Browsing by Author "Çivi, C"

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    Comparison of drinking milk production with conventional and novel inductive heating in pasteurization in terms of energetic, exergetic, economic and environmental aspects
    Basaran, A; Yilmaz, T; Azgin, ST; Çivi, C
    Scarcity of natural resources and global warming increase the importance of environmental awareness while making an economic decision for any kind of industry. The dairy industry is one of the impactful areas with high labor, water and energy demand is responsible for air pollution among other sectors in the food industry. In this study, drinking milk production was investigated for milk pasteurization system and its' utilities such as steam, air, and water were studied in terms of energetic, exergetic, economic, and environmental aspects. A novel system including inductive heating (IMP) was proposed in this study with the aim of improving energy and exergy efficiencies and reducing environmental impacts. Each system was selected providing a temperature profile for high-temperature short time (HTST) for processing drinking milk. It was found that a novel design could be performed for 10 ton.h-1 milk with 44.35% less energy and less 53.27% exergy input compared to conventional application. In terms of processing cost, just replacing the heating process help reducing expenditure 3.38 EUR to 2.88 EUR per m3 milk. Apart from thermodynamic and economic performance, simplified Life Cycle Assessment (LCA) results showed that the IMP system generated smaller global warming potential (41%) and ozone layer depletion (51%) impact per m3 milk comparing the conventional system.
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    Characterization of hot forged P285NH steel by metallurgical investigation and reliability analysisCharakterisierung von warmgeschmiedetem P285NH-Stahl durch metallurgische Untersuchungen und Zuverlassigkeitsanalyse
    Saklakoglu, N; Çivi, C; Hocalar, Ç; Demirok, S
    An extensive study was carried out to investigate the effect of cooling rate after hot forging process and normalization step on the hardness, strength and impact toughness and microstructure of P285NH steel. Understanding of the combined effect of cooling rate and normalization on the mechanical and microstructural properties of the steel would help to select conditions required to achieve optimum mechanical properties. The results indicated that the microstructures of all forging and cooling conditions were dominated by ferrite and pearlite phases with different morphologies and grain sizes according to various cooling rates. Conveyor cooling led to a formation of relatively fine acicular ferrite and pearlite grains in comparison to batch cooling which presented coarse polygonal ferrite with pearlite. Based on the data fluctuation of Charpy tests, the normal distribution provided a statistical analysis method for assessing the reliability. Through the statistical analysis of the distribution function, it can be concluded that normalization step is necessary for higher reliability. Both batch cooling and conveyor cooling did not give the required reliability level for safety components due to heterogeneities in the microstructure.
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    Rotating bending fatigue behavior of high-pressure diecast AlSi10MgMn alloy based on T5 heat treatment parameters
    Gülmez, CÇ; Çivi, C; Eyici, G
    The study investigates fatigue failure, a common phenomenon in machine elements subjected to cyclic stresses. The analysis emphasizes that the actual stress experienced by materials often falls below their tensile and yield strengths due to repetitive variable stresses, leading to fatigue damage. Fatigue life is measured by the number of cycles endured before failure. This paper focuses on the aluminum alloy of AlSi10MgMn, extensively used in manufacturing due to its strength, low density, and corrosion resistance. Experimental procedures encompassed tensile testing, microstructural examination, SEM analysis, and fatigue testing. Tensile tests provided initial stress values for fatigue testing. Microstructure analyses verified that heat-treated samples exhibited precipitates. SEM analysis disclosed microstructural characteristics, while fracture surface examinations demonstrated higher fatigue resistance in heat-treated specimens. Hardness measurements were conducted, with heat-treated samples showing higher values. Theoretical calculations based on stress and cycle numbers were compared to experimental fatigue results. The derived equations aligned well with the tests. Ultimately, the study underlines the importance of heat treatment on material behavior and fatigue resistance, shedding light on alloy performance and durability enhancement.
