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computational fluid dynamics (cfd)

در نشریات گروه علوم پایه
  • Amirhossein Sharifi, Babak Beheshti *, Mohammad Qahdrijani

    Today, the development of food systems and agricultural goods is often the largest contributor to national economies and plays a key role in achieving sustainable development goals. Meanwhile, food and nutrition are essential to citizens' health, and food preservation specialists are systematically working toward progress in creating a more sustainable system. Saffron is a highly valuable spice extracted from the flower's stigma. Drying is a crucial process in saffron production, as it helps preserve the spice's flavor, aroma, and color. Proper storage helps maintain the quality of saffron over a long period. In this study, the Computational Fluid Dynamics (CFD) method was used to model the saffron experimental Fluidized bed dryer. The behavior of the fluid within the dryer was examined utilizing computational fluid dynamics and the turbulent flow ε-k as a turbulence model using the Fluent software. The device was simulated at three different air temperatures—60, 65, and 70 oC—and three different air speeds: 1.5, 52.5, and 5.3 m/s. Results of analysis of the coefficient of variance of inlet air temperature and dryer air velocity on humidity with Mean square humidity (20.96) demonstrated that better results are attained when the dryer's air speed is lowered and its input air temperature is raised, or vice versa. Thus, if a dryer is manufactured, it needs to be able to change both the speed and the temperature to reach 10% humidity (wetness-based).

    Keywords: Computational Fluid Dynamics (CFD), Fluidized Bed Dryer, Simulation, Saffron
  • M. Zabihinpour *, Z. Khaniki, S. Mohammadi
    Radon is a radioactive gas that nowadays is considered one of the most harmful natural factors in residential areas all over the world. After cigarettes, radon gas is considered to be the biggest cause of lung cancer. Therefore, it is very important to study the measurement of radon concentration in different parts of the building. In this research, by choosing a sample building, the distribution of radon concentration in different regions is modelled by using Computational Fluid Dynamics (CFD) in two conditions, non-ventilation and natural ventilation. Then the results measured by a continuous work radon detector have been compared in a similar condition. Also, to confirm the results, the average radon concentration in the building and for different conditions was compared with the data obtained from the analytical method. The results show that the modelling performed in a non-ventilation method with an error of less than 16% is consistent with the experimental data. Also in natural ventilation conditions, the experimental results confirm the numerical modelling results. On the other hand, the results derived from the analytical solution in both non-ventilation and natural ventilation conditions confirm the results obtained from the simulation of the distribution of radon concentration. Our emphasis on this study is to determine the proper location of sleeping, sitting, and standing in a building, to reduce the dose received from radon gas.
    Keywords: Radon, Natural Ventilation, Computational Fluid Dynamics (CFD), Analytical Method
  • Bahman Zormand, Susan Khosroyar *, Ali Araste Nodeh, Hossein Ghahremania
    The scrubber of the industrial urea production unit had to be modified after increasing the urea production capacity. It was modified based on the computational fluid dynamics modeling results. Increasing the number of outlet holes in the scrubber’s CAP improved the transient flow of carbamate and scrubber efficiency. In addition, the gas outlet flow rate in the initial design equaled an error level of <1%, while this rate was less than 7% when capacity was enhanced. All measurable parameters were measured and compared before scrubber modification (Plant-0) and after modification (Plant-1). The modification led to an increased average concentration of urea from 71.33 to 71.35 w%, enhanced CO2 purity from 98.81% to 99.09%, a decline in vapor consumed in the studied unit from 104.1 to 100.5 ton/h, and a reduction in the outlet ammonium of Prill tower's synthesis unit from 11.5 to 0.81w% within the two-month interval. Before the modification of the scrubber, ammonium consumption, urea production, and ammonium/urea consumption index equaled 1494.9, 870 ton/day, and 0.5824, respectively, while reached 1503.3, 869.2 ton/day, and 0.5782, respectively after modifications. According to reported values, there was a 1.7 ton/day reduction in ammonium use and an 8.5 ton/day rise in urea production, resulting in considerable savings for the company.
    Keywords: Computational Fluid Dynamics (CFD), Urea Industrial Plant, Scrubber, Carbamate, Modification
  • اکبر جعفرنژاد، حسام الدین سالاریان*، سعید خردمند، جهانفر خالقی نیا
    زمینه و هدف

