فهرست مطالب

Transport Phenomena in Nano and Micro Scales - Volume:7 Issue:2, 2019
  • Volume:7 Issue:2, 2019
  • تاریخ انتشار: 1398/04/10
  • تعداد عناوین: 5
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  • Hamed Safikhani *, Moein Taheri, Mostafa Usefi Pages 80-87
    In the present study, the effective parameters of water-Al2O3 nanofluid flowing in flat tubes are investigated using the EFAST Sensitivity Analysis (SA) method. The SA is performed using GMDH type artificial neural networks (ANN) which are based on validated numerical data of two phase modeling of nanofluid flow in flat tubes. There are five design variables namely: tube flattening (H), flow rate (Q), wall heat flux ( ), nanoparticle diameter (dp) and nanoparticle volume fraction (φ) and there are two objective functions namely: pressure drop (∆P) and heat transfer coefficient (h). The results show that among design variables, the tube flattening has the highest effect on variations of pressure drop (74%) and heat transfer coefficient (40%). Except tube flattening, the flow rate and the nanoparticle volume fraction has the highest effect on pressure drop (24%) and heat transfer coefficient (25%) respectively. The effects of all of the design variables on objective functions are shown in the results.
    Keywords: Sensitivity analysis, EFAST method, Nanofluid, flat tubes
  • Reza Abdollah Pour Malakshah, Mahdi Mohseni * Pages 88-96
    In this study, turbulent compressible gas flow in a rectangular micro-channel is numerically investigated. The gas flow assumed to be in the subsonic regime up to Mach number about 0.7. Five low and high Reynolds number RANS turbulence models are used for modeling the turbulent flow. Two types of mesh are generated depending on the employed turbulence model. The computations are performed for Reynolds number up to 19000 and two inlet pressures of 1102 kPa and 499 kPa. The longitudinal variations of flow characteristics such as pressure, temperature, Mach number and friction factor are investigated. The experimental data are also used for the sake of comparison and to find which turbulence model has the best performance. The results show that the turbulence models with wall functions have generally better agreement with the experimental data than those one without wall function. The numerical results are different for normal size pipe flow.
    Keywords: Compressible flow, microchannel, numerical simulation, turbulence models
  • Mohammad Mohsen Peiravi, Javad Alinejad *, Davood Ganji, Soroush Maddah Pages 97-112
    This investigation is a three dimensional comprehensive heat transfer analysis for partially differentially heated enclosure with the vertical fin mounted on the hot wall. The thermal lattice Boltzmann based on D3Q19 method is utilized to illustrate the effects of vertical fins and nanoparticles on the flow and thermal fields. The effects of Rayleigh number and different arrangement of fins on the fluid flow and heat transfer have been scrutinized. The streamlines and isotherms and Nusselt number along the hot wall are illustrated for 104<Ra<108 and nanoparticles volume fraction 0.01<φ6 and two fins in Ra =104), the average Nu could be increased by more than 60%, but the effect of using the nanofluids (φ=0.03, Cuo/Water) is less than 30%. So arrangement of fins and nanofluids (φ=0.03, Cuo/Water) effects improve the heat transfer mechanism in the cubical enclosure.
    Keywords: Cubical enclosure, Lattice Boltzmann Method, nanoparticles effects, natural convection, vertical fins
  • Ramin Ehsani, Ahmad Reza Rahmati * Pages 113-119
    A huge number of deaths in the world are the direct or indirect consequence of a disease which is called atherosclerosis. The disease could be due to an artery blockage by the interaction of an externally second phase with a particle which is entered to the bloodstream. The effect of some most important physical and geometrical affecting parameters on the blockage time of a microchannel due to the impact of a particle and a second moving second phase is investigated. Shan-Chen Lattice Boltzmann multi-phase model is used in present study. It is investigated that the small change in the Capillary number does not affect the dynamics of the mechanism and the procedure steps significantly. But, smaller Capillary numbers cause breaking up the second phase in to more parts and with these smaller parts, the risk of small capillaries blockage in the arterial section of bloodstream decreases significantly. The blockage time will increase by an increase in the ratio of particle size to the channel width and the initial size of the second phase to channel width ratio has the highest effect on the blockage time.
    Keywords: Lattice Boltzmann Method, Shan-Chen Method, Two-Phase Flow-Particle Interaction
  • Gbeminiyi Sobamowo *, Akin Akinshilo, Ahmed Yinusa Pages 120-129
    In this work, variation of parameter method is applied to study two-dimensional flow of nanofluid in a porous channel through slowly deforming walls with suction or injection. The results of the developed approximate analytical solution using the variation of parameter method is verified with the results of numerical solution using fourth-order Runge-Kutta method coupled with shooing techniques. Thereafter, parametric studies are carried. The graphical illustrations of simulated results of the approximate analytical solutions show that during the expansion, the axial velocity at the center of the channel decreases as the Reynolds number increases while the axial velocity increases slightly near the surface of the channel when the wall contracts at the same rate. Also, the axial velocity decreases at the center of the channel but increases near the wall as the wall expansion ratio increases. Due to the high accuracy of the variation of parameter method, the results given in the work may be used for benchmark analysis of the subsequent studies on laminar flow behaviour of nanofluid in a porous channel through slowly deforming with injection or suction.
    Keywords: Nanofluid, Porous Channel, Expanding or Contracting walls, Variation of parameter method