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    A detailed analysis of CPV/T solar air heater system with thermal energy storage: A novel winter season application
    (Elsevier, 2021) Ceylan, Ilhan; Gurel, Ali Etem; Ergun, Alper; Ali, Ismail Hamad Guma; Agbulut, Umit; Yildiz, Gokhan
    The interest in solar energy is increasing day by day because it is clean and limitless. Concentrated photovoltaic and thermal systems (CPV/T) are one of the systems that use in the winter and the summer, attract great attention among solar energy systems. The main purpose of this research is to discuss the capacity of a CPV/T to simultaneously convert solar energy into electrical energy and thermal energy, especially in winter seasons. While only thermal energy is obtained in many concentrated air collectors (CAC) used in the literature, in this study, energy is stored with the help of phase change material (PCM). Ethyl alcohol and water blend were utilized as a working fluid and paraffin wax was also utilized as a PCM. In this study, system performance was handled by applying energy, exergy and environmental economic analyzes. In the results, the average solar radiation was concentrated from 536 W/m(2) to 737 W/m(2). The average overall thermal efficiency and PV module efficiency of the CPV/T were calculated as 73% and 15%, respectively. In other words, the overall system efficiency of the CPV/T was obtained as 88%. The average exergy efficiency of the CPV/T was calculated as 10%. Concerning the environmental aspect, 1.11 kg of CO2 emission per hour into the atmosphere could be prevented by using such a system. In the conclusions, the present paper has reported that the integration of a PCM and air collector into a CPV/T system provided higher energy efficiency in the winter season.
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    THE EFFECT OF MALFUNCTIONS IN AIR HANDLING UNITS ON ENERGY AND EXERGY EFFICIENCY
    (Begell House Inc, 2020) Ceylan, Ilhan; Yildiz, Gokhan; Gurel, Ali Etem; Ergun, Alper; Tosun, Abdulkerim
    In this study, the effects of malfunctions and problems occurring in the system components of air handling units, which are the main elements of the air conditioning system, on the energy consumption were investigated. Investigations were carried out in 10 air handling units located in 5 different shopping centers of Turkey. The malfunctions and problems that may occur in operation of air handling units were determined and the problems causing the decrease in the efficiency prescribed by the design characteristics were determined. For this purpose, rod-type anemometer measuring the airflow in the air handling unit ducts, propeller-type anemometer, and thermal camera were used to measure air tightness and heat losses in the body structure. Also, the tension control of the belt of the fan motors, which is one of the main components of the energy consumption unit, and the pollution control of the air filter have also been carried out. The flow rate of water circulating in air handling units was determined, and losses were detected by energy and exergy analyses with thermodynamic parameters for summer and winter periods. As a result of the calculations, it was determined that the energy efficiency of the air handling units in the cooling period was 63.7% and the exergy efficiency was 59.6%. The energy loss is 471 kW and the exergy loss is 27 kW in the cooling period. The energy loss is 957 kW and the exergy loss is 127 kW in the heating period. The energy efficiency and the exergy efficiency during the heating period was calculated to be 75% and 41.7%, respectively.
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    ENERGY, EXERGY, AND ENVIRONMENTAL (3E) ASSESSMENTS OF VARIOUS REFRIGERANTS IN THE REFRIGERATION SYSTEMS WITH INTERNAL HEAT EXCHANGER
    (Begell House Inc, 2020) Gurel, Ali Etem; Agbulut, Umit; Ergun, Alper; Yildiz, Gokhan
    A comprehensive thermodynamic analysis of a refrigeration system with an internal heat exchanger was reported for four various refrigerants as an alternative to R134a. The preferred refrigerants in this paper have zero ozone-depleting potential and fairly low global warming potential value compared with reference R134a. These refrigerants are from both the HC group (R290 and R600a) and the HFO group (R1234yf and R1234ze(E)). Basically, the refrigeration system consists of a compressor, condenser, evaporator, expansion valve, and internal heat exchanger as well. Energy-exergy analyses and environmental impact assessments depending on the compressor energy consumptions are evaluated in the current study. The system performance was theoretically carried out at two different evaporation temperatures of 0 and -8 degrees C. Based on the obtained results from this study, the highest performance was achieved in R600a from HC group refrigerants and R1234ze(E) from HFO group refrigerants. As compared with R134a, in the COP value of R600a an increase of 3.2% at the evaporation temperature of 0 degrees C and 3.4% for the evaporation temperature of -8 degrees C was achieved. On the other hand, the COP value for R1234yf was decreased by 2% at the evaporation temperature of 0 degrees C and by 2.57% at the evaporation temperature of -8 degrees C. Considering the CO2 emissions, R600a was located at the first order in terms of the lowest CO2 emissions and R1234ze(E) follows R600a. In conclusion, R600a presented the highest performance compared with R134a in a refrigeration system with an internal heat exchanger.