    سیکلون ها به طور گسترده در کنترل آلودگی هوا وظیفه جداسازی مخلوط گاز ذره را به عهده دارند و در صنعت مورد استفاده قرار می گیرند. از مزایای این دستگاه در صنایع مختلف سادگی نسبی ساخت آن، هزینه عملیاتی پایین و سازگاری با شرایط دشوار صنعتی می باشد. امروزه جداسازهای سیکلونی به یکی از مهمترین دستگاه های حذف ذرات در زمینه های علمی و مهندسی تبدیل شده است. با توجه به کاربرد وسیع سیکلون ها در فرایند های صنعتی به ویژه نیروگاه های حرارتی، بررسی عملکرد سیکلون ها در درجه حرارت های بالا از اهمیت ویژه ای برخوردار می باشد. در این مطالعه شبیه سازی جریان دوفازی درون سیکلون با استفاده از دیدگاه اویلری-لاگرانژی به صورت سه بعدی انجام خواهد گرفت تا در محدوده وسیع دمایی عملکرد سیکلون مورد بررسی دقیق قرار بگیرد و در نهایت مشکل افت عملکرد آن با استفاده از طراحی مناسب هندسه گرداب یاب به طور قابل ملاحظه ای حل خواهد شد.

    روش بررسی

    در این مطالعه، تاثیر دمای ورودی بر میدان جریان و عملکرد جداسازی یک سیکلون به طور جامع با استفاده از شبیه سازی CFD مورد بررسی قرار گرفته است. رویکرد اویلر-لاگرانژی برای شبیه سازی جریان هوا و دینامیک ذرات در سیکلون استفاده شده است. علاوه بر این، در این مطالعه چهار هندسه گرداب یاب پیشنهادی مورد استفاده قرار گرفته و به منظور ارزیابی چگونگی تاثیر گرداب یاب بر عملکرد سیکلون تحت یک طیف وسیعی از دما (293 K-700 K) با هندسه پایه مقایسه گردیده است. اعتبار مدل عددی با مقایسه افت فشار پیش بینی شده با داده های تجربی مرجع و نتایج عددی مرجع که در آن تطابق خوبی وجود داشته، تایید گردیده است.

    یافته ها

    نتایج نشان داده است که افزایش دمای ورودی به میزان قابل توجهی سرعت مماسی را کاهش داده و منجر به کاهش شدید راندمان جداسازی سیکلون شده است. تمامی گرداب یاب های ارائه شده بر الگوی جریان درون سیکلون در همه دماهای ورودی تاثیر گذاشته اند. نتایج شبیه سازی نشان داده است که بالاترین سرعت مماسی مشاهده شده در سیکلون با CVF 1 بوده که همچنین بر راندمان جداسازی مربوطه تاثیر مثبتی گذاشته است. همچنین، ثابت شده است که سیکلون پیشنهادی با CVF 1 قادر به جمع آوری ذرات ریزتر (2 میکرومتر) در دمای ورودی بالا (T = 700 K) بوده است.

    بحث و نتیجه گیری

    در مطالعه حاضر ضمن بررسی عملکرد سیکلون با استفاده از دیدگاه اویلری-لاگرانژی به صورت سه بعدی در یک محدوده دمایی وسیع، راهکاری مناسب جهت بهبود راندمان و حل مشکل افت راندمان در دماهای بالا ارائه شده است. با تغییر مناسب ابعاد و هندسه گرداب یاب، می توان جریان در فضای پیش جدایش را به خوبی کنترل کرد تا راندمان جداسازی ذرات را بهبود بخشید.

