Yazar "Kilic, Mustafa" seçeneğine göre listele

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    A performance analysis of hydrodynamic journal bearing lubricated with hybrid MWCNTs-TiO2 nanolubricants considering thermal effects
    (Springer, 2025) Kilic, Mustafa; Dal, Abdurrahim; Sahin, Mahir
    The new development of nanotechnology proposes cost-effective and upgrading solutions for tribological characteristics of the lubricant. One of these solutions is the coexistence of two or more types of nanoparticles known as hybrid nanoparticles. This work presents useful results of research on the performance features of the circular journal bearings operated with SAE30/TiO2-MWCNTs (SAE 30-grade base oil blended with titanium dioxide and multi-walled carbon nanotube hybrid nanoparticles) hybrid nanolubricant. In this study, the mathematical model of the lubricant with hybrid nanolubricant is based on the Dowson equation and three-dimensional heat transfer equations. Furthermore, the thermophysical specifications of the hybrid nanoparticle are formulized in terms of characteristics of the base lubricant, TiO2, and MWCNTs, as well as an empirical formula for the viscosity-temperature relationship. To obtain bearing performance features, a series simulation is conducted under various volume and mass fractions of hybrid nanoparticle and operational conditions (a range of eccentricity ratio from 0.05 to 0.8 and a range of rotating speed from 1000 to 9000 r/min) with a developed algorithm for the iterative solution. The results showed that the effect of the hybrid nanoparticles on the maximum pressure and the load capacity are more visible at high eccentricity ratio, and nanolubricants could increase the load capacity, maximum pressure, and friction force till 11%, 13%, and 15%, respectively. Besides, when the bearing operates with a lubricant containing MWCNTs-TiO2, the pressure values are higher than the lubricant containing solely MWCNTs nanoparticles by 0.2%, while they are lower than the lubricant containing solely TiO2 nanoparticles by 1%.
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    Öğe
    Investigation of heat transfer enhancement using hemispherical turbulators in a double-pipe regenerative heat exchanger with phase change material
    (Springer, 2025) Sahin, Mahir; Kilic, Mustafa; Karadag, Mehmet Anil
    Improving energy efficiency is crucial for minimizing environmental impact and lowering operational expenses across a variety of industrial processes. This study explored the impact of a novel designed hemispherical turbulator configuration on the melting process of RT35 phase change material (PCM) within a double-pipe heat exchanger. The validated numerical model was simulated in ANSYS Fluent, revealing that increasing the Reynolds number from 200 to 1000 improved heat exchanger effectiveness by 15.8% due to enhanced fluid mixing and a thinner thermal boundary layer, promoting effective convective heat transfer. The addition of turbulators further boosted performance, increasing the heat transfer surface area by 13.4% and NTU by 47%, resulting in a 26% increase in effectiveness at Re = 200. However, as the Reynolds number increased, the effect became less significant. At Re = 1000, only a 15.6% improvement was observed, indicating that in the absence of turbulators, the development of the hydrodynamic boundary layer is primarily influenced by the Reynolds number. The distance between the turbulators (L) gradually decreased from 25 to 5 mm, leading to an overall enhancement of 4.1% in the effectiveness of the heat exchanger. Additionally, the effect of turbulator size (D) was evaluated, and a gradual reduction in turbulator diameter from D = 20 mm to D = 2.5 mm resulted in a 3.5% increase in heat exchanger effectiveness. The analysis of flow characteristics and geometric configurations demonstrated a notable improvement in heat transfer performance. These findings underscore the potential for further enhancing heat exchanger efficiency through the refined design of turbulence-promoting elements and the strategic integration of phase change materials.