One of the fundamental challenges in photovoltaic (PV) systems is the rise in panel temperature under intense solar radiation, which leads to reduced efficiency and service life. The use of phase change materials (PCM) as thermal energy storage can help reduce the surface temperature of panels. In this study, the combination of PCM with metal foams (MF) is investigated; metal foams, due to their high porosity and suitable thermal conductivity, can accelerate heat transfer and reduce PCM melting time. This research employs a computational fluid dynamics (CFD) approach to numerically simulate a PV-PCM-MF system and analyzes the effect of parameters such as metal foam porosity and geometric dimensions of the heat sink on the thermal and electrical performance of the solar panel. The main objective is to present a novel method for optimizing heat transfer and enhancing the electrical efficiency of photovoltaic systems. The results of this study are expected to demonstrate that appropriate selection of cavity geometry and optimal combination of PCM and metal foam can lead to reduced panel operating temperature, increased thermal storage capacity, and significant improvement in electrical efficiency. This research provides practical guidance for the optimal design of hybrid PV-PCM-MF systems in the field of renewable energy.

در اين پژوهش، عملكرد ستون‌هاي سنگي به عنوان روشي موثر در تقويت خاك‌ها و افزايش پايداري شيب‌ها مورد بررسي قرار گرفته است. هدف اصلي تحقيق، تحليل سه‌بعدي راندمان ستون‌هاي سنگي با توجه به آرايش‌هاي هندسي مختلف در شيب‌هاي مختلف مي‌باشد. بهسازي و تقويت شيرواني‌هاي خاكي در برابر تغييرمكان‌هاي جانبي، نشست و كاهش ضريب اطمينان از موضوعات مهم در مهندسي ژئوتكنيك است. ستون‌هاي سنگي به‌عنوان يكي از كارآمدترين روش‌هاي بهسازي زمين، با ايجاد محصورشدگي جانبي، بهبود زهكشي و افزايش سختي توده خاك، نقشي مؤثر در افزايش پايداري شيرواني‌ها ايفا مي‌كنند. با وجود اين، كارايي ستون‌هاي سنگي تا حد زيادي به آرايش هندسي، طول ستون، قطر و نحوه اندركنش آن‌ها با لايه‌هاي خاكي وابسته است. در اين پژوهش، عملكرد سه آرايش هندسي ستون‌هاي سنگي (مثلثي، مربعي و شش‌ضلعي) و همچنين تأثير طول ستون، به‌صورت عددي و سه‌بعدي با استفاده از نرم‌افزار PLAXIS-3D   مورد بررسي قرار گرفته است. نتايج نشان داد كه آرايش‌هاي هندسي مختلف اثر قابل توجهي بر رفتار مكانيكي شيب دارند. آرايش مثلثي بهترين عملكرد را از نظر كاهش جابه‌جايي افقي و افزايش ضريب اطمينان پايداري ارائه كرد؛ به‌طوري‌كه بيشترين مقدار ضريب اطمينان برابر با 6/1 براي اين آرايش به‌دست آمد. در مقابل، آرايش شش‌ضلعي ضعيف‌ترين عملكرد را داشته و كمترين ضريب اطمينان برابر با   28/1 ثبت شد. اين اختلاف بيانگر بهبود حدود 25 درصدي ضريب اطمينان در آرايش مثلثي نسبت به شش‌ضلعي است. بررسي تأثير طول ستون نيز نشان داد كه افزايش طول ستون از 3 متر به 6 متر موجب افزايش حدود 2/21 درصدي ضريب اطمينان پايداري شيب مي‌شود. همچنين با افزايش طول ستون، جابه‌جايي افقي به‌طور معني‌داري كاهش يافته و رفتار شيب پايدارتر شده است. از نظر تنش‌ها نيز مشاهده شد كه آرايش مثلثي بالاترين مقدار تنش برشي پيك را در حدود 390 كيلوپاسكال ايجاد مي‌كند، در حالي‌كه آرايش مربعي مقدار مياني حدود 350 كيلوپاسكال و آرايش شش‌ضلعي كمترين مقدار را نشان داد كه ناشي از محصورشدگي جانبي كمتر است. به‌طور كلي، نتايج تحقيق نشان داد كه انتخاب آرايش مناسب ستون‌هاي سنگي و بهينه‌سازي طول آن‌ها مي‌تواند كاهش قابل توجهي در نشست قائم، جابه‌جايي جانبي و افزايش چشمگيري در ايمني شيب ايجاد كند. يافته‌هاي اين پژوهش مي‌تواند به‌عنوان مرجعي براي طراحي بهينه ستون‌هاي سنگي در پروژه‌هاي عمراني به‌ويژه در شرايط خاك‌هاي سست و لايه‌اي مورد استفاده قرار گيرد.   

