Browsing by Author "Jafari, Rahim"

Now showing 1 - 7 of 7

Citation - WoS: 9
Citation - Scopus: 8
Enhanced 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.; Automotive Engineering; 06. School Of Engineering; 01. Atılım University
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.
Citation - WoS: 9
Citation - Scopus: 9
Experimental and Numerical Study of Turbulent Flow and Thermal Behavior of Automotive Brake Disc Under Repetitive Braking
(Sage Publications Ltd, 2022) Jafari, Rahim; Tekin, Ozan; Akyuz, Recep; Gurer, Mehmet; Automotive Engineering; 06. School Of Engineering; 01. Atılım University
The frictional brake system is the most safety critical equipment to decelerate or stop a vehicle. Thermal performance of the frictional region parts, disc and pads, necessitates to evaluate precisely in the design and test steps. In this study, a brake test setup was designed and fabricated with exactly the same braking components used in a common passenger vehicle as disc, pads, rim, tire, and dust shield to simulate the sequential braking. The local temperature on the disc and pads and the brake fluid pressure were measured. In addition, a three dimensional numerical model was designed to simulate the aerodynamics and thermal performance of the braking in detail. Finite element method was employed to simulate the frictional heat between the brake disc and the pads. The results showed that although the velocity of mainstream airflow reduces significantly into the rim, turbulent flow develops in the form of eddies of swirling airflow. Additionally, transient temperature distribution on the braking components was predicted. The cooling vanes in the brake disc have considerably enhanced the convection heat transfer. The amount of convective heat transfer on the inner radial vanes was more than 58% of the total amount of convective heat transfer.
Citation - WoS: 26
Citation - Scopus: 30
Experimental 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, Ozgur; Automotive Engineering; 06. School Of Engineering; 01. Atılım University
This 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.
Citation - WoS: 2
Citation - Scopus: 2
Investigation 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, Rahim; Automotive Engineering; 06. School Of Engineering; 01. Atılım University
Overcrowded 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.
Citation - WoS: 21
Citation - Scopus: 24
Modeling and Analysis of Surface Roughness of Microchannels Produced by Μ-Wedm Using an Ann and Taguchi Method
(Korean Soc Mechanical Engineers, 2017) Jafari, Rahim; Kahya, Muge; Oliaei, Samad Nadimi Bavil; Unver, Hakki Ozgur; Ozyurt, Tuba Okutucu; Automotive Engineering; Department of Mechanical Engineering; 15. Graduate School of Natural and Applied Sciences; 06. School Of Engineering; 01. Atılım University
Microchannel heat exchangers are used to remove the high heat fluxes generated in compact electronic devices. The roughness of the microchannels has a significant effect on the heat transfer characteristics, especially the nucleate boiling and pumping power. Therefore, development of predictive models of surface texture is of significant importance in controlling heat transfer characteristics of these devices. In this study, micro-Wire electrical discharge machining (mu-WEDM) was employed to fabricate metal-based microchannel heat sinks with different surface textures. First, experiments were conducted to achieve the desired surface roughness values. Oxygen-free copper is a common material in the cooling systems of electronic devices because of its high thermal conductivity and low cost. Design of experiment approach based on the Taguchi technique was used to find the optimum set of process parameters. An analysis of variance is also performed to determine the significance of process parameters on the surface texture. An artificial neural network model is utilized to assess the variation of the surface roughness with process parameters. The predictions are in very good agreement with results yielding a coefficient of determination of 99.5 %. The results enable to determine mu-WEDM parameters which can result in the desired surface roughness, to have a well-controlled flow and heat transfer characteristics for the microchannels.
Citation - WoS: 16
Citation - Scopus: 22
Optimization and Energy Analysis of a Novel Geothermal Heat Exchanger for Photovoltaic Panel Cooling
(Pergamon-elsevier Science Ltd, 2021) Jafari, Rahim; Jafari, Rahim; Jafari, Rahim; Automotive Engineering; Automotive Engineering; 06. School Of Engineering; 01. Atılım University
Electrical energy and conversion efficiency of the photovoltaic (PV) solar panels are measured under standard test conditions in some microseconds at the room temperature (25 degrees C). It also is seen that the actual working conditions, on the other hand, with higher ambient temperature and continuous generated heat in the PV cells can lead to reduction in reduce their electricity generation and long-term sustainability. In the current work, the coolant (water + ethylene glycol) circulates between two heat exchangers; the minichannel heat exchanger is bounded to the PV cells and geothermal heat exchanger is buried underground, and it is set to remove the heat from PV cells to the ground. Six control factors of the geothermal cooling system are considered for the purpose of optimization using Taguchi design and main effect analysis. These parameters are pipe length, soil thermal conductivity, coolant flow rate, adjacent coil distance, pipe inner diameter and pipe thickness. The experimental results show that the average net electricity generation of the cooled PV panel is improved 9.8% compared to the PV panel without cooling system. However, with the same geothermal heat exchanger it drops to 6.2% as the cooled panel number is doubled. The simulation results reveal that the optimum configuration of the geothermal cooling system is capable of enhancing the net electricity generation of the twin cooled panels up to 11.6%. The LCOE of the optimized geothermal cooling system was calculated 0.089 euro/kWh versus the reference panel of 0.102 euro/kWh for the case study of 30 kW PV solar plant.
Citation - WoS: 21
Citation - Scopus: 29
Optimization and Thermal Analysis of Radial Ventilated Brake Disc To Enhance the Cooling Performance
(Elsevier, 2022) Jafari, Rahim; Akyuz, Recep; Automotive Engineering; 06. School Of Engineering; 01. Atılım University
Ventilated 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.