List of Articles ضریب اصطکاک

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  1 - Determination of Some Physical Properties of Pistachio Nut and Its Kernel (Qazvini Varieties)
  mohammad gholami porshokohi milad mohammadi shamami shahram mohseni ali mashallah kermani ehsan abdolalizadeh
  Introduction: Understanding the physical and mechanical characteristics and knowledge of agricultural products are important and vital and knowledge steps for post harvesting storage and preservation. In this study, several physical properties of the Qazvinian cultivars More

  Introduction: Understanding the physical and mechanical characteristics and knowledge of agricultural products are important and vital and knowledge steps for post harvesting storage and preservation. In this study, several physical properties of the Qazvinian cultivars (Qazvini and Boein zahra) of pistachio nut and their kernel and the effect of different levels of moisture content on their characteristics were evaluated.Materials and Methods: Physical properties that consisted of dimensional specifications such as three major diameter (length, width, thickness), unit mass, sphericity, geometric and arithmetic mean diameter, surface area, true volume, true density, bulk density, porosity and the static coefficient of friction at five levels of moisture content (3.5%, 12%, 19.5%, 27%,35.5% ) were measured.Results: The results of this investigation concerned with geometrical properties indicated that moisture had significant effects on the dimension, geometric and arithmetic mean diameter,sphericity, surface area of pistachio nut and its kernel in both cultivars.Conclusion: By increasing the moisture content, all the listed properties of both cultivars (Qazvini and Boein Zahra) have been increased. The highest static coefficient of friction for Qazvini and Boein Zahra cultivars is on aluminum and the lowest is on plastic surfaces. The kernels of Qazvini and Boein Zahra pistachio, had the highest coefficient on wood and the lowest coefficient on plastic and glass surfaces respectively. Manuscript profile
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  2 - The effect of volume fraction and size of Al2O3 nanoparticle on heat transfer and flow characteristics in the heat exchanger with louvered strip inserts
  Meysam Pouyanian Ashkan Ghafouri
  In this study, the effect of using louvered strip inserts in heat exchangers on flow and transfer characteristics is numerically investigated. The continuity, momentum, and energy equations have been solved using a finite volume method. The wall of the tube is heated wi More

  In this study, the effect of using louvered strip inserts in heat exchangers on flow and transfer characteristics is numerically investigated. The continuity, momentum, and energy equations have been solved using a finite volume method. The wall of the tube is heated with a uniform heat flux boundary condition. This paper uses a louvered strip insert arrangement (forward) with a Reynolds number of 10,000. The effects of louvered strip slant angle of  and pitch of 50 mm were used for Al2O3 nanoparticles with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 20 nm to 50 nm, mixed in a base fluid (water) is used. The comparison of numerical analysis results with existing equations has shown a good convergence. The numerical results reveal that the Nusselt number has increased with decreasing the nanoparticle diameter. The results indicate a slight change in the skin friction coefficient when nanoparticle diameters of Al2O3 nanofluid are varied. The Nusselt number increases with increasing nanoparticle volume fraction of Al2O3 /water nanofluid, while it is found that pure water has the lowest Nusselt number value. Also, the nanofluid has reduced the wall's temperature more than the base fluids (water), which indicates the advantage of using nanofluids in improving the system's thermal performance. Manuscript profile
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  3 - Experimental Study of Interfacial Friction Factor and Shear Stress in Counter-current Two-phase Flow in a Vertical Pipe
  Arash Ghafouri Ashkan Ghafouri Abbas kosarineia Alireza Daneh-Dezfuli
  In the experimental study, the formation of the annular flow pattern in a vertical pipe with the counter-current two-phase flow has been investigated with the help of image recording and processing techniques. After separating the created two-phase flow regime, the rang More

