Yazar "Kanoglu, Mehmet" seçeneğine göre listele

Listeleniyor 1 - 7 / 7
  • [ X ]
    Öğe
    A Systematic Approach to Exergy Efficiency of Steady-Flow Systems
    (Mdpi, 2025) Cengel, Yunus A.; Kanoglu, Mehmet
    Exergy efficiency is a measure of thermodynamic perfection. A device that operates reversibly has an exergy efficiency of 100 percent and is said to be thermodynamically perfect. A reversible process involves zero entropy generation and thus zero exergy destruction since Xdestroyed = T0Sgen. Exergy efficiency is generally defined as the ratio of exergy output to exergy input eta ex = Xoutput/Xinput = 1 - (Xdestroyed + Xloss)/Xinput or the ratio of exergy recovered to exergy expended eta ex = Xrecovered/Xexpended = 1 - Xdestroyed/Xexpended. In this paper, exergy efficiency relations are obtained first for a general steady-flow system using both approaches. Then, explicit general relations are obtained for common steady-flow devices, such as turbines, compressors, pumps, nozzles, diffusers, valves and heat exchangers, as well as heat engines, refrigerators, and heat pumps. For power and refrigeration cycles, five different forms of exergy efficiency relations are developed, and their equivalence is demonstrated. With the unified approach presented here and the insights provided, the controversy and confusion associated with different exergy efficiency definitions are largely alleviated.
  • [ X ]
    Öğe
    Effect on the Thermal Performance of a Bio-based Phase Change Material with the Addition of Graphite with Surfactants
    (Taylor & Francis Inc, 2024) Sheikh, Yahya; Orhan, Mehmet Fatih; Kanoglu, Mehmet; Umair, Muhammed; Mehaisi, Elmehaisi
    This work presents an experimental investigation into how adding graphite with different surfactants to a bio-based phase change material (PCM) affects its cooling performance. Graphite-based phase change materials (GraPCMs) are prepared by stirring and sonicating graphite with different surfactants, including Sodium Stearoyl Lactylate, Sodium Dodecylbenzene Sulfonate (SDBS), and Sodium Dodecyl Sulfate (SDS), in a liquid bio-based PCM. Based on the experiments, the thermal conductivity of the bio-based PCM is increased by 240% to 0.748W/m center dot K and 218% to 0.70W/m center dot K when mixed with graphite-SDBS and graphite-SDS, respectively, at a 5% mass fraction of graphite. The ratio of 1:3 graphite to surfactant at a 5% mass fraction of graphite results in the longest amount of time for GraPCM-SDBS and GraPCM-SDS to reach the reference temperature of 43 degrees C, with delays of 185 and 175 s, respectively. It is observed that increasing the concentration of surfactant leads to further delay in reaching the reference temperature in the case of GraPCM-SDS. The results agree with the literature, as the surfactants and graphite enhanced the thermal conductivity of the PCM.
  • [ X ]
    Öğe
    Exergy Efficiency of Closed and Unsteady-Flow Systems
    (Mdpi, 2025) Cengel, Yunus A.; Kanoglu, Mehmet
    Exergy efficiency is viewed as the degree of approaching reversible operation, with a value of 100 percent for a reversible process characterized by zero entropy generation or equivalently zero exergy destruction since Xdestroyed = T0Sgen. As such, exergy efficiency becomes a measure of thermodynamic perfection. There are different conceptual definitions of exergy efficiency, the most common ones being (1) the ratio of exergy output to exergy input eta ex = Xoutput/Xinput = 1 - (Xdestroyed + Xloss)/Xinput, (2) the ratio of the product exergy to fuel exergy eta ex = Xproduct/Xfuel = 1 - (Xdestroyed + Xloss)/Xfuel, and (3) the ratio of exergy recovered to exergy expended eta ex = Xrecovered/Xexpended = 1 - Xdestroyed/Xexpended. Most exergy efficiency definitions are formulated with steady-flow systems in mind, and they are generally applied to systems in steady operation such as power plants and refrigeration systems whose exergy content remains constant. If these definitions are to be used for closed and unsteady-flow systems, the terms need to be interpreted broadly to account for the exergy change of the systems as exergy input or output, as appropriate. In this paper, general exergy efficiency relations are developed for closed and unsteady-flow systems and their use is demonstrated with applications. Also, the practicality of the use of the term exergy loss Xloss is questioned, and limitations on the definition eta ex = Wact,out/Wrev,out are discussed.
  • [ X ]
    Öğe
    Heat transfer enhancement of a bio-based PCM/metal foam composite heat sink
    (Elsevier, 2022) Sheikh, Yahya; Orhan, Mehmet Fatih; Kanoglu, Mehmet
    Effects of phase change materials (PCMs) filling height and copper foam pore densities on the cooling perfor-mance of a bio-PCM composite-based heat sink are investigated. In this respect, three filling height ratios of 1.0, 1.3, and 1.6 as well as three copper foam samples with pore densities of 35, 80, and 95 pores per inch (PPIs) are examined. Temperature profiles of the flat plate, the time required to reach specified temperatures, and the enhancement ratios at various temperatures and filling ratios are used to evaluate the thermal performance of the PCM composite-based heat sink. The investigation enables the determination of the optimal PCM filling height for maximum cooling performance of the heat sink. The results show that the optimal PCM filling height is 1.3 times the copper foam thickness and that a PCM/copper foam composite with 95 PPI pore density produces the best cooling performance with enhancement ratios of 1.54 and 1.44 under 10 and 15 W heat loads, respectively.
