In this paper, we describe the development of a microfluidic centrifuge with two inlets and two outlets potentially capable of rapidly separating nanoparticles and nanovesicles. Compared with the microfluidic centrifuge with a single inlet and outlet, the 2 ×2 microfluidic centrifuge gives improved centrifugation performance by increasing momentum flux transfer, angular velocity, and centrifugal acceleration. The center of flow rotation and the symmetry of the horizontal velocity in the microchamber were examined numerically. On the basis of the determined maximum velocity, the angular velocity and centrifugal acceleration were also evaluated. The centrifugation time of three different nanoparticles was examined by calculating the time when the nanoparticles left the microchamber for the first time. For visual observation and quantitative measurement of nanoparticle centrifugation, a 2 ×2 microfluidic centrifuge was fabricated and the experimental results demonstrate similar physical behavior to those of a mechanical centrifuge. On the basis of a comparison of the centrifugation time of two different nanoparticle populations of 300 and 700 nm in diameter, we propose that nanoparticles of different sizes can be physically separated by time under a range of inlet volume flow rates.
The size-selective microfluidic separation of glass beads in a curved rectangular microchannel was fabricated in our previous work. In this study, we improve its separation performance and attempt an experimental visualization to examine the separation resolution. In the previous work, we found by visualization that the trajectory of 20 µm glass beads was influenced by their travelling path along a straight inlet channel. Using a forced sheath flow, a consistent bead trajectory along the middle of the straight inlet channel was obtained, and the sheath angle to minimize the focusing width of the flowing distributed beads was determined to be 45°. The physical explanation for the dynamic behavior of microbeads was elaborated. When the ratio of Stokes force to centrifugal force mainly acting on a glass bead fell under unity, the glass bead moved out to the wall in spite of the fact that its size was less than the height of the zero velocity position. To examine the separation resolution, the newly designed size-selective separation microchannel with the sheath was fabricated and its separation performance was visualized. The movement of the glass beads showed a good agreement with the separation mechanism explained by the force ratio. The resolution of the separation was visualized to be 10 µm for the size of glass beads used in the experiment. The size-selective separation performance was explained in terms of physical forces and was improved by solving the previous problems. A cascade device for the continuous separation of microbeads of various sizes can improve the separation resolution.
A new thermography system with high time resolution was put into operation at ASDEX-Upgrade and is routinely used to determine the energy flux onto the lower diverter plates. The measurements allow the power deposition to be chamcterized during dynamic events such as ELMS and disruptions, as well as the asymmetry of the inboardloutboard power load. A power balance is set up even during single discharges and the losses are found to be fairly equal to the power input.
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