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 Gemi Sevk Gücü ve Isı Transferinin Yapısal Gelişim Teorisi ile İlişkisi(TMMOB Gemi Mühendisleri Odası, 2022) Güneş, Ümit; Çetkin, Erdal; Şahin, BahriYapısal Gelişim Teorisi 1996 yılında literatüre kazandırılmış olup tabiattaki ve mühendislikteki tasarım prensiplerini açıklar. Teori, yeryüzündeki akış sistemlerini bütüncül bir şekilde ele alır. Akışın (hareketin) olmadığı yerde çoğu zaman canlılıktan bahsetmemiz dahi mümkün olmamaktadır. Akış sistemlerinin çözümünde anahtar davranış biçimi bu sistemlerin minimum dirençli yol ile hareketini sürdürmesidir. Belli bir zaman dilimi için minimum direnç ile hareket eden sistem zaman geçtikçe kendine yeni yollar (kanallar) bulmakta ya da bazı yolları hiç kullanmayarak yönünü değiştirmektedir. Yapısal Gelişim Teorisi ise hayati öneme sahip olan akış sistemlerinin fiziksel arka planını ortaya koymaktadır. Bu makalede özellikle mühendislik çözümlerinin başında gelen akış sistemlerinin yapısı (gemilerde kurulu ana makine gücü ve ısı transferi örnekleri özelinde) ve Yapısal Gelişim Teorisi’ne göre ilişkisi araştırılmıştır. Bunun için 1085 adet petrol tankeri için DWT ile bu tankerler için gerekli olan güç ilişkisi nonlineer regresyon ile analiz edilmiştir. Sonuç olarak gemilerdeki genel gelişimin ve ısı transferinin yapısal gelişim prensiplerine uygun şekilde gerçekleştiği gösterilmiştir.Review Citation - WoS: 103Citation - Scopus: 136Digital Twin of Electric Vehicle Battery Systems: Comprehensive Review of the Use Cases, Requirements, and Platforms(Elsevier, 2023) Naseri, Farshid; Gil, S.; Barbu, C.; Jensen, A. C.; Larsen, P. G.; Gomes, Claudio; Çetkin, Erdal; Yarımca, GülşahTransportation electrification has been fueled by recent advancements in the technology and manufacturing of battery systems, but the industry yet is facing serious challenges that could be addressed using cutting-edge digital technologies. One such novel technology is based on the digital twining of battery systems. Digital twins (DTs) of batteries utilize advanced multi-layer models, artificial intelligence, advanced sensing units, Internet-of-Things technologies, and cloud computing techniques to provide a virtual live representation of the real battery system (the physical twin) to improve the performance, safety, and cost-effectiveness. Furthermore, they orchestrate the operation of the entire battery value chain offering great advantages, such as improving the economy of manufacturing, re-purposing, and recycling processes. In this context, various studies have been carried out discussing the DT applications and use cases from cloud-enabled battery management systems to the digitalization of battery testing. This work provides a comprehensive review of different possible use cases, key enabling technologies, and requirements for battery DTs. The review inclusively discusses the use cases, development/integration platforms, as well as hardware and software requirements for implementation of the battery DTs, including electrical topics related to the modeling and algorithmic approaches, software architec-tures, and digital platforms for DT development and integration. The existing challenges are identified and circumstances that will create enough value to justify these challenges, such as the added costs, are discussed.Article Citation - WoS: 5Citation - Scopus: 6Asymmetric Y-Shaped Micromixers With Spherical Mixing Chamber for Enhanced Mixing Efficiency and Reduced Flow Impedance(Isfahan University of Technology, 2021) Çetkin, Erdal; Miguel, A. F.Microfluidic devices have many attractive qualities such as low cost, small size, and in-field use. Micromixers are very important components of these devices because affect their efficiency. In a passive mixer, the structural characteristics of the mixer are crucial and must be analyzed. This paper presents a numerical study of the mixing in passive Y-shaped micromixers with a spherical mixing chamber for a volume constrained system. The effect of asymmetric bifurcated ducts, the angle in between the inflow ducts, eccentricity and, obstacles inserted in the mixing sphere, on the mixing efficiency and flow impedance is evaluated. Vortical structures characteristics and the possible occurrence of engulfment are also identified. The results show that flow impedance (pressure drop for unit volumetric flow rate) can be decreased greatly for the same mixing efficiency as the volume of the spherical mixing chamber