Sürdürülebilir Kalkınma Amaçları

• 3
• 1
• 1

• MakaleAçık Erişim2026Scopus SJRQ2/r/munzur/1247
  Examination of the thermal and metallographic characteristics at high temperatures of natural stones (andesite) extracted from different elevations

  Işık, Erdem; Kahraman, Gökhan; Atalar, Aydın

  This study examines the high‑temperature thermal response of andesite stones extracted from two different elevations of Mount Ağrı (Türkiye) in order to improve material selection strategies for engineering applications. Thermal conductivity and density values of the samples were first measured under laboratory conditions. The specimens were then heated to 850 °C and cooled by natural convection while surface temperatures were recorded at fixed time intervals using a thermal camera. Based on these measurements, convective heat transfer coefficients were determined, and the time‑dependent thermal diffusivity and Biot numbers were subsequently calculated using the first-term approximation of the Fourier series. Metallographic examinations were conducted to correlate the thermal behavior with microstructural characteristics. Results indicate a pronounced effect of elevation on thermal performance. The sample obtained from the higher elevation exhibited substantially greater thermal diffusivity, reaching 2.93 × 10⁻5 m2 s−1 at 360 s and decreasing to 8.96 × 10⁻6 m2 s−1 at 1300 s. In contrast, the lower‑elevation andesite showed lower diffusivity values (1.83 × 10⁻5 m2 s−1 at 360 s and 5.9 × 10⁻6 m2 s−1 at 1300 s). Conversely, Biot numbers were consistently higher for the lower‑elevation sample, decreasing from 0.60 to 0.29 during the cooling process, whereas the high‑elevation sample displayed values from 0.314 to 0.165. Metallographic analysis confirmed that variations in microstructure—linked to different geological formation conditions—directly influenced these thermophysical properties. Overall, the findings demonstrate that andesite sourced at higher elevations possesses superior thermal diffusivity and more favorable heat‑transfer characteristics at elevated temperatures. These results highlight the importance of geological origin in the design, assessment, and selection of natural stone materials for high‑temperature engineering applications.

  İncele
• 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.

  • 
  • 
  • 
  İncele
• MakaleAçık Erişim2025Scopus SJRQ2/r/munzur/1144
  Investigation of the effect of the metallographic properties of vertical and horizontal cylinders made of ferrochrome with different contents on heat transfer by natural convection

  Kahraman, Gökhan; Taşgın, Yahya

  In this study, ferrochrome materials containing elements with different content ratios were manufactured into six-cylinder specimens, 13 mm in diameter and 16 mm in length, and heated in a furnace up to 500 °C. The heated cylinders were removed and left to cool in vertical and horizontal positions in a 16 °C environment. The temperatures were recorded using thermal cameras at certain intervals while the materials cooled down. The six specimens, whose metallographic differences were identified using SEM and XRD analysis devices, were placed vertically and horizontally, and their heat transfer by natural conviction was noted. In the calculations, each specimen’s Nusselt and Rayleigh numbers were identified based on time and then compared. The fastest cooling among the specimens occurred in the ferrochromium material with 55.93% Cr, 31.11% Fe, 11.56% C, 0.48% Si, 0.83% O, and 0.09% Al compound ratios, both in vertical and horizontal positions. Additionally, since the Nusselt number of the horizontal cylinders remained below one based on their position, their natural convection flows were not initiated. The cooling in the horizontal cylinders occurred via conduction.

  İncele
• MakaleYalnız künye2024Scopus SJRQ2/r/munzur/2294
  Investigation of thermal, crystal and magnetic behavior of addition of Nd rare earth element effect on CuAlMn shape memory alloy

  Kanca, Muhammed Sait

  In this study, CuAlMn alloys, a popular Cu-based shape memory alloy, were chosen because they exhibit superior shape memory properties and improved ductility compared to other Cu-based SMAs. The rare earth element Nd (neodymium) was added to CuAlMn alloy at the specified atomic percentages in the composition Cu70-xAl24Mn6Ndx(x = 0,2,4,8) and their thermal behavior, crystal structure, surface morphology and magnetic properties were investigated after fabrication. As a result of the thermal analysis measurements, it was observed that for low Nd ratios, the austenite phase transformation initial temperature of the CuAlMn alloy was increased, while at high Nd ratios, a decrease in the shape memory property was detected. Martensitic phase and precipitate phase α phase were observed in the crystal structure properties of CuAlMn alloys without and with Nd doping. These results were also detected in surface morphology observations. In addition, the crystal size decreased from 135 to 105 nm with Nd doping. As a result of magnetic measurements, CuAlMn ternary shape memory alloy was found to be paramagnetic at room temperature. Magnetic susceptibility values of the alloys showing paramagnetic magnetic properties were calculated as 11.5 × 10–6, 12.5 × 10–6, 9.15 × 10–6 and 6.15 × 10–6 emu.Oe−1.g−1, respectively. According to these results, the magnetic susceptibility value decreased with increasing Nd ratio.

