جستجوی مقالات مرتبط با کلیدواژه « micro-channel » در نشریات گروه « فنی و مهندسی »

The flow of micronutrients into micro channels and the manufacture of micro fluidic devices has been an important topic in recent decades and has been applied to various industries and sciences including biological sciences, pharmaceutical, food, water and wastewater, minerals and more. Many scholars and researchers today are looking for techniques to model two-phase currents of this type. The research method in this paper is based on experimental and numerical methods. Experimental experiments were carried out on a rectangular micro channel with a height of 200 μm. Due to the dilution of the coupling current under investigation, the particle size used is 20, 31.7 and 51.7 microns with a density of 1.05 g / cm3 and a refractive index of 1.59. Also, the studied regime of Stokes with Reynolds number is lower than one and laminar and thus ignores the turbulence effects of the current.As the Reynolds number increases, particle settling decreases

In the present study, mixing of two fluids of different viscosities in a micro channel with an oscillating curved stirrer was simulated by MRT-LBM and the effect of geometric shape, oscillating speed and amplitude and viscosity logarithmic ratio on mixing efficiency was analyzed. Most researches in this field have studied the mixing of two same fluids but the mixing makes sense when two miscible fluids have different properties. Also in these researches, stirrers in micro channel are considered cylinder or rectangle shape. In this study, a curved stirrer was used for mixing two fluids of different viscosities in micro channel for the first time. The simulation was performed at Re=80 and Sc=10 and NASA/LANGLEY LS(1)-0417 (GA(W)-1) airfoil shape was used for curved stirrer. At the study of geometric shape, results showed that mixing efficiency of two fluids of same and different viscosities in micro channel with oscillating curved stirrer was higher than micro channel with oscillating rectangle stirrer. The results of stirrer oscillating amplitude and velocity survey revealed that increase in Strouhal number causes increase in mixing efficiency on studied oscillating amplitude and Optimum efficiency is on oscillating amplitude 0.5 on all studied Strouhal numbers. Also mixing efficiency decreases with increase of viscosity logarithmic ratio on studied Strouhal numbers and this decrease is noticeable in high Strouhal numbers.

In recent years, forming a 3D microfluidic channels on the electrical non-conductive material such as Polydimethylsiloxane (PDMS) in the micro-electromechanical system (MEMS) and medical applications is of great interest. Lithography is the most know process to create patterns on the PDMS however there are a few drawbacks to this process such as high operational cost and time, and sidewall angle. In all applications, the quality of the micro-channel surface determines the performance of it. In this research as innovatively the electrochemical discharge milling (ECDM) which is known for lower operational cost and proper material removal rate (MRR; i.e. process time), and is capable of creating patterns on electrical non-conductive material, was used to form a micro-channel on the PDMS. To that end, the effect of process parameters such as electrolyte concentration, feed rate and cutting speed and voltage on the surface roughness and surface integrity deeply investigated. It was observed that ECDM is capable of creating patterns on the PDMS with surface integrity which is comparable with the lithography microchannel. It is also observed that decreasing the rotational speed from 10000 to 0rpm results in increasing the surface roughness 2 to 4 times. This happens due to the increasing the thickness of the gas film around the tool, and subsequently increasing the flying sparks which results in higher surface roughness. Increasing the Voltage from 38 to 42V results in 36% enhancement of surface roughness. The 25% electrolyte concentration results in lower surface roughness.

The study of micro-scale fluid behavior is known as microfluidics, which has received much attention in many scientific fields. In the current research, the droplet generation in the micro channel has been studied numerically and experimentally. Two micro channels were fabricated by soft lithography method and the results of generated droplets were compared. The process of droplet formation was investigated using two fluids including water (dispersed fluid phase), and oil (continuous fluid phase) at different flow ratios. The images of the droplet formation and crossing steps in the micro channels were analyzed using image processing. The results showed that by increasing the ratio of dispersed to continuous flow, the size of droplets was increased, the droplet formation distance (the distance of the produced droplets) was increased, and the frequency of droplets generation was decreased. Also, the proposed new geometry leads to the production of smaller droplets with higher production frequencies. In the basic geometry, the droplet diameter was observed to be between 117 and 700 micrometers while in the proposed geometry, the diameter of droplets is between 46 and 466 micrometers. In the proposed geometry, the size of the produced droplets decreases, and the production frequency increases.

