In this work, we have systematically analyzed the scaling law of droplet formation by cross-flow shear method in T-junction microfluidic devices. The droplet formation mechanisms can be distinguished by the capillary number for the continuous phase (Ca c ), which are the squeezing regime (Ca c \ 0.002), dripping regime (0.01 \ Ca c \ 0.3), and the transient regime (0.002 \ Ca c \ 0.01). Three corresponding correlations have been suggested in the different range of Ca c . In the dripping regime, we developed a modified capillary number for the continuous phase (Ca c 0 ) by considering the influence of growing droplet size on the continuous phase flow rate. And the modified model could predict droplet diameter more accurately. In the squeezing regime, the final plug length was contributed by the growth and 'squeeze' stages based on the observation of dynamic break-up process. In the transient regime, we firstly suggested a mathematical model by considering the influences of the above two mechanisms. The correlations should be very useful for the application of controlling droplet size in T-junction microfluidic devices.

In our previous work, a new flow route was developed-a so-called perpendicular shear force-induced droplet formation-in a self

This letter presents a simple way to prepare monodisperse O/W and W/O emulsions in the same T-junction microfluidic device just by changing the wetting properties of the microchannel wall with different surfactants. Highly uniform droplets ranging from 50 to 400 mum with a polydispersity index (sigma) value of less than 2% were successfully prepared. With the change in surfactants and surfactant concentrations, the interfacial tension and the wetting properties varied, and disordered or ordered two-phase flow patterns could be controllable. Monodisperse O/W and W/O emulsions were prepared under the action of a cross-flowing shear force or a perpendicular shear force by using an oil solution with 0.1-2.0 wt % Span 80 and an aqueous solution with 0.1-2.0 wt % Tween 20 as a continuous-phase flow, respectively. It gives a controllable method of preparing O/W and W/O emulsions in the same microfluidic device.

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This work focuses on the dispersion of micromonodispersed droplets and bubbles in the capillary embedded T-junction microfluidic devices. The effects of the microchannel structure, operating conditions, and physical properties on the dispersion rules were carefully investigated. It was found that the extended capillary could greatly affect the dispersion rules, which was favorable for reducing the dispersed size. The dispersed size was mainly dominated by the Ca number, and the effects of dispersed phase flow rate and viscosity ratio of the two phases were also very important. The dispersion mechanism and size rules in the capillary embedded microfluidic devices were discussed seriously by comparing the similarities and differences of the liquid/ liquid and gas/liquid dispersion processes. V V C 2010 American Institute of Chemical Engineers AIChE J, 57: [299][300][301][302][303][304][305][306] 2011

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Our purpose is to simulate the airflow inside the healthy Chinese nose with normal nasal structure and function by computational fluid dynamics (CFD) method and to analyze the relationship between the airflow and physiological function. In this study, we used the software MIMICS 13.0 to construct 20 3-dimensional (3-D) models based on the computer tomography scans of Chinese adults' nose with normal nasal structure and function. Thereafter, numerical simulations were carried out using the software FLUENT 6.3. Then the characteristics of airflow inside the airway and sinuses were demonstrated qualitatively and quantitatively in steady state. We found that during the inhalation phase, the vortices and turbulences were located at anterior part and bottom of the nasal cavity. But there is no vortex in the whole nasal cavity during the expiratory phase. The distributions of pressure and wall shear stress are different in two phases. The maximum airflow velocity occurs around the plane of palatine velum during both inspiratory and expiratory phases. After the airflow passed the nasal valve, the peak velocity of inhaled airflow decreases and it increases again at the postnaris. Vice versa, the exhaled airflow decelerates after it passed the postnaris and it accelerates again at nasal valve. The data collected in this presentation validates the effectiveness of CFD simulation in the study of airflow in the nasal cavity. Nasal airflow is closely related to the structure and physiological functions of the nasal cavity. CFD may thus also be used to study nasal airflow changes resulting from abnormal nasal structure and nasal diseases.

Unlike airflow in the controls, airflow in the septal deviation models showed asymmetry in bilateral nasal cavities. The airflow patterns varied in the convex and concave sides in different septal deviation models. Caudal septal deviation models had the maximal peak velocity, while the the minimal peak velocity was found in the media deviation models. The peak velocity was not always located in the convex side, but was sometimes in the concave side.