    کلید واژگان: سیکلون گازی، گرداب یاب، راندمان جداسازی، دما-بالا، دینامیک سیالات محاسباتی.
    Akbar Jafarnezhad, Hesamoddin SALARIAN *, Saeid Kheradmand, Jahanfar Khaleghinia
    Background and Objective

    Cyclones are widely used in air pollution control to separate particulate gas mixtures and are used in industry. The advantages of this device in different industries are its relative simplicity of construction, low operating cost and reliable under extreme working conditions. Today, cyclone separators have become one of the most important particle removal devices in the fields of science and engineering. Due to the wide application of cyclones in industrial processes, especially thermal power plants, the study of the performance of cyclones at high temperatures is of particular importance. In the present study, two-phase flow simulation within a cyclone will be performed in three different dimensions using the Eulerian-Lagrangian approach in order to study the cyclone performance in a wide range of temperatures, and finally the problem of its lower performance will be substantially resolved by using appropriate geometry of vortex finder.

    Material and Methodology

    In this study, the effect of inlet temperature on the flow field and the separation performance of a cyclone has been comprehensively investigated using CFD simulation. The Euler-Lagrangian approach has been used to simulate airflow and particle dynamics in cyclones. In addition, four proposed vortex finder geometries were considered and compared with the basic geometry in order to evaluate how the vortex finder affects the cyclone performance under a wide temperature range (293 K-700 K). The validity of the numerical model is confirmed by comparing the predicted pressure drop with the experimental data and numerical results in which there is a good agreement was achieved.

    Findings

    The results demonstrated that increasing of inlet temperature significantly reduced the tangential velocity and led to a sharp decrease in the cyclone separation efficiency. All of the proposed vortex finders affected the flow pattern within the cyclone at all inlet temperatures. The simulation results showed that the highest tangential velocity observed in the cyclone was with CVF 1, which also had a positive effect on the relevant separation efficiency. Also, it is proved that the proposed cyclone with CVF 1 was able to collect finer particles (2 μm) at high inlet temperature (T = 700 K).

    Discussion and Conclusion

    In the present study, while examining the performance of cyclone using the Eulerian-Lagrangian approach in three dimensions over a wide temperature range, a suitable solution to improve efficiency and solve the problem of efficiency drop at high temperatures was presented. By properly changing the dimensions and geometry of the vortex finder, the flow in the pre-separation zone can be well controlled to improve particle separation efficiency.

    Keywords: Gas Cyclone, Vortex Finder, Separation Efficiency, High-Temperature, Computational Fluid Dynamics (CFD)
  • Urooj Fatima, Muhammad Shakaib

    The numerical study in this paper investigates the effect of inlet and outlet areas of micromixer channels on fluid flow behavior and mass transfer performance. The ratio of the outlet to the junction area is varied from 0.6−2 while the ratio of the inlet to junction area is from 0.6−1.4. The flow patterns obtained for various mixers indicate that vortices or recirculation zones are created as the two fluids turn and enter the outlet channel. The formation of recirculation regions results in enhanced mixing rates. The micromixers are evaluated in terms of mixing quality, pressure drop, and mixing effectiveness parameters. The mixing quality increases up to 10 times when the outlet area ratio increases from 0.6 to 2. The rise in pressure drop due to the increased outlet area is about 50%. The inlet area also influences the mixing rate and pressure drop. The mixing quality first increases and then decreases with an increase in area. The pressure drop, whereas, continuously decreases when the inlet area ratio increases from 0.6 to 1.4. Suitable dimensions of micromixers are suggested based on mixing effectiveness. A mixer device with an outlet/junction area ratio of 1.2 and an inlet/junction area ratio 0.8−1 is found to provide better performance.