  Abstract Biosensors have attracted special attention in recent years as key tools in biomedical, environmental, and pharmaceutical fields. The increasing demand for rapid, accurate, and low-cost diagnostic methods has led researchers to use Field-Effect Transistors, specifically Tunnel Field-Effect Transistors (TFETs). Due to their low power consumption, subthreshold swing of less than 60 mV/decade, and compatibility with nano-scale technologies, these devices are ideal candidates for developing the next generation of biosensors. In this thesis, three different architectures of short-gate TFET-based biosensors, including Continuous-Gate Structure , Multi-Segment Gate Structure , and Fractional-Gate Structure, were designed, simulated, and analyzed. To investigate the effect of dielectric materials on sensor sensitivity, four different dielectric constants (1, 7, 9, and 11) were considered for filling the biosensor cavities. Simulations were performed using the Atlas environment in SILVACO software based on advanced physical models, including Band-to-Band Tunneling (BTBT), SRH and AUGER recombination, and field-dependent mobility models (CONMOB and FLDMOB). Simulation results showed that the choice of architecture and dielectric constant plays a decisive role in the sensitivity and efficiency of biosensors. In the continuous-gate structure, drain current sensitivity decreased from approximately2500 for k=11 to 400 at higher voltages. In the multi-segment gate structure, the initial sensitivity for k=11 was reported at about 600, which decreased to 70 at higher voltages. In the fractional-gate structure, sensitivity for k=11 was over 70 at low voltages and reached about 2 as the drain voltage increased. This comparison indicates that the continuous-gate structure with high dielectric constants offers optimal sensitivity performance, while the fractional-gate structure provides greater stability. The results of this research show that through optimizing gate architecture and selecting high-k dielectric materials, biosensors with higher accuracy and lower power consumption can be developed for real-world environments. These achievements can play a significant role in rapid disease diagnosis, environmental monitoring, and the development of portable medical devices. Keywords: Biosensor, Tunnel Field-Effect Transistor (TFET), Short Gate, Sensitivity, Dielectric Constant, SILVACO Simulation.

   Nowadays nonlinear analysis methods are employed for the seismic evaluation and strengthening of various structural systems. Detailed investigation of the actual performance of buildings during earthquakes and the development of economically optimized designs clearly demonstrate the necessity of performing nonlinear analyses. In performance-based seismic design, structures are designed to achieve different expected performance levels corresponding to different seismic hazard levels. One of the most important steps in performance-based seismic design is the determination and calculation of the performance point. To evaluate the structural performance, nonlinear analyses can be utilized, which are generally >Accordingly, various approximate methods for determining the structural performance have been proposed in seismic codes and guidelines. Among these methods are the Displacement Coefficient Method, the Capacity Spectrum Method, and the Improved Capacity Spectrum Method (N2 method). The objective of this study is to evaluate the accuracy of these methods in estimating the performance point. For this purpose, several reinforced concrete building frames are modeled, and their performance points are calculated using the aforementioned methods. To assess the accuracy of the results obtained from these methods, nonlinear time history analyses are performed on the same frames. The results of the nonlinear time history analyses are considered as reference (exact) results and are used as a basis for evaluating the level of approximation and accuracy of the Displacement Coefficient Method, the Capacity Spectrum Method, and the Improved Capacity Spectrum (N2) Method.          Keywords: Performance Point, Nonlinear Static Analysis, Capacity Spectrum, N2 Method

Unsaturated polyester resin (UPR) is widely used in the composite industry due to its desirable properties such as low cost and good processability. However, its low corrosion resistance, high brittleness, and flammability limit its applications in various industrial fields. To overcome these limitations, the incorporation of reinforcing particles into the resin has recently been proposed as an effective approach. In this study, bimetallic metal–organic frameworks (Fe/Al-BDC-NH?) were employed as reinforcing additives to investigate their effect on the physical–mechanical properties and corrosion resistance of unsaturated polyester resin. Owing to their hybrid structure, the MOF particles—with metallic sites enhancing mechanical performance and organic linkers enabling interfacial bonding with polymer chains—prevented particle sedimentation and improved the uniformity and adhesion of the polymer network. Structural and performance analyses of the composites were carried out using XRD, FT-IR, FE-SEM, DMA, and electrochemical impedance spectroscopy (EIS). The results revealed that the incorporation of a small amount of Fe/Al-MOF significantly increased the storage modulus, improved interfacial adhesion, enhanced electrochemical stability, and reduced the permeability of the resin in corrosive environments. Overall, the presence of bimetallic MOF particles remarkably improved the mechanical and anti-corrosion performance of the unsaturated polyester resin and offers a promising route for developing high-performance, corrosion-resistant coatings and composites for industrial applications.   

Abstract

   In recent years, fluidized beds have garnered attention across various industries due to their advantageous characteristics, such as uniform temperature distribution, effective phase mixing, and high heat transfer rates. One effective method to enhance the efficiency of these beds is the use of a pulsed inlet. This technique improves the homogeneity of the bed and eliminates inactive and stagnant zones (dead zones) within the particles by varying the inlet air flow. Despite extensive research on the simulation of conventional fluidized beds, the study of pulsed bed systems has been relatively limited. In this thesis, the gas-particle two-phase flow in a spouted fluidized bed with a rectangular geometry and pulsed air inflow was numerically investigated. The simulation was carried out using a combination of Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). To reduce computational costs, the geometry was defined as quasi-two-dimensional with a depth of 6 particles. The modeling was performed in a transient state, where a specific number of particles were initially placed at a certain height within the bed, and then gas was injected into the bed at a specified pulsed velocity. In this study, the pulses were applied in three waveforms: square, sinusoidal, and sawtooth, with frequencies of 1, 4, and 10 Hz. The results showed that when fluidizing (side) gases were present in the bed, applying a pulsed inlet in the spout positively impacted the elimination of dead zones and the circulation of particles across all three frequencies and waveforms. It was demonstrated that a frequency of 10 Hz and a square waveform yielded the best results. For instance, in a spouted fluidized bed at 10 Hz, the particle travel distance improved by 12.81%, 5.99%, and 5.97% for square, sinusoidal, and sawtooth waveforms, respectively. Similarly, improvements of 55%, 35%, and 30% were observed in the reduction of dead zones. In rectangular beds, it was found that the removal of fluidizing gases had significant negative effects on particle circulation and increased the dead zones, with the proportion of dead zones rising from 0.5% to 7.7% of the total particles. Finally, to examine the effect of fluidizing gases, different configurations with varying spout and fluidizing gas velocities were investigated. In these configurations, the spout velocity was gradually decreased while simultaneously increasing the fluidizing gas velocity, keeping the total inlet gas flow constant. The results showed that in two configurations where the fluidizing gas velocity reached its maximum, the dead zones were completely eliminated, particle mixing improved, and homogeneity in particle distribution increased. In the optimal gas inlet configuration, applying a square pulsed inlet at 10 Hz resulted in a 1.55% improvement in the average particle travel distance. In this study, it was demonstrated that by applying a pulsed flow and adjusting the inlet gas velocities, the hydrodynamic performance of the bed can be improved without the need for changes in the system geometry or the total inlet flow rate.

