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    B4C-based nanoenhancement on the thermophysical and stability performance of solar salt: a novel approach for high-temperature TES applications
    (Elsevier, 2025) Gurgenc, Ezgi; Oztop, Hakan F.; Yamac, Halil ibrahim; Canbay, Canan Aksu; Senocak, Safak Melih; Ozabaci, Murat; Gurgenc, Turan
    Enhancement of the thermophysical properties of molten salt-based nanofluids is essential for improving energy density and efficiency in high-temperature thermal energy storage (TES) systems. However, the mechanisms behind the anomalous increase in specific heat capacity upon nanoparticle addition remain unclear. In this study, solar salt (60 wt% NaNO3-40 wt% KNO3) was modified with boron carbide (B4C) nanoparticles at concentrations of 0.5, 1.0, 1.5, and 2.0 wt% using a wet dispersion method. The structural and thermal behaviors of the nanofluids were investigated through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FE-SEM/ EDX), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The DSC results from the second thermal cycle confirmed that the addition of B4C significantly enhanced the Cp of the base salt. Specifically, the 2.0 wt% B4C sample exhibited average enhancements of 31.5 % in the solid phase (100-220 degrees C) and 49.83 % in the liquid phase (250-400 degrees C) compared to pure solar salt, with a peak value of 2.11 J/g.K at 250 degrees C. FE-SEM analyses revealed more uniform nanoparticle distribution at lower concentrations, while higher loadings led to particle agglomeration. Thermal conductivity increased by 142.8 %, from 1.05 to 2.55 W/m.K. Although latent heat decreased with higher nanoparticle content (from 108.7 J/g to 97.2 J/g), thermal stability improved, with the decomposition onset temperature shifting from 607 degrees C to 644 degrees C at 1.5 wt% B4C. These results identify B4C as a promising non-oxide nanoadditive for TES applications, offering balanced improvements in thermal performance and stability.
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    Effect of hot air inclined jet impingement to container for controlling of energy storage of PCM: experimental and numerical investigation
    (Emerald Group Publishing Ltd, 2024) Oztop, Hakan F.; Kiyak, Burak; Aksoy, Ishak Gokhan
    PurposeThis study aims to focus on understanding how different jet angles and Reynolds numbers influence the phase change materials' (PCMs) melting process and their capacity to store energy. This approach is intended to offer novel insights into enhancing thermal energy storage systems, particularly for applications where heat transfer efficiency and energy storage are critical.Design/methodology/approachThe research involved an experimental and numerical analysis of PCM with a melting temperature range of 22 degrees C-26 degrees C under various conditions. Three different jet angles (45 degrees, 90 degrees and 135 degrees) and two container angles (45 degrees and 90 degrees) were tested. Additionally, two different Reynolds numbers (2,235 and 4,470) were used to explore the effects of jet outlet velocities on PCM melting behaviour. The study used a circular container and analysed the melting process using the hot air inclined jet impingement (HAIJI) method.FindingsThe obtained results showed that the average temperature for the last time step at CYRILLIC CAPITAL LETTER EF = 90 degrees and Re = 4,470 is 6.26% higher for CYRILLIC CAPITAL LETTER EF = 135 degrees and 14.23% higher for CYRILLIC CAPITAL LETTER EF = 90 degrees compared with the 45 degrees jet angle. It is also observed that the jet angle, especially for CYRILLIC CAPITAL LETTER EF = 90 degrees, is a much more important factor in energy storage than the Reynolds number. In other words, the jet angle can be used as a passive control parameter for energy storage.Originality/valueThis study offers a novel perspective on the effective storage of waste heat transferred with air, such as exhaust gases. It provides valuable insights into the role of jet inclination angles and Reynolds numbers in optimizing the melting and energy storage performance of PCMs, which can be crucial for enhancing the efficiency of thermal energy storage systems.
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    Experimental and numerical investigation on melting of phase change material in a disc-shaped container via hot air jet impinging
    (Pergamon-Elsevier Science Ltd, 2024) Kiyak, Burak; Oztop, Hakan F.; Aksoy, I. Gokhan
    Experimental and numerical analyses were performed to investigate the control parameters of a Phase Change Material (PCM) melting by impinging a hot air jet. A novel container was designed to store PCM. The RT25HC was chosen as the PCM, with a 22-26 degrees C melting temperature. Experiments were conducted under a constant air temperature (Tair) of 40 degrees C with two different Reynolds (Re) numbers, 2235 and 4470. The analysis was performed for three jet length-to-container diameter ratios (H/D): 0.4, 0.5, and 0.6. The Finite Volume Method (FVM) was used to solve three-dimensional and time-dependent governing equations. It was found that the optimum melting time was attained when the H/D = 0.5. The measurements, thermal camera images and the numerical results displayed good agreement. The influence of H/D on the melting time decreases as the Reynolds number increases, decreasing the difference between the maximum and minimum melting rates from 23.05 % at Re = 2235 to 7.67 % at Re = 4470. In the experimental comparison, when considering H/D = 0.5, which corresponds to the case with the maximum stored energy at both Reynolds numbers, the energy stored by the H/ D = 0.6 cases is 26.4 % lower at Re = 2235. In contrast, this difference reduces to 5.03 % at Re = 4470.
