Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Review Citation - WoS: 13Citation - Scopus: 13A Review on Battery Thermal Management Strategies in Lithium-Ion and Post-Lithium Batteries for Electric Vehicles(Yıldız Technical University, 2023) Güngör, Şahin; Göçmen, Sinan; Çetkin, ErdalElectrification on transportation and electricity generation via renewable sources play a vital role to diminish the effects of energy usage on the environment. Transition from the conven- tional fuels to renewables for transportation and electricity generation demands the storage of electricity in great capacities with desired power densities and relatively high C-rate values. Yet, thermal and electrical characteristics vary greatly depending on the chemistry and struc- ture of battery cells. At this point, lithium-ion (Li-ion) batteries are more suitable in most applications due to their superiorities such as long lifetime, high recyclability, and capacities. However, exothermic electrochemical reactions yield temperature to increase suddenly which affects the degradation in cells, ageing, and electrochemical reaction kinetics. Therefore, strict temperature control increases battery lifetime and eliminates undesired situations such as lay- er degradation and thermal runaway. In the literature, there are many distinct battery thermal management strategies to effectively control battery cell temperatures. These strategies vary based on the geometrical form, size, capacity, and chemistry of the battery cells. Here, we focus on proposed battery thermal management strategies and current applications in the electric vehicle (EV) industry. In this review, various battery thermal management strategies are doc- umented and compared in detail with respect to geometry, thermal uniformity, coolant type and heat transfer methodology for Li-ion and post-lithium batteries.Article Citation - WoS: 3Boşluk İletim Tabakasız ve Esnek Organo Kurşun İyodür Perovskit Güneş Hücresinin Çevresel Etki Değerlendirmesi(Gazi Üniversitesi, 2022) Sarıaltın, HüseyinPerovskit güneş pilleri (PSC) esneklik ve düşük maliyetli rulodan ruloya üretim gibi avantajlarla birlikte son zamanlarda güç dönüşüm verimliliğinde de önemli bir ilerleme kat etmiştir. PSC'lerin ticarileştirilmesinden önce çevresel performansının yaşam döngüsü değerlendirme (LCA) yöntemi ile araştırılması önemlidir. Bu çalışmada, literatür verilerinden istifade edilerek, esnek Polietilen tereftalat (PET) alt tabaka ve boşluk iletim katmanı (HTL) eliminasyonunu içeren çözelti bazlı organo-kurşun iyodür perovskit güneş hücresinin beşikten kapıya yaşam döngüsü analizi (LCA) gerçekleştirilmiştir. 1 m2 hücre alanı üretiminden kaynaklanan çevresel etkiler altı Uluslararası Referans Yaşam Döngüsü Veri Sistemi (ILCD) kategorisinde belirlenmiştir. Analizin sonucunda, en fazla etki değerinin yüksek elektrik enerjisi tüketimine sahip vakum biriktirme işlemi gereksinimine sahip olan alüminyum metal elektrot tabakasının imalatından kaynaklandığı bulunmuştur. Ticari fotovoltaik teknolojilerle karşılaştırma yapabilmek için en yaygın kullanılan çevresel göstergelerden birisi olan küresel ısınma potansiyeli (GWP), birim kWh elektrik üretimi için hesaplanmıştır. Buna göre, bu çalışmada incelenen HTL'siz esnek (HFF) PSC'nin ticari PV'lerle rekabetçi GWP değerine ulaşmak için 15-20 yıl cihaz ömrüne ihtiyacı olduğu bulunmuştur.Article Stab and Ballistic Performances of Aramid Fabrics Impregnated With Silica Based Shear Thickening Fluids(Niğde Ömer Halisdemir Üniversitesi, 2021) Çolpankan Güneş, Oylum; Yıldız, Sema; Güneş, Mehmet Deniz; Şenel, Fikret; Tanoğlu, MetinThis study focuses on the production of aramid fabric with improved stab and ballistic resistances treated with shear thickening fluids (STFs). The STFs were prepared by homogenization of various amount of silica particles within the PEG and ethyl alcohol, drying, and grinding steps. The rheological measurements showed that the addition of silica nanoparticles into the PEG, shear thickening behavior was enhanced. As silica concentration increased, the interparticle forces increased and so the friction between particles greatly increased, causing an enhanced shear- thickening property. Quasi-static and dynamic stab resistance tests showed that increasing shear thickening response corresponded to increased stab performance in the STF/aramid targets as compared to untreated aramid fabric. Ballistic test results showed that there was an increment in the ballistic resistance between untreated fabric and STF/aramid composites. It was also found that the flexibility of STF/aramid targets did not decrease significantly compared to the untreated aramid fabricArticle An Experimental and Comparative Study of the Self-Loosening of Bolted-Joints Under Cyclic Transverse Loading(Sakarya University, 2021) İnce, U.; Güden, M.The capabilities of analytic models in predicting the experimental critical displacements of the self-loosening of bolted-joints were investigated experimentally and numerically. The experimental loosening rates were determined in a Junker test bench at a constant transverse displacement amplitude (0.45 mm) and under varying initial clamp force and clamp length and controlled bearing and thread friction coefficients. The analytic critical displacements were then calculated using experimental parameters. In addition, a three-dimensional accompanying finite element (FE) model was developed in order to calculate the ratio of spring constants engaging the thread to spring. The results showed relatively low capabilities of present analytic model in the prediction of the critical displacements of the self-loosening of bolted-joints. The efforts to modify the nut reaction moment and the inclination compliance of bolt head portion in the investigated equations however resulted moderate increase in the appropriate predictions. On the other side, the use of the reaction moment determined by FE model increased the appropriate prediction from 58.3 to 73.4%. The accuracy of the equations was further increased by the use of an appropriate