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Article Citation - WoS: 10Citation - Scopus: 9Enhanced Photovoltaic Panel Energy by Minichannel Cooler and Natural Geothermal System(Wiley, 2021) Jafari, Rahim; Erkilic, Kaan T.; Ugurer, Doruk; Kanbur, Yunus; Yildiz, Murat o.; Ayhan, Ege B.Commercial photovoltaic (PV) solar panels convert the solar energy directly to electricity but their efficiency is low. The rest of the energy is mostly converted to heat. Although the conversion efficiency of PV panels is low, getting hot causes increase in the temperature of the PV cells which results in further dramatic decrease of their efficiency and the technical lifetime. In the present study, a PV panel with cooling system was made in which a polymer minichannel heat exchanger was fully integrated with the PV cells during the fabrication of the panel. Heat exchangers containing minichannels and microchannels have higher heat transfer capability than pipes and channels as they have a higher ratio of area to volume. Besides, since the heat exchanger is adhered to the solar cells during the panel fabrication, the thermal contact resistance drops to minimum. Circulated coolant dissipates the extracted heat from the panel to the ground by buried long life and low-price plastic tubes. Since the earth temperature beyond a depth of 4 m is relatively constant, 10 degrees C to 16 degrees C, the earth acts as a cooling medium for free. The experimental results show that the cooling system is capable to dispose of 570 W heat from the PV panel in the ground. The daily electricity generation rises about 10%. The levelized cost of energy (LCOE) is minimum compared to the available PV panels with active cooling techniques in the literature.Article Citation - WoS: 27Citation - Scopus: 31Experimental Investigation of Surface Roughness Effects on the Flow Boiling of R134a in Microchannels(Elsevier Science inc, 2016) Jafari, Rahim; Okutucu-Ozyurt, Tuba; Unver, Hakki Ozgur; Bayer, OzgurThis study experimentally investigates the effect of surface roughness on the hydrodynamic and thermal performance of microchannel evaporators. Three micro-evaporators of the same dimensions and different surface roughness have been fabricated by micro-WEDM. Each micro-evaporator consists of forty rectangular microchannels of 700 mu m height, 250 mu m width, and 19 mm length. A microscale vapor compression refrigeration cycle has been constructed to carry out the experiments. R134a is used as the refrigerant. Heat transfer coefficient, pressure drop and COP results are presented at variously imposed heat fluxes, and at mass fluxes of 85 and 200 kg/(m(2)s). The results demonstrate up to 45% enhancement in the two-phase heat transfer coefficient at low to moderate heat flux values as the surface roughness increases. Considering the surface roughness effect of the microchannel walls, a new correlation is developed to predict the heat transfer coefficient of R134a boiling in microchannels. (C) 2016 Elsevier Inc. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Investigation of the Effectiveness of Pcm on the Energy Saving, Thermal Comfort and Indoor Air Quality in Overcrowded Area(Elsevier Science Sa, 2023) Al-Malaki, Fadhil A. M. K.; Hussen, Hasanen M.; Turkakar, Goker; Jafari, RahimOvercrowded areas like hospitals, jails, and shelter elevators pose a risk in terms of excessive temperatures, excessive CO2 concentrations, or even the presence of toxins and viruses. Hence, ventilation, thermal comfort and energy management are crucial issues for these kinds of places. In the present study, a prototype (1:4) of a prison quarry located in Baghdad, Iraq has been examined. Indoor air quality, humidity, temperature distribution and energy consumption of the room have been monitored for the identical weather conditions of the real prison cell, including five dummy occupants, each dissipating 100 W/m2 of heat, releasing CO2 of 0.3 l/min and water vapor. To reduce the cooling energy consumption of the building and the temperature deviation during the day, two layers of Phase Change Materials, PCMs, have been embedded in the ceiling of the prototype. Experiments have been recorded for three hours in Baghdad's harsh weather conditions in August. In addition, numerical analyses were conducted and compared with experimental findings, and a good match is obtained. Energy saving of 47.2% have been calculated by using PCM for the inlet air velocity of 0.5 m/s.Article Citation - WoS: 24Citation - Scopus: 34Optimization and Thermal Analysis of Radial Ventilated Brake Disc To Enhance the Cooling Performance(Elsevier, 2022) Jafari, Rahim; Akyuz, RecepVentilated brake discs are preferable to automobile application because of their higher heat dissipation ability than solid discs. The shape, geometry and number of the cooling fins are interested parameters to be investigated to improve the cooling performance of the discs. In the present study, the optimum design of the brake disc with radial vanes is investigated numerically using the Taguchi design of experiments with taking into account nine design parameters. Finite element method is employed to simulate the detailed airflow and temperature distribution in the disc considering adjoined components as pads, rim, tire and dust shield. It has been found that the ventilation gap width has the highest impact on the brake disc cooling. The cooling time of the disc decreases 21% as the ventilation gap increases from 8 mm to 14 mm. In addition, it reduces about 10% with the increment of the channel width between two adjacent vanes (inverse of vane numbers from 43 to 30) and the twist point from 225 mm to 266 mm. In a decreasing order of importance, fin angle, inner and outer diameters of fin, dust shield, bell link and disc material affect the cooling performance of the ventilated disc.