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    An intelligent approach to investigate the effects of container orientation for PCM melting based on an XGBoost regression model
    (Elsevier Sci Ltd, 2024) Kiyak, Burak; Oztop, Hakan F.; Ertam, Fatih; Aksoy, I. Gokhan
    The orientation of the container filled with phase change material (PCM) is a critical parameter that significantly effects the performance of thermal energy storage systems. In this study, the Computational Fluid Dynamics (CFD) method is utilised to analyse the effects of container position on the melting process of PCM. Unlike conventional methods, the melting process of PCM was conducted using the hot air jet impingement method. The study investigated the impact of two various Reynolds numbers (2235 and 4470) and three different H/D ratio (the ratio of the distance between the jet and the container to the container diameter) which were 0.4, 0.5, and 0.6, on the PCM melting process. In addition, regression analysis was executed using the Extreme Gradient Boosting algorithm (XGBoost). The outcomes unveiled that the artificial intelligence model attained a minimum accuracy of 97.89 % and reached a maximum accuracy of 99.35 % across the 12 datasets for comparing performance metrics. These results serve as a testament to the prowess of the XGBoost algorithm in providing precise predictions of the target variable within a notably extensive range of accuracy for the datasets under consideration.
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    Novel boride-enhanced solar salts: Thermophysical and structural properties for thermal energy storage
    (Elsevier, 2026) Gurgenc, Ezgi; Oztop, Hakan F.; Yamac, Halil Ibrahim; Canbay, Canan Aksu; Senocak, Safak Melih; Ozabaci, Murat; Gur, Muhammed
    Molten nitrate salts, widely used as thermal energy storage (TES) media in concentrated solar power (CSP) systems, suffer from intrinsic drawbacks such as low thermal conductivity, moderate thermal stability, and limited heat capacity. Conventional oxide nanoparticles have been explored to mitigate these limitations, yet their improvements are often restricted by relatively low intrinsic conductivity and stability. In this context, boride-based nanoparticles (HfB2, TiB2, and ZrB2) have attracted increasing attention owing to their exceptional thermal conductivity, chemical inertness, and high-temperature stability. In this study, solar salt (60 wt% NaNO3-40 wt% KNO3) was modified with different weight fractions (0.5-2.0 wt%) of HfB2, TiB2, and ZrB2 nanoparticles, and their thermophysical properties were systematically investigated. The results revealed that boride addition significantly enhanced density, specific heat capacity (Cp), thermal conductivity, and thermal stability compared to pure solar salt. Specifically, Cp increased from 1.51 J/g.K (pure salt) to 2.68 J/g.K with 2 wt% HfB2 (77.8 % increase), while ZrB2 and TiB2 yielded 2.39 J/g.K (58.4 %) and 1.60 J/g & sdot;K (6.2 %), respectively. Thermal conductivity rose from 0.632 W/m.K (pure salt) to 1.53 W/m.K (HfB2), 1.60 W/m.K (TiB2), and 1.38 W/m.K (ZrB2) at 2 wt% loading. TGA confirmed improved decomposition stability, with TiB2 showing the highest thermal stability at 651 degrees C. Additionally, density measurements indicated systematic increases with additive concentration, with the highest value (2.2411 g/cm3) recorded for ZrB2 at 2 wt%. These findings demonstrate that boride nanoparticles, even at relatively low concentrations, can effectively enhance the thermophysical performance of solar salt, surpassing many conventional oxide-based additives. Among the additives, HfB2 is most promising for maximizing energy density, TiB2 for high-temperature stability and conductivity, and ZrB2 for balanced multipurpose performance. Such improvements highlight the potential of boride-based nanocomposite salts for next generation CSP and thermal energy storage applications, particularly in hightemperature operation regimes where both energy density and efficient heat transfer are critical.
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    Three dimensional analysis of melting performance of phase change materials in a disk-shaped container with partial circular heating
    (Taylor & Francis Inc, 2023) Kiyak, Burak; Oztop, Hakan F.; Aksoy, I. Gokhan
    Three dimensional analysis of melting performance of phase change materials in a disk-shaped container with partial circular heating has been studied. The phase change materials (PCMs) have succeeded in coming to the fore with their superior features in energy storage. However, the energy storage efficiency of these materials affected by many physical parameters, and determining the appropriate parameters is important for efficient energy storage. This study explores melting and energy storage performance of PCM-RT25 in a disk-shaped container with various partial circular heating cases and aspect ratios (AR). PCM melting analysis was performed with partial heating by selecting equal heating surface area on the disk. The effects of AR on melting performance were analyzed by observing the PCM melting behavior for different disk heights while keeping the disk diameter constant. Governing equations are solved by using finite volume method. Obtained results showed that the PCM melting time decreases as the AR increases in the case of full heating. In partial heating, the increase in AR not only extended the melting time, but also decreased the liquid fraction at the end of the melting. Parameters of AR = 4 and Delta T = 45 degrees C was provided the maximum liquid fraction in partial heating cases. Under these conditions, 90%, 94% and 96% liquid fractions were obtained at the end of melting for the cases that the heater is located in the center of the disk, in the middle near the inner part of the disk and in the middle near the outher part of the disk, respectively.