is 20% of the total volume. Insertion of the obstacles into the sphere mixing chamber decreases the mixing efficiency while they increase the flow impedance. The results also show that spherical mixing chamber enhances mixing efficiency while decreasing flow impedance if the volume reserved for it is greater than a limit value which depends on the diameter and length scale ratios in between the mother and daughter ducts as well as the total volume. Overall, the paper documents the variation of mixing efficiency and flow impedance based on the geometrical parameters of three-dimensional asymmetric passive micromixer with sphere mixing chamber.Article Citation - WoS: 1Citation - Scopus: 2Emergence of Taperedducts in Vascular Designs With Laminar and Turbulent Flows(Begell House, 2014) Çetkin, ErdalHere we show that tapered ducts emerge in volumetrically bathed porous materials to decrease the resistance to the flow in laminar and turbulent flow regimes. The fluid enters the volume from one point and it is distributed to the entire volume. After bathing the volume, it is collected and leaves the volume from another point, i.e., two trees matched canopy to canopy. This paper shows that the flow architecture (i.e., design of the void spaces in a porous material) should be changed to obtain the minimum resistance to the flow as its size increases. Tapering the ducts decreases the order of the transition size, i.e., the size for changing from one construct to another to obtain the minimum pressure drop. The decrease in the pressure drop is 16% and 38% with the tapered ducts when the flow is laminar and turbulent, respectively. In addition, the volume ratios and the shape of the tapered ducts are documented. There is no design existing in nature with diameters of constant size in order to distribute and/or collect heat, fluid, and/or stress such as bones, rivers, veins, and tree branches. The emergence of the tapered ducts in designed porous materials is natural.Article Citation - WoS: 12Citation - Scopus: 11Inverted Fins for Cooling of a Non-Uniformly Heated Domain(Yıldız Teknik Üniversitesi, 2015) Çetkin, ErdalThis paper shows that the peak temperature of a non-uniformly heated region can be decreased by embedding high-conductivity tree-shaped inserts which is in contact with a heat sink from its stem. The volume fraction of the high-conductivity material is fixed, and so is the volume of the solid region. The length scale of the solid domain is L. Inside there is a cube-shaped region with length scale of 0.1L and heat production 100 times greater than the rest of the domain. The location of this hot spot was varied to uncover how its location affects the peak temperature and the design of inverted fins, i.e. highconductivity tree-shaped inserts. The volume fraction of the high-conductivity tree was varied for number of bifurcation levels of 0, 1 and 2. This showed that increasing the number of the bifurcation levels decreases the peak temperature when the volume fraction decreases. The optimal diameter ratios and optimal bifurcation angles at the each junction level are also documented. Y-shaped trees promise smaller peak temperatures than T-shaped trees. The location of the vascular tree in the z direction also affects the peak temperature when the heat generation is non-uniform. In addition, the peak temperature is minimum when z = 0.65L even though the hot spot is located on z = 0.75L.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 Citation - WoS: 18Citation - Scopus: 22A Review of Heat and Fluid Flow Characteristics in Microchannel Heat Sinks(John Wiley and Sons Inc., 2020) Coşkun, Turgay; Çetkin, ErdalHeat transfer and flow characteristic in microchannel heat sinks (MCHS) are extensively studied in the literature due to high heat transfer rate capability by increased heat transfer surface area relative to the macroscale heat sinks. However, heat transfer and fluid flow characteristics in MCHS differ from conventional ones because of the scaling effects. This review summarizes the studies that are mainly based on heat transfer and fluid flow characteristic in MCHS. There is no consistency among the published results; however, everyone agrees on that there is no new physical phenomenon in microscale that does not exist at macroscale. Only difference between them is that the effect of some physical phenomena such as viscous dissipation, axial heat conduction, entrance effect, rarefaction, and so forth, is negligibly