Browsing by Author "Bayram, Halil"

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Effect of weld current on the microstructure and mechanical properties of a resistance spot-welded TWIP steel sheet
(MDPI, 2017-11-14) Tutar, Mümin; Aydın, Hakan; Bayram, Halil; Uludağ Üniversitesi/Mühendislik Mimarlık Fakültesi/Makine Mühendisliği Bölümü.; 0000-0002-7286-3433; 0000-0001-7364-6281; J-2753-2016; 54406234300; 16312009400; 7004197848
In this study the effect of the weld current on the microstructure and mechanical properties of a resistance spot-welded twinning-induced plasticity (TWIP) steel sheet was investigated using optical microscopy, scanning electron microscopy-electron back-scattered diffraction (SEM-EBSD), microhardness measurements, a tensile shear test and fractography. Higher weld currents promoted the formation of a macro expulsion cavity in the fusion zone. Additionally, higher weld currents led to a higher indentation depth, a wider heat-affected zone (HAZ), coarser grain structure and thicker annealing twins in the HAZ, and a relatively equiaxed dendritic structure in the centre of the fusion zone. The hardness values in the weld zone were lower than that of the base metal. The lowest hardness values were observed in the HAZ. No strong relationship was observed between the hardness values in the weld zone and the weld current. A higher joint strength, tensile deformation and failure energy absorption capacity were obtained with a weld current of 12 kA, a welding time of 300 ms and an electrode force of 3 kN. A complex fracture surface with both brittle and limited ductile manner was observed in the joints, while the base metal exhibited a ductile fracture. Joints with a higher tensile shear load (TSL) commonly exhibited more brittle fracture characteristics.
Elektrikli taşıtlar için iklimlendirme sistemlerinde performans ve enerji kullanımı açısından iyileştirme yöntemlerinin araştırılması
(Bursa Uludağ Üniversitesi, 2019-08-06) Bayram, Halil; Sevilgen, Gökhan; Bursa Uludağ Üniversitesi/Fen Bilimleri Enstitüsü/Otomotiv Mühendisliği Ana Bilim Dalı.; 0000-0002-4664-3883
Geleneksel içten yanmalı motorlu taşıtlarda taşıt kabin ısıtma ihtiyacı motor soğutma suyu atık ısısından faydalanılarak karşılanmaktadır. Ancak elektrikli taşıtlarda taşıt kabin ısıtma ihtiyacını düşük dış ortam sıcaklık değerlerinde de karşılayabilecek miktarda atık ısı kaynağı bulunmadığından dolayı elektrikli ısıtıcılar, ısı pompası sistemleri gibi farklı çalışma prensiplerine sahip çözümler geliştirilmiştir. Elektrikli ısıtıcılar hızlı ısıtma performansları göstermelerine rağmen yüksek enerji tüketimlerinden dolayı taşıtın sınırlı olan enerjisini hızlı bir şekilde tüketmekte ve taşıt menzilinde hissedilir derecede düşüşler görülmesine sebep olmaktadır. Diğer yandan hava kaynaklı ısı pompası sistemleri ise düşük dış ortam sıcaklıklarında yetersiz kalmaktadır. Bu çalışmada, bahsedilen bu olumsuzlukların iyileştirilmesine yönelik elektrikli taşıt atık enerjilerinden faydalanabilen ve ortam koşullarına göre farklı çalışma prensipleri sergileyebilen bir boyutlu yenilikçi taşıt iklimlendirme sistemi modeli geliştirilerek farklı ortam koşulları altında NEDC sürüş çevrimi çerçevesinde performans incelemeleri gerçekleştirilmiştir. Ayrıca geleneksel taşıt iklimlendirme sistemi elemanları kullanılarak bir boyutlu geleneksel taşıt soğutma ve ısı pompası sistemi modelleri de geliştirilmiş ve performans incelemelerine dahil edilmiştir. Elde edilen sonuçlara göre elektrikli taşıtların ısıtılmasında, tekil ısıtmada kullanılan elektrikli ısıtıcılara göre daha düşük seviyelerde enerji tüketen ve düşük dış ortam sıcaklıklarında da yeterli ısıtma performansı sergileyebilen, taşıt üzerindeki atık enerjilerden faydalanabilen, ısı pompası ve elektrikli ısıtıcıların birlikte kullanıldığı hibrit bir ısıtma sistemi kullanılması önerilmiştir.
