Stability Of Flow In Microchannels Of Environmental Monitoring Chip

Environmental monitoring chip is becoming a hot research area for its outstanding advantages, such as accurate, economic, high efficient, fast response, et al. In this dissertation, the mean flow and its stability in microchannels of environmental monitoring chip is studied. The study is focused on the effects of microscale, such as the modifications of apparent viscosity and boundary slip, and viscous stratification on the stability of plane Poiseuille flow.The effects of apparent viscosity and boundary slip modifications on the stability of microchannel flow are discussed in the first part of this dissertation. Apparent viscosity is employed in the N-S equations while Navier boundary slip is adopted to predict flow stability. It is found out that the profile of mean velocity closing to wall appears inflexions and those results in reducing the critical Reynolds number and becomes smaller than the conventional one when considering the apparent viscosity. Conversely, the boundary slip makes mean flow fat and stabilizes the flow. It also shows that the effects of boundary slip are reduced sharply when the model parameters ( n andξ) of apparent viscosity become large. It means that the interaction between the close-wall molecules of liquid and those of wall is strong enough to resist boundary slip. The different materials of the wall boundary are studied. It is found that the microchannel with different slip length is easer to lose stability than that with same boundary slip length. The unstable area of critical wave number with different slip length is larger than that with the same slip length (the larger slip length).The stability of stratified flows is investigated in the second part of the dissertation. For the viscosity-stratified plane Poiseuille flow, the break interface model is proposed to simulate the structure of liquid-liquid interface. Adopting Navier boundary slip, the stability of stratified flow is studied by considering the four major factors, i.e. the ratio of viscosity, surface tension, gravity parameter, the location of interface. Numerical results show that the positions of the fluid interface and the ratio of viscosity have great impact on the stability of flow than the other factors. The critical Reynolds number is increased by same boundary slip and reduced by different boundary slip when comparing to the no boundary slip case. To distinguish with break interface model, single film model is mentioned which assumes that there is a thin film between two fluid interface layer film .The nature of fluid is continues in the film. The research content is almost same with break interface model.The Chebyshev Collocation method is adopted in all calculations. The numerical results lay a solid basis on the study of environmental monitoring chip.