  AtıfScopus3·WoS3·OpenAlex3

  İncele
• MakaleYalnız künye2024Scopus SJRQ2/r/munzur/1826
  Evaluating the metallographic properties and performance of heat transfer by natural convection of graphene-coated glass used for heating

  Kahraman, Gökhan; Taşgın, Yahya

  In this study, a decorative electric heater was manufactured to reduce carbon emissions related to residential and office heating, and this heater was metallographically evaluated. In addition, the heating performance of the manufactured plate was investigated by examining its heat transfer capacity by natural convection. For this purpose, the surface of the tempered glass plate was coated with graphene by spraying to improve its electrical and heat conduction properties. Copper strips were attached to both sides of the plate to allow for an electric current. The plate was connected to mains electricity, and its change in surface temperature over time was measured. Using the measured temperature values, the heat transfer rate by natural convection on the plate surface was calculated. As a result of the calculations, it was determined that the graphene-coated tempered glass plate reached a heating performance of 40 watts after 2400 s of electrical energy supply. This value can be increased by increasing the heat transfer surface area. This study, taking advantage of the excellent thermophysical properties of graphene, will contribute to other studies conducted in this field.

  • 
  AtıfScopus2·WoS2·OpenAlex2

  İncele
• MakaleAçık Erişim2023Scopus SJRQ2/r/munzur/1842
  Preparation of composite supported phase change materials from inorganic-based microcapsules of cetyl alcohol and investigation of their phase change material (PCM) behaviors

  Karabulut, Serap; Sekerci, Memet; Adiguzel, Ragip; Karagoz Genc, Zuhal

  In this study, cetyl alcohol (CA) (CH3(CH2)15OH), which is a fatty alcohol, was microencapsulated by the coacervation method with the titanium-n-butoxide (TNBO). Firstly, at the beginning of the experimental process by thermal and structural analyses, the CA was determined as having a phase change material (PCM) property, then it was microencapsulated with TNBO. In the second step of the study, barite, boron nitride, marble powder, and fly ash were separately added to prepare a series of microencapsulated with TNBO. Lastly, structural and thermal properties of both microencapsulated PCM and composite supported microencapsulated PCMs (CSM-PCMs) have been analyzed by FTIR, DSC, TGA, and SEM devices. Surprisingly, the SEM image of CA turned from torn fiber structure into a particulate structure in the form of groundnut in the SEM images of the microencapsulated CA-Ti taken at different magnifications. After the thermal cycling test, the same analyses have been made before and after thermal cycling to compare the structural and thermal properties. It has been investigated whether to use as insulation material. It is concluded that the most suitable samples, compared with structural and thermal properties, are barite (B) and boron nitride (BN) with microencapsulated samples. The obtained results are shown that CATi-B and CATi-BN are CSM-PCMs and could be suggested in terms of thermal energy storage in buildings as promising PCMs.

  AtıfScopus3·WoS3·OpenAlex3

  İncele
• MakaleAçık Erişim2022Scopus SJRQ1/r/munzur/2554
  Corrosion behavior and crystal-microstructural analysis of non-equiatomic NiTi shape memory alloys

  Kanca, M. Sait; Kök, Mediha; Qader, Ibrahim Nazem

  NiTi shape memory alloys (Nitinol) are one of the most widely used families of smart materials that are used in smart systems and medical applications. The NiTi alloy with a composition of around 50 at. % Ni is very sensitive and just a small change in the components can make a big difference in the physical properties of the alloy. In this study, five non-equiatomic NiTi alloys with different compositions were fabricated with arc-melting in a controlled atmosphere. The crystal structure and morphology of the alloys were analyzed with x-ray diffraction (XRD) and scanning electron microscope (SEM), also the caloric properties of the alloys were investigated as a function of composition. Additionally, the samples were examined by the Tafel test to determine the corrosivity rate for one year in a simulated body fluid. The XRD and DSC results showed that only Ni44.56Ti55.44 at. % has martensite phase at room temperature, while the other alloys with higher Ni contents did not show martensitic phase transformation for the range of 230 K to more than 400 K. It was found that the alloys have corrosion rate around 10–4 mmpy which has comparably better than CuAlNi-based alloys. On the other hand, it was found that the corrosivity does not depend on the matrix phase of the NiTi alloy, but the composition ratio and other secondary phases play an important role.

