Browsing by Author "Mehrtash, Mehdi"

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Ankara'da uzak komünite için sıfır enerji binalarında bağımsız mikrogrıd hibrit enerji sisteminin techno-ekonomik optimizasyonu
(2020) Hayalı, Othman Jasım Mohammed Al; Mehrtash, Mehdi; Eseller, Kemal Efe; Energy Systems Engineering
Artan elektrik enerji tüketimi, fosil yakıtların azalması, iletim hatlarının yüksek fiyatları ve çevre kirliliği sorunları ülkeleri yenilenebilir enerji kaynaklarından elektriğin üretildiği sıfır enerji binaları (ZEB) geliştirmeye itmektedir. Rüzgar ve güneş enerjileri ümit verici kaynaklardır. Ancak, bu kaynakların kesintili doğası sistem güvenilirliğini azaltır. Hibrid yenilenebilir enerji sistemi (HRES), bu soruna bir çözüm olarak kabul edilir. Bir HRES tasarlamak için yatırımcıların minimum yapılandırma maliyetini göz önünde bulundurmaları gerekir. Bu çalışmada, Ankara'da uzak bir bölgede 30 evin elektriklendirmek için fotovoltaik (PV) ve rüzgar türbini (WT) sistemlerinin kurulması simüle edilmiştir. Yükü en az maliyetle karşılayabilecek en uygun hibrit sistemi elde etmek için farklı senaryolar düşünülmüştür. Optimal konfigürasyon elde etmek için Çoklu Enerji Kaynakları için Hibrid Optimizasyon Modeli (HOMER) yazılımı ve Parçacık Sürüsü Optimizasyonu (PSO) algoritması uygulanmıştır. 107 kW PV, 3 × 10 kW WT, 10 kW dizel jeneratör (DG) ve 45 × 7.15 kWh pillerden oluşan HRES, elektrik yükü talebini karşılamak için en uygun seçim olarak seçilmiştir. Enerji maliyeti (COE) ve net yüzde maliyeti (NPC) sırasıyla 0.25 $/kWh ve 568431 $ olarak bulunmuştur. Duyarlılık analizinde sonuçları doğrulamak için PV ve WT sermaye maliyetlerinin, yakıt fiyatının ve pillerin türünün sistem performansı üzerindeki etkileri incelenmiştir. Sonuç olarak, yakıt fiyatını ikiye katlamak, COE ve NPC'yi sırasıyla 14% ve 13% oranında arttırdıgı gözlenmiştir. PV ve WT sermaye maliyetleri yarıya düştüğünde, COE ve NPC sırasıyla 20% ve 12% oranında azalmıştır. Belirli bir pil teknolojisinin kullanılmasının hem genel fiyatı hem de gaz emisyonlarını azalttığı görülmüştür. Anahtar Kelimeler: Off-grid ZEB, Yenilenebilir Enerji, PSO, HOMER, Ankara
Citation Count: 2
A Combined Experimental and Numerical Thermo-Hydrodynamic Investigation of High-Temperature Fluidized-Bed Thermal Energy Storage
(Mdpi, 2022) Mehrtash, Mehdi; Karadiken, Esra Polat; Tari, Ilker; Energy Systems Engineering
The present research describes the design, analysis, and modeling of an air-granular particle fluidized-bed system with dimensions of 0.08 m x 0.4 m x 0.08 m. The hydrodynamic and thermal experiments are designed to verify the numerical model previously created for this purpose. The gas-solid two-phase flow is described using a three-dimensional, two-fluid model based on the Eulerian-Eulerian method. The experiment is conducted, and the numerical model is updated for the new geometry while maintaining the solution parameters. Silica sand and sintered bauxite particles are employed in both experimental and numerical investigations to examine the behaviors of these particles. The hydrodynamic validity of the numerical model is established by the use of experimental findings for pressure drop and bed expansion ratio. The thermal tests are conducted with 585 K hot sand, and the temperature distribution in the bed is measured using K-type thermocouples and compared with the simulation data. Both the hydrodynamical and thermal experimental data appear to agree with the conclusions of the computational analyses. The validated model is then used to mimic the performance of the bed at elevated temperatures. The performance indicators are discussed and calculated for 973 K, demonstrating that as the temperature rises, the system efficiency increases.