    Keywords: Computational Fluid Dynamics (CFD), Micromixer, Mixing quality, Pressure drop mixing effectiveness
  • Hossein Fatahian *, Esmaeel Fatahian
    The present study is mainly focused on proposing an effective way to improve the efficiency of a square cyclone separator. For this purpose, a dipleg is attached under the square cyclone to investigate its effect on the performance of the square cyclone. A three-dimensional Computational Fluid Dynamics (CFD) simulation is done by solving the Reynolds-Averaged Navier-Stokes equations with the Reynolds Stress Model (RSM) turbulence model and applying the Eulerian-Lagrangian two-phase method. The turbulent dispersion of particles is predicted by the application of the Discrete Random Walk (DRW) model. The numerical results demonstrate that using dipleg produced an increase in pressure drop but it positively enhances the separation efficiency of the square cyclone. Using dipleg significantly increases the separation efficiency of the square cyclone, especially at higher inlet velocities. This can be more obvious when using dipleg which is minimized the 50% cut size of square cyclone by about 26.3%.
    Keywords: Cyclone separator, Dipleg, Separation efficiency, Eulerian-Lagrangian, Computational Fluid Dynamics (CFD)
  • کیهان لایقمند، نیما غیاثی طبری*، مهران زرکش
    زمینه و هدف

    افزایش روز افزون جمعیت نیاز به توسعه پایدار انرژی را روز به روز بیشتر می کند. همچنین افزایش سطح گازهای گلخانه ای و کاهش سطح ذخایر انرژی فسیلی، مراکز تحقیقاتی دنیا را به سمت انرژی های تجدیدپذیر معطوف کرده است. در میان انرژی های تجدیدپذیر، انرژی باد یکی از مطرح ترین گونه های انرژی های تجدیدپذیر می باشد. در این مطالعه با استفاده از مانع ایرفویل شکل راندمان توربین بادی ساونیوس به طور قابل توجهی افزایش یافته است. این افزایش راندمان به صورت ارتقای قابلیت شروع بکار خودکار توربین بادی ساونیوس و کاهش گشتاور منفی ایجاد شده توسط پره برگشتی انجام شده است.

    روش بررسی

    پیکربندی های مختلف سیستم منحرف کننده (مانع) پیشنهاد شده با استفاده از تکنیک دینامیک سیالات محاسباتی (CFD) به صورت عددی بررسی شده است. شبیه سازی سه بعدی ناپایا معادلات ناویر-استوکس متوسط گیری شده رینولدز (URANS) همراه با مدل توربولانسی SST k-ω انجام شده و با داده های تجربی موجود اعتبارسنجی گردیده است.

    یافته ها

    نتایج پیش بینی شده نشان می دهد که عملکرد روتور ساونیوس بسیار به موقعیت و زاویه مانع بستگی دارد. بنابراین، مقادیر موقعیت و زاویه مناسب برای به دست آوردن بالاترین ضرایب گشتاور و توان وجود داشته است. استفاده از مانع مطلوب ایرفویل شکل، به طور قابل توجهی مقادیر ضریب گشتاور ایستاتیکی را در تمام محدوده زاویه ای خصوصا در زاویه چرخش بین 0 تا 30 درجه و 150 درجه تا 180 درجه افزایش می دهد. با پوشش صحیح پره برگشتی با استفاده از مانع ایرفویل شکل، مقادیر ضریب گشتاور استاتیکی تا 2 برابر بیشتر از مقدار تولید شده در حالت بدون مانع افزایش می یابد.

    بحث و نتیجه گیری

     توربین ساونیوس از راندمان پایینی برخوردار است. بنابراین، مطالعه حاضر با ارایه یک سیستم بهبود دهنده منحرف کننده (مانع) منجر به تولید توان و ضرایب گشتاور بالاتر می شود که در نهایت باعث ایجاد راندمان بالاتر و قابلیت شروع به کار خودکار بهتر می شود.

    کلید واژگان: توربین بادی، مانع ایرفویل شکل، ساونیوس، دینامیک سیالات محاسباتی
    Keyhan Layeghmand, Nima Ghiasi Tabari *, Mehran Zarkesh
    Background and Objective

    With the increment of population, the need for sustainable energy development has been raised. By increasing greenhouse gas emissions and decreasing the fossil energy reserves have also shifted research centers around the world to renewable energy sources. Among renewable energies, wind energy is one of the most important types of renewable energy. In this study, the efficiency of the Savonius wind turbine is significantly increased by using an airfoil-shaped deflector. This increase in efficiency is carried out by upgrading the self-starting performance capability of the Savonius wind turbine and reducing the negative torque generated by the returning blade.