  In the experimental study, the formation of the annular flow pattern in a vertical pipe with the counter-current two-phase flow has been investigated with the help of image recording and processing techniques. After separating the created two-phase flow regime, the range of superficial velocity of air (upward) and water (downward) is 3.66-20.94 m/s and 0.06-0.31m/s for annular flow, respectively. The interfacial friction factor (liquid and gas phase) has been evaluated according to the hydrodynamic parameters of the flow. Comparing the average deviation of the results obtained from the current research with the previous research shows that the results are in good agreement. Also, the interfacial shear stress has been calculated and evaluated for two test pipes in the center-current two-phase flow pattern in the annular flow regime. In this research, the interfacial friction factor (liquid and gas phase) is also presented as a new correlation depending on the Reynolds number of the gas flow and the Reynolds number of the liquid flow with a coefficient of determination of R2=0.98. Manuscript profile
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  4 - Entropy generation in a sample gas distribution network using steel and polyethylene pipes
  Ali Heydari
  Natural gas is extracted from wells and after purification, it reaches to consumption stages by transmission and distribution network. Energy losses in this section is vital and must be calculated appropriately. In this study, the network of distribution with low workin More

  Natural gas is extracted from wells and after purification, it reaches to consumption stages by transmission and distribution network. Energy losses in this section is vital and must be calculated appropriately. In this study, the network of distribution with low working pressure is examined. A network sample of natural gas is investigated using analitical solution of a steady flow of natural gas. Flow equations initially provided for a tube considering all parameters. Then, using the existing rules in pipe networks the network sample is analyzed. Effect of tube material as an important factor on network performance are evaluated and analyzed And finally, the rate of entropy generation in steel and polyethylene pipes were compared. The results show that by increasing the diameter or decreasing the gas flow rate, the tube material and friction coefficient is less effective on entropy generation in practice. Furthermore, the gas flow in lower diameters cause more entropy production using steel pipes in compare with polyethylene pipes. Manuscript profile
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  5 - Investigation Effective Factors On Energy Depreciation Of Stepped Spillways
  saeed razmara Abbas mansori
  In recent decades, stepped spillways have been a significant role in this case.. This research is based on The flow energy calculated on these edged steps and simple steps in nappe flow and skimming flow regimes. Difference in height, width and edge slopes will determin More

  In recent decades, stepped spillways have been a significant role in this case.. This research is based on The flow energy calculated on these edged steps and simple steps in nappe flow and skimming flow regimes. Difference in height, width and edge slopes will determine the effects of each of these parameters on energy dissipation ratio And then the analysis of sixteen model with different geometries were conducted by Gambit and Fluent software for two discharges ٣/٦ lit/s (nappe flow) and ٢٥ litr/s (skimming flow) by the total of ٣٢ models. And with regard to the results achieved, the influence of the edge for nappe flow has been regarded according to Chamani and Rajaratnani equations. With regard to the results, it is suggested that the existence of the edge at the step end can be enhanced the energy dissipation ratio along the stepped chute. Of course the ratio of this effect in flow and skimming regimes are not the same and these effects are decreased by increasing of discharge. Manuscript profile
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  6 - بررسی عددی انتقال حرارت و جریان آرام نانوسیال آب-اکسید آلومینیم در ‏میکروکانال مستطیلی دندانه‌دار
  داود طغرایی آرش کریمی پور امید علی اکبری مجید زرین قلم حبیب اله عالی‌پور
  This paper numerically examines the laminar forced convection of a water–Al2O3 nanofluid flowing through a horizontal rib-microchannel. The middle section of the down wall microchannel is Affected by cold temperatures with a constant and uniform tempreture Tc. The m More

  This paper numerically examines the laminar forced convection of a water–Al2O3 nanofluid flowing through a horizontal rib-microchannel. The middle section of the down wall microchannel is Affected by cold temperatures with a constant and uniform tempreture Tc. The middle section is also influenced by a transverse rib array. The effects of height rib in a two dimensional rib-microchannel on flow and heat transfer parameters of laminar water-Al2O3 nanofluid are investigated. The characteristics of this research are numerically investigated by the commercial software Fluent 6.3 in a Reynolds number as Re=10 and Re=100. Four different states of hight rib are analyzed. Higher conventional internal ribs or increasing the turbulators can significantly improve the performances of the convective heat transfer within a microchannel. It is seen that larger height rib and volume fraction of nanoparticles corresponds more heat transfer rate; however the added high ribs can cause a larger friction factor than that in the corresponding microchannel by constant height rib. At present article the effect of height rib on the fluid flow parameters are also studied for all different states of it. The results show that the microchannel performs better heat transfers at higher values of the Reynolds numbers. For all values of the Reynolds numbers and volume fraction of nanoparticles considered in this study, the average Nusselt number on the middle section surface of the microchannel increases as the solid volume fraction increases. Manuscript profile
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  7 - بررسی تأثیر ضریب اصطکاک بر میزان عیب دم ماهی در فرایند نورد حلقوی گرم
  امیر حسین قیصری محمدرضا فروزان عبدالعلی مراثی
  نورد حلقوی گرم یک فرایند به شدت غیر خطی و ناپایدار است. ضریب اصطکاک میان رینگ با غلتک محرک و هرزگرد از این جمله اند که بر کیفیت محصول نهایی تأثیر به‌سزایی دارند. در این مقاله تأثیر این دو پارامتر بر نورد حلقوی گرم به کمک مدل  سه بعدی المان محدود کوپل مکانیکی- حرارت More