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    Experimental investigation and evaluation of the thermodynamical performance of a novel hybrid design for milk pasteurization
    Basaran, A; Yilmaz, T; Çivi, C
    In this study, a novel pasteurization system with an electrical-assisted, waste heat-recovered hybrid design was proposed for more clean and more versatile production. The novel system is designed to recover both the dissipated and extracted heat for milk pasteurization in a single thermodynamic cycle, thus enhancing energy and exergy efficiency. For experimental design, system parameters were selected as an LTLT and the target temperature was set to 65 & PLUSMN; 5 degrees C. It was experimentally determined that 2.328 kW of heat was recovered in the specifically designed heat exchanger. The novel pasteurization system had 0.71% energy efficiency whereas the pasteurization system without energy recovery shows 0.48% energy efficiency. It is concluded that heat recovery thanks to a specific condenser may increase energy efficiency by about 148%. Considering computed exergy input (4.303 kW) and output (0.3096 kW), the exergy efficiency of the whole pasteurization system was nearly 7.2%. It is found that the compressor had a 0.9884 kW exergy destruction rate corresponding to a 25% exergy destruction percentage. It is followed by the evaporator with 0.5662 kW, the secondary condenser with 0.2297 kW, by condenser with 0.1555 kW, and by expansion valve with 0.08221 kW, respectively. Consequently, the novel system has a promising design by performing good thermodynamic efficiency and recovering waste heat to reduce secondary heating energy requirement which is not valorized in conventional systems. The novel system causes approximately 33% fewer carbon emissions compared to a pasteurization system without energy recovery for the same amount of milk processing.
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    The effect of welding on reliability of mechanical properties of AISI 1020 and AISI 6150 steel materials
    Çivi, C; Iren, E
    Welding is one of the most important manufacturing and repair method of today's technology. Though it is known that it can reduced the mechanical properties of materials, it is a necessity in many areas and in some cases, it is preferred because of the efficient and fast manufacturing. The widespread use of welding has raised the problem of reliability of welded structure. It is important to carry on reliability analysis especially on critical welded constructions or some critical materials. In this study, two steel material (AISI 1020 and AISI 6150) which different weldability levels were selected. Gas metal arc welding (GMAW), Gas Tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) were chosen as widespread industrial welding techniques. Welded and non-welded mechanical properties of these materials were examined taking into consideration the reliability, and effect of welding and welding methods were investigated. Reliability analyzes revealed that non-predictable mechanical properties and microstructures are main characteristic of welding process especially in some materials or methods.
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    Design and manufacturing of an inductive liquid food heat treatment-filling system
    Çivi, C; Akkaya, S; Yilmaz, T
    In this study, an inductive heat treatment-filling system for milk pasteurization was designed and constructed. To identify the design parameters of the system, basic computational fluid dynamics (CFD) and lethality (reduction of a target pathogen during heating or thermal destruction of microorganisms) analyses were carried out simultaneously. In this context, the temperature-time combination of heated milk related to pipe design was taken into consideration. Induction calculations were made to provide the necessary heating for the selected flow rate and pipe construction material and diameter. Required frequency, power, and optimum coil design for the system were identified and validated. In the study, analyses were made for three different temperatures (90, 120, 150 degrees C) with different designs (straight pipe, flow breaker blades on the surface, central shaft) to define the required pipe length to obtain milk temperature (85 degrees C). Pipe dimensions were evaluated by CFD design and the shortest pipe length was 540 mm for the pipe having surface modification at 150 degrees C. However, for simplicity and applicability, a straight pipe at 90 degrees C constant surface temperature was selected for prototyping. From lethality calculations, 80 degrees C outlet temperature for 2700 mm pipe length was found to be sufficient and these parameters were considered for calculating induction parameters such as coil design and induction power. Experimental validation showed that heat balance was achieved compared to CFD calculations for the given system in steady condition; however, 130 s is required for reaching steady condition and this gap can be considered as come-up time. Although heat provided by induction was sufficient to heat milk to the desired temperature at the given pipe length, time was needed to heat the pipe to 90 degrees C with 25 degrees C milk passing inside at 1 L/s capacity.
