Showing 4 results for Microchannel
A. R. Rahmati, S. Niazi,
Volume 34, Issue 1 (7-2015)
Abstract
In this study, for the first time, a comparison of single-relaxation-time, multi-relaxation-time and entropic lattice Boltzmann methods on non-uniform meshes is performed and application of these methods for simulation of two-dimensional cavity flows, channel flows and channel flows with sudden expansion is studied in the slip and near transition regimes. In this work, Taylor series expansion and least squares based lattice Boltzmann method is utilized in order to apply the lattice Boltzmann models on non-uniform meshes. A diffuse scattering boundary condition and a combination of bounce-back and specular boundary conditions are employed to obtain the slip at the walls. Besides, the relaxation times of lattice Boltzmann methods are computed in terms of Knudsen number. Different lattice Boltzmann methods are used to simulate lid-driven micro cavity flows and their results are compared with each other and with those obtained in the literature. Then, the best model in accuracy and stability, i.e. multi-relaxation-time lattice Boltzmann method, is applied to simulate the micro channel flow in different Knudsen numbers. Results show that the proposed method on non-uniform meshes is capable of simulating micro flows problems in the slip and the transition regimes.
R. Rajabi, M. Saghafian,
Volume 35, Issue 1 (9-2016)
Abstract
In this paper, viscous dissipation and roughness effects on heat transfer and fluid flow are investigated in microchannels using perturbation method in slip flow regime. The flow is considered to be laminar, developing thermally and hydrodynamically, two-dimensional, incompressible and steady-state. The working fluid is air, flowing between two parallel plates. The equations obtained from developing Navier-Stokes and energy equations are solved numerically according to different orders of Knudsen number, with second-order velocity slip and temperature jump boundary conditions. The effects of thermal creep has been ignored. Tempreture and velocity fields are obtained and estimated for both constatnt heat flux and constant wall tempreture. The effects of roughness height, space between roughness elements, roughness elements length, Re number and Kn number on slip behavior of gas flow are investigated.The results indicate considerable effect of viscous dissipation and roughness on fluid flow and heat transfer in microchannel.
H. Bazai, A. Azari, M. Moshtagh,
Volume 38, Issue 1 (8-2019)
Abstract
The purpose of this article is the numerical study of flow and heat transfer characteristics of Nanofluids inside a cylindrical microchannel with rectangular, triangular, and circular cross-sections. The size and shape of these sections have a significant impact on the thermal and hydraulic performance of the microchannel heat exchanger. The Nanofluids used in this work include water and De-Ethylene Glycol (DEG) as the base fluids and Al2O3, Cu, SiO2 and CuO as the nanoparticles. To solve the problem and extract the required data, a 3-D simulation was performed for the microchannel using ANSYS FLUENT 15.0 software and the effect of the cross-sectional shape of the fluid flow and the type of nanoparticles on the thermal transfer and fluid flow parameters was studied. From the obtained results, it can be observed that the addition of nanoparticles to the base fluid increases the heat transfer and pressure drop. The results also show that rectangular channels have the best performance among the three geometries examined as its heat transfer coefficient was 19.26% higher than the triangular cross section which had the worst performance.
F. Shabani, M. Saghafian, D. Saeidi, F. F. Momennasab ,
Volume 39, Issue 2 (2-2021)
Abstract
Particulate separation has many applications in medicine, biology and industry. In this research, the separation of polystyrene particles with a diameter of 10, 20 and 30 μm in the fluid flow of a microchannel is investigated. The microchannel consists of a spiral region and a straight region under the influence of acoustic waves. In the spiral region, the particles under hydrodynamic effects undergo the initial separation; then the particles enter the straight region of the microchannel, and the final separation of the particles is done by the force generated and exerted through the acoustic waves. The effects of acoustic frequency and the number of spiral region loops on separation are investigated. The results show that for measured dimensions and parameters, at 1 MHz acoustic wave, when the number of loops is 2 for the spiral region, the particles at the end of the path are in a suitable position for separation. In addition, the results show that the separation of particles with this hybrid system is better than that done by the simple methods, and the separation rate can be as high as 100%