  نورد حلقوی گرم یک فرایند به شدت غیر خطی و ناپایدار است. ضریب اصطکاک میان رینگ با غلتک محرک و هرزگرد از این جمله اند که بر کیفیت محصول نهایی تأثیر به‌سزایی دارند. در این مقاله تأثیر این دو پارامتر بر نورد حلقوی گرم به کمک مدل  سه بعدی المان محدود کوپل مکانیکی- حرارتی بررسی شده است. بدین منظور مدلی سه بعدی از فرایند نورد حلقوی گرم شامل رینگ، غلتک­های محرک، هرزگرد و راهنما در نرم افزار آباکوس ایجاد شده و میزان عیب دم ماهی به ازای ضریب اصطکاک­های مختلف میان غلتک محرک و حلقه و همچنین غلتک هرزگرد و حلقه اندازه‌گیری شده است. نتایج نشان می­دهد که با افزایش ضریب اصطکاک میان رینگ و غلتک هرزگرد یا کاهش ضریب اصطکاک میان رینگ و غلتک محرک میزان عیب دم ماهی کاهش می­یابد. همچنین میزان تغییرات این دو پارامتر باید در محدوده معینی حفظ شده و از آن تجاوز ننماید. نتایج به‌دست آمده می­تواند به عنوان راهنمایی به منظور بهینه سازی فرایند مزبور به کار گرفته شود. Manuscript profile
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  8 - بررسی آزمون اصطکاکی تی شکل برای آلیاژ تیتانیوم در دمای بالا
  فرزان براتی یاسر نعمتی
  متغیرهای متعددی بر فرایند شکل­دهی فلزات تاثیر گذار می­باشند که یکی از مهمترین آنها اصطکاک است.اصطکاک بر نحوه سیلان ماده و همچنین نیروی مورد نیاز برای شکل­دهی اثر گذار می باشد. برای تعیین میزان و نحوه تاثیر آن داشتن مقدار دقیق ضریب اصطکاک ضروری است. این مقاله More

  متغیرهای متعددی بر فرایند شکل­دهی فلزات تاثیر گذار می­باشند که یکی از مهمترین آنها اصطکاک است.اصطکاک بر نحوه سیلان ماده و همچنین نیروی مورد نیاز برای شکل­دهی اثر گذار می باشد. برای تعیین میزان و نحوه تاثیر آن داشتن مقدار دقیق ضریب اصطکاک ضروری است. این مقاله مربوط به مطالعه تجربی و عددی روی آلیاژ تیتانیوم با استفاده از آزمون اصطکاکی تی شکل در دمای بالا است. و با استفاده از شبیه سازی اجزا محدود و آزمایش‌های تجربی اثرات پارامترهای دما، سرعت ، شعاع گوشه قالب، و شرایط اصطکاکی در آزمون تی شکل مورد مطالعه قرار گرفته است. بر اساس نتایج تجربی و عددی مشخص شد حساسیت اصطکاک در آزمایشتی شکلبا افزایش سرعت قالب یا کاهش شعاع لبه قالب و دمای آزمون،افزایش می­یابد. همچنین همخوانی بین مقادیر ضریب اصطکاک به دست آمده به وسیله نرم افزار تحلیل اجزا محدود و منحنی کالیبراسیون اصطکاکی برای شرایط مختلف اصطکاک دیده شد. Manuscript profile