Citation Count: 7
Numerical modeling of visco-elasto-plastic hygro-thermal stresses and the effects of operating conditions on the mechanical degradation of PEFC membranes
(Elsevier, 2018) Mehrtash, Mehdi; Tari, Ilker; Yesilyurt, Serhat; Energy Systems Engineering
Durability of membranes is one of the concerns for widespread commercialization of polymer electrolyte fuel cells. Effects of membrane swelling on the durability pose important challenges for the fabrication of the catalyst-coated membrane. This study provides insight into vulnerable locations of the membrane under hygrothermal loading, mechanical loading due to clamping and realistic conditions where a combination of both of these loadings are imposed. With a half rib-channel model, we simulate a polymer electrolyte fuel cell that operates under varying loads and clamping pressure. Model considers anisotropic diffusion in the gas diffusion layer as well as complex interactions of water transport dynamics between gas diffusion layers and the membrane. Mechanical responses of the membrane subject to conjugate hygro-thermo-mechanical loadings during typical scenarios of fuel cell operation reveal the effects of operating parameters as well as individual contributing factors on the development of local stresses in the membrane.
Citation Count: 1
Parametric Sensitivity Analysis and Performance Evaluation of High-Temperature Macro-Encapsulated Packed-Bed Latent Heat Storage System Operating with Transient Inlet Boundary Conditions
(Mdpi, 2022) Mehrtash, Mehdi; Tari, Ilker; Energy Systems Engineering
This paper presents the results of comprehensive numerical analyses in the performance of a packed-bed latent heat storage (PBLHS) system in terms of key performance indicators, namely charging time, charging rate, charging capacity, and charging efficiency. Numerical simulations are performed for the packed bed region using a transient two-dimensional axisymmetric model based on the local thermal non-equilibrium (LTNE) approach. The model considers the variation in the inlet temperature of the system as these storage systems are typically integrated with solar collectors that operate with intermittent solar radiation intensity. The model results are validated using the experimental data for temperature distribution throughout the bed. The simulations are carried out while changing the operating parameters such as the capsule diameter, bed porosity, inlet velocity, and the height-to-diameter aspect ratio to investigate their impact on the performance indicators. Observations indicate that low porosity, large-sized capsules, low inlet velocity, and a low height-to-diameter aspect ratio increase the charging time. In terms of achieving a high charging rate, a bed with low porosity, small-sized capsules, a high inflow velocity, and a high height-to-diameter aspect ratio is deemed advantageous. It is shown that raising the flow velocity and the height-to-diameter aspect ratio can improve the charging efficiency. These findings provide recommendations for optimizing the design and operating conditions of the system within the practical constraints.
Reevaluation of Plate-Fin Heatsink Natural Convection Correlations for Sideways and Three-Dimensional Inclinations
(Taylor & Francis inc, 2024) Mehrtash, Mehdi; Energy Systems Engineering
The common orientations of the plate-fin heat sink for natural convection cooling of electronics are vertical and upward-facing horizontal. However, depending on various use scenarios, the heat sink may be inclined, intentionally or otherwise. In our previous papers concerning this subject, the author proposed a set of correlations for plate-fin heat sinks covering all inclination angles backward and forward (pitch rotation) from the vertical position of the heat sink. The set was based on a series of computational simulations with a validated model. At the time, tilting the heat sink sideways (roll rotation) was not considered. In the present study, though, the sideways inclination of the plate-fin heat sinks is simulated using our previous model only by adjusting the direction of the gravitational acceleration vector, thus requiring no additional validation. It is determined that the previously proposed correlation is valid up to 80 degrees sideways inclinations of the heat sink. Interesting flow structures are observed when the heat sink is tilted 90 degrees sideways. Furthermore, it is demonstrated that the correlation surprisingly remains valid if the heat sink is simultaneously rotated in both axes (pitch and roll).