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    The effect of inductive sintering to iron based powder metal parts
    Çivi, C; Atik, E
    Sintering is carried out by heating the graphite mold during pressing rather than direct heating of samples by eddy currents in many sintering applications. The effect of the induction on the powder metal samples is not fully visible due to graphite mold. The aim of this study is to observe the direct effect of eddy currents to powder metal parts. For this purpose, sintering was performed in a copper coil after pressing without a mold. Pure iron powder and two different iron based powder mixtures were used. Copper was added to the iron powder for liquid phase formation, and carbon was added for the formation of alloy. Effect of sintering method, sintering duration, pre-sintering and sintering temperature were investigated. In addition, conventional sintering has also been applied for comparison. As the result of the studies it was observed that, direct heating of powder metal samples with induction generates completely different sintering kinetics. It provides better mechanical properties in shorter sintering durations only in some instances and electrical resistivity values play an important role about this. Also resistivity values can give a preliminary idea about the mechanical strength after sintering. (C) 2018 Elsevier B.V. All rights reserved.
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    INVESTIGATION OF INDUCTION AND CLASSICAL-SINTERING EFFECTS ON POWDER-METAL PARTS WITH THE FINITE-ELEMENT METHOD
    Akpinar, G; Çivi, C; Atik, E
    Induction sintering provides large time and energy savings because the components heat up rapidly and the sintering time is lower than in classical sintering in a furnace. Therefore, induction sintering is an important alternative to classical sintering. In this study, mechanical properties of induction-sintered Fe-based components including Cu and carbon (graphite) were compared with those sintered in a classical furnace. For this purpose, microstructure photographs of both samples were taken. A tensile analysis of the sintered powder-metal samples was carried out with the finite-element method, and the micro-stress values were found to change depending on the amount and distribution of the porosity.
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    Energy and exergy analysis of induction-assisted batch processing in food production: a case study-strawberry jam production
    Basaran, A; Yilmaz, T; Çivi, C
    Traditional and additive free conservation techniques for long shelf life of fruits can be counted as drying and canning or processing to jam-marmalade. Conventional systems consume fuel or electricity to produce required energy with low efficiency due to losses and irreversibilities through heat transfer. For strawberry jam production, heat is applied as a batch system by vacuum-jacketed agitated vessel with a water or heating oil (heat transfer fluid-HTF), which is heated by electricity inside the jacket. In this study, energy and exergy efficiencies of conventional jacketed vessels and inductive heater were compared theoretically for jam processing. It is found that water and HTF used systems works with 82.27% and 93.38% energy efficiencies, respectively, while inductive processing system works with 95.00% efficiency. In terms of irreversibilities, the inductive system generates 79.90 kJ K-1 entropy, while other systems generate 674.19 kJ K-1 for HTF system and 753.90 kJ K-1 for the water system. It is determined that the batch system with induction heater needs less energy and exergy input than conventional electrical heater systems to provide the same desired output. Direct heating by induction heater has several benefits at thermal food processing systems as strawberry jam production by lowering energy and exergy losses. Graphic abstract
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    Reliability of mechanical properties of induction sintered iron based powder metal parts
    Çivi, C; Tahrali, N; Atik, E
    Reliability and safety are important for machine and construction elements. In this study, iron based powder metal parts (3% Cu, 0.5% Graphite and 1% Kenolube lubricant by weight) were sintered at 1200 degrees C by medium frequency induction sintering mechanism (30 KW powered and 30 kHz frequency). Mechanical property values of components were determined according to changing sintering time. Three point bending, % maximum strain, MicroVickers hardness (HV) and Rockwell-B hardness tests were applied. Statistical distribution functions were drawn and ultimate strength, ultimate strain, MicroVickers and Rockwell-B hardness values were determined depending on various reliability. As a result of the experiments, it was concluded that, the hardness of powder metal materials should not be based on MicroVickers hardness. (C) 2013 Elsevier Ltd. All rights reserved.
