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مشخص کردن احتراق گاز سنتز پیش مخلوط در کانال های میکرو
Characterizing Premixed Syngas Combustion in Micro-Channels
Increasing demands in the next-generation portable power-generation devices such as unmanned aerial vehicles (UAV), microsatellite thrusters, micro-chemical reactors and sensors calls for fuels with high specific energy and low emissions to meet the current demand of green energy. Fuel-lean synthesis gas (syngas) meets both these requirements exhibiting a promising route to a clean and green environment. Thus, it is of critical importance to characterize syngas combustion and understand its properties in the micro-combustion industry. In addition to complicated flame dynamics in microscale systems, varying the syngas-fuel mixture composition as well as the boundary conditions and geometry of a combustor significantly affect the burning process in the system. This work investigates the characteristics of a premixed syngas flame in a horizontal two-dimensional micro-channel of length 20 mm and half-width 1 mm by means of computational simulations using the ANSYS Fluent commercial software. A fixed temperature gradient is employed at the upper wall such that the temperature grows linearly, from 300 K at the inlet to 1500 K at the outlet to account for the conjugate heat transfer. The chemical kinetics of the combustion process is imitated by the San Diego mechanism with 46 species and 235 reactions, which is implemented using the Chemkin mechanism in ANSYS Fluent. Stoichiometric premixed burning of syngas comprised of carbon monoxide (CO), methane (CH<sub>4</sub>) and hydrogen (H<sub>2</sub>), with various compositions and inlet fuel-air flow velocities, is considered. Various properties of the combustion process such as ignition, stabilization and extinction are characterized. It is further shown how instabilities can be eliminated by increasing the inlet flow velocity to form a stable, stationary flame. As a result, it is demonstrated how various combustion characteristics depend on the inlet velocity and composition of a syngas mixture.
میکرومیکسرهای غیرفعال برای آنالیز DNA با استفاده از مدل سازی CFD
Passive Micromixers for DNA Analysis Using CFD Modelling
Mixing efficiency is an important issue in the design of micromixers, since effective mixing is required between Deoxyribonucleic acid (DNA) sample and restriction enzyme for a fast digestion process. Mixing is improved by chaotic advection through serpentine mixing channels. This leads to the desired reduction in the fluid diffusion path while at the same time increasing the fluid contact areas. The purpose of this research is to evaluate mixing efficiency in microchannel mixers, through a numerical study of different micromixing configuration. To accomplish this, a numerical study is conducted using computational fluid dynamics (CFD) approach using ANSYS Fluent and CFX Software for different geometries designed. Different geometric configuration were proposed and used: bottleneck near the inlet and along the zig zag and curved shaped rectangular zig zag geometry. Mixing analysis is done by different conditions such as Reynold’s number, effect of geometry on fluid flow and different diffusion coefficients by evaluating mixing index of the fluid. Results have shown better and faster mixing index around bottleneck region compared to other. This geometry can be used to model passive micromixers and other microfluidic devices with shorter mixing length and for faster mixing between reagents.