small at macroscale, whereas it is not at microscale. The effect of these physical phenomena on the heat transfer and flow characteristics becomes significant with respect to specified conditions such as Reynolds number, Peclet number, hydraulic diameter, and heat transfer boundary conditions. Here, the literature was reviewed to document when these physical phenomena become significant and insignificant.Article Citation - WoS: 23Citation - Scopus: 24Constructal Branched Micromixers With Enhanced Mixing Efficiency: Slender Design, Sphere Mixing Chamber and Obstacles(Elsevier Ltd., 2019) Çetkin, Erdal; Miguel, Antonio F.Here we uncover the passive micromixer designs with the maximum mixing efficiency under a lesser flow impedance. Three different designs of micromixers were considered for volume constrained systems: branched systems of ducts, branching ducts with sphere mixing chamber and branching ducts with obstacles. The best performing designs, with maximum mixing efficiency and minimum flow impedance, are uncovered numerically by considering three degrees of freedom (ratios between diameters, between lengths, and between length and diameter) under total volume constraint. The mixing efficiency, the flow impedance and the mixer performance (or mixer quality) for all the designs are determined based on numerical results. The results uncover that the branched micromixer should have long mother ducts with larger diameter than daughter ducts. Our results also show that branching ducts with sphere mixing chambers and obstacles also enhance the mixing efficiency but with an additional penalty on flow impedance. Besides, systems with a sphere mixing chamber insertion in the junction between mother and daughter ducts have greater mixing efficiency than systems with embedded obstacles into the mother channel. However, for a given flow impedance, the mixing efficiency is greater for branched systems of ducts than for branching ducts with sphere mixing chamber and with obstacles. For mixer systems built in a space with limited size, branching ducts with sphere mixing chamber may be a good option because they require less space than the other systems. Here new analytical models are also proposed to predict the mixing efficiency and mixer performance based on numerical results. In summary, this paper provides important insights for the designers of micromixer based on Constructal law. (C) 2018 Elsevier Ltd. All rights reserved.Article Citation - WoS: 23Citation - Scopus: 26Thermal Management of Electric Vehicle Battery Cells With Homogeneous Coolant and Temperature Distribution(American Institute of Physics, 2020) Göçmen, Sinan; Güngör, Şahin; Çetkin, ErdalElectric vehicles play an integral role in eliminating pollution related to transportation, especially if the electricity is generated via renewable sources. However, storing electricity onboard requires many battery cells. If the temperature of the cells is not strictly regulated, their capacity decreases in time, and they may burn or explode due to thermal runaway. Battery thermal management systems emerged for safe operations by keeping the battery cell temperatures under limit values. However, the current solutions do not yield uniform temperature distribution for all the cells in a pack. Here, we document that constant temperature distribution can be achieved with uniform coolant distribution to the channels located between batteries. The design process of the developed battery pack begins with a design used in current packs. Later, how the shape of the distributor channel affects flow uniformity is documented. Then, the design complexity was increased to satisfy the flow uniformity condition, which is essential for temperature uniformity. The design was altered based on a constructal design methodology with an iterative exhaustive search approach. The uncovered constructal design yields a uniform coolant distribution with a maximum of 0.81% flow rate deviation along channels. The developed design is palpable and easy to manufacture relative to the tapered manifold designs. The results also document that the peak temperature difference between the cells decreases from a maximum of 12K to 0.4K. Furthermore, homogenous distribution of air is one of the limiting factors of the development of metal-air batteries. This paper also documents how air can be distributed uniformly to metal-air battery cells in a battery pack.
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