  One of the most important sources of energy for the

      Abstract The present study investigates and analyzes the energy and exergy of solar desiccant cooling systems with the aim of providing thermal comfort in residential buildings with high internal loads in three cities: Ahvaz, Bushehr, and Rasht. Considering the increasing energy demand in buildings and the environmental challenges arising from the consumption of fossil fuels, the use of innovative and sustainable systems in air conditioning has become more important than ever. Accordingly, desiccant cooling systems, which operate based on moisture absorption, have been introduced as an efficient solution for optimizing energy consumption and reducing environmental impacts. The results indicate the high potential of desiccant cooling systems. In this research, a maximum COP (Coefficient of Performance) of 0.404 was recorded for the system at temperatures of 15°C. Additionally, at temperatures of 35°C and 45°C, the COP decreased to 0.32 and 0.33, respectively, indicating better performance of this system at lower temperatures. The analyses also emphasize that the cooling capacity at temperatures ranging from 28°C to 40°C in Bushehr varies between 18.2 to 20.6 kW, and in Ahvaz between 19.5 to 21.5 kW. This research, while providing a roadmap for selecting optimal design parameters, hopes to offer practical solutions for ensuring thermal comfort in hot and humid regions. Overall, the results suggest improved performance of air conditioning systems and achieving thermal comfort in residential buildings through the use of desiccant materials and solar energy. Key words: Solar Desiccant Cooling, Thermal Comfort, Energy and Exergy Analysis, Residential Buildings, Hot and Humid Climates   

در بسياري از صنايع مهندسي ذرات جامدي كه همراه سيالات حمل مي¬شوند، توانايي آسيب سايش به خطوط لوله و خصوصاً اتصالات را دارند و آن¬ها را در معرض نشت و شكست قرار مي¬دهند. در واقع سايش يك مكانيسم مكانيكي است كه سبب جداشدن مواد از سطح به دليل برخورد مكرر ذرات جامد است و خسارت¬هاي مالي و جاني در پي دارد. به همين سبب باعث شده است كه اين موضوع اهميت پيدا كند و روش¬هايي در جهت كنترل سايش پيشنهاد شود. يك روش مناسب براي پيش¬بيني نرخ سايش حل ديناميك سيالات محاسباتي است كه در سال 1990 امكان استفاده از اين روش فراهم شد. پژوهش حاضر سعي در استفاده از رويكرد اويلر - لاگرانژ با نرم‌افزار انسيس فلوئنت دارد بدين منظور كه شبيه‌سازي جريان سيال (فاز پيوسته) در ديدگاه اويلري و شبيه‌سازي رديابي ذرات جامد (فاز گسسته) در ديدگاه لاگرانژي صورت مي¬گيرند. در ادامه فرايند استقلال از شبكه و ذرات براي جريان دوفازي گاز - جامد در هندسه زانويي 90 درجه استاندارد انجام مي¬شود. همچنين اعتبارسنجي داده¬هاي عددي حاضر مساله با داده¬هاي تجربي ديگر مقالات تحت شرايط يكسان، براي جريان تك¬فاز و دوفاز مقايسه مي¬گردند تا نتايج قابل‌قبولي لحاظ گردد. در همين راستا سبب شد مدل آشفتگي از نوع تنش رينولدز، كوپل يك¬طرفه، مدل سايش اوكا، مدل ضريب بازگشت ذرات گرانت و تاباكف و نيروهاي وارده بر ذرات شامل پسا، جرم مجازي، شناوري و گرانش در حل عددي اين پايان‌نامه انتخاب شوند. پارامترهاي زيادي در ميزان سايش دخيل هستند كه در اين پژوهش برخي پارامترها شامل سرعت جريان، اندازه قطر ذرات، نرخ ورودي ذرات و تأثير زبري سطح ديواره مورد بررسي عددي قرار داده شدند. در بين اتصالات، زانويي¬ها در معرض خطر جدي¬تري هستند. با پيشنهاد جايگزيني اتصالات ديگر كه هدف و ماهيتي شبيه به كارايي زانويي دارند، انتخاب مي¬شوند و سايش را نسبت به زانويي 90 درجه استاندارد كاهش مي¬دهند. اتصالات شامل دو نوع خم مايتر، سه نوع اتصال كور، زانويي كاهنده و دو نوع زانويي كروي شكل هستند. شرايط حل عددي براي تمام اتصالات جهت مقايسه نتايج با يكديگر به¬صورت مشابه تنظيم مي¬گردند. سپس نتايج عددي نهايي پايان‌نامه بيان مي¬كند كه در سرعت جريان و قطر ذرات يكسان براي بحراني‌ترين حالت، اتصالات ذكر شده مقاومت سايشي را 22/5% تا 39/6% نسبت به زانويي 90 درجه استاندارد افزايش مي¬دهند.