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    Investigating the impacts of using TiO2-ZnO/POE hybrid nanolubricant in a heat pump system: An experimental study
    (Pergamon-Elsevier Science Ltd, 2024) Yildiz, Gokhan
    Heating, cooling, and ventilation systems have a share in the majority of energy consumption in buildings. The use of heat pumps (HP) is becoming widespread to reduce energy consumption in buildings to improve this circumstance around the world. The slightest improvement in the heating, cooling and ventilation system will provide significant energy savings in total. For this reason, the use of nanoparticles in these systems has become quite common due to the increase in the thermal properties of fluids. In this study, the thermodynamic and economic performances of the system used at different mass flow rates (10 g/s, 30 g/s and 50 g/s) with the addition of mono and hybrid nanoparticles to pure POE (Polyol ester oil) used in an air -to -water HP were compared. TiO2 and ZnO nanoparticles were used in 0.8 g/L and 1.6 g/L fractions to obtain mono and hybrid nanolubricants. As a result of the experiments, significant improvements were determined in the thermal conductivity and viscosity values of mono and hybrid nanolubricants compared to pure POE. An increase of 4.89 % was observed in the COP value of the system using 1.6 g/L TiO2-ZnO/POE hybrid nanolubricant compared to pure POE. The exergy efficiency of the HP improved by 8.39 % compared to pure POE in the same nanolubricant. The lowest heating cost was obtained in 1.6 g/L TiO2-ZnO/POE hybrid nanolubricant as 4.7844 kWh/$ at 50 g/s mass flow rate. It is seen that as the fractions of mono and hybrid nanolubricants increase, the COP and exergy efficiency of the system increases compared to pure POE. Consequently, better results were obtained from mono and hybrid nanolubricants used in the HP compared to pure POE, energetically, exergetically and economically. In addition, better performance was obtained as the mass flow rate of the system and the fraction of hybrid nanolubricants increased.
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    A review of stability, thermophysical properties and impact of using nanofluids on the performance of refrigeration systems
    (Elsevier Sci Ltd, 2021) Yildiz, Gokhan; Agbulut, Umit; Gurel, Ali Etem
    The popularity of the studies on improving the thermal properties of base fluids in thermal engineering applications is considerably increasing day by day. Recently, many researchers have proved that the use of nanoparticles along with the base fluids exhibits better thermal properties as well as better system performance. In line with this, it is noticed a respectful increase in the number of studies regarding nanoparticle use in refrigeration systems. Accordingly, the present paper aims to summarize the preparation of nanofluids, the variation of thermophysical properties, the stability of nanofluids, impacts on the system performances of nanofluid usage, limitations, and challenges of nanoparticle usage, particularly in the refrigeration systems. Previous studies revealed that the heat transfer mechanism of the lubricants and refrigerants is highly improved with nanoparticle addition. It is observed that the increase in thermal properties becomes more visible as nanoparticle fractions increase, but this case may worsen the viscosity of nanofluids. The enhanced thermal properties contribute to improving refrigeration system performance. Many papers emphasize that nanoparticle-doping triggers an increase in system performance by both reducing the compressor power input and increasing the cooling capacity of the refrigeration systems. However, some critical points such as stability, homogeneous distribution, agglomeration, and sedimentation considerably influence the sustainability of performance improvement. In conclusion, nanoparticle-doping for refrigeration systems can be accepted as a very promising way of improving the performance, nevertheless, some questions such as high cost, toxic effect, poor stabilization, erosion effect, high viscosity, clogging issues should be more addressed in the future. (c) 2021 Elsevier Ltd and IIR. All rights reserved.