  • [ X ]
    Öğe
    Performance evaluation of a geothermal and solar-based multigeneration system and comparison with alternative case studies: Energy, exergy, and exergoeconomic aspects
    (Pergamon-Elsevier Science Ltd, 2022) Guler, Omer Faruk; Sen, Ozan; Yilmaz, Ceyhun; Kanoglu, Mehmet
    This study modeled and analyzed the performance evaluation of a geothermal and solar-based multigeneration system and comparison with alternative case studies. For this purpose, three different models have been developed. In Model 1, a parabolic trough collector is used to transfer the energy in one stage. In Model 2, a parabolic trough collector transfers the heat in two stages. In Model 3, a system performs heat transfer with flat plate collectors in two stages. In addition, a hydrogen production system integrated into these models is also considered to store excess energy. These models are investigated for an existing region using geothermal and solar actual data from Afyonkarahisar in Turkey. The geothermal source is at a temperature of 130 degrees C and a flow rate of 85 kg/s. The solar incident varies between 400 and 1000 W/m2, with an average of 600 W/m2. The residual heat from the systems is used for residential heating. An electrolyzer and a fuel cell are integrated into the models. The costs of hydrogen and the conversion of electricity from hydrogen are investigated. When the exergy efficiencies are analyzed, they are 32.1%, 32.4%, and 30.6%. Hydrogen production costs of the models are calculated as 1.585 $/kg, 1.551 $/kg, and 1.585 $/kg. The conversion electricity costs of fuel cells are calculated as 0.0792, 0.0781, and 0.0792 $/kW, respectively.
  • [ X ]
    Öğe
    Thermodynamic assessment of a geothermal power and cooling cogeneration system with cryogenic energy storage
    (Pergamon-Elsevier Science Ltd, 2022) Cetin, Tugberk Hakan; Zhu, Jie; Ekici, Ekrem; Kanoglu, Mehmet
    Geothermal energy is one of the main renewable energy sources for power generation and district cooling, and liquid air energy storage is an emerging technology suitable for both power and cold storages. Accordingly, a combined power and cooling cogeneration system with cryogenic energy storage is proposed in this paper, which is powered by geothermal energy and connected with the grid. The system is formed by integrating a turbine ejector cogeneration cycle with an air liquefaction cycle, a liquid air direct expansion cycle and a cryogenic organic Rankine cycle. In normal operation mode, only the turbine ejector cogeneration cycle works in the system based on the cooling load requirement. In charging operation mode, all the power produced in the system is used to liquefy air in the air liquefaction cycle owing to cheap electricity tariff. In discharging operation mode, the additional electricity is provided to meet peak time energy requirement by the direct expansion cycle and cryogenic organic Rankine cycle. A geothermal source at 180 degrees C with a flow rate of 100 kg/s is used as the heat source in this study, the cogeneration system has the ability to produce 15,470 kW of power and supply 4800 kW of cooling simultaneously, the system round trip efficiency is 41.07%, and the exergy efficiency of cryogenic energy storage is 60.43%. Also, the effects of geothermal energy temperature, system size, turbine mass split ratio and normalized mass flow rate on the system performance are clarified.
  • [ X ]
    Öğe
    Thermodynamic modeling and analysis of a solar and geothermal assisted multi-generation energy system
    (Pergamon-Elsevier Science Ltd, 2021) Sen, Ozan; Guler, Omer Faruk; Yilmaz, Ceyhun; Kanoglu, Mehmet
    A geothermal and solar energy-assisted multi-generation energy system supplying electricity for the residences is modeled and analyzed. The system considered is a novel configuration consisting of a binary geothermal power plant and a parabolic trough concentrating solar power plant for electricity production and water electrolysis and fuel cell unit for hydrogen storage and utilization. Thermodynamic performance evaluation of the system is performed using Afyonkarahisar's geothermal and solar energy values. In Afyonkarahisar province, geothermal water temperature ranges between 70 and 130 degrees C and mass flow rate between 70 and 150 kg/s. Also, solar radiation incident varies between 300 and 1000 W/m(2). The geothermal and solar power plants could produce 2900 kW power. If this is used entirely for hydrogen production, 0.0185 kg/s hydrogen could be produced. One can produce 1615 kW power by using this hydrogen in the fuel cell. The overall system's energy and exergy efficiencies are calculated to be 5.90% and 18.99%, respectively. The system's parametric study is performed considering geothermal resource temperatures and solar radiation values on the power output and hydrogen production.