Developing the scope of application of new material depends on understanding the behavior of these in different environments and also gaining knowledge on the effect of various factors such as heat treatment parameters on their properties.   With regard to this issue we focused on the investigation the effect of partial austenitizing duration on creating a matrix with a dual structure of ferrite-ausferrite, corrosion resistance, bending strength, time to failure in crosive media under applied bending loads and stress corrosion threshold stress of a carbidic austempered ductile iron (CADI) which has been known as new family of ADI. In this regard, cast parts from a non-alloy carbidc cast iron were first subjected to ferritizing annealing to obtain full ferritic matrix. Then, the samples were partially austenitized at 870 ?C for 10, 15, and 20 minutes, followed by austempering in a molten salt bath at 350 ?C for one hour. After it, samples microstructures were examined with an optical microscope. In the next step, electrochemical corrosion tests were performed with Tafel polarization method. Then, by preparing notched and smooth C-ring samples, the loads leading to their failure were determined under the bending tests in air. Finally, the behavior of C-ring samples in corrosive caustic soda solution were investigated under bending loads. According to the obtained results, with the increase of the partial austenitizing time, the ausferrite phase fraction increased according to the JMAK equation. The creation of dual matrix structure of ferrite-ausferrite caused the corrosion resistance of the samples to be weakened compared to the samples with fully ferritic matrix and conventional ADI. As the partial austenitizing time increased, the corrosion resistance, bending tensile strength in air and time to failure in corrosive media under constant load, increased. The bending loads leading to the failure of notched samples in air were significantly lower than those of smooth samples. The results of stress analysis in C-ring samples under bending test in air showed that the reduction of cross-sectional area, change the outer effective radius and neutral radius of the samples, and stress concentration are three contributing factors in reducing the tolerable bending load without occouranse failure with the contribution of 35%, 35% and 30%, respectively. The notch strength ratio (NSR) was independent of the effect of partial austenitizing time and it was about 0.87. All the smooth samples endured 100 hours of stress-corrosion testing under maximum applied loads (equivalent to 85% of failure load in air) without occurrence of failure. By decreasing the applied load in the corrosive environment, the time to failure of all samples increased greatly. There was a power relationship between the stress-corrosion threshold stress and the ultimate tensile strength of the samples. Also, during stress-corrosion testing the gradual fracture along with growth of cracks was not observed and failure of all samples in both environments air and caustic soda occurred via very rapid crack propagation in a completely brittle mode over the whole range of the applied loads.   

  In

   Identification of two-phase flows and its Taylor bubble characteristics is one of the most important parameters designing industrial installations for intermittent gas-liquid two-phase flow. Also, it is important to know the characteristics of two-phase flow in order to improve the exploitation of oil wells and to optimize the process of maintenance and repair of flow transmission lines with the purpose of cleaning pipelines along with reducing its costs in the oil and gas industries and in chemical and electronic chip cooling industry. The purpose of this research to analyze bubble flow patterns, achieve two-phase flow patterns of water and air using numerous experimental tests and investigate the effect of pulsating gas flow on the characteristics of the Taylor flow field (Taylor bubble length and velocity) under different two-phase inlet conditions air and water done in the form of an upward parallel flow. The range of studied apparent velocity Gas and Liquid phase is 0.12-0.28 m/s and 0.05-0.25 m/s, respectively, and the pulsating gas flow frequency is 0.25-0.4 Hz. In this study, by examining more than 100 different apparent velocities for the phases, three patterns of bubble, slug and churn were observed and a map of the two-phase flow pattern of water and air was drawn. Also, the effect of pulsating gas flow on the length of the Taylor bubble was investigated in 150 different experiments, and the results of this study showed that with the increase of the pulsating gas flow and the frequency, the stability of the Taylor bubble flow increased and the length of the Taylor bubble decreased significantly. So that at the frequencies of 0.25, 0.5, 1, 2 and 4 Hz, respectively, the maximum bubble length was observed at the liquid velocity of 0.12 m/s and gas velocity of 0.25 m/s are 455.5, 367, 313.1, 286.3 and 244.2 mm.   Also, at a constant frequency, the length of the Taylor bubble increases with the increase of the apparent velocity of the gas phase. For example, at a constant frequency of 1 Hz and a liquid velocity of 0.12 m/s, the bubble length increased from 147.8 mm to 1.313 mm when the gas velocity increased from 0.10 to 0.25 m/s. In addition, in this research, with the help of image processing, the movement speed of the Taylor bubble was measured and determined for 15 different apparent speeds using the speed measurement technique. Comparison of the obtained linear equation with previous studies showed that the relationship has a good fitting accuracy. The results of the present work proves that the pulsating gas flow technique enables the control of the gas-liquid Taylor bubble flow pattern and the stability of the motion of the Taylor bubbles, which will be very useful for future industrial applications in gas-liquid reactions.

Abstract: Due to the limitations of mineral resources on the earth and the distant horizon for long-term life on this planet, preservation and maintenance of materials against damage and destruction becomes very important in industrial societies. On the other hand, the growing process of industrialization of human life has increased the share of industrial sectors in the financial portfolio of governments, and governments are forced to send a large amount of their financial resources to the industrial market every year in order to reach the desired level of industry. Abrasion is one of the main destructive events in the fluid transfer sector in industries. Especially when two-phase and multi-phase fluid flows are involved. Obviously, the countries where the transfer of refinery, power plant, oil and gas fluids is considered their vital artery are more involved in this phenomenon in their industries than others. Today, software simulations compete strongly with laboratory research. Because laboratory research, despite all its inherent advantages and advantages, has disadvantages such as high costs. On the other hand, the increasing power of computer systems for analysis and simulation is a powerful support. This research is a simulation with the help of numerical methods, in which a 90 degree elbow is considered as a sample piece (which is one of the most damaged industrial connections). To carry out the desired simulation, a computational fluid dynamic model has been used along with the discrete cell method. The continuous fluid and the particles injected into the flow at the elbow inlet were simulated in different geometries. The final simulation model includes McLaury's Erosion model based on the validation results. Particles are tracked by Lagrangian method along with random collisions of Grant-Tabakoff recursive model. To ensure the correctness of this choice, another validation has been used in this section. Considering that particle momentum plays an important role in Erosion, in this research, it has been tried to make the injected particles lose their momentum by rotating the water flow lines. Therefore, changes were made in the same direction in the knee geometry. The result of this research shows that changing the geometry of the elbow reduces the momentum of the particles when they collide with the internal surfaces to the extent that it increases the life of the elbow by about 8 times in the case of using internal spiral blades. Key word: Erosion, elbow, helical blades, computational fluid dynamics, Euler Lagrange, particle tracking   

