| The flow in micro-scale is the essence of micro-fluidic system,which is related to the realization of specific functions of micro-fluidic system.The cases involved in chemical and biomedical fields are mainly non-Newtonian fluids and two-phase flow.Therefore,in this paper,the influences of the non-Newtonian characteristics of liquid in microchannels on the flow characteristics of gas-liquid two-phase flow are conducted.The main research contents are as follows.1.The viscosity characteristics of polyacrylamide(PAM)solutions with three concentrations were evaluated,and the Ostwald-de wale power law equation was substituted to express the rheological properties of PAM solution.Combined with the viscosity equation of the PAM solution,the dimensionless parameters that affect the fluid:motion characteristics in the microchannel are modified to provide the basis for theoretical analysis.2.A high-speed camera system was used to observe the formation of bubble in nitrogen/PAM solutions with different concentrations in a T-shaped microchannel,focusing on the analysis of the effects of flow rate,gas-liquid flow rate ratio and dimensionless parameters on bubble dynamics.Three types of flow patterns were observed in T-shaped microchannel,namely insertion flow,slug flow and bullet-plug flow.The gas-liquid flow rate ratio increased,the size of bubble increased,and the void fraction increased.The movement velocity of bubble increases,the void fraction increases.With the increase of Reynolds number,Capillary number and Weber number,the length of the bubble shows a power-law downward trend.Accordingly,the prediction equation for bubble length is established.3.The pressure drop of the two-phase flow in the microchannel was measured.The influence of the gas-liquid flow rate ratio and the solution concentration on the pressure drop was analyzed.The results indicate that the pressure drops after the system pressure drop stabilized were larger with larger flow velocity.The large the concentration of the PAM solution,the large the pressure drop after the system pressure drop stabilized.With flow speed increasing,the difference affected by concentration becomes more obvious.Friction pressure drop in two phase laminar flow was calculated by separated model.The separated flow model is used to calculate the friction pressure drop of the laminar two-phase flow.The pressure drop calculated by the established pressure drop model is slightly smaller than the experimental value.4.Computational fluid dynamics is used to numerically simulate the motion characteristics of the gas-liquid two-phase flow in the microchannel.The results show that the flow pattern is the same as the flow pattern photographed in the experiment.The pressure drops are slightly higher than those of experimental result.The maximum flow velocity occurs before the formation of bubble,where it contacts the wall of the nitrogen,and the polyacrylamide solution above the nitrogen is located throughout the slowest part of the system. |
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