    Material and Methodology

    Different configurations of the proposed deflector system are considered numerically using the CFD solver. A three-dimensional incompressible unsteady Reynolds-Averaged Navier-Stokes simulation in conjunction with the SST k-ω turbulence model is done and validated with the available experimental data.

    Findings

    The predicted results indicated that the performance of the Savonius rotor is highly dependent on the position and angle of the deflector. Thus, there was an appropriate position and angle values to obtain the highest torque and power coefficients. It was concluded that using the favorable airfoil-shaped deflector significantly enhanced the static torque coefficient values in all angular ranges especially in the rotation angles between 0° to 30° and 150° to 180°. By properly covering the returning blade using the airfoil-shaped deflector, the static torque coefficient values increased up to 2 times higher than that generated by without deflector case.

    Discussion and Conclusion

    The Savonius turbine suffers from poor efficiency. Hence, the present work dealt with proposing an improved deflector system led to generate higher power and torque coefficients which resulted in capturing a higher efficiency and better self-starting capability.

    Keywords: Wind turbine, Airfoil-shaped deflector, Savonius, Computational Fluid Dynamics (CFD)
  • مجید رسولی*، سید محمد موسوی، یحیی عجب شیرچی
    درک این که یک فرایند چگونه کار می کند، لازمه ی طراحی و بهره برداری موفق از آن فرآیند می باشد. هضم بی هوازی یک فرایند بیوشیمیایی پیچیده ی چند مرحله ای است که شامل تعدادی واکنش های میانی است که توسط گروه های گوناگونی از میکروارگانیسم های بی هوازی صورت می گیرد. در این پژوهش شبیه سازی بر پایه ی دینامیک سیال های محاسباتی (CFD) سه بعدی جفت شده با واکنش ها در یک راکتور نیمه پیوسته ی پلاگ انجام شد. از نرم افزار تجاری FLUENT 6.3  برای حل معادله های حاکم استفاده شد. شبیه سازی جریان دو فازی گاز مایع با استفاده از مدل چند فازی اولر و مدل آشفتگی k-e (RNG) انجام شد. هیدرودینامیک و واکنش های هضم بی هوازی درون راکتور از روش قاب مرجع چندگانه (MRF) مورد بررسی قرار گرفت. نتیجه های شبیه سازی نشان داد الگوی جریان درون راکتور به شدت تحت تاثیر لزجت و چگالی سوبسترا و شدت همزدن است. مقایسه سه سرعت هم زدن نشان داد هم زدن با شدت زیاد، فاز گاز بالای راکتور را تحت تاثیر قرار می دهد. کانتور غلظت های مولی CH4 و CO2 در سامانه بی هوازی یک الگوی جریان پلاگ را نشان داد.
    کلید واژگان: فرآیند هضم بی هوازی، راکتور جریان پلاگ (PFR)، دینامیک سیالات محاسباتی (CFD)، شبیه سازی، مدل چند فازی اولر
    Majid Rasouli *, Seyyed Mohammad Mousavi, Yahya Ajabshirchi
    In order to design and exploit a process successfully, it's necessary to understand how it works. Anaerobic digestion is a sequential complex biochemical process that involves a series of reactions that are mediated by several different groups of anaerobic microorganisms. This research describes a simulation-based on three-dimensional Computational Fluid Dynamics (CFD) coupled with reactions in a semi-continuous Plug Flow Reactor (PFR). The commercial software FLUENT 6.3 was employed to solve the governing equations. The gas-liquid flow was modeled using a Eulerian multiphase and k-e turbulence (RNG) model. Hydrodynamics and anaerobic digestion reactions investigated the mixing regime using the Multiple Reference Frame (MRF) model within the whole multiphase bioreactor. Simulation results indicate that flow pattern within the reactor was highly influenced by the substrate density and viscosity, and stirring intensity. A comparison of three impellers mixing speed in the reactor demonstrates that mixing intensity has affected the gas phase above the fluid surface. Such a mixing intensity may create a turbulent region with a homogenous mixture of gas and liquid, which is not suitable for this anaerobic digestion. Concentration profiles of CH4 and CO2 in the anaerobic system displayed a plug flow pattern.
