Bulletin of the American Physical Society
77th Annual Meeting of the Southeastern Section of the APS
Volume 55, Number 10
Wednesday–Saturday, October 20–23, 2010; Baton Rouge, Louisiana
Session JA: Microfluidics: Computational and Experimental Challenges |
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Chair: Michael Martin, Louisiana State University Room: Nicholson Hall 119 |
Friday, October 22, 2010 3:45PM - 4:15PM |
JA.00001: Counter-flow Microfluidics for Stable Flow Thermodynamics Invited Speaker: Microfluidic thermal reactors are able to achieve high temperature ramping rates due to their low thermal mass. Of these, the most thermodynamically efficient are flow systems that rely on a steady-state temperature distribution to induce temperature change of the moving fluid. Rather than inserting or extracting heat at controlled time intervals, the fluids are heated and cooled only through local heat transfer with the substrate material in which the microchannels are embedded. In addition to accelerated ramping and reduced energy consumption, such systems have the potential to provide greater control of the heating rates. This is because the temperature change is simply a function of the fluid velocity vector with respect to the stable temperature distribution within the material. However, the operation of such a system is complicated by the thermal perturbation that the fluid flow introduces into the system. When predicting the temperature change of the fluid, it is common to ignore the effect of the fluid flow on the original temperature distribution within the substrate. However, this has been shown to be the dominant behavior in many scenarios. This behavior is particularly problematic in polymeric microfluidic devices, where thermal conductivities are on the order of 0.2 W/m-K. This presentation will address a powerful solution to this thermal instability. By implementing a counter-flow microfluidic geometry, it will be shown how the temperature smearing common to microflow thermal reactors can be virtually eliminated. The deleterious effect of the insulative properties of popular polymer substrates is minimized, allowing for higher flow rates and temperature ramp rates. This is achieved by creating a preferred heat path for the thermal energy that is being driven into or out of the fluid during flow. Theory will be presented; experimental data will be discussed; application to lab-on-a-chip systems will be demonstrated. [Preview Abstract] |
Friday, October 22, 2010 4:15PM - 4:45PM |
JA.00002: Quantized Concentration Gradient in Picoliter Scale Invited Speaker: Generation of concentration gradient is of paramount importance in the success of reactions for cell biology, molecular biology, biochemistry, drug-discovery, chemotaxis, cell culture, biomaterials synthesis, and tissue engineering. In conventional method of conducting reactions, the concentration gradients is achieved by using pipettes, test tubes, 96-well assay plates, and robotic systems. Conventional methods require milliliter or microliter volumes of samples for typical experiments with multiple and sequential reactions. It is a challenge to carry out experiments with precious samples that have strict limitations with the amount of samples or the price to pay for the amount. In order to overcome this challenge faced by the conventional methods, fluidic devices with micrometer scale channels have been developed. These devices, however, cause restrictions on changing the concentration due to the fixed gradient set based on fixed fluidic channels.\footnote{Jambovane, S.; Duin, E. C.; Kim, S-K.; Hong, J. W., Determination of Kinetic Parameters, $K_{M}$ and $k_{cat}$, with a Single Experiment on a Chip. textit{Analytical Chemistry, }81, (9), 3239-3245, 2009.}$^,$\footnote{Jambovane, S.; Hong, J. W., Lorenz-like Chatotic System on a Chip In \textit{The 14th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS)}, The Netherlands, October, 2010.} Here, we present a unique microfluidic system that can generate quantized concentration gradient by using series of droplets generated by a mechanical valve based injection method.\footnote{Jambovane, S.; Rho, H.; Hong, J., Fluidic Circuit based Predictive Model of Microdroplet Generation through Mechanical Cutting. In \textit{ASME International Mechanical Engineering Congress {\&} Exposition}, Lake Buena Vista, Florida, USA, October, 2009.}$^,$\footnote{Lee, W.; Jambovane, S.; Kim, D.; Hong, J., Predictive Model on Micro Droplet Generation through Mechanical Cutting. \textit{Microfluidics and Nanofluidics, }7, (3), 431-438, 2009.} \textbf{Acknowledgement:} All this work has been done by Sachin Jambovane, Kirn Cramer, Woon Seob Lee, and Hoon Suk Rho. The presenter would like to thank them. [Preview Abstract] |
Friday, October 22, 2010 4:45PM - 5:15PM |
JA.00003: Multiphase flow modeling: A tool to aid in scale up of processes Invited Speaker: Multiphase flows are ubiquitous in chemical processing industries. Traditional approach has been to ignore fluid dynamical effects by invoking simplifying assumptions of homogeneity, but pay the price during scale-up of processes. The question that I address is ``Can Multiphase flow modeling come to our rescue in minimizing the need for pilot scale experiments?'' On the fundamental side, we have developed algorithms for direct numerical simulation of multiphase flows. For dispersed rigid particles as in suspension flows, sedimentation etc, we couple the Navier-Stokes equations with the rigid body dynamics in a rigorous fashion to track the particle motion in a fluid. For deformable bubbles/droplets dispersed in another fluid, we also track their motion in an Eulerian grid. The two classes of algorithms show great promise in attempting direct simulation of multiphase flows, from which we can extract statistically meaningful average behavior of suspensions or bubbly flows. On the other hand, there is an immediate need to study flow of complex fluids of industrial importance. Such cases include polymer blending processes, erosion in pipelines and process vessels and mass transfer in packed beds. In such studies we use volume averaged equations as the basis of flow models coupled with experimental validation of such predictions in an effort to develop scale invariant closure models that are needed as part of the volume averaged flow models. [Preview Abstract] |
Friday, October 22, 2010 5:15PM - 5:45PM |
JA.00004: $\mu -$PIV/Shadowgraphy measurements to elucidate dynamic physicochemical interactions in a multiphase model of pulmonary airway reopening Invited Speaker: We employ micro-particle image velocimetry ($\mu $-PIV) and shadowgraphy to measure the ensemble-averaged fluid-phase velocity field and interfacial geometry during pulsatile bubble propagation that includes a reverse-flow phase under influence of exogenous lung surfactant (Infasurf). Disease states such as respiratory distress syndrome (RDS) are characterized by insufficient pulmonary surfactant concentrations that enhance airway occlusion and collapse. Subsequent airway reopening, driven by mechanical ventilation, may generate damaging stresses that cause ventilator-induced lung injury (VILI). It is hypothesized that reverse flow may enhance surfactant uptake and protect the lung from VILI. The microscale observations conducted in this study will provide us with a significant understanding of dynamic physicochemical interactions that can be manipulated to reduce the magnitude of this damaging mechanical stimulus during airway reopening. Bubble propagation through a liquid-occluded fused glass capillary tube is controlled by linear-motor-driven syringe pumps that provide mean and sinusoidal velocity components. A translating microscope stage mechanically subtracts the mean velocity of the bubble tip in order to hold the progressing bubble tip in the microscope field of view. To optimize the signal-to-noise ratio near the bubble tip, $\mu $-PIV and shadow images are recorded in separate trials then combined during post-processing with help of a custom-designed micro scale marker. Non-specific binding of Infasurf proteins to the channel wall is controlled by oxidation and chemical treatment of the glass surface. The colloidal stability and dynamic/static surface properties of the Infasurf-PIV particle solution are carefully adjusted based on Langmuir trough measurements. The Finite Time Lyapunov Exponent (FTLE) is computed to provide a Lagrangian perspective for comparison with our boundary element predictions. [Preview Abstract] |
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