Two-phase Flow With Non-newtonian Fluid

Microfluidic systems are widely used in the field of biology,chemistry and medicine.Non-Newtonian and gas-liquid two-phase flow in microchannel are often involved in above system.Special-shaped microchannels have significant influence on fluid motion characteristics.Therefore,the study on the influence of different wall structures of microchannels on fluid motion characteristics is particularly important for the design of microfluidic system.Based on nitrogen gas as gas phase,water and three different concentrations of sodium carboxymethyl cellulose(CMC)solution as liquid phase,single-phase flow and gas-liquid two phase flow experiment were conducted for non-Newtonian fluid in different structure size of serrated and corrugated wall within the microchannel.And the numerical simulation analysis of the gas liquid two phase flow movement characteristics in microchannel was also explored.The main content of the thesis is as follows.1.Water and CMC solutions with different concentrations were inserted into microchannels with different wall structures,and single-phase flow experiments were carried out at different flow rates.The pressure drop characteristics of single-phase flow in the special-shaped microchannels were measured by pressure sensors,and compared with the pressure drop characteristics of the plane wall microchannels.It is found that the greater the fluctuation of wall structure size,the greater the increase of the pressure drop.When the liquid phase is water,the pressure drop difference is small.For liquid phase of CMC solution,the solution concentration increases,the pressure drop difference gradually increases.Microchannel wall structure affects shear thinning characteristics of non-Newtonian fluids.Under the same working conditions,the larger the size fluctuation of microchannel structure is,the smaller the decreasing trend of pressure drop growth is,and the shear thinning phenomenon of CMC solution is weakened.2.Nitrogen,water and CMC solutions of different concentrations were injected into microchannels with different wall structures,and gas-liquid two-phase flow experiments were carried out at different gas-liquid flows.The pressure drop characteristics of gas-liquid two-phase flow in the special-shaped microchannels were measured by pressure sensors,and the movement trajectory of bubbles in the special-shaped microchannels was observed by high-speed cameras.It is found that the addition of gas phase increases the two-phase flow,and the pressure drop of two-phase flow is slightly greater than that of single-phase flow.The decreasing trend of pressure drop in plane wall microchannels is larger than that in special-shaped microchannels,which indicates that microchannel wall structure affect shear thinning of non-Newtonian fluids.3.With dimensionless analysis,the continuous phase Reynolds number of water is significantly larger than that of CMC solution,and the non-Newtonian fluid in the micro-channel is more affected by viscous force than water,so that the fluid is subjected to greater flow resistance,resulting in a larger pressure drop.In addition,the fluid disturbance will attenuate due to the increase of viscous force,making the bubble flow pattern stable.After modifying the prediction model of the pressure drop in the plane wall microchannel,the prediction model of the pressure drop in the special-shaped microchannel was obtained,and the errors of the prediction model method were all within 20%.4.Through the numerical simulation analysis based on computational fluid dynamics,it is found that in the micro-channels with special-shaped wall structure,the wall structure obstructs the bubble shape and fluid flow,which makes the pressure change more sharply,and the pressure tends to oscillate up and down in the downward trend.Because the wall structure of the special-shaped microchannel obstructs the flow of fluid,the distribution range of vortex flow in the flow field becomes larger.In the plane microchannel,vortex only appears at the head and tail of bubble,but in the special-shaped microchannel,vortex also appears when the liquid plug is blocked by the wall.However,when the liquid phase was0.3%CMC solution,a liquid film was generated in the bubble due to the large viscous force,and the bubble head became sharp,the vortex flow distribution decreased,and the streamline was relatively regular.