Sürdürülebilir Kalkınma Amaçları

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• MakaleAçık Erişim2026Scopus SJRQ2/r/munzur/691
  Production and Thermal–Structural Characterization of Nano-Oxide-Doped Paraffin-Based Phase Change Composite Materials for Thermal Storage Applications

  Yücel, Halit Lutfi; Özdemir, Osman; Kahraman, Gökhan

  Paraffin-based composite phase change materials (PCMs) have been synthesized for thermal energy storage applications to enhance thermal conductivity and stability while maintaining latent heat storage capacity. In this study, RT42 paraffin was modified with inorganic nano-oxides (Al2O3, CuO, SiO2, and ZnO) in the presence of sodium dodecyl sulfate (SDS) as a surfactant. The incorporation of SDS improved nanoparticle dispersion and reduced agglomeration, resulting in enhanced phase-change behavior and improved structural homogeneity. Differential scanning calorimetry (DSC) analysis revealed slight variations in melting and crystallization temperatures, while the ZnO-doped composite retained up to 92% of the latent heat storage capacity of pure RT42. Among all the investigated composites, the Al2O3-doped sample exhibited the highest thermal conductivity and specific heat capacity. Thermogravimetric analysis (TGA) indicated an increase of approximately 15–20°C in the decomposition temperature, demonstrating enhanced thermal stability. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed the preservation of the crystalline structure and improved microstructural uniformity. The developed SDS-assisted nano-oxide/RT42 composites exhibit significant potential for passive thermal regulation in renewable energy and building applications.

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  AtıfScopus1·WoS1·OpenAlex1

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• MakaleYalnız künye2026Scopus SJRQ2/r/munzur/623
  Experimental ınvestigation of hybrid passive cooling strategies for photovoltaic modules using nano-enhanced PCM and graphene-coated finned structures under hot climate conditions

  Özdemir, Osman; Yücel, Halit Lutfi; Kahraman, Gökhan

  This study experimentally investigates the use of several passive cooling techniques to enhance the electrical performance of photovoltaic (PV) modules under high ambient summer temperatures in Elazığ, Turkey. Throughout the trial period of July, August, and September, a system comprising four photovoltaic panels, one designated as a reference, was developed. The first passive cooling arrangement utilized a paraffin-based phase change material (PCM) RT42HC. In the second configuration, a nano-enhanced PCM (NePCM) composite was employed, prepared by dispersing 1 mass% of Al2O3 nanoparticles into the paraffin matrix and stabilizing them with 3 mass% of sodium dodecyl sulfate (SDS) to ensure homogeneous distribution. The third, hybrid configuration integrated 14 graphene-coated parabolic pin-tipped fins mounted externally onto the aluminum enclosure housing the NePCM composite. Experimental results demonstrated that the implemented passive cooling techniques markedly decreased the panel surface temperature, thereby enhancing electrical power output and photovoltaic efficiency. The hybrid graphene-coated fin-NePCM system demonstrated superior performance, achieving a maximum surface temperature reduction of 12.65 °C, a sustained electrical efficiency increase of 6–13%, and an average daily electrical energy gain of 26.23 Wh day−1 compared to the reference module. These findings demonstrate that the integrated hybrid design is an effective and reliable passive cooling method for sustaining photovoltaic system performance under hot climate conditions.

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• MakaleYalnız künye2023Scopus SJRQ1/r/munzur/2617
  Mathematical modeling of vibration failure caused by balancing effect in hydraulic turbines

  Kahraman, Gökhan; Özdemir, Osman

  This article discusses the causes of vibrations depending on unbalanced hydraulic forces in rotating and non-rotating equipment in hydraulic plants within the scope of vibration measurement standards. The radial and axial positions of the turbine shaft, normal operating conditions, the absolute vibration of the signal output velocity during startup and shutdown during unbalance condition of the turbine, the proximity probes have been measured by TMO 793 accelerometer sensor and TMO 793 velocity sensor. The results obtained from the monitoring are analyzed and the first discussion is over the comparison of the current operating levels and vibration standards. Secondly, the comparison is analyzed in order to examine the improvement in vibration level of the elimination of hydraulic imbalance more comprehensively, considering the stability of the hydro turbine-generator unit, a proportional row damping force, proportional-order oil-film force and a hydraulic force and by creating a new non-linear proportional-order mathematical model. Changes in vibration levels and spectral bands for failure types are stated as well. The solution of this integrated and accurate mathematical model shows that it is useful and concise in the diagnosis and prediction of faults in hydropower plants.

  AtıfScopus13·WoS13·OpenAlex16

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• Yüksek Lisans TeziAçık Erişim2020/r/munzur/7250
  Hidrolik santrallerde titreşim analizi ve titreşim arızaları için çözüm yöntemleri

  Osman Özdemir

  Vibrasyon bütün döner makinelerde olduğu gibi hidroelektrik santrallerde de büyük önem arz etmektedir. Normal vibrasyon değerleri dışında çalışan bir makinede arızanın hangi kısımda oluşacağını tahmin etmek çok zordur. Ayrıca oluşan arızalar hidroelektrik santrallerin ünitelerine büyük hasarlar vererek uzun süre enerji üretimini engelleyebilir. Bu nedenle türbin-jeneratör ünitelerinde vibrasyon şiddetini izlemek ve oluşan vibrasyonun kaynağını tespit ederek önlemler almak makine için hayati önem taşımaktadır. Bu çalışmada, hidroelektrik santrallerde vibrasyon oluşumunun nedenleri araştırılmıştır. Vibrasyonun temel olarak üç dengesizlikten meydana geldiği ifade edilmiştir. Bunlar dinamik, hidrolik ve manyetik dengesizliklerdir. Bu dengesizliklerin hidroelektrik santrallere verdiği zararlar incelenmiş ve nasıl önlem alınması gerektiği açıklanmıştır. Bu tez çalışması kapsamında aktif bir şekilde çalışarak elektrik üretimine devam eden Keban HES' e ait Francis türbinlerinin tasarım dışı kısmi yüklerde çalışması ile oluşabilecek titreşim kaynaklı problemlerin çeşitleri ve bu problemlerin çözüm metotları açıklanmıştır. Keban HES ünitelerinde online izleme sistemi ile tespit edilen dengesizlik arızasının öncesi ve arızayı giderme çalışması sonrası türbine ait çalışma verilerinin iyileşmesinin matematiksel modelleme ile ispat edilerek karşılaştırması yapılmıştır.

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