Yazar "Yildiz, Gokhan" seçeneğine göre listele

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    Assessment of a novel defrost method for PV/T system assisted sustainable refrigeration system
    (Pergamon-Elsevier Science Ltd, 2022) Karaagac, Mehmet Onur; Ergun, Alper; Gurel, Ali Etem; Ceylan, Ilhan; Yildiz, Gokhan
    Energy consumption has continuously increased depending on the rapidly growing human population, enlarging economies, advancing technologies, and improving living standards. A noteworthy share of the energy consumption has been arising from the buildings all across the world. Refrigeration, heating, and air conditioning systems have accounted for a significant portion of the energy consumption in the buildings. Therefore, it is possible to both reduce energy consumption, and mitigate the carbon footprints by efficiently designing, constructing, and operating these systems. In this framework, the present research has centered on the refrigeration systems, and aimed to develop a novel defrost method for photovoltaic thermal (PV/T) assisted sustainable refrigeration systems. In the conventional refrigeration systems, the frost process occurs when air condenses on the evaporator surface as a result of the evaporator surface temperature being below the freezing point of water or the dew point temperature of the air in the conditioned space. Differently in the present work, PV/T system is used to prevent the frost process in the refrigeration system, unlike the conventional systems. Accordingly, the efficiency loss caused by the temperature increment will be prevented by cooling the PV module, and it is aimed to be more efficient by reducing the daily power consumption as an alternative solution method to the frost that occurred on the evaporator in refrigeration systems. On this purpose, a novel evaporator design is developed, and used for defrosting in this study. Accordingly, this novel design includes a refrigerant line inside the evaporator and a hot water line from the PV/T in this design. In the results, it is noticed that the system designed for winter conditions could be used for defrosting. While an average of 605 W for heat energy was used for each defrost process, the average defrost duration was recorded to be approximately 4 min. While the average electrical efficiency of the PV module was found to be 13.6%, the average total efficiency was found to be 38%. Besides, Average PV module surface temperature was determined as 36.4 degrees C, average water storage tank temperature was determined as 26.4 degrees C. In addition, the coefficient of performance (COP) of the refrigeration system is calculated to be 4.18. COP increased by an average of 9% during defrosting. Furthermore, the environmental economic cost was calculated to be 14.6 $/h. In the conclusion, it is proven that the novel defrost method proposed in the present work can be used for refrigeration systems, and contribute to both the reduction of energy consumption and mitigation of carbon emissions arising from the buildings.
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    Öğe
    Ecological stoichiometry of macroalgae from Sinop Peninsula coast of Black Sea, Türkiye: characterization of C:N:P
    (Springer, 2025) Yildiz, Gokhan; Karacuha, Ali
    This comprehensive ecological investigation systematically analyzed the temporal and spatial variations in carbon (C), nitrogen (N), and phosphorus (P) concentrations across diverse macroalgal assemblages inhabiting the upper infralittoral zone of the Sinop peninsula. The study encompassed seasonal sampling conducted at five distinct stations between October 2019 and July 2020, targeting nine prevalent macroalgal species representing three major taxonomic groups: Chlorophyta, Rhodophyta, and Phaeophyceae. Statistical analyses revealed statistically significant (p < 0.05) variations in mean elemental concentrations across seasonal, regional, and species-specific dimensions. The elemental concentration ranges demonstrated substantial diversity, with carbon concentrations spanning from 14.73% in Corallina officinalis to 43.04% in Pterocladiella capillacea. Nitrogen concentrations exhibited remarkable variability, ranging from 0.50% in C. officinalis to 5.14% in Ceramium spp., while phosphorus concentrations varied from 0.02% in Ceramium spp. to 0.32% in Ulva rigida. The elemental ratio analyses uncovered intricate inter-specific variations, with carbon/phosphorus ratios ranging from 157 in C. officinalis to 4255 in Laurencia obtusa, nitrogen/phosphorus ratios varying from 9 to 304, and carbon/nitrogen ratios spanning from 9 to 51. Taxonomic group-level analyses revealed nuanced nutritional characteristics, with nitrogen concentrations showing slight variations across green (1.98%), brown (1.76%), and red (2.20%) algae, and phosphorus concentrations exhibiting similar patterns across these taxonomic groups. The macroalgal community presented a mean C:N:P atomic ratio of 1187:57:1, with a median ratio of 859:41:1. These stoichiometric signatures predominantly indicate phosphorus limitation across the studied macroalgal assemblages along the Sinop coastal region, with C. officinalis emerging as a notable exception.
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    Öğe
    Thermodynamic analyses of a novel hybrid photovoltaic-thermal (PV/T) module assisted vapor compression refrigeration system
    (Elsevier, 2023) Yildiz, Gokhan; Gurel, Ali Etem; Ceylan, Ilhan; Ergun, Alper; Karaagac, Mehmet Onur; Agbulut, Umit
    Buildings have a respectable share of global energy consumption and it is well-known that refrigeration, heating and air conditioning systems have crucially contributed to this share. Therefore, even a small improvement in these systems has a noteworthy potential in globally saving energy. Accordingly, the performance of Photovoltaic-Thermal module-assisted vapor compression refrigeration system (PV/T-VCRS) has been handled in the present research. PV/TVCRS has been integrated with PV module, refrigeration system, and their hybrid. Additionally, different from the conventional superheating methods, superheating has been performed with a PV/T module in this work. In order to discuss the system performance, and observe the differences between conventional and modified hybrid systems, energy and exergy analyzes have been applied. In the results, the average PV module surface temperature in PV module and PV/T-VCRS is recorded to be 56.16 degrees C and 40.93 degrees C, respectively. This case leads to a direct increment in PV module electrical efficiency. Electrical efficiency, average electrical efficiency in PV module, and PV/T-VCRS are calculated to be 13.49% and 14.69%, respectively. The average COP values are found to be 5.23 for VCRS, and 5.68 for PV/T-VCRS. Total exergy destruction in VCRS and PV/TVCRS has been calculated to be 175.85 W and 443 W. On the other hand, the exergy efficiency is found to be 50.79% in VCRS and 60.73% in PV/T-VCRS. In the conclusion, it is well-noticed that hybrid PV/T-VCRS presented promising results in terms of electrical efficiency, COP, energy, and exergy analyses as compared to those of the conventional system.