بيماري‌هاي ريه داراي آمار بالاي مرگ و مير در جهان هستند. دراين‌ميان آسم به عنوان شايع‌ترين بيماري شناخته‌مي‌شود و طبق گزارشات در سال ???? بيش از ?? ميليون نفر در آمريكا مبتلا به آسم بوده‌اند. بسياري از روش‌هاي درماني بيماري‌هاي ريوي و همچنين برخي بيماري‌ها، استنشاقي مي‌باشند، بنابراين شناخت رفتار ذرات استنشاقي (آلودگي‌ها و ذرات دارويي) همراه هوا درون مجاري تنفسي امري ضروري است. در مطالعه حاضر چهار نسل از ريه يك خانم ?? ساله سالم و غير سيگاري از تصاوير پزشكي سي تي اسكن استخراج شد. هندسه به 7 ناحيه تقسيم شد، سپس توسط شبكه بي‌سازمان با روش هموارسازي و با سلول‌هاي چندوجهي جهت حل عددي شبكه‌بندي گرديد. جهت شبكه‌بندي، ابتدا هندسه وارد محيط نرم‌افزار اسپيس‌كليم شده و در آن‌جا يكپارچه‌سازي هندسه انجام شد. سپس با استفاده از قابليت توپولوژي مجازي محيط انسيس مشينگ ، صفحات انتخاب شده و با گزينه تركيب سلول، تلفيق صفحات جهت ورود به محيط فلوئنت مشينگ انجام‌شد. سپس به وسيله استقلال حل از شبكه، شبكه مناسب انتخاب شد. از مدل آشفتگي k-?   براي شبيه‌سازي جريان آرام تا آشفته استفاده‌گرديد. ذرات با ديدگاه لاگرانژي و با استفاده از مدل فاز گسسته به ناحيه محاسباتي تزريق شد و مسيريابي و مدل‌سازي الگوي نشست در نواحي مختلف انجام شد. بر روي ساختار جريان در مجاري تنفسي براي نرخ‌هاي جريان مختلف و اثرات پديده‌هاي مختلف به‌وجودآمده در اين مجاري بر روي نشست ذرات بحث گرديد. الگوي نشست ذرات براي نرخ‌هاي مختلف جريان، به صورت منطقه‌اي و كلي به‌دست‌آمد و اثر نرخ جريان، اندازه و شكل ذرات بر ميزان نشست بررسي شد و در نهايت با استفاده از بهينه‌سازي و بهره‌گيري از روش پاسخ سطح و الگوريتم ژنتيك، حالت بهينه براي كمينه و بيشينه نشست ذرات در ناحيه درخت برونش به‌دست‌آمد. راندمان نشست بر حسب پارامتر برخورد نشان داد كه در تمامي نواحي مدل از جمله دهان- گلو، ناي و درخت برونشي، برخورد اينرسي نقش مهمي در نشست ذرات دارد. تحليل ساختار جريان سيال در مدل هندسه نشان داد كه جريان برگشتي، تشكيل گردابه و جت حنجره همگي بر ساختار جريان هوا و الگوي نشست ذرات اثرگذار هستند. ناحيه دهان-گلو داراي بيشترين كسر نشست به ازاي نرخ‌هاي جريان مختلف است. نتايج نشان داد كه تزريق به دو صورت تك ذره و استفاده از تابع توزيع بر ميزان نشست ذرات اثرگذار است. همچنين افزايش قطر ذرات باعث تغيير الگوي نشست ذرات شده و كسر نشست در ناحيه دهان-گلو افزايش يافت و شكل ذرات با اثرگذاري بر روي ضريب پسا، موجب تغيير الگوي نشست ذرات گرديد. از جمله نتايج ديگر اين بود كه بيشترين كسر نشست مربوط به ذرات كروي است. بررسي همزمان اثر قطر، شكل ذرات و سرعت ذرات و آناليز حساسيت نشان داد كه قطر با تاثير 60%، موثرترين پارامتر بر ميزان نشست ذرات است و پس از آن، ضريب شكل و سرعت قرار مي‌گيرند. در نهايت پيش‌بيني الگوريتم ژنتيك، بيشينه نشست ذرات در ناحيه درخت برونش را، 17% گزارش‌كرد، درحالي‌كه براساس نتايج عددي بيشينه نشست ذرات در ناحيه درخت برونش 20% گزارش شد. همچنين كمينه نشست ذرات توسط الگوريتم ژنتيك در ناحيه درخت برونش، 2/0 % گزارش گرديد، درحالي‌كه براساس نتايج عددي كمينه نشست ذرات در اين ناحيه، 24/0 % گزارش‌شد.   

