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- MakaleAçık Erişim2026Scopus SJRQ1Exergy and DFT-Based Thermodynamic Analysis of a Rankine–VCR Marine Waste Heat Recovery System
Keven, Arzu; Akçay, Enes; Gümüş, Hacer
This study investigates the performance of a diesel engine exhaust gas-driven Rankine Cycle-supported vapor compression refrigeration system using quantum chemical approaches beyond conventional thermodynamic analyses. The study focuses on R448A and its components, namely R32, R125, R134a, R1234yf, and R1234ze(E), evaluated at both the system level and the molecular level. At the system level, the Rankine–VCR system was analyzed using a Fortran-based macroscopic thermodynamic model, in which the thermophysical properties of the working fluids were obtained from the NIST Chemistry WebBook. At the molecular level, Density Functional Theory (DFT) calculations were performed to determine molecular structure parameters, including entropy, heat capacity, chemical hardness, and thermal enthalpy correction. The main objective is to investigate the possible relationships between these molecular descriptors and system-level performance indicators, while considering that mass flow rate is primarily governed by cycle thermodynamic properties. The results show that molecular stability and structural order are strongly associated with system performance. Among the R448A components, R32, with the highest chemical hardness (8.19 eV) and lowest molecular entropy (58.9 cal/mol K), exhibits the most favorable exergetic behavior and achieves the highest plant exergy efficiency of 44.92%. In contrast, R1234ze(E), chemically softer (η = 4.42 Ev) and higher in entropy, exhibits the lowest performance. Additionally, R32’s lower thermal enthalpy correction is associated with higher latent heat of vaporization under the selected operating conditions, reducing the required mass flow by approximately 60–70% compared to the other components. This study demonstrates that, in refrigerant selection, not only the global warming potential (GWP) but also quantum parameters such as chemical hardness, molecular entropy, heat capacity, and thermal enthalpy correction can serve as important complementary performance indicators when interpreted together with macroscopic thermodynamic and exergetic results.
- MakaleYayıncıda açık erişim2024Scopus SJRQ1Energy, exergy, environmental, and enviroeconomic (4E) analysis of cascade vapor compression refrigeration systems using nanorefrigerants
Yılmaz, Metin; Cimşit, Canan; Keven, Arzu; Karaali, Rabi
The refrigerants used in traditional vapor compression refrigeration systems are harmful to the ozone layer and contribute to global warming. The demand for refrigeration is increasing because of global warming. In this study, for the first time, an energy, exergy, environmental, and enviroeconomic (4E) analysis was performed using different refrigerants and nanoparticles to reduce the energy required in low-temperature vapor compression cascade refrigeration systems and to determine more environmentally friendly nanorefrigerants. The R290 refrigerant was used for the Low-Temperature Circuit (LTC), while the High-Temperature Circuit (HTC) used RE170, R1234yf, R600, R600a, and R450A refrigerants. The nanoparticles used in the analysis were Al2O3, CNT, CuO, TiO2, ZnO, and SiO2. The R600 nanorefrigerant performed the best, whereas the R1234yf nanorefrigerant performed the worst. The results indicate that the CuO nanoparticles provided the highest performance. In addition, the results showed that the R290+R600-CuO nanorefrigerant emitted 11 % less CO2 than the pure R290+R600 refrigerant. The nanorefrigerants provide a more environmentally sustainable option because of their high efficiency and lower energy consumption than conventional refrigerants.
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İncele - MakaleAçık Erişim2024Scopus SJRQ1Analysis of cascade vapor compression refrigeration system using nanorefrigerants: Energy, exergy, and environmental (3E)
Yilmaz, Metin; Cimsit, Canan; Keven, Arzu; Karaali, Rabi
Nanorefrigerants are considered the most efficient heat transfer fluids for improving heat transfer properties in the refrigeration and air conditioning equipment. For the first time in this study, energy, exergy, and environmental evaluation (3E) analyses were performed by the addition of different nanoparticles to a low GWP refrigerant pair such as R290/R1233ZDE in a cascade refrigeration system. CNT, CuO, and, TiO2 nanoparticles were added to the refrigerant. The effect of nanoparticles on the cascade refrigeration system was analyzed using a model based on density changes. A detailed thermodynamic analysis was performed of the cascade refrigeration system at different evaporator temperatures and mass ratios. The power consumption of the compressor decreases as the evaporator temperature increases for all types of nanoparticles, resulting in an increase in COP values. The analyses showed that CuO nanoparticles had the highest performance. It has been observed that the energy and exergy efficiency increase as compressor work decreases with increasing mass ratios in all nanorefrigerants. In addition, the results indicated that all nanorefrigerants emit lower monthly CO2 emissions compared to the pure refrigerants. The nanorefrigerants play a crucial role in reducing energy consumption and promoting environmental protection compared to traditional refrigerants.
