Jafari, Rahim
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Name Variants
Jafarı, Rahım
Jafari,R.
J.,Rahim
R.,Jafari
Rahim, Jafari
Jafari, Rahim
R., Jafari
J., Rahim
Jafari,R.
R.,Jafari
Jafari, Rahim
J.,Rahim
Rahim, Jafari
Jafari,R.
J.,Rahim
R.,Jafari
Rahim, Jafari
Jafari, Rahim
R., Jafari
J., Rahim
Jafari,R.
R.,Jafari
Jafari, Rahim
J.,Rahim
Rahim, Jafari
Job Title
Doçent Doktor
Email Address
rahim.jafari@atilim.edu.tr
ORCID ID
Scopus Author ID
Turkish CoHE Profile ID
Google Scholar ID
WoS Researcher ID
Scholarly Output
12
Articles
8
Citation Count
68
Supervised Theses
3
12 results
Scholarly Output Search Results
Now showing 1 - 10 of 12
Conference Object Citation Count: 1Numerical Evaluation of Thermal Comfort, IAQ Indices, and TES for the Improvement of the Energy Performance in Crowded Area(Institute of Electrical and Electronics Engineers Inc., 2022) Jafari, Rahim; Jafari,R.; Automotive EngineeringThis paper proposed new strategies for investigating the reality of indoor air quality (IAQ). The actual crowded cell was simulated by scale of 1:4 containing five persons in which two of them are lying. It was aimed to keep the stability of the oxygen / air ratio to prevent suffocation by controlling the air velocity as quickly as possible from HVAC systems, especially in the overcrowded area. Phase change materials (PCMs) were used to reduce the fluctuations of inside space temperatures for the thermal performance. Two different organic PCMs were used to analyse the temperature distribution in the prototype model. This study also is focused on the analysis of the thermal efficiency of PCMs that is established on thermal energy storage (TES) for energy embalmment in the prototype model, for thermal management of special zone temperature applications. In addition, temperature distributions inside the cell with and without the embedded PCM in the ceiling have been illustrated. Using of PCM has reduced the cell temperature about 7°C. © 2022 IEEE.Article Citation Count: 16Modeling 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 EngineeringMicrochannel 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.Article Citation Count: 6Optimization and energy analysis of a novel geothermal heat exchanger for photovoltaic panel cooling(Pergamon-elsevier Science Ltd, 2021) Jafari, Rahim; Automotive EngineeringElectrical 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.Master Thesis Otomobil fren diskinin termal performansının ölçülmesi(2023) Jafari, Rahim; Jafarı, Rahım; Automotive EngineeringHızlanma bir araç için çok önemli bir dinamiktir, ancak yavaşlama araç güvenliği için kilit unsurdur. Fren sistemi otomobili yavaşlatacak veya durduracak en önemli ekipmandır. Bir fren sisteminin işlevi, disk ve balatanın sürtünmesi ile gerçekleşir. İçerdiği komponentlerin tasarım ve test adımlarında ısıl performansları hassas bir şekilde ölçülmeli ve komponentin çalışma koşulları altında gereken performansı göstermesi gerekmektedir. Bu çalışmada, fren disklerinin hem aerodinamik hem de termal karakteristiklerinin gözlemleneceği bir deney düzeneği tasarlanmış ve üretilmiştir. Deney düzeneği üzerindeki disk, balata, jant ve lastik gibi parçalar tipik bir binek otomobilde kullanılanlar ile birebir aynıdır. Komponentlerle birlikte binek bir otomobilin çeyrek ağırlığı deney düzeneğine silindirik ağırlıklar yardımıyla şaft üzerine uyarlanmıştır. Bunun yanında, deney düzeneğinde tekrarlamalı fren senaryosu kullanılmış olup frenlemenin aerodinamik ve termal çıktılarının ayrıntılı numerik modeller kullanılarak simülasyonları gerçekleştirilmiştir. Gerçekleştirilen deneyler ve simülasyonlarda, otomobilin hızı sebebiyle oluşan hava akışının jant içerisinde yavaşladığı ve buna rağmen jant içerisinde türbülanslı bir hava akışı olduğu gözlemlendi. Termal simülasyonlar ve deneyler sonucunda ise fren diski üzerindeki sıcaklık dağılımı gözlemlenmiş olup fren diskinin balata ile temas ettiği alanın temas alanının tam karşısındaki alanın sıcaklığına göre daha yüksek olduğu ve sıcaklığın eşit dağılmadığı tahmin edilmiştir.Article Citation Count: 20Experimental 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 EngineeringThis 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.Master Thesis Tek silindirli hbo motorun performans gelişimi(2020) Jafari, Rahim; Jafarı, Rahım; Automotive EngineeringThe development of 2 and 4 stroke cycle prototype spark ignition engines using gasoline, manufactured by Minisan A.