   In the process of additive manufacturing of metals, the ability to predict and control the microstructure can reduce the need for subsequent heat treatment. In this research, the numerical simulation of the additive manufacturing process of 316L stainless steel was studied. The ability to predict and control the microstructure of materials in selective laser melting (SLM) requires understanding the thermal conditions during the solidification process. In this research, process parameters were selected with transient thermal characteristics, i.e. temperature and cooling rate. The relationship between the cooling rate and the temperature gradient during local freezing, and the control parameters of the laser selective melting process were investigated, which were the control parameters of the laser scanning speed and the thickness of the powder layer. Also, solidification parameters, namely thermal gradient (G) and solidification rate (R) were investigated to predict the microstructure. In this project, the cooling rate and thermal gradient during solidification were calculated numerically by solving the relevant heat transfer equation using the finite element method in Comsol software, and then the results included the solidification parameters mentioned on the solidification map of 316L stainless steel alloy to predict the solidification microstructure. was imaged The results of this research (obtained using simulation) showed that the microstructure of 316L stainless steel produced by the selective laser melting (SLM) process will be columnar or cellular dendrites. Also, it was found that high laser scanning speed (i.e. speed of 1000 mm/s) leads to finer microstructure. Furthermore, the values of G × R increase from the bottom to the top of the melt pool geometry, leading to a finer structure in the top region. But the values of G/R decrease from the bottom to the top of the molten pool geometry. Also, in this research, it was found that the greater the thickness of the powder in each layer, the lower scanning speed should be used so that the laser heat flux can melt the powder and the sub-layer completely. By increasing the laser scanning speed from 200 to 1000 mm/s, the width decreases from 85 microns to 58 microns and the depth of the molten pool decreases from 23 to 13 microns, but the length of the pool increases from 93 to 97 microns.

  Separation of gas-solid flows is an important process in many industries. Cyclone separators are the most common devices for separating solid particles from gas flows, which indicates the importance of studying and researching to increase their efficiency and reduce energy consumption by reducing the pressure drop. In this regard, the present study used an additional inlet to enter flow into the cyclone with the aim of increasing the separation efficiency of a standard gas cyclone. To find the optimal height, this additional inlet was added at four different heights along the length of the cyclone, including the heights of 0.95D, 1.4D, 1.5D and 1.95D (D is the diameter of cylindrical section of cyclone) and the results were obtained for two conditions of inlet flow distributions: Increasing the inlet flowrate and division the inlet flowrate. In the first case, in addition to the polluted air flow entered through the original inlet (that was equal to the flowrate of cyclone without an additional inlet), an extra flowrate (20% of flowrate of original inlet) was injected through the additional inlet. In other words, the total flowrate of the cyclone was 20% more than it in cyclone without additional inlet. In second case, part of the inlet flow (83.33%) was injected through the original inlet and part of it (16.67%) was injected through the additional inlet, so the total inlet flowrate was equal to it in cyclone without additional inlet. The Reynold stress turbulence model (RSM) was used to solve the Averaged Navier- Stokes equations and Eulerian- Lagrangian approach and discrete phase model (DPM) was applied to track particles with a uniform diameter of 0.5 to 1.8 micron as discrete phase. The results showed that, in both flow distribution cases, installing the additional inlet at a height of 0.95D has the most positive effect on the separation efficiency. The separation efficiency increased 28.8% in flowrate increasing case and 19.6% in flowrate division case for particles with diameter of 0.5 micron compared to cyclone without additional inlet. In addition, in both of the flow distribution cases, increasing the separation efficiency of sub-micron particles was greater than it of bigger particles.

Controlling the heat generated by electronicequipment and microelectromechanical systems at high capacities is importantfor optimal performance and greater reliability. Open microchannel heat sinksare a new geometry of microchannels heat sinks that are important due to theirlower manufacturing cost and better heat transfer performance. In this research, heat transferand fluid flow characteristics of open microchannel heat sink in 17 differentgeometries, which includes 3 main shape of rectangular fins, plano convex fins andplano concave fins, that variable fins base heights varied from 0.4-0.7 mm, andin 2 shape of plano convex fins and plano concave fins on the same variablecurve range coefficients 0.20-0.5 for plano convex fins shape and 0.35-08 Forplano concave fins shape   on an equal finsbase height which the convective surface area and the materials that arerequired to build a heat sink are equal have been investigated. Openmicrochannel heat sink cooled by water fluid in   a laminar flow and single phase flow   that Reynolds number varied from 100-600 andheat flux 100-600 kWm2   that numericallyand in a three-dimensional geometry analyzed by Ansys Fluent software. At thesame heat flux, Reynolds number and fins base height, the Nusselt number of therectangular fins shape is less than the two shapes of plano convex fins andplano concave fins.in Comparison of two shapes of plano convexfins and plano concave fins in the lower fins height, the Nusselt number of theplano concave is more than plano plano convex and in the higher fins height,the Nusselt number of the plano convex is more than the plano concave. Despite the fact that at high heightsin the fins, where the Nusselt number of the plano convex fins shape is greaterthan the rectangular and plano concave   shape,but the plano convex pressure drop is less than these two shaps. The results show that at the end of the path, where theheat sink temperature is higher, in the plano concave model due to the moreconvective surface area at the end of the path has a lower critical temperatureand temperature non-uniformity. Despite the higher Nusselt number in plano convex finsshape in the curve coefficient of 0.80, 0.65 and 0.50 Compared to other plano concavefins shape in curve range coefficients of 0.35 and0.20, have a lower pressure drop than the above shapes.  

