فهرست مطالب

Transport Phenomena in Nano and Micro Scales - Volume:6 Issue:1, 2018
  • Volume:6 Issue:1, 2018
  • Special Issue
  • تاریخ انتشار: 1397/03/09
  • تعداد عناوین: 7
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  • Naghmeh Jamshidi, Hossein Gholami Pages 1-7
    Heat transfer is one of the most critical processes in the industry, and by increasing the efficiency of the heat exchanger, energy consumption of systems will be reduced. Very tiny particles in nanoscale dimensions, when uniformly dispersed and stably suspended in the base fluid, efficiently improve the thermal properties of the base fluid. With the help of nanofluids, the heat transfer rate increase. The purpose of this research is to investigate the thermal and hydraulic characteristics of nanofluid in turbulent flow regime in a plate heat exchanger with a sine pattern in which cold and hot flows alternately pass through the plates. First, problem geometry is modeled and simulated in ANSYS-FLUENT software. All properties of nanoparticles are dependent on temperature, velocity, and particles diameter, and are added to software in the form of a separate code. Simulations are for different parameters such as wavelength to amplitude ratio (L/A), Reynolds number, volume fractions of nanoparticles and nanoparticle diameter. The results indicate that the best shape of the wave for the highest heat transfer rate in the heat exchanger is gained for equal wave amplitude and wave length.
    Keywords: Computational Fluid Dynamics, Nanofluid, plate heat exchanger, sinusoidal plate
  • Bahram Ghorbani *, Hani Roshani Pages 8-14
    Advanced exergoeconomic analysis is applied on process configurations for co-production of LNG and NGL. This analysis provides information on the origin of the irreversibility as well as the irreversibility value of the process. The exergy destruction, exergy destruction cost, and also investment cost, are divided into two available/unavailable and endogenous/exogenous parts. The results of advanced exergy analysis show that in C1MR2, AC20, AC1, AC4, AC5 equipment, a large part of the irreversibility is due to the exogenous exergy destruction, and in other equipment, it is due to the endogenous exergy destruction. Except for the MSHX1 heat exchanger, the available exergy destruction equipment is more than the unavailable one, which indicates that by improving the efficiency of these equipment, a decrease in losses is possible in the system. In advanced exergoeconomic analysis, it is also shown that the priority should be to improve system performance on MSHX1, CMR1 and C1MR3, because in comparison with other equipment, it has the highest cost of endogenous available exergy destruction.
    Keywords: Integration, LNG, NGL, advanced exergy analysis, advanced exergoeconomic analysis
  • Shahrzad Ebadati, Danial Zarbaf, Mohammad Zabetian *, Yaser Oghabneshin Pages 15-19
    The induced flow effect is the rotary motion generated in the fluid flow due to the temperature gradient. The phenomenon of thermophoresis is the movement of particles from the warmer side of the fluid to the cooler side. Laser is a very suitable device for creating a temperature gradient due to its unique features such as high power density, harmonic waves, single wavelength and very low divergence. Thermophoresis phenomenon and induced flow have many uses in the transfer of particles and in various fields such as medicine and industry. In the present work, the phenomena of laser thermal interactions and flows of microparticles were studied. Thermophoresis phenomenon and induced flow were investigated experimentally using laser. Scale analysis of the migration velocity caused by the laser thermal effects shows that the induced flow in the fluid has a larger scale in comparison with the thermophoresis phenomenon. Thus, the focus of the experimental study was on the laser induced flow by the local heat absorption of Rhodamine B solutions. Review of recent researches show that the idea of Rhodamine B topical absorption to create fluid motion has not been previously published. Therefore, it is considered as the most important novelty of the present work.
