فهرست مطالب

Transport Phenomena in Nano and Micro Scales - Volume:7 Issue:1, 2019
  • Volume:7 Issue:1, 2019
  • تاریخ انتشار: 1397/11/23
  • تعداد عناوین: 7
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  • Hamed Safikhani*, Saeed Mahdavifar Pages 1-8

    In this paper, multi-objective optimization (MOO) of Al2O3-water nanofluid flow in microchannel heat sinks (MCHS) with triangular ribs is performed using Computational Fluid Dynamics (CFD) techniques and Non-dominated Sorting Genetic Algorithms (NSGA II). At first, nanofluid flow is solved numerically in various MCHS with triangular ribs using CFD techniques. Finally, the CFD data will be used for Pareto based multi-objective optimization of nanofluid flow in MCHS with triangular ribs using NSGA II algorithm. In the MOO process there are seven geometrical and non-geometrical parameters and the conflicting objective functions are to simultaneously maximize the amount of heat transfer and minimize the pressure drop. Five optimum designs are determined and discussed for both nanofluid and base fluid flows. Details of design variables for each of five optimum points are deeply discussed. It is shown that the achieved Pareto solution includes important design information on nanofluid flow in MCHS with triangular ribs.

    Keywords: Microchannel heat sink (MCHS), nanofluid, multi-objective optimization (MOO), NSGA II
  • Mousa Farhadi* , Soheil Ghanami Pages 9-27

    Enhancement of heat and mass transfer and decrease of energy dissipation are great necessities of the evolution of fluid flow devices. Utilizing oscillatory or pulsatile fluid flow for periodic disturbing of velocity and thermal boundary layers is one of the methods with exciting results. Passive methods of generating oscillatory flow are preferred to active methods because of simplicity, no need for an external source of power and low cost of implementation and maintenance. Fluidic oscillators are a kind of no-moving part devices which convert steady pressurized inlet flow to oscillatory flow or pulsatile flows at exit without any need for external power. In this article, the structure and physics of conventional fluidic oscillators is explained and a comprehensive review over various aspects of their application is done. Also, numerical and experimental studies with the subject of fluidic oscillators are reviewed and existing correlations are presented. Our review shows that fluidic oscillators have great potentials in all processes that oscillatory or pulsatile flow could be effective in their enhancement.

    Keywords: Feedback channel, Fluidic oscillator, Passive method, Sweeping flow
  • Ahmad REza Rahmati *, Hossien Khorasanizadeh, M. R. Arabyarmohammadi Pages 28-36

    The aim of the present work is to analyze the accuracy and to extend the capability of lattice Boltzmann method in slip EOF; a phenomenon which was previously studied by molecular dynamics and less considered by LBM. At the present work, a numerical experiment on boundary conditions of slip velocity is performed and the proportionality of slip with shear stress in electroosmotic pump is proved. Results show that LBM can capture the slip length in EOF with liquid operating fluid. Implementing slip velocity at the walls of a microchannel, the electroosmotic flow with adverse pressure gradient over a hydrophobic surface is investigated in view of mixing reduction. The fluid flow is assumed to be laminar, steady and viscous. Slip at the channel boundaries will decelerate the development process of the flow. Unlike no-slip condition, transverse change in velocity magnitude near the walls decreases and also more resistant pressure is required to create reverse centerline velocity; so mixing probability and performance of EOF pump can alter considerably.

    Keywords: KEYWORDS lattice Boltzmann, electroosmotic flow, slip velocity boundary conditions
  • GhanbarAli sheikhzadeh, farhad Monfaredi, Alireza Aghaei*, Soroush Sadripou, ehsan doakhan, Mohammad Adibi Pages 37-52

