Direct matching between the flow factor approach model and molecular dynamics simulation for nanochannel flows

Mathematically formulating nanochannel flows is challenging. Here, the values of the characteristic parameters were extracted from molecular dynamics simulation (MDS), and directly input to the closed-form explicit flow factor approach model (FFAM) for nanochannel flows. By this way, the physical nature of the simulated system in FFAM is the same with that in MDS. Two nano slit channel heights respectively with two different liquid-channel wall interactions were addressed. The flow velocity profiles across the channel height respectively calculated from MDS and FFAM were compared. By introducing the equivalent value $${{\Delta_{im} } \mathord{\left/ {\vphantom {{\Delta_{im} } D}} \right. \kern-\nulldelimiterspace} D}$$ Δ im / D , FFAM fairly agrees with MDS for all the cases. The study values FFAM in simulating nanochannel flows.

Microvalve with Trapezoid-Shaped Cross-Section for Deep Microchannels

Simple microfluidic systems for handling large particles such as three-dimensional (3D) cultured cells, microcapsules, and animalcules have contributed to the advancement of biology. However, obtaining a highly integrated microfluidic device for handling large particles is difficult because there are no suitable microvalves for deep microchannels. Therefore, this study proposes a microvalve with a trapezoid-shaped cross-section to close a deep microchannel. The proposed microvalve can close a 350 μm deep microchannel, which is suitable for handling hundreds of micrometer-scale particles. A double-inclined lithography process was used to fabricate the trapezoid-shaped cross-section. The microvalve was fabricated by bonding three polydimethylsiloxane layers: a trapezoid-shaped liquid channel layer, a membrane, and a pneumatic channel layer. The pneumatic balloon, consisting of the membrane and the pneumatic channel, was located beneath a trapezoid-shaped cross-section microchannel. The valve was operated by the application of pneumatic pressure to the pneumatic channel. We experimentally confirmed that the expansion of the pneumatic balloon could close the 350 μm deep microchannel.

Fingertip-Sized Pressure Sensor for Luer Taper of Three-Way Stopcock in Liquid Channel

We developed an easily attachable fingertip-sized pressure sensor (FSPS) for a three-way stopcock in a liquid channel of a heart–lung machine. The FSPS has a double-pipe structure with a semispherical soft film cap on the pointed end and a diaphragm semiconductor strain sensor on the other end. An enclosed space of variable volume covered with the soft film cap prevents the semiconductor strain sensor from coming into direct contact with blood, and the double-pipe structure decreases the strain on the strain sensor when inserting the FSPS into the female-fitting part of the luer taper. It is difficult to fabricate a very fine double-pipe structure by cutting or injection molding. Instead, we fabricated it by using a three-dimensional (3D) printer. Moreover, it is difficult to fabricate a semispherical soft film cap with a 3D printer, so we fabricated it with a resin casting method using silicone resin. Experiments on the FSPS using a variable pressure liquid channel showed that it is not affected by inserting it into the female-fitting part of the luer taper and that it can accurately measure pressure in a liquid channel within a pressure range from 0 to 100 kPa.

Thermodynamic Assessment of Mushy Zone in Directional Solidification

Solidification of AlSiFe alloys was studied using a directional solidification facility and the CALPHAD technique was applied to calculate phase diagrams and to predict occurring phases. The specimens solidified by electromagnetic stirring showed segregation across, and the measured chemical compositions were transferred into phase diagrams. The ternary phase diagrams presented different solidification paths caused by segregation in each selected specimen. The property diagrams showed modification in the sequence and precipitation temperature of the phases. It is proposed in the study to use thermodynamic calculations with Thermo-Calc which enables us to visualize the mushy zone in directional solidification. 2D maps based on property diagrams show a mushy zone with a liquid channel in the AlSi7Fe1.0 specimen center, where significant mass fraction (33%) of β-Al5FeSi phases may precipitate before α-Al dendrites form. Otherwise liquid channel occurred almost empty of β in AlSi7Fe0.5 specimen and completely without β in AlSi9Fe0.2. The property diagrams revealed also possible formation of α-Al8Fe2Si phases.