    Keywords: Induced flow, Thermophoresis phenomenon, Laser, Rhodamine B solutions
  • Arash Mahboubidoust *, Amirhosein Ghasemi, Abbas Ramiar, Pouyan Vatani Pages 20-28
    Cross-corrugated triangular channels increase heat transfer in heat exchangers. The mixing effect increases the heat transfer coefficient at the surfaces. In this study, the fluid flow and heat transfer in a triangular corrugated channel are modeled under two constant heat fluxes and different Reynolds numbers. In order to validate, k-ω turbulence model is used. Also, the effect of magnetic field is investigated in different locations of the channel and the channel entrance area is shown as the optimal area for application of the magnetic field both in terms of heat transfer coefficient and friction coefficient. It is also observed that the Nusselt number always increases with Reynolds increase, but the friction coefficient only increases when the magnetic field is positioned at the entrance area of the channel with the Reynolds increase and decreases in other cases. The presented results can be helpful for improving the performance of plate heat exchangers.
    Keywords: Convection heat transfer, Cross-corrugated triangular channel, Magnetic field, Nusselt number, OpenFOAM
  • Saber Deldar, Ali Jafarian Dehkordi *, Hamidreza Kharinezhad Arani Pages 29-36
    Presence of salts in water has been one of the biggest problems of industrial equipment such as evaporators, boilers, and pipes. These salts gradually form scales on evaporators and boilers tubes and reduce their efficiency. Pretreatment processes are conducted to remove these salts; with sedimentation tanks being one of the essential equipment used in these processes. This study numerically simulates multiphase flows in the sedimentation tanks using Discrete Phase Model (DPM). Various important parameters, such as sedimentation tank entrance and existence of baffle in the case of non-homogenous injected particles are studied. The results indicated that the bottom entrance tank provides maximum sedimentation efficiency of 70.3%. In addition, baffle influence is dependent on entrance location; and in the case of the top entrance, baffle presence improves efficiency by 5.2%. Sedimentation tank efficiency is also demonstrated for different particle sizes, indicating a 100% efficiency rate of the sedimentation for particle sizes at 50 microns or higher.
    Keywords: Sedimentation, discrete phase modeling, tank entrance, baffle, efficiency
  • Omid Torabipoor, Zoha Azizi * Pages 37-43
    Convective heat transfer of MgO-water nanofluid in a microchannel heat sink is experimentally investigated in various concentrations of 0.01, 0.05, 0.1, and 0.6 wt%. The microchannel consisted of 48 parallel rectangular cross section channels with the height of 800 µm, width of 524 µm and length of 52 mm. A well stability duration (ca. 1 month) was resulted by a 180 min ultra-sonication of the MgO suspension. The experiments in the microchannel were then performed in a flow rate range of 0.5 to 2.2 l/min while the inlet temperature and heat flux were constant. The results indicated that using the MgO nanofluid in low flow rates and concentration has less effect in improving the heat transfer coefficient, while it becomes highly efficient by the simultaneous increase of flow rate and concentration. An enhancement of 162.3% in convective heat transfer coefficient at the channel inlet was achieved at the concentration of 0.6 wt% and the flow rate of 2.2 l/min. The average Nusselt number also increased at the mentioned condition up to 52.8%. However, the nanofluid at 0.1 wt% was more efficient compared to the other concentrations in increasing Nu at higher Re.
    Keywords: Convective heat transfer coefficient, Microchannel heat sink, MgO nanofluid, Stability
  • Mojtaba Sepehrnia *, Ahmadreza Rahmati Pages 44-50
    In this work, slip flow of helium gas has been studied in a three dimensional rectangular microchannel heat sink with 11 microchannel and 10 rectangular fins. Helium gas flow is considered ideal and incompressible. The finite volume method with using coupled algorithm is employed to carry out the computation. To validate the present work, comparison with numerical and experimental studies is done and it is seen that the computed results have good agreement. To investigate the effect of fins and walls material on heat sink performance, all simulations are carried out and compared with each other for three materials consisting of aluminum, silicon and copper. The results show that along the microchannel, local Knudsen number decreases. Also thermal resistance increases continuously with increasing Knudsen number from 0.006 to 0.048. The results indicate that for various inlet Knudsen numbers, copper heat sink has the lowest thermal resistance. Furthermore, copper heat sink has the highest average Nusselt number for Knudsen number higher than 0.024 but for Knudsen number lower than 0.024, silicon heat sink has higher average Nusselt number than copper heat sink.
    Keywords: Slip flow, Heat sink, Rectangular microchannel, Ideal gas, Incompressible flow