    In this study the effects of corrugated absorber plate and using aerosol-carbon black nanofluid on heat transfer and turbulent flow in solar collectors with double application and air heating collectors, were numerically investigated. The two-dimensional continuity, momentum and energy equation were solved by finite volume and SIMPLE algorithm. In the present investigation all the simulations were done for two different angles of tilt of collector according to horizon, that these angles were the optimum ones for the period of six months setting. As a result the corrugated absorber plate was inspected in the case of triangle, rectangle and sinuous with the wave length of 1 mm and wave amplitude of 3 mm in turbulent flow regime and Reynolds number between 2500 to 4000. Choosing the proper geometry was carried out based on the best performance evaluation criteria (PEC), for collectors with dual usage and increasing the air temperature from collector inlet to outlet for air heating collector. The results revealed that using corrugated absorber plate has a considerable influence on flow field and heat transfer. For all times of the year the highest PEC was obtained for corrugated Sinusoidal model, however the highest temperature increase from inlet to outlet was obtained for rectangular corrugated model.

    Keywords: Solar collector, corrugated absorber plate, turbulent flow, performance evaluation criteria, nanofluid
  • Mahin Ghannadi *, Seyed Fazlolah Saghravani, Hamid Niazmand Pages 53-61


    The present study considers of the water and air flow and Micro-Bubble production inside the venturi tube, by the use of dimensional analysis. Numerical analysis of Micro-Bubble creation in venturi tube requires fast computers and large amounts of storage space. Up to now, there has been no numerical analysis concerning Micro-Bubble creation and all other existing studies are experimental. To save time and storage space, dimensional analysis has been used.
    in this research OpenFOAM software has been used for numerical analysis, and for statestical analysis used of SPSS software. This study shows, if the aim is to study the pressure and velocity in the venturi tube, the results of the scaled model can be quite reliable. But if the goal is to study the results of alpha and formation of micro-bubbles, analys results achived from scaled models can not be used. Therefore, since the purpose of this study is to study micro-bubble formation in a Venturi tube and the results of alpha should also be considered, scalable models can not be used.Then, in future studies, we need to simulate actual models in openFOAM software and study the formation of micro-bubbles, which will require more time and cost

    Keywords: Micro-bubble, OpenFOAM, Venturi tube, Dimensional similarity Statistics
  • Sima Bahei Islami *, Salman Ahmadi Pages 62-71

    The previous studies of authors on passive micromixers indicated that the micromixers dividing the flow to several layers, such as rhombus micromixers and micromixers with obstacles in the middle of the mixing channel, have higher mixing degree than other types. Also, using of oscillatory inlet velocities is an active method to enhance the mixing efficiency of micromixers. Therefore, in this study these two passive and active methods have been combined and a rhombus micromixer with obstacles in the middle of the mixing channel has been studied. Sinusoidal oscillatory velocities in two inlets have been applied with a phase difference of 180 degrees. The governing equations have been solved numerically using the finite volume method. The effect of Reynolds number, Strouhal number and amplitude on mixing degree has been investigated. Results show that degree of mixing decreases with Reynolds number at almost all Strouhal numbers. There is an optimum Strouhal number for each Reynolds number. Also, there is optimum amplitude and this optimum value decreases as Reynolds number increases.

    Keywords: passive micromixer, oscillatory inlet velocity, mixing degree, Strouhal number
  • ehsan abdi elmi, Hamed Uosofvand* Pages 72-79

    This paper experimentally studies the heat absorption performance of a heat sink with vertical embedded heat pipes in the aluminum blade. The cooling system with embedded heat pipes distributes heat from the CPU to both the base plate and the heat pipes, and then transfer heat from fins to the Environment. The thermal resistance and heat transfer coefficient are evaluated for natural convection under steady-state condition, by changing the heat input from 25W to 100 W. the heat pipe is filled distilled water, Ethylene Glycol, Ethanol, Ethylene glycol distilled water solution, copper oxide/ water Nano-fluid (Cu/H2O) with different weight percentage. The results indicate that the presence of copper oxide/ water Nano-fluid in heat pipe increase heat transfer in a computer CPU cooling system and reduce the thermal resistance of the pipe rather than other fluids. In fact, the use of nanofluids removes heat transfer significantly in CPU cooling systems and can be a good replacement for the common working fluid in this device.

    Keywords: Heat pipe, Convection, CPU, Computer, Cooling