kw value, but the increase in this case was only ~4%. © 2021, Sakarya University. All rights reserved.Article Non-Equilibrium Molecular Dynamics for Calculating the Thermal Conductivity of Graphene-Coated Aluminum(2020) Toprak, Kasım; Yılmaz, Ahmet BerkNon-equilibrium Molecular Dynamics (NEMD) simulations have been created in C++ using Message Passing Interface (MPI) library to calculate the phonon thermal conductivity of bare graphene, aluminum, and graphene-coated aluminum. This study focuses on how graphene can alter the thermal conductivity of graphene-coated aluminum. The effect of length, graphene, and the number of graphene layers are analyzed. Even though electrons are dominant on thermal conductivity of aluminum, the effect of graphene coating can be seen in the results. The results show that the thermal conductivity of aluminum increases by up to 149% by graphene coating. When the number of layers increases to two layers, the thermal conductivity increases by up to 261%. Moreover, the results increase with the length of all models.Article Citation - WoS: 11Citation - Scopus: 13Effect of Cnt Incorporation on Pan/Ppy Nanofibers Synthesized by Electrospinning Method(TÜBİTAK, 2020) İnce Yardımcı, Atike; Tanoğlu, Metin; Yılmaz, Selahattin; Selamet, YusufIn this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H2SO4/HNO3/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.Article Citation - WoS: 1Performance Analysis of Thermal Storage Assisted Cooling Tower With Night Cooling(Gazi Üniversitesi, 2020) Ouedraogo, Kiswendsida Elias; Toprak, KasımAs global warming and water scarcity issues continue to grow, it is essential to increase resources efficiency for air conditioners and power plants. In order to increase the efficiency, the systems need to be modified to take the advantages of the low night temperature and thermal storage tanks. In this study, the low night temperature and thermal storage tanks effects on the cooling tower is studied using TRNSYS. Using a chiller operating from 8:00 to 16:00 as a case study, hot water from the condenser is partially stored on daytime and cooled slowly during the night. The storage tank volume is optimized by considering two big tanks and five small tanks. The results show that night cooling reduces cooling water temperature by 5.8 degrees C or 21.8% while the cooling efficiency is increased by 36%. The thermal storage tanks enable to have the low continuous flow rate and help to reduce the fan power by 67.1%. On the storage side, compared to two tanks system, the tanks volume is reduced by 16.5% when 5 tanks are used. In theory this reduction can go up to 50% by increasing the number of tanks and reducing their individual size.Article The Effect of Time Delay of Fluid Flow in a Vascularized Plate(MIM Research Group, 2018) Yenigün, Onur; Coşkun, Turgay; Çetkin, ErdalIn this study, we show the effect of time delay of coolant fluid flow into a vascularized plate on the peak temperature. Coolant flows along vascular channels which were embedded in a rectangular plate. Two kinds of vascular channel designs were investigated experimentally: parallel and tree-shaped. In the study, the peak temperatures were monitored and the coolant was pumped when the peak temperature reaches to 50°C, 70°C and 90°C. The performance comparison of two distinct designs is based on two criteria: the time required for the steady state condition after the coolant is pumped and the peak temperature after the steady state condition is conformed. The results show that the time required to reach steady-state condition increases as the time delay increases. The parallel and tree-shaped designs show similar performance (time required to reach steady state) with slightly improved performance in the tree-shaped design as the preset temperature for time delay increases. For instance, 4% decrease in the time required to reach steady-state with the tree-shaped design relative to the parallel design was achieved when the preset temperature for time delay is 90°C.Article Optimum Design of Anti-Buckling Behavior of Graphite/Epoxy Laminated Composites by Differential Evolution and Simulated Annealing Method(MIM Research Group, 2019) Akçaır, Mehmet; Savran, Melih; Aydın, Levent; Ayakdaş, Ozan; Öztürk, Savaş; Küçükdoğan, NilayStacking sequence design and optimization of 64 layered symmetric-balance graphite/epoxy laminated composite have been performed. The optimization problems aim to find the optimum stacking sequence maximizing the critical buckling load by single objective optimization approach. Differential Evolution (DE) and Simulated Annealing (SA) optimization algorithms are proposed to solve the problems. The effect of the aspect ratios (a/b) and in-plane biaxial compressive loading ratios (Nx/Ny) on critical buckling load are investigated. In order to see the effect of discrete increments of fiber orientation angle on critical buckling load, 1°, 5°, 15°, 30° and 45° fiber angle increments are also considered. The results show that (i) the proposed algorithms DE and SA exhibit comparable performance in terms of critical buckling load when compared Genetic algorithm (GA) and Generalized pattern search algorithm (GPSA), (ii) DE and SA find distinct stacking sequence configurations in terms of buckling load for the same laminated structure design problems.Article Casting the Swarms Problem in the Ensembles Context(Çukurova Üniversitesi, 2016) Kok, Çağatay; Çellek, Seven Burçin; Koşun, Çağlar; Özdemir, SerhanSürü robotları yüzlerce farklı şekilde modellenmiştir. Kalabalık olmaları sürülerin bir özelliğidir. Sayılamayacak kadar çok sayıya ulaştıklarında, termo-istatiksel mekanik devreye girebilir. Yazarlar bu avantajı kullanarak sürü robotları için evrensel istatistik oluşturmak istediler. Üç temel topluluk açıklandı ve formüle edildi. Sürüler izole edildiklerinde mikrokanonik uyum ortama hakim olurken, ortama av veya avcı girişi olur ise, duruma bağlı olarak değişimler gözlemlenir. Bu yüzden formulasyonlar ve geçişler şarta bağlıdır. Son olarak gözlemlenen olasılıklar tartışıldı