   Proper design of solar panels and increasing their thermal performance is one of the most important issues of the day. In this dissertation, using Ansys Fluent 19.2 software, a three-dimensional solar chimney power plant for Kermanshah weather conditions and the effect of collector geometric dimensions such as collector height and radius, solar radiation and ambient temperature on mass flow rate, air pressure temperature In the chimney, the output power, thermal efficiency and total efficiency of the power plant as well as the distribution of temperature, pressure and pressure meters were examined. In this study, the collector height was 2 to 8 meters, the collector radius was 100 to 400 meters, the chimney height was 2 meters, the chimney radius was 4 meters and the sunlight was 400 to 1000 watts per square meter. Increased sunlight leads to increased mass flow in the chimney. Increasing the ambient temperature reduces the fluid flow and thus the output power. There is a direct relationship between heat flux and power output of the power plant so that with increasing (decreasing) solar radiation, the output power also increases (decreases) and the thermal efficiency of the solar chimney power plant increases. Increasing the collector radius increases the mass flow rate and thus the power output of the power plant, but increasing the collector height has an inverse relationship with power. As the collector radius or height increases, the total power plant efficiency decreases. Changing the collector radius from 100 meters to 400 meters for a solar flux of 800 watts per square meter increases the output power by 93.6%.    Keywords: Thermal performance, Chimney power plant, Solar energy, Numerical simulation

  در پايان­نامه حاضر جريان پايا و گذراي خون در مدل

  Abstract Social networks has attracted many users. These social networks have enabled user to connect to each other and share text, image and videos. A social network that allows users to share their location is named a location-based social network. Users can leave their tips on places they have visited and share it with others. User feedback is reflection of how they feel about the places they have visited. In social networks, people are connected to each other’s. One of the issues of these networks is the prediction of communication that may be created between two users in the future. Link prediction is the name chosen for this issue. There are many approaches used to predict links. Network structure information, user information such as their interests and characteristics, and location information that users have visited are used to predict links. User’s sentiment is one of the information that can be used to improve link prediction. Their tips can be analyzed to gain a sentiment for users in location-based social networks. This can provide a new algorithm for link prediction by combining the information of network structure, the information of the places they visited and their sentiments. The algorithm was tested on a foursquare network dataset, and it was found to perform better than one that does not use user sentiment. Therefore, it can be concluded that the role of sentiment is effective in creating new links among users. Keywords: social network, location-based social networks, link prediction, sentiment, location sharing

Numerical Study of Magnetic Field Effect on Convection Heat Transfer of Nanofluid Flow in a Microchannel  

  Investigation of thermal performance of a direct-expansion solar-assisted heat pump water heater system using N2O refrigerant

    Numerical Analysis of the influence of the aspect ratio and angle of tube in vacuum tube solar collectors with modified structure

  در اكثر محاسبات مهندسي مكانيكبراي جريان­هاي در ابعاد معمول به­جاي تحليل پيچيده­ي اثرات واقعي ملكول­ها از يكفرض توزيع پيوسته ماده استفاده مي­شود و محاسبات جريان با اين فرض پيوستگي انجاممي­شود. اگرمتوسط مسير پويش آزاد ملكولي با كوچكترين طول مسأله هم­مرتبه باشد فرضپيوستگي ماده صادق نيست. براي تحليل اين جريان بايد از روش­هاي پايه­اي­تر مانندروش­هاي ملكولي استفاده كرد. در چندسال اخير با گسترش زمينه­هاي مكانيك سيالاتجريان در ابعاد ميكرو و نانو بيشتر مورد توجه محققين قرار گرفته است. جريان­هايگازي ميكرو و نانو به­واسطه­ي طول مشخصه كوچك­شان معمولا در محدوده­ي ناپيوستگيجريان قرار دارند. يكي از پركاربردترين روش­ها براي حل اين جريان­ها استفاده مي­شودروش ذره­مبناي شبيه­سازي مستقيم مونت­كارلو (DSMC) مي­باشد.اين روش در جريان­هاي با عدد نودسن بالا به­خوبي عمل مي­كند.اما مشكل اين روش در جريان­هاي كم­سرعت مشاهده مي­شود. نوسانات آماري موجود در روشDSMCمانع از شكل­گيري درست جريان در مواردي كه سرعت پايين است مي­شود. يكي از روش­هاييكه براي رفع اين مشكل ارائه شده است روش ذره­مبناي نگه­داري اطلاعات(IP) مي­باشد. در اين روش قوانين بقا (بقاي جرم، بقاي مومنتوم و بقايانرژي) مشابه تحليل­هاي ماكروسكوپي، در خصوص اطلاعات IPپياده مي­شود. در اين پايان­نامه اساس روش­ DSMC-IPبه­عنوان ابزار عددي و ذره­مبنا براي حل جريان­هاي گازي رقيق­شده ارائه شده است.كد DSMC2 توسعه داده شده و روش IP بهآن اضافه شده است. هندسه­ي مورد مطالعه ميكرومحفظه­ي مربعي با ديواره­ي متحرك مي­باشد.اين جريان به واسطه­ي گردابه­هاي موجود در آن جرياني پيچيده است.برهم­كنش بينملكولي با استفاده از مدل كره­ي سخت متغير مدل­سازي شده و همچنين از طرح برخورد SBT براي انتخاب جفت برخوردي استفاده شده است. جريان دما ثابت است وگاز تك اتمي آرگون به­عنوان سيال مدل­سازي شده است. نتايج به­دست آمده موفقيت روش IP را در رفع نوسانات چگالي، سرعت، تنش برشي و... را نشان مي­دهد.همچنين علاوه­بر رفع نوسانات موجود در جريان­هاي سرعت پايين، نوساناتي كه در جريان­هايبا نودسن كوچك ايجاد مي­شود را نيز برطرف مي­كند. روش IPعلاوه­بر رفع نوسانات، در كاهش هزينه­ي محاسباتي نيز بسيار مؤثر است. نتايج حاصلاز حل IP نشان مي­دهد كه موقعيت مركز گردابه­ي اصلي با افزايش سرعت ديوارهدر جهت حركت ديواره جابه­جا مي­شود و همچنين با كاهش عدد نودسن جريان مركز گردابهبه سمت بالا جابجا مي­شود.

