Abstract Numerical studies have been performed to analyze the fluid flow and heat transfer characteristics of nine microchannel heat sinks (MCHS) with different shapes and different arrangements of the ribs and cavities on the sidewalls, using three common shapes (square, triangle, and circular) of ribs or cavities as the basic structure in this work. The boundary conditions, governing equations, friction factor ( f ), Nusselt number (Nu), and performance evaluation criteria ( ξ ) were considered to determine which design was the best in terms of the heat transfer, the pressure drop, and the overall performance. It was observed that no matter how the circular ribs or cavities were arranged, its heat sink performance was better than the other two shapes for Reynolds number of 200–1000. Therefore, circular ribs or cavities can be considered as the best structure to improve the performance of MCHS. In addition, the heat sink performance of the microchannel heat sink with symmetrical circular ribs (MCHS-SCR) was improved by 31.2 % compared with the conventional microchannel heat sink at Re = 667. This was because in addition to the formation of transverse vortices in the channel, four symmetrical and reverse longitudinal vortices are formed to improve the mixing efficiency of the central fluid (low temperature) and the near-wall fluid (high temperature). Then, as the Reynolds number increases, the heat sink performance of MCHS-SCR dropped sharply. The heat sink performance of microchannel heat sinks with staggered ribs and cavities (MCHS-SCRC, MCHS-STRC, and MCHS-SSRC) exceeded that of MCHS-SCR. This indicated that the microchannel heat sink with staggered ribs and cavities was more suitable for high Reynolds number (Re > 800).
Abstract This paper reports a simple and rapid method for fabrication of microfluidic chips on polymethylmethacrylate (PMMA) substrate using a flexible and low-cost CO 2 laser system. The CO 2 laser employed has a wavelength of 10.6 μm. The laser power used for channel fabrication ranged from 3 and 12 W, the beam travel speeds ranged from 5 to 50 mm/s and the passes were varied in the range of 1 to 3 times. Typical channel depths were between 100 and 900 μm, while the width of fabricated channels ranged from 100 to 300 μm. The effects of the process parameters (the laser power, the beam travel speed of the laser beam and the number of passes) on the dimensional quality (the depth, the width and their aspect ratio) of the microchannel manufactured from PMMA were experimentally investigated. The change law of the channel geometry depending on process parameters was obtained. A high reproducibility of micro-channel geometry was attained. At last, a CO 2 laser output power of 5.5 W and a laser beam travel speed of 35 mm/s combining a hot press bonding technique were chosen to fabricate a microfluidic chip within half hour. The pattern qualities and experimental results confirm that the CO 2 laser micromachining technology has a great potential for application in flexible, rapid and economic production of polymeric microfluidic chips.
Abstract With the aim to optimize design, a simulation in system level has been presented for the square-wave micromixer in this article. The square-wave micromixer is divided into straight channels and square-wave units. The reduced-order model based on proper orthogonal decomposition is applied in calculating concentration of the sample in the straight channels, and numerical simulation is applied in calculating concentration of the sample in the square-wave units. The data can mutually be transferred between straight channels and square-wave units by data fitting and interpolation. The maximal relative deviation is 1.52% between simulation in system-level and only simulation. The computational efficiency will be improved significantly with the numbers of straight channels increasing. The Polymethyl methacrylate (PMMA) micromixer is fabricated with mill and hot bonding method. The mixing experiment of fluorescein sodium solution with different concentrations is carried out to verify simulation. The relative deviations between simulation in and experimental results are below 8.26%.
Abstract Microfluidic mixing is an essential part of the process of microfluidic chip technology in the analysis, and micromixer has also become the key components of microfluidic chip analysis system. For DNA hybridization, protein folding and enzyme reaction, some biochemical processes need to react quickly to achieve on analysis and research has the vital significance. A simple, rapid and low-cost passive micromixer is presented in this paper. In order to improve the mixing efficiency of the species, the concept of a splitting and recombination (SAR) was used to shorten the mixing time of the species. This study simulated the species mixing in a micromixer with traditional T-type micromixer and diamond-like micropillar in laminar flow state through COMSOL multiphysics 3.5a to computational fluid dynamics (CFD). Linking artificial neural network (ANN) and CFD was used to optimize the diamond-like micropillar. Finally, simulation results proved that the micromixer with SAR diamond-like concept achieves a high-efficiency mixing than T-type micromixer. Numerical results also show that the mixing efficiency of the SAR micromixer with diamond-like micropillar can be up to 99 %, and that efficiency can reach rapidly 90 % in a short channel distance.
A 'point-to-line' architecture and a strong chemical bonding strategy is developedThe sensor exhibits high sensitivity and ultra-broad linearity range An overall classification rate of 98.61% on six human actions is achieved The high-performance pressure sensor shows the merit of antibacterial
In this paper, the microflown with SHS configuration is analyzed by numerical simulation. Compared to conventional acoustic sensors, microflown measures the particle velocity rather than the sound pressure. It has three resistors, two outermost resistors of which are used as sensors, while the resistor located in the middle is used as a heater. As air flows across the sensor, upstream resistor cools down and gives off some heat to the passing air. Hence, downstream resistors lose less heat because the warmer air passes through. The temperature difference can be calculated and analyzed by assuming the ideal circuit structure for the microflown with SHS configuration, respectively.
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