In this study, we investigated the flow of blood plasma in which white blood cell, erythrocyte and platelet nanoparticles were suspended with a percentage of actual concentrations inside a three-dimensional rectangular micro channel. The chamber rotates around the vertical axis at constant angular velocity and is affected by electrical double layer .The numerical results on white blood cell, erythrocyte and platelet nanoparticles were extracted in plasma at different angular velocities and the movement of suspended particles in the blood was studied that was observed that in the angular velocity increases, the pressure decreases along the channel and along the axis of rotation of course the velocity has the maximum amount in the center of channel. Numerical studies of the velocity and distribution of particles also show that the velocity variations are the same in all particles and the velocities of white blood cells, erythrocytes and platelets at the end of the channel are more than another place and the streamlines more compact.

In this paper, numerical simulation of the convection heat transfer in micro-channel heat sinks is investigated. The main objective of this research is to study the effect of diameter, distance between fins and fins height, as well as the inlet fluid velocity on the average temperature fins, average temperature of fluid at outlet, temperature distribution in longitudinal direction of the micro-channel and heat flux passing fins. For this purpose, the cooling fluid flow passing through a micro-channel heat sinks with bar fins which have the elliptical cross-section and placed in a linear arrangement is simulated using a finite volume method. Simulation results indicate that changes in diameter and distance between the fins as well as the velocity of the inlet fluid have a significant effect on the heat transfer rate of the heat sink, but the temperature variations due to the change in the height of the fins are low.

In this paper, an analytical analysis for thermal and mass transfer effects of a non-homogeneous catalytic mixture into a microchannel is investigated with considering flow regime effects. The importance of the present work is to find out the selective Knudsen number and investigating the possessions of mass and heat jump coefficients on the present problem. The governing equations include energy, molar fraction and catalytic conversion equations, and the effects of flow regime is introduced into the problem through boundary conditions. The obtained results are compared in three different values of the Knudsen number with experimental data. The maximum errors rather than experimental data for Knudsen number equal to 0.1 is 7.54 percent but for Knudsen numbers of 0.01 and 0.001, the errors is increased to 35.4 percent. Therefore, the selective Knudsen number for catalytic micro-channel is equal to 0.1. The greatest increase in fuel conversion with increasing Knudsen number is occurred in the low Reynolds number with a value of 35.2%. Furthermore, the increasing rates of fuel conversion and surface mole fraction with increase of Knudsen number are nearly equal, which this issue is due to entrance of fluid from continuous to slip regime.

In this paper, DPD method is used to simulate the polymer chain in a micrometers channel with respect to electrosomalic micro pump and the influence of the effective parameters on the displacement of the polymeric chain will be investigated. Also, The effective parameters are validated. In the following, a two fixed ends polymeric chain is placed in the channel and the fluid flow will cause the polymer chain to move. It is shown that the amount of variation of the chain in addition to the influence of the parameters of the electro-osmotic current on the main parameters of the polymer chain is the same as the number of beads and the elastic property between the beads, and the best control parameter as well as the direction of movement of the polymer chain during operation is the electric field. It has been shown that with the change of electric field from 50 to 150 V / m, the amount of chain movement would be twice, while if the number of beads is added to 40, at electric field of 100 V / m, the displacement rate will be increased approximately 3 times. Also, the effect of the position of the installation has been checked and shown by changing the position of the installation from the vertical coordinates 4 and 4 to 9.5 and -9.5 micrometer, with consideration of the same chain movement, the electric field strength decreased by half, and the amount of oscillation decreases.

In this paper, the dissipative particle dynamic method is used to simulate the electrosmotic micro pump as the main part of a spatial-chemical propulsion system. In this simulation, the micro-pump is driven by the principle of  electrosmotic flow.Furthermore,the effective parameters, such as channel dimensions, applied voltage, surface effect, or zeta potential are analyzed. This research focuses on developing a simulation method for applying external force (electrosmotic force) as well as developing a method to a channel with different sizes and conditions. Our results include velocity profile in a channel with different effective parameters. The result were compared with and validated by analytical solution. It was shown that the electrosmotic method is an ideal method for transferring fluid as a micro-pump in different conditions and also in fine-scales applications, such as in micro-satellites.

