Effects of shear rate and small periodic corrugation on the slip velocity in microscopic domain

We obtain analytically the slip velocity (up to the second order) of shear-thinning fluids inside the periodically corrugated microtube by using the verified fluid model and boundary perturbation method. Our results show that, even the slip length being zero, there is a slip velocity which is proportional to the small amplitude of periodic corrugation, the (referenced) shear rate, the applied forcing, and the orientation or the angle. Our results could be applied to the flow control in microfluidics as well as biofluidics.     

Mesoscopic simulations of electroosmotic flow and electrophoresis in nanochannels

We review recent dissipative particle dynamics (DPD) simulations of electrolyte flow in nanochannels. A method is presented by which the slip length δB at the channel boundaries can be tuned systematically from negative to infinity by introducing suitably adjusted wall-fluid friction forces. Using this method, we study electroosmotic flow (EOF) in nanochannels for varying surface slip conditions and fluids of different ionic strength. Analytic expressions for the flow profiles are derived from the Stokes equation, which are in good agreement with the numerical results. Finally, we investigate the influence of EOF on the effective mobility of polyelectrolytes in nanochannels. The relevant quantity characterizing the effect of slippage is found to be the dimensionless quantity κδB, where 1/κ is an effective electrostatic screening length at the channel boundaries.     

Modeling, analysis and design of centrifugal force-driven transient filling flow into a circular microchannel

Recently, centrifugal pumping has been regarded as an excellent alternative control method for fluid flow inside microchannels. In this paper, we have first developed the physical modeling and carried out the analysis for the centrifugal force-driven transient filling flow into a circular microchannel. Two types of analytic solutions for the transient flow were obtained: (1) pseudostatic approximate solution and (2) exact solution. Analytic solutions include expressions for flow front advancement, detailed velocity profile and pressure distribution. The obtained analytic results show that the filling flow driven by centrifugal force is affected by two dimensionless parameters which combine fluid properties, channel geometry and processing condition of rotational speed. Effects of inertia, viscous and centrifugal forces were also discussed based on the parametric study. Furthermore, we have also successfully provided a simple and convenient analytic design tool for such microchannels, demonstrating two design application examples.     

Boiling and two-phase flow in channels with extremely small dimensions: a review of Japanese research

Research concerning micro-actuators utilizing vapor–liquid interfacial phenomena has been carried out extensively to develop thermal devices applied to micromachines. On the other hand, the application of two-phase flow is useful for the removal of waste heat from the semiconductor chips with highly increased heat generation density to be integrated in notebook PCs. In the present paper, the latest Japanese research on boiling and two-phase flow in minichannels is reviewed, covering the topics for the fundamental phenomena and practical applications. Boiling in a narrow channel between parallel plates is an ideal system for the development of high-performance heat exchangers with extremely small sizes. The promising approaches to increasing the critical heat flux (CHF) are introduced, including those by the present author, to compensate for the disadvantages inherent in this system.     

Integrating scientific modeling and supporting dynamic hazard management with a GeoAgent-based representation of human–environment interactions: A drought example in Central Pennsylvania, USA

Recent natural disasters indicate that modern technologies for environmental monitoring, modeling, and forecasting are not well integrated with cross-level social responses in many hazard-management systems. This research addresses this problem through a Java-based multi-agent prototype system, GeoAgent-based Knowledge System (GeoAgentKS). This system allows: (1) computer representation of institutional regulations and behavioral rules used by multiple social institutions and individuals in cross-level human–environment interactions, (2) integration of this representation with scientific modeling of dynamic hazard development, and (3) application of automated reasoning that suggests to users the appropriate actions for supporting cooperative social responses. This paper demonstrates the software architecture of GeoAgentKS and presents such an integrated approach by modeling the drought management processes in Central Pennsylvania, USA. The results show that it is possible to use GeoAgentKS to represent multilevel human–environment interactions and to use those interactions as input to decision making in hazard management.     

Direct numerical simulations of transverse and spanwise magnetic field effects on turbulent flow in a 2:1 aspect ratio rectangular duct

Magnetic fields are used extensively to direct liquid metal flows in material processing. Continuous casting of steel uses different configurations of magnetic fields to optimize turbulent flows in rectangular cross-sections to minimize defects in the solidified steel product. Realizing the importance of a magnetic field on turbulent flows in rectangular cross-sections, the present work is aimed at understanding the effect of a magnetic field on the turbulent metal flow at a nominal bulk Reynolds number of ∼5300 (based upon full duct height) (Re_τ = 170, based upon half duct height) and Hartmann numbers (based upon half duct height) of 0, 6.0 and 8.25 in a 2:1 aspect ratio rectangular duct. Direct numerical simulations in a non-MHD 2:1 aspect ratio duct followed by simulations with transverse and span-wise magnetic fields have been performed with 224 × 120 × 512 cells (∼13.7 million cells). The fractional step method with second order space and time discretization schemes has been used to solve the coupled Navier-Stokes-MHD equations. Instantaneous and time-averaged natures of the flow have been examined through distribution of velocities, various turbulence parameters and budget terms. Spanwise (horizontal) magnetic field reorganizes and suppresses secondary flows more strongly. Turbulence suppression and velocity flattening effects are stronger with transverse (vertical) magnetic field.