Rotary Regenerative Air Preheater (RRAPH) is one of the main equipment for energy recovery in the steam boiler of the power plants. In the present study, Ljungstrom air preheater of the Bisotoun Thermal power plant has been investigated with the aim of optimizing its thermal performance. In this regard, with Computational Fluid Dynamics (CFD), three-dimensional simulation of the rotary air preheater was performed to solve the continuity, momentum and energy equations in porous medium. Considering the structure of the plates of the Ljungstrom matrix, the use of the porous medium assumption is acceptable. The results of simulation show acceptable accuracy in comparison with the experimental results which is achieved from Bisetoon power plant data. In this research, the effect of rotational speed on the efficiency of air preheater in variety of loads and mass flow rates for both without leakage and with leakage conditions was investigated. The results of the present study show that the impact of the rotational speed on the performance of RRAPH is in the range of 0.5 to 4 rpm, and after this increase in speed does not have a significant effect on efficiency. The present study also shows that leakage has a significant effect on reducing the efficiency of the RRAPH in all thermal loads and rotational speeds. In the following, the optimum rotary speed was studied in different loads, mass flow rate of air and flue gas. For this purpose, both without leakage and with leakage have been studied. Results show, the efficiency of the power plant was almost constant for various thermal loads, and performance is only increasing with increasing rotating speed. On the other hand, with considering leakage effect, the maximum RRAPH efficiency is related to the power plants nominal load (320 MW). One of the most important and limiting factors in increasing the speed of rotation is the dew point temperature forms acid. Therefore, in this study, this index was extracted for optimal rotary speeds in different thermal loads. In the following, the effect of material change on the efficiency of RRAPH was investigated. According to the results, for both without leakage and with leakage the best thermal performance is related to the stainless steel, which has the lowest thermal diffusivity, lowest thermal performance is related to the copper, which has the highest thermal diffusivity.  

بررسي كارايي حرارتي مبدل صفحه ايي با استفاده از نانو سيال

  AbstractIn this thesis, a model has been introduced to simulate the capture efficiency of 3D high gradient magnetic filters for the separation of iron sulfide particles from the amine solution in the sweetening gas process. The geometry of the filter consists of a matrix of rods located in a channel with a square cross section. In order to study this problem, initially the Navier-Stokes equations coupled with Ampere equation are solved numerically in a 2D geometry. Having the flow field, the problem of particle capturing has been studied due to Lagrangian viewpoint and the effects of governing parameters including the particle diameter, fluid velocity and the geometrical parameters of the matrix have been investigated. Finally, the results of 2D analysis have been extended to simulate the particle capturing in a 3D filter. The 2D numerical simulations have been performed with COMSOL MULTIPHISICS 5.0 based on the finite element method and the extension of results to the 3D case has been carry out with proper code in MATLAB. This code interpolates or extrapolates the 2D results for any cases rather than those simulated in COMSOL. It has been demonstrated that the capture efficiency of filters with triangular configuration is higher than the rectangular one in the same conditions because the triangular configuration provides a better fluid mixing. However, the difference between capture efficiency of these two filters decreases with the increase in fluid velocity or distance between the matrices or decrease in particle diameter. Also, it has been demonstrated that the capture efficiency of these filters is directly related to the particles diameter and reversely dependent to the fluid velocity and the distance between the matrices. In addition, the performance of these filters are investigated in the case of non-uniform distribution of particles in the inlet. In order to demonstrate a useful graph, the performance contours of the 3D filter in the operational conditions are presented in terms of Reynolds number and the distance between the matrices. These counters show that the capturing efficiency of 60% will maintained when the dimensionless distance between the matrices is less than 1.2 independent of the Reynolds number.   Keywords: Magnetic filter, Capture efficiency, High gradient magnetic separation, Particle tracing

  Thermoelectric devices produce electricity if a temperature gradient is applied to them (direct effect), and vice versa, by applying an electric current generate temperature (inverse effect).These devices are composed of a number of n-type and p-type semiconductor junctions connected electrically in series and thermally in parallel. If an electric current is applied to a thermoelectric cooler, heat is transferred from one side of the thermoelectric cooler to the other side. Therefore, one face of the thermoelectric cooler is cooled and the opposite face is heated. This study aims to investigate the effect of Piezo-fan boundary conditions on the efficiency of thermoelectric refrigerators. Piezoelectric fans are vibrating beams, disks, or plates whose vibratory motion is actuated using a piezoelectric material. Typically they consist of a flexible fan blade to which the piezoelectric element is bonded. By applying an alternating input signal to the piezoelectric element, beam begins to oscillate and induce a flow in the surrounding fluid. This could be used enhance heat transfer. Numerical results show that the maximum convection heat transfer coefficient in which fan tip to the wall distance is 1.5 mm and the wall is experiencing a constant thermal flux of 650 W/m2 is 73.55 W / m2.K. The boundary conditions imposing on thermoelectric elements affect their efficiency and by altering it the temperature of the insulated end could reach 73.66 Kelvin relative to ambient temperature. The results show that using a cooling system consisting of a heat sink and Piezo-fan on the hot end could meet the refrigerators thermal requirements. Depending on the heat sink type and the Piezo-fan configuration, the refrigerators performance would be different. Namely, a cooling system consisting of a pin-fin heat sink and a vertical arrangement of Piezo-fans has increased the refrigerators effective electric current range by 6.5% and has increased the maximum temperature drop by 8.4% with the cooling flux to be 20,000 watts W/m2.