The experimental and numerical investigation of the thermal behaviors of a jacketed heat exchanger with a stirrer
(Bursa Uludağ Üniversitesi, 2023) Bayram, Halil; Cesur, Mert; Sevilgen, Gökhan; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Otomotiv Mühendisliği Bölümü; 0000-0002-7746-2014
In this study, the thermal performance of a jacketed heat exchanger with a stirrer was experimentally and numerically investigated under different jacket side water inlet temperature and flow rate conditions. In the numerical study, a three-dimensional computational fluid dynamics (CFD)model of the heat exchanger was generated and the analyzes were performed with the ANSYS-Fluent software package. In addition, a stirrer was added to both the experimental and the numerical study to obtain the effects of the stirrer on the temperature and velocity values of the water in the tank. It was seen that the results of the analyzes performed under similar conditions to the experimental study were in good agreement with the experimental study. It was concluded that the effect of the flow rate decreases with increasing inlet temperature. When the stirrer was activated and the flow rate was increased from 0.5 to 2.5 l/min in 30, 40, and 50°C inlet temperature conditions, the time to reach the target temperature inside the tank decreased from approximately 1600 to 900, from 2500 to 1350, and from 4900 to 1400, respectively. In general, it was observed that the effect of the stirrer increased with increasing inlet temperature in all flow rate conditions.
Investigation of the geometrical accuracy and thickness distribution using 3D laser scanning of AA2024-T3 sheets formed by SPIF
(Inst Za Kovinske Mateiale I In Tehnologie, 2016-12-16) Köksal, Nurullah Sinan; Bayram, Halil; Uludağ Üniversitesi/Mühendislik Fakültesi/Otomotiv Mühendisliği Bölümü.; 57195356819
Incremental sheet forming (ISF) is developed in order to meet the increasing demand for sheet metal forming and because it is a more economical method. First of all, this method gains attention become it is a die-less method. Furthermore, process flexibility and higher formability are other advantages of this method. In this study, AA2024-T3 sheets with a determined geometry and parameters were formed using the ISF method. Among the forming process parameters, tool path, step size and lubrication parameters were changed. The tool diameter, feed rate, spindle speed, angle of the wall and the tool coating parameters were kept constant. The thickness distributions and geometrical accuracy of the processed samples with the three-dimensional laser scanning method were examined accurately. It is clear from the results that the tool path that spirals and always keeps in touch is more successful than the tool path that makes it an incremental process. ISF is preferable to die production for limited production runs because it is more economic and the processing time is short.
Investigation of thermal sensation in a railway vehicle during cooling period
(Sage Publications, 2020-10) Sayaral, Gürcan; Bayram, Halil; Sevilgen, Gökhan; Kılıç, Muhsin; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makina Mühendisliği Bölümü.; 0000-0003-2113-4510; 0000-0002-7746-2014; O-2253-2015; ABG-3444-2020; 24722267300; 57202677637
The paper presents an investigation of local thermal comfort of passengers in a railway vehicle. The railway vehicle model includes five different parts called modules, and each module had different properties such as passenger capacity and seating arrangement. A virtual manikin model was developed and added to the numerical model which includes convection and radiation heat transfer between the human body and the environment. The numerical simulation was conducted according to the EN 14750-1 standard describing the thermal comfort conditions for different climatic zones. Two different cases were performed for steady-state conditions. Meanwhile, measurements were taken in a railway vehicle cabin to validate the numerical simulation, and the numerical results were in good agreement with the experimental data. It is observed that the local heat transfer characteristics of the human body have significant importance for the design of an effective heating, ventilation, and air conditioning (HVAC) system because each module had different heat transfer and air flow characteristics. It is also shown that the thermal sensation (TSENS) index helps railway vehicle HVAC researchers to determine the reasons for discomfort zones of each occupant. Another important result is that using a single air flow channel did not meet the thermal comfort demands of all passengers in this railway vehicle. Therefore, multiple air flow channel design configurations should be considered and developed for these vehicles. Local thermal comfort models allow HVAC systems to achieve better comfort conditions with energy saving. The numerical model can be used for effective module design, including seating arrangements, to achieve better thermal comfort conditions.