In this paper, the analytical investigation of two thermal and mass transfer effects for non-homogeneous catalytic reaction mixture into a micro-channel has been achieved considering the continuous regime properties. In this problem, the Knudsen number is considered smaller than 0.1 where the flow is in the continuous or slip regime. The governing equations are consisting of energy, mole fraction and catalytic conversion where the wall effects have been achieved from thermal and mass jump boundary conditions. The solution results at three different values of Knudsen number are compared with experimental data, and at all points, when the Knudsen number is equal to 0.01 the best validity by experimental data be available. The results of slip-jump solution, with maximum error of 2.54%, has a better validated experimental values than based modeling data without slip and jump condition, with maximum error of 26.6%. The greatest increase in fuel conversion occurs at low-level Reynolds number, with a value about 80.04%. Increasing thermal jump effect coefficient, normalized temperature reduces while with increase in mass jump effect coefficient, fuel conversion decreases and surface mole fraction increases.

The intermolecular potential model of the lattice Boltzmann method is used to simulate the droplet formation and breakup process of mixing of immiscible fluids. The aim of this research is to investigate non-Newtonian droplet formation in Newtonian continuous phase in a co-flowing micro-channel. The dimensionless numbers such as Capillary and velocity ratio are the most important dimensionless numbers in determination of fluid flow characteristics in the micro-channel. The influences of capillary number, nonNewtonian index and velocity ratio are studied on the droplet formation. The final droplet size, droplet generation frequency and detachment point of the droplet are completely analyzed. The results reveal that with increasing the non-Newtonian index, the required time for detachment of the droplet and the formation length is decreased. Increasing the Capillary number leads to a reduction in the detachment length. The size of droplet is also decreased due to the reducing velocity ratio and Capillary number. Moreover, the effect of non-Newtonian index on the distance between the droplets is checked.

With the development of micro-mechanical systems, human became interested in concentrating on the small-scale impact on the flow and heat transfer in micro-channels. A micro-channel is required for a gas sensor to guide the gas flow. Reducing the size of channel has lead the scientist to concentrate on micro-sensor. Metal oxide gas micro-sensors are used to detect gases such as O3, SO2, CO2, NO, NH3, CH4 and etc. Metal oxide gas micro-sensors are small in size, low cost in fabrication and consume little power. The purpose of the current study is to numerically investigate the micro-channel wall thickness and diameter on gas inlet temperature under the influence of thermal creeping. The governing nonlinear differential equations, mass, momentum, energy, and species, are coupled and solved by a commercial code. The channel is assumed to be two dimensional. Since the Knudsen number is between 0.01 and 0.1, the slip boundary condition, Maxwell equation, is utilized. The result shows that as wall thickness increases the gas inlet temperature increases and temperature difference between gas inlet and outlet decreases. On the other hand as channel diameter decreases the gas inlet temperature increases.

Metal bipolar plates are key components in fuel cells that are considered as the best alternative to replace graphite plates. Material selection in bipolar plates depends on its weight and corrosion resistance. Metallic bipolar plate can be considered as the best alternative instead of graphite and composite plates. One of the new processes in order to produce this plat is gas blow forming process. In this study, forming of AA8111 bipolar plates with 200 µm thickness in concave groove dies is investigated by gas blow forming process at various pressures (20, 30 and40 bar) and temperatures (300 and 400 ° C). The filling percent of die at various wall angles and depth to width ratios are examined. According to the dimension of channels, maximum and minimum thinning percentage at high temperature and pressure are investigated. Results show that at wall angle of ∝=0, and the depth to width ratio of h/w=0.5, rupture occurs at pressure of 20bar and at temperature of 300° C and at pressures of 20 and 40 bar at temperature of 400° C. The best channel filling with lowest thinning obtained at ∝=15 and h/w=0.5.