Ş., is intended in this study. The engines, designed to operate with carburetors and conventional ignition system, functioned successfully. The first designed engine was manufactured with a similar cylinder head, valve configuration, spark plug location and equal cylinder diameter and piston stroke with the ACME model engine, for comparison. The geometry of the connecting rod was altered. The center of the crankshaft shifted approximately 40 – 70 mm from the center of the cylinder. The specific fuel consumption of the new engine was lower and a decision was made to develop it. After the first 340 cc prototype, 2 cylinder, air and water cooled prototype engines were manufactured. A 340 cc engine was also developed within the scope of this thesis. Appropriate combustion chamber geometry and valve configuration for the thermodynamic cycle of these engines were not included in this study. Within the scope of the thesis, commercial electronic fuel injection and ignition systems were acquired and adapted to the engines. These systems were operated by electronic control units (ECU) which were acquired. Theoretical simulation and experimental performance and mapping work were done on the engines for programming the ECU. Two dimensional tables were constructed for the injectors and igniton systems to follow according to the working modes of the engines and were uploaded to the ECU's. Performance tests were conducted with the iv upgraded electronic injection and ignition system of the engines. In comparison to the operation of the engines with carburetors and conventional ignition system, for same engine speed ranges and loads up to 20 percent increase was observed for the excess air coefficient and up to 30 percent decrease was observed for the brake specific fuel consumption. Keywords: Internal combustion engine, ignition system, performance evaluation tests.Article Citation Count: 1Investigation of the effectiveness of PCM on the energy saving, thermal comfort and indoor air quality in overcrowded area(Elsevier Science Sa, 2023) Jafari, Rahim; Hussen, Hasanen M.; Turkakar, Goker; Jafari, Rahim; Automotive EngineeringOvercrowded 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 Count: 0Dimensional optimization of two-phase flow boiling in microchannel heat sinks(2021) Jafari, Rahim; Automotive EngineeringThe heat transfer coefficient (HTC) of microchannel heat sinks (MHS) is higher than common heat sinks due to higher area to volume ratio. Its value for two-phase flow boiling is much superior to single-phase flow. In addition, the two-phase flow boiling provides uniform wall temperature close to the coolant’s saturation temperature in low vapor qualities. In the present study, a heat sink is optimized dimensionally after modeling of the boiling of R134a refrigerant in the microchannels. Firstly, mixture two-phase method along with the wall heat flux partitioning are utilized to introduce an applied thermal model to design MHSs. The heat sink mounted on the backside of an Intel core i7-900 desktop processor with dimensions of 19 mm×14.4 mm× 1 mm is numerically simulated to investigate the thermal performance. The HTC and the exit vapor quality are comparable with the available empirical correlations and first law of thermodynamics, respectively. Then the proposed model is developed to optimize the dimensions of the microchannels to design the heat sink with minimized wall temperature. Bound optimization by quadratic approximation (BOBYQA) method results in the optimized dimensions of the microchannels in the heat sink. Optimization of heat sink’s geometry in terms of the dimensions of the microchannels at various boundary conditions will be practical as the unique application of the model.Article Citation Count: 9Optimization and thermal analysis of radial ventilated brake disc to enhance the cooling performance(Elsevier, 2022) Jafari, Rahim; Akyuz, Recep; Automotive EngineeringVentilated 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.Article Citation Count: 8Enhanced 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 EngineeringCommercial 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.
