Stochastic Model And Detection Method Of Two–phase Flow Through Parallel Microchannels

Reactor miniaturization is one of the main research topics of reaction engineering.The fundamental strategy for microreactor approaching commercial practice is numbering-up,which definitely faces great challenge in uniformly distributing fluids in every channel,especially for multiphase systems.Fluidic erratic behavior due to nonlinearity of multiphase and crosstalk between channels under capillary domination substitutes for duplicating the same outcome through channels.Consequently we focused on modeling description and operational stability of fluids in heterogeneous microchannels in parallel,the main contents are as follows:Firstly,uniformity of slug flow in multiple microchannels,defined as homogeneity of emerging bubbles,was quantitatively measured,simulated and described in two parallel microchannels,each one of 500 ?m width,500 ?m depth and 50 mm length interconnected with two dichotomic distributors for gas and liquid phases,respectively.The experimental results showed that increasing gas or liquid velocity would narrow the distributions of length and frequency of bubbles in each microchannel but worsen the uniformity between microchannels.Interaction between dual channels was investigated by analyzing pressure differences at distributors.At low flow rates input,hysteresis of compensation between microchannels worsened the unformity in every channel,retraction of gas head was captured by a CCD camera and its disturbance to bubble producing was reduced with increase of phase velocity.The structure of millipede paralleled microchannels was optimized,it was found that increaseing the falling step when droplets is forming will produce homogeneous drop size,even with high viscous oil.Secondly,a home-made multi-point optical detection system for fluids distribution in parallelized microchannels was constructed,providing reasonable sampling for stochastic models and stability analysis.The system is able to capure for long term,a program could calculate length,frequency and velocity of passing by bubbles and liquid slugs acculately,and then arrange them in actual sequence.Thirdly,A model of stochastic differential equations(SDEs)was proposed based on the experimental data recorded by the long–term optical measurement to well quantify the stochastic trajectories of gas bubbles and liquid slugs in parallel microchannels interconnected with two dichotomic distributors.The expectation and variance of each subflow rate are derived explicitly from the SDEs associated with the Fokker–Planck equation and solved numerically.A bifurcation in the trajectory is found using the original model,then a modification on interactions of feedback and crosstalk is introduced,the evolutions of subflow rates calculated by the modified model match well with experimental results.Fourthly,bubble appearance frequency,characterizing channels performance,was measured in hierarchical and bifurcated microchannel networks by a long–term optical measurement,and time series were processed to evaluate the parametric sensitivity of flow rates,channel number,as well as arrangement to operating robustness.Chaotic behavior was verified experimentally by calculating the largest Lyapunov exponent,a transition to chaos occurs intermittently at first and then grew evidently with increasing of flow rate or channel number.Fractal dimension was introduced to evaluate geometrical placements to correlation,a generalized criterion was built to distinguish the transition to chaos by which a feasible predictable operating zone was selected.Models combinated from Logistic equation and species competition equation were chosen to discribe the trend of crosstalk between parallelized microchannels,which match well with experiment.Fifthly,a method to detect low–abundance mutant KRAS in both cell level and gene level was tested.Mixing experiment of mutation and wild type KRAS was designed,in which only mutation was amplified by adding PNA and labeled with fluorescence.Microfluidic chips involved in processes of making drop,encapsulation and pico injection were made.