    Keywords: Anaerobic digestion process, Plug-flow reactor (PFR), Computational Fluid Dynamics (CFD), Simulation, Eulerian multiphase model
  • Zahoor Hussain, Muhammad Zaman, Muhammad Nadeem, Atta Ullah *
    Granular flow simulation using CFD has received a lot of attention in recent years. In such cases, CFD is either, coupled with Discrete Element Method (DEM) techniques for appropriate incorporation of inter-particle collisions, or the Eulerian CFD approach is used in which granular particles are treated as they were fluid. In the present study, a CFD analysis was performed for granular flow in an industrial screw feeder to study the choking phenomena. Eulerian multiphase flow model, also known as two-fluid model in the case of two phases, was used along with the solids closures based on Kinetic Theory of Granular Flow (KTGF). The rotating effect of the half pitch screw was incorporated by using the immersed boundary method (IMB). Variation of mass flow through change in revolution per minute (RPM) and moisture content was studied in this work. A jump condition in the axial profiles of both the solid phase volume fraction and pressure was observed near the inlet. It was found that the jump condition in solid phase volume fraction and pressure profiles reduces by increase in the RPM of the screw.
    Keywords: Computational Fluid Dynamics (CFD), Kinetic Theory of Granular Flow (KTGF), Immersed Boundary Method (IBM), Screw Feeder
  • Seyed Ebrahim Ghasemi *, Ali Akbar Ranjbar, Seyed Mohammad Javad Hoseini
    In this paper, the cooling performance of water-cooled heat sinks for heat dissipation from electronic components is investigated numerically. Computational Fluid Dynamics (CFD) simulations are carried out to study the rectangular and circular cross-sectional shaped heat sinks. The sectional geometry of channels affects the flow and heat transfer characteristics of minichannel heat sinks. The three-dimensional governing equations in steady state and laminar flow are solved using Finite Volume Method (FVM) with the SIMPLE algorithm. The results show that the numerical simulation is in good agreement with the experimental data. The thermal and hydrodynamic characteristics of the heat sinks including Nusselt number, friction factor, thermal resistance and pumping power for various geometries of heat sinks are discussed in details. The results indicate that the heat sink with rectangular cross-section has a better heat transfer rate and the circular channel heat sink has the lower pumping power.
    Keywords: Cooling performance, Computational Fluid Dynamics (CFD), Heat sink, Circular channel, Rectangular channel
  • S. Asadi
    A novel computational fluid dynamics and molecular kinetic theory (CFD-MK) method was developed to simulate the impingement of a nanodroplet onto a solid surface. A numerical solution of the Navier–Stokes equation using a volume-of-fluid (VOF) technique was used to model nanodroplet deformation. Dynamic contact angle during droplet impact was obtained by molecular kinetic theory. This dynamic contact angle was then implemented in the numerical model used to simulate the process. The spreading behavior was analyzed for the wettable, partially wettable and nonwettable surfaces. The consistency between the two results was good both qualitatively and quantitatively.
    Keywords: Nanodroplet impact, Free surface flows, Molecular kinetic theory, Numerical simulation, Computational fluid dynamics(CFD)
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  • نتایج بر اساس تاریخ انتشار مرتب شده‌اند.
  • کلیدواژه مورد نظر شما تنها در فیلد کلیدواژگان مقالات جستجو شده‌است. به منظور حذف نتایج غیر مرتبط، جستجو تنها در مقالات مجلاتی انجام شده که با مجله ماخذ هم موضوع هستند.
  • در صورتی که می‌خواهید جستجو را در همه موضوعات و با شرایط دیگر تکرار کنید به صفحه جستجوی پیشرفته مجلات مراجعه کنید.
درخواست پشتیبانی - گزارش اشکال