Browsing by Author "Jafari, Rahim"

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Aşırı kalabalık alanların enerji performansının iyileştirilmesi için termal konfor, IAQ endeksleri ve termal enerji depolamasının deneysel değerlendirmesi ve çalışması
(2022) Al-malakı, Fadhıl Asaad Mohammed Kadhım; Jafarı, Rahım; Al-saedi, Hasanen M.; Automotive Engineering
In recent years, buildings, including prison halls, have contributed significantly to the world's rising energy use, with 34 % of the energy used by these buildings being attributed to cooling and heating. This study examines the use new combination of phase change materials (PCMs) for energy conservation in buildings through thermal storage, including the use of double layers of PCMs paraffin waxes with different properties. The study evaluates the indoor air quality characteristics of two protocols for cooling and heating in four different scenarios that are classified according to the seasons in a location, with a high daily temperature range, similar to that of Iraq. An experimental facility for the study was designed, constructed, and tested at Technology University in Baghdad. The experimental measurements were taken in a small-scale model 1:4 of a prison quarry, with dimensions of 1.2 by 0.6 by 0.8 meters and a side inlet grill. This prototype model was used to investigate the impact of integrating double layers of panels on the roof of the space and their ability to minimize fluctuations, energy usage, and shift peak load. The computational work involved solving the partial differential equation for the conservation of mass, momentum, and energy and its rate of dissipation using the finite volume technique. Modifications to the algorithm were made to simulate the space with and without PCMs in the roof for all scenarios. The majority of the computed data were presented as temperature contours and other thermal contours, and when compared to the experimental results, a reasonable level of agreement was observed. The use of PCMs as latent heat thermal energy storage (LHTES) in the room envelope for passive cooling has gained significant attention due to their ability to store large amounts of energy. The results of this study show that the use of TES can reduce the energy required for the space by 47.2 % in the summer and in varying proportions during other seasons, also when PCMs are used in hot weather, in door temperature drops by 7 °C at average, compared to when they are not used.
Citation Count: 0
Comparison of the Membrane-based Desorber and Plate Heat Exchanger Desorber for Solar Assisted Absorption Refrigeration Systems
(Toronto Metropolitan University, 2023) Ozvaris,Y.G.; Jafari,R.; Ozyurt,T.O.; Automotive Engineering
The Absorption Refrigeration System (ARS) is a type of cooling system that uses non-toxic, non-volatile, and nonflammable working fluids. The system includes a pump and a heat exchanger for the molten solution, in addition to evaporator and condenser components found in a vapor compression refrigeration cycle. Instead of using a compressor, a thermal mechanism such as solar or geothermal energy is utilized for circulation, resulting in significant energy savings. Although generally it is used in large industrial applications, the use of membrane technology in the absorber and/or desorber makes it suitable for residential applications due to the large area-to-volume ratios of the resulting components. In this study, the numerical investigation of the membrane-based desorber, which is known to have the highest COP for the ARS, is performed. Working fluid is H2O–LiBr solution. The pore diameter of microporous polytetraphluoroethylene (PTFE) membrane is 0.45 μm and thickness is 200 μm that is used to separate the solution from the vapour. The results for two type desorbers obtained for hot water and solution heat transfer coefficients, COP, volumetric cooling effect and cooling power are provided and compared to each other. © 2023, Toronto Metropolitan University. All rights reserved.
Citation Count: 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
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 Count: 7
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
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 Count: 20
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
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 Count: 1
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
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 Count: 16
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
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 Count: 1
Numerical 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) Al-Malaki,F.; Jafari,R.; Automotive Engineering
This 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.
Citation Count: 9
Optimization and thermal analysis of radial ventilated brake disc to enhance the cooling performance
(Elsevier, 2022) Jafari, Rahim; Akyuz, Recep; Automotive Engineering
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.
Otomobil fren diskinin termal performansının ölçülmesi
(2023) Erkılıç, Kaan Tamer; Jafarı, Rahım; Automotive Engineering
Hızlanma 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.
Tek silindirli hbo motorun performans gelişimi
(2020) Fendal, Metin; Jafarı, Rahım; Automotive Engineering
The 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.