Biomedical subjects

Hsien-Hung Wei

Publications and source records attributed to Hsien-Hung Wei.

4 recordsLinked to original sources

PubMed2005

Stability of a viscoelastic falling film with surfactant subjected to an interfacial shear.

The long-wavelength stability is analyzed for a surfactant-laden, viscoelastic liquid flowing down an inclined plane when the liquid undergoes additional interfacial shear. The upper convected Maxwell model is employed for describing the elastic nature of the fluid. The system stability is characterized by the interface and the surfactant modes. The interface mode involves both elastic and Marangoni effects that modulate the stability with applied shears and gravity-driven flow. The surfactant mode is only determined by the shear-induced Marangoni effects. A phase diagram is established to identify the dominant mode and the overall features of instability. It reveals that the system is susceptible to instability, except in a stable window when the applied shear opposes the gravity-driven flow.

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PubMed2005

Linear stability of a surfactant-laden annular film in a time-periodic pressure-driven flow through a capillary.

This paper analyzes the effect of surfactant on the linear stability of an annular film in a capillary undergoing a time-periodic pressure gradient force. The annular film is thin compared to the radius of the tube. An asymptotic analysis yields a coupled set of equations with time-periodic coefficients for the perturbed fluid-fluid interface and the interfacial surfactant concentration. Wei and Rumschitzki (submitted for publication) previously showed that the interaction between a surfactant and a steady base flow could induce a more severe instability than a stationary base state. The present work demonstrates that time-periodic base flows can modify the features of the steady-flow-based instability, depending on surface tension, surfactant activity, and oscillatory frequency. For an oscillatory base flow (with zero mean), the growth rate decreases monotonically as the frequency increases. In the low-frequency limit, the growth rate approaches a maximum corresponding to the growth rate of a steady base flow having the same amplitude. In the high-frequency limit, the growth rate reaches a minimum corresponding to the growth rate in the limit of a stationary base state. The underlying mechanisms are explained in detail, and extension to other time-periodic forms is further exploited.

Journal Article↗

PubMed2005

Shear-modulated electroosmotic flow on a patterned charged surface.

The effect of imposing shear flow on a charge-modulated electroosmotic flow is theoretically investigated. The flow structures exhibit either saddle points or closed streamlines, depending on the relative strength of an imposed shear to the applied electric field. The formation of closed streamlines could be advantageous for trapping nondiffusive particles at desired locations. Different time periodic alternating flows and their corresponding particle trajectories are also examined to assess strategies for creating efficient mixing.

Journal Article↗

PubMed2003

Reversible switching of high-speed air-liquid two-phase flows using electrowetting-assisted flow-pattern change.

This work is the first demonstration of electrical modulation of surface energy to reversibly switch dynamic high-speed gas-liquid two-phase microfluidic flow patterns. Manipulation of dynamic two-phase systems with continuous high-speed flows is complex and interesting due to the multiple types of forces that need to be considered. Here, distinct stable flow patterns are formed through a multipronged approach: both surface tension forces generated by surface chemistry modulation as well as viscous and inertial forces produced by fluid flows are employed. The novel fluidic actuation mechanism provides insights into better understanding microscale two-phase flow dynamics and offers new opportunities for the development of two-phase biochemical microsystems that are mechanically simple and operational at high speeds.

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