Fluids microfluidics

Barisik M, Beskok A (2011) Equilibrium molecular dynamics studies on nanoscale confined fluids. Microfluid Nanofluid. doi 10.1007/sl0404-011-0794-5... 

While active particle d)mamics can address the motion of any suspended particle in a fluid, microfluidic researchers are usually interested in pol)mer chains because these structures in general do not follow the fluid flow, have a high degree of flexibility, and model important biological subsystems such as DNA and many types of proteins. If we want to track or manipulate different polymer chains in... 

Kang, Y.J., Yang, S., 2013. Integrated microfluidic viscometer equipped with fluid temperature controller for measurement of viscosity in complex fluids. Microfluid. Nanofluid. 14 (3 ), 657-668. Available at http //link.springer.eom/10.1007/sl0404-012-1085-5. 

The Navier-Stokes equation and the enthalpy equation are coupled in a complex way even in the case of incompressible fluids, since in general the viscosity is a function of temperature. There are, however, many situations in which such interdependencies can be neglected. As an example, the temperature variation in a microfluidic system might be so small that the viscosity can be assumed to be constant. In such cases the velocity field can be determined independently from the temperature field. When inserting the computed velocity field into Eq. (77) and expressing the energy density e by the temperature T, a linear equahon in T is... 

In chemical micro process technology there is a clear dominance of pressure-driven flows over alternative mechanisms for fluid transport However, any kind of supplementary mechanism allowing promotion of mixing is a useful addition to the toolbox of chemical engineering. Also in conventional process technology, actuation of the fluids by external sources has proven successful for process intensification. An example is mass transfer enhancement by ultrasonic fields which is utilized in sonochemical reactors [143], There exist a number of microfluidic principles to promote mixing which rely on input of various forms of energy into the fluid. 

The constraint to be implemented at the three-phase contact line between the two fluids and a solid surface requires that the contact angle 0 (compare Figure 2.58) assumes a prescribed value. As discussed in Section 2.2.3, the contact angle might also be allowed to vary with the velocity of the contact line. Especially in microfluidic... 

Miniaturized fluid handling devices have recently attracted considerable interest and gained importance in many areas of analytical chemistry and the biological sciences [50], Such microfluidic chips perform a variety of functions, ranging from analysis of biological macromolecules [51, 52] to catalysis of reactions and sensing in the gas phase [53, 54], They commonly consist of channels, valves and reaction... 

Fig. 2.6.10 Specialized experimental set-up for microfluidic flow dispersion measurements. Fluid is supplied from the top, flows via a capillary through the microfluidic device to be profiled and exits at the bottom. The whole apparatus is inserted into the bore of a superconducting magnet. Spatial information is encoded by MRI techniques, using rf and imaging gradient coils that surround the microfluidic device. They are symbolized by the hollow cylinder in the figure. After the fluid has exited the device, it is led through a capillary to a microcoil, which is used to read the encoded information in a time-resolved manner. The flow rate is controlled by a laboratory-built flow controller at the outlet [59, 60].

A knowledge of v can give an indication of the transit time of a plug of chemical or an ensemble of cells through a microfluidic channel network and thus to assess whether there is enough time for complete mixing or chemical reaction. Both Eq. (11) and Eq. (12) are strictly only valid under idealized conditions (i.e. incompressible and non-viscous fluids and steady flow), but can still be helpful for overall estimation and assessment. 

FIGURE 11.32 Flow profiles in microchannels, (a) A pressure gradient, - AP, along a channel generates a parabolic or Poiseuille flow profile in the channel. The velocity of the flow varies across the entire cross-sectional area of the channel. On the right is an experimental measurement of the distortion of a volume of fluid in a Poiseuille flow. The frames show the state of the volume of fluid 0, 66, and 165 ms after the creation of a fluorescent molecule, (b) In electroosmotic flow in a channel, motion is induced by an applied electric field E. The flow speed only varies within the so-called Debye screening layer, of thickness D. On the right is an experimental measurement of the distortion of a volume of fluid in an electroosmotic flow. The frames show the state of the fluorescent volume of fluid 0, 66, and 165 ms after the creation of a fluorescent molecule [165], Source http //www.niherst.gov.tt/scipop/sci-bits/microfluidics.htm (see Plate 12 for color version). 

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