  AtıfScopus4·WoS4·OpenAlex6

  İncele
• MakaleAçık Erişim2020Scopus SJRQ2/r/munzur/3704
  Fabrication of a novel acrylate polymer bearing chalcone and amide groups and investigation of its thermal and isoconversional kinetic analysis

  Biryan, Fatih; Pihtili, Güzin

  The aim of the article was to examine the thermal degradation, thermal decomposition kinetics and dielectric behavior of novel poly(APHP-Am–Ac). For this purpose, the novel monomer, 4-(3-(4-acetamidophenyl)-3-oxoprop-1-en-1-yl)phenyl acrylate (APHP-Am–Ac), was synthesized from 1-(4-aminophenyl)-3-(4-hydroxyphenyl) prop-2-en-1-one (APHP) and acetic anhydride reaction. The homopolymer P(APHP-Am–Ac) was prepared by free radical polymerization within dimethylformamide at 80 °C. The presence of rigid and bulky chalcone units in polymer side chains significantly improved the solubility of polyamides, giving them an amorphous nature and good thermal stability. The structural characterization of homopolymer was accomplished using FT-IR and NMR techniques. The thermal stability and degradation features of homopolymer have been performed by using TG analysis and FT-IR during partial degradation at different temperatures. The glass transition temperature of homopolymer was determined by DSC analysis. For thermal decomposition kinetics of poly(APHP-Am–Ac), Flynn–Wall–Ozawa and Kissinger methods were applied to thermogravimetric curves and apparent activation energies (Ea) calculated from these two methods. According to FWO, the activation energy (Ea) of the first step and the second step was found as: 157.78 kJ mol−1 and 151.81 kJ mol−1, respectively. For Kissinger’s model, Ea was calculated as 154.3 kJ mol−1 and 142.83 kJ mol−1, respectively. The dielectric and conductivity measurements of homopolymer were investigated by impedance analyzer technique in a range of 10 Hz–20 kHz frequency at different temperatures (from 25 to 120 °C). The results have been plotted as a function of frequency and temperatures. The values increased significantly with temperature.

  AtıfScopus18·WoS17·OpenAlex18

  İncele
• MakaleAçık Erişim2020Scopus SJRQ2/r/munzur/3571
  Thermal studies and influence of the thermal decomposition on dielectric properties of a new coumarin copolymers

  Biryan, Fatih; Pihtili, Güzin; Demirelli, Kadir

  In this study, firstly 7-hydroxy-4-chloroethyl coumarin compound was synthesized in accordance with the literature (Peterson et al. in Macromol Chem Phys 202: 775–784, 2001). Then, this compound was reacted with acryloyl chloride to form the 4-(chloromethyl)-2-oxo-2H chromen-7-yl-acrylate) monomer. A series of copolymers were prepared using this monomer and n-butyl acrylate monomer. TGA analysis system was used to examine the thermal properties of homopolymers and copolymers. The activation energies were calculated for thermal decomposition of homopolymer and certain copolymers according to Flynn–Wall–Ozawa method. TGA measurements were taken at different heating rates and given comparatively. The glass transition temperatures of the copolymers were determined by DSC analysis and these results were given comparatively. For investigating the dielectric properties of copolymers, dielectric constant, dielectric loss factor, and ac conductivity values were calculated in the range of 100 Hz–20 kHz frequencies. The results were plotted as a function of frequency. In addition, dielectric behaviors of residues were determined after heating to the first decay temperature of the two-stage decay polymers and compared with the first states.

  AtıfScopus6·WoS6·OpenAlex6

  İncele
• MakaleYalnız künye2020Scopus SJRQ2/r/munzur/3564
  The effect of graphene oxide on structural, opto-electrical and thermal properties of manganese sillenite (Bi12MnO20) nano-powders

  Aydin, C.; Taskin, M.; Aydin, H.

  In this study, manganese sillenite nano-powders were produced by hydrothermal method by adding graphene oxide in different mass amounts. Structural, morphological, thermal, optical and electrical properties of the obtained undoped and graphene-oxide-doped samples were investigated. XRD results showed that the produced samples had nano-sizes and the crystal sizes changed with the addition of graphene oxide. SEM and TEM images showed that the microstructures of the samples were nano-sized and composed of randomly oriented particles without orientation relationship between them. From FT-IR spectra of the samples, chemical properties and bond structures were determined. With the help of thermal analysis measurements, reactions in the sample structures at increasing temperatures, reaction temperatures, reaction energies and total mass losses were determined. The forbidden energy ranges of the samples decreased at significant rates with the addition of graphene oxide. By checking the P–E hysteresis cycles, the samples are understood to show ferroelectric properties. Dielectric measurements and temperature-dependent electrical conductivity measurements of the produced nano-powders confirmed that the samples exhibited semiconductor behaviour. The obtained results showed that manganese sillenites can be synthesised by low-temperature hydrothermal method and physical, chemical and thermal properties can be controlled by adding different amounts of graphene oxide for use in electronic and energy applications.

  • 
  AtıfScopus6·WoS6·OpenAlex6

  İncele