AtıfScopus16WoS16OpenAlex17İncele - MakaleYalnız künye2022Analysis of Some Tribological Properties of Hazelnut Oil in Gasoline Engines
Keven, Arzu; Karaali, Rabi
In this article, oil obtained from vegetable was used to lubricate a single-cylinder 2-stroke gasoline engine as lubricating oil, and tribological function of the obtained oil was investigated. To investigate the tribological functions of the lubricating oils, a 2-stroke single-cylinder gasoline engine was used. For mineral oil and hazelnut oil, the test engine was run for 100 hours for each one and were used to lubricate in the test engine as lubricating oils. Samples were prepared for the aim of the determining the wear on the cylinder surface, and also EDS (Energy Dispersive Spectrograph) analysis were obtained. The results of the analyses showed that, the wear on the cylinder surface were increased in the studies using hazelnut oil and the C content of the cylinder sample increased compared to the study with mineral oil. Al element was detected in the cylinder sample in the hazelnut study, that the reason for this, is the transport of the Al element during the friction event in the piston material to the cylinder surface.
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İncele - MakaleAçık Erişim2022Scopus SJRQ3Evaluation of four different cogeneration cycles by using some criteria
Karaali, Rabi; Keven, Arzu
The purpose of this article is to evaluate four different gas turbine cogeneration cycles which are basic, absorption cooling, air heating and air fuel heating cogeneration cycles by using the most important six evaluation criteria for different excess air coefficient, different compression rates, and different compressor inlet air temperatures. These six evaluation criteria are electrical heat ratio, exergy efficiency, incremental heat rate, artificial thermal efficiency, fuel energy saving ratio, and specific fuel consumption. It is seen that the air-fuel heating cogeneration cycle is the most efficient among the cycles examined for a certain compressor compression ratio, followed by the air heating, basic, and absorption cooling cycles.
AtıfScopus20WoS18OpenAlex30İncele - MakaleAçık Erişim2022Scopus SJRQ3Exergy analyses of two and three stage cryogenic cycles
Atasbak, Musa; Keven, Arzu; Karaali, Rabi
Cryogenics has an important influence on industry and science. In this study, optimum working conditions are obtained by applying exergy analysis and local optimization methods to two- and three-stage vapor compression cascade cryogenic cycle. The first and second laws of thermodynamics, exergy analysis, and local optimization methods are applied to the two- and three-stage cascade cryogenic cycle. By considering the needs and demands, it is possible to create new cycles by adding new devices and/or new stages to these cycles. The results of the optimum operating conditions are obtained for the two- and three-stage vapor compression cascade cryogenic cycle. It is seen that to achieve high COP values and high efficiency; it is necessary to reduce the compression ratio of the compressor as much as the fluid allows. For the two-stage cycle, the minimum total work required for cryogenic cooling is around P 7 = 2,400 kPa. The COP value is 0.30 between P 7 = 2,400 and 2,800 kPa, and the maximum exergy efficiency is obtained around 0.235. It is seen operating the first-stage compressor at high pressures increases the total losses of the entire cycle from 7,500 to 18,550 kW. The increase in total exergy losses is around 247%, and operating the first-stage compressor at high pressures increases the exergy efficiency of the entire cycle. The increase in total exergy efficiency is around 160%. When the second-stage compressor is operated at low pressure, the COP value increases by 2%, the exergy efficiency increases by 20%, and the exergy losses decrease by around 40%.
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