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    Application of inductive forced heating as a new approach to food industry heat exchangers: A case studyTomato paste pasteurization
    Basaran, A; Yilmaz, T; Çivi, C
    Heat exchangers are one of the main equipment used in food industry because of their convenience to transfer energy to both auxiliary facilities and various food products. In food industry, there are several reasons for heat transfer such as pre-heating, pasteurizing and sterilizing in which heat exchangers require high amount of energy. On the other hand, as being a unique quality assurance unit heat exchangers should be cleaned easily and extensively. Having high operating costs due to energy consumption and requiring high investment cost due to ensure a reliable hygienic design make heat transfer units an expensive and energy-consuming unit. Therefore, developing new approaches to generate energy and transferring it hygienically with minimum loses will be an opportunity for the food industry. With the view of developing new equipment for industry, induction-driven heating system was investigated in this study and energy and exergy efficiencies were calculated and compared with conventional heat exchanger system. Selected food system was the tomato paste sterilization/pasteurization which is a part of tomato paste production line. After assumptions and theoretical calculations for both conventional application and inductive heating, it was found that inductive heating system has 95.00% energy efficiency and 46.56% second law efficiency while the conventional heating system with electric boiler has 75.43% energy efficiency and 16.63% exergy efficiency. As a consequence, inductive method was found more beneficial compared to a commercial method having higher energy and exergy efficiencies.
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    Mechanical properties of conventionally and induction sintered Fe-based powder metal bushings
    Çivi, C; Akpinar, G; Atik, E
    Mechanical properties of powder metal parts are directly related to the shape, distribution and the amount of pores. In this study, mechanical properties of induction sintered Fe based components were investigated dependent on the changing of sintering time and pore structures. For this purpose, compression tests were applied to sintered bushings and microstructural photographs were taken. The compression tests were accompanied by respective finite element analyses. The numerical values were compared to experimental results. It turned out that the micro-stress values were dependent on the amount and distribution of porosity.
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    Reliability evaluation of hardness test methods of hardfacing coatings with hypoeutectic and hypereutectic microstructures
    Çömez, N; Çivi, C; Durmus, H
    Hardfacing coatings involve hard carbide/boride phases dispersed in a relatively soft steel matrix. For the hardness measurements of hardfacing coatings, depending on the micro structure, both the hardness test method and the applied load affect the hardness results; therefore, they affect the wear performance predictions of the coating. For this reason, the proper hardness test method should be determined according to the microstructure of the coating, and the reliability of the obtained hardness data should be established. This study aimed to determine the most suitable hardness test method for hypoeutectic and hypereutectic microstructures of hardfacing coatings by analyzing the reliability of Rockwell-C and Vickers hardness test results. Reliability analyses showed that Rockwell-C is not a suitable hardness test method for hypereutectic hardfacing coatings. Based on the relationship between wear resistance and hardness, Vickers hardness method was found more suitable for the considered materials.
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    Reliability Analysis of Brinell Hardness Results for Aged Alumix321/SiC Composites
    Gül, C; Çömez, N; Çivi, C; Durmus, H
    Aluminum/SiC composites are widely employed in the automotive industry. Aluminum composites can be produced by hot pressing which forms a final product with a low porosity level and a denser structure. Homogeneous distribution of reinforcement particles, the level of porosity, and heat treatment not only affect the mechanical properties of the composites but also the reliability of their mechanical test results. In this study, Brinell hardness test reliability analyses of the hot-pressed Alumix321/SiC composites were carried out. The effects of increasing SiC amount and aging treatment on the reliability of hardness test results were discussed. Reliability analysis revealed that the aging treatment and increasing amount of SiC reinforcement decreased the reliability of the hardness test results. The reason for this was researched and resulting cases were discussed.
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    Comparison Of Effect Of Induction And Classical Sintering To Mechanical Properties Of Powder Metal Components
    Çivi, C; Atik, E
    Because of solidifying to component, sintering is the most important step of the production of powder metal parts. Generally it is made classical furnace. Alternatively sintering furnace, it is done that induction sintering studies. Induction sintering provide a grand time and energy savings since components hot up rapidly and sintering time is lower than classical sintering in furnace. Because of that induction sintering is an important alternative at sintering process. In this study, mechanical properties of induction sintered Fe based components included Cu and Graphite were compared with classical sintered components. Parameters of same mechanical properties of induction sintered and classical sintered components were identified.