Numerical investigation of the effect of variable baffle spacing on the thermal performance of a shell and tube heat exchanger
(MDPI, 2017-08-01) Bayram, Halil; Sevilgen, Gökhan; Uludağ Üniversitesi/Mühendislik Fakültesi/Otomotiv Mühendisliği Bölümü.; 0000-0002-7746-2014; ABG-3444-2020; 57195356819; 24722267300
In this present study, numerical and theoretical analysis were both used to investigate the effect of the variable baffle spacing on the thermal characteristics of a small shell and tube heat exchanger. The numerical study was performed by using a three dimensional computational fluid dynamics (CFD) method and the computations were performed under steady-state conditions. We employed five different cases where the first had equal baffle spacing and the others had variable ones considering different configurations for balancing the pressure drop on the shell side. Theoretical calculations were run using the Bell-Delaware and Kern methods which are the most commonly used methods in the available literature. We show that the thermal performance of a shell and tube heat exchanger can be improved by evaluating together the results of the CFD and Bell-Delaware methods. From the numerical results, we can say that variable spacing with centered baffle spacing scheme can be proposed as an alternative shell side construction layout compared to an equal baffle spacing scheme. The numerical results were in good agreement with the theoretical data in the available literature.
Numerical investigation of the effect of variable baffle spacing on the thermal performance of a shell and tube heat exchanger
(MDPI, 2017-12-04) Bayram, Halil; Sevilgen, Gökhan; Uludağ Üniversitesi/Mühendislik Fakültesi/Otomotiv Mühendisliği Bölümü.; 0000-0002-7746-2014; ABG-3444-2020
The authors wish to make the following corrections to this paper [1]: On page 3, Equation (8) should be changed from: Nu = (f/2)·Re·Pr/1.07 × 12.7 × (f/2)2 × (Pr0.66 -1) (8) to the following correct version: Nu = (f/2) )·Re)·Pr/1.07 + 12.7)·(f/2)1/2)· (Pr2/3 - 1) (8) The authors would like to apologize for any inconvenience caused to the readers by these changes.
The investigation of the innovative hybrid heat pump system designed and prototyped for heating process of electric vehicles
(Elsevier, 2023-01-25) Bayram, Halil; SEVİLGEN, GÖKHAN; KILIÇ, MUHSİN; Kılıç, Muhsin; Dursun, Harun; Başak, Enes; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Otomotiv Mühendisliği Bölümü.; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makina Mühendisliği Bölümü.; 0000-0002-7746-2014; 0000-0003-2113-4510; JPA-3189-2023; O-2253-2015
In this paper, the investigation of the innovative hybrid heat pump system (HHPS) included Positive Temperature Coefficient (PTC) heater commonly used in electric vehicles (EVs) was performed in different heating modes to reach the desired temperature in a target time. The developed HHPS was evaluated in different heating modes in order to reach the desired temperature considering the both target time and also vehicle driving range. It was shown that the driving range can be increased up to 15 % by using HHPS. As a result, a high-capacity PTC heater and HP should be work together at the beginning of the heating, and then the PTC capacity should be reduced gradually at lower ambient conditions. Another important result is that HHPS represent a promising solution for the new generation EVs that the target temperature was obtained lower than 300 s at lower ambient conditions. A numerical model was also developed to investigate the flow and the thermal characteristics of the EV cabin interior that enable to design more effective heating, ventilation and air-conditioning (HVAC) systems of EVs under different environmental conditions and the numerical results were in good agreement with the experimental data used in this study.(c) 2023 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
Thermal analysis of different heat pump systems for heating process of electric vehicles
(Begell House, 2021-03-05) Bayram, Halil; Sevilgen, Gökhan; SEVİLGEN, GÖKHAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Otomotiv Mühendisliği Bölümü.; 0000-0002-7746-2014; ABG-3444-2020
In this paper, three different 1D models of electric vehicle heating, ventilation, and air conditioning (HVAC) system integrated with the vehicle cabin model for heating process were developed. The numerical results were compared in terms of thermal performance to get the desired thermal conditions inside the vehicle cabin. The results of the hybrid heat pump 1D model including both HVAC components and an additional electrical heater showed better thermal performance than the others and it was proposed for the heating process of electric vehicles. At the end of the driving cycle, the average temperature inside the cabin was increased up to about 7 degrees C and 14 degrees C by using the conventional heat pump and innovative heat pump models, respectively, at -5 degrees C ambient temperature and the target temperature cannot be reached. However, under the same conditions, the vehicle cabin could be heated up to about 25 degrees C by using the hybrid heat pump model with a 1-kW electrical heater. In addition, the thermal performance of different heat pump systems can be improved by using electric vehicle thermal management system that allows performing transient simulations for the estimation of the dynamic behavior of system. This study also contributes to decrease of energy usage for HVAC processes that considerably affects the mileage of the vehicle and also life cycle of batteries. These 1D models can be used not only in thermal performance but also can be utilized for thermal comfort conditions of electric vehicles.