WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7150

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Department: search.filters.department.İzmir Institute of Technology. Mechanical EngineeringPublisher: search.filters.publisher.Taylor and Francis Ltd.

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Now showing 1 - 10 of 19
  • Conference Object
    Citation - WoS: 7
    Modeling of Low Temperature Geothermal District Heating Systems
    (Taylor and Francis Ltd., 2004) Yıldırım, Nurdan; Gökçen, Gülden
    In this work, low temperature geothermal district heating systems with heat pumps have been studied and compared with fuel-oil boiler heating systems for intermittent and continuous regimes according to the optimum indoor air temperature and operational cost. Izmir Institute of Technology (IZTECH) Campus is taken as a case study. Various heat pump and boiler configurations are studied to meet required duty. Operational cost analysis for each alternative is conducted. According to the results, for IZTECH Campus the best alternative, which gives the optimum indoor air temperature and the lowest operational cost, is heat pump continuous regime.
  • Book Part
    Citation - WoS: 2
    Rapid Development of Geothermal Power Generation in Turkey
    (Taylor and Francis Ltd., 2014) Karadaş, Murat; Gökçen Akkurt, Gülden
    [No abstract available]
  • Article
    Citation - WoS: 18
    Citation - Scopus: 17
    Wetting of Single Crystalline and Amorphous Silicon Surfaces: Effective Range of Intermolecular Forces for Wetting
    (Taylor and Francis Ltd., 2020) Özçelik, Hüseyin Gökberk; Özdemir, Abdullah Cihan; Kim, Bohung; Barışık, Murat
    Wetting at nanoscale is a property of a three-dimensional region with a finite length into the solid domain from the surface. Understanding the extent of the solid region effective on wetting is important for recent coating applications as well as for both crystalline and amorphous solids of different atomic ordering. For such a case, we studied the wetting behaviour of silicon surfaces at various crystalline and amorphous states. Molecular distributions of amorphous systems were varied by changing the amorphisation conditions of silicon. Semi-cylindrical water droplets were formed on the surfaces to be large enough to remain independent of line tension and Tolman length effects. Contact angles showed up to 38% variation by the change in the atomic orientation of silicon. Instead of a homogeneous solid density definition, we calculated different solid densities for a given surface measured inside different extents from the interface. We correlated the observed wetting variation with each of these different solid densities to determine which extent governs the wetting variation. We observed that the variation of solid density measured inside a 0.13 nm extent from the surface reflected the variation of wetting angle better for both single crystalline and amorphous silicon surfaces.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    The Effect of Cell Wall Material Strain and Strain-Rate Hardening Behaviour on the Dynamic Crush Response of an Aluminium Multi-Layered Corrugated Core
    (Taylor and Francis Ltd., 2021) Güden, Mustafa; Canbaz, İlker
    The effect of the parameters of the Johnson and Cook material model on the direct impact crushing behaviour of a layered 1050 H14 aluminium corrugated structure was investigated numerically in LS-DYNA at quasi-static (0.0048 m s(-1)) and dynamic (20, 60, 150 and 250 m s(-1)) velocities. Numerical and experimental direct impact tests were performed by lunching a striker bar onto corrugated samples attached to the end of the incident bar of a Split Hopkinson Pressure Bar set-up. The numerical impact-end stress-time and velocity-time curves were further compared with those of rigid-perfectly-plastic-locking (r-p-p-l) model. Numerical and r-p-p-l model impact-end stress analysis revealed a shock mode at 150 and 250 m s(-1), transition mode at 60 m s(-1) and quasi-static homogenous mode at 20 m s(-1). The increase of velocity from quasi-static to 20 m s(-1) increased the numerical distal-end initial peak-stress, while it almost stayed constant between 20 and 250 m s(-1) for all material models. The increased distal-end initial peak-stress of strain rate insensitive models from quasi-static to 20 m s(-1) confirmed the effect of micro-inertia. The numerical models further indicated a negligible effect of used material models on the impact-end stress of investigated structure. Finally, the contribution of strain rate to the distal-end initial peak-stress of cellular structures made of low strain rate sensitive Al alloys was shown to be relatively low as compared with that of strain hardening and micro-inertia, but it might be substantial for the structures constructed using relatively high strain rate sensitive alloys.
  • Article
    Citation - WoS: 15
    Citation - Scopus: 15
    Enhancement of Heat Transfer in Partially Heated Vertical Channel Under Mixed Convection by Using Al2o3 Nanoparticles
    (Taylor and Francis Ltd., 2018) Çelik, Hasan; Mobedi, Moghtada; Manca, Oronzio; Buonomo, Bernardo
    Laminar mixed convection in a two-dimensional symmetrically and partially heated vertical channel is investigated. The heaters are located on both walls and uniform temperature is applied on the heated sections. The number of heaters is considered as 1, 4, 8, and 10. Aluminum oxide/water nanofluid is considered as working fluid and the inlet velocity is uniform. The continuity, momentum and energy equations with appropriate boundary conditions are solved in dimensionless form, numerically. The study is performed for Richardson number of 0.01 and 10, Reynolds number of 100 and 500, and nanofluid volume fraction of 0% and 5%. Based on the obtained velocity and temperature distributions, the local and mean Nusselt number is calculated and plotted for different cases. The variation of the mean Nusselt number with the number of the heated portions is also discussed. It is found that the addition of nanoparticles into the base fluid increases mean Nusselt number but the rate of increase depends on Reynolds, Richardson numbers and number of heated portions. It is possible to increase mean Nusselt number 138% by increasing Reynolds number from 100 to 500, Richardson number from 0.01 to 10 and number of heated portions from 1 to 10 when volume fraction value is 5%.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 7
    An Entropy-Based Analysis of Lane Changing Behavior: An Interactive Approach
    (Taylor and Francis Ltd., 2017) Koşun, Çağlar; Özdemir, Serhan
    Objectives: As a novelty, this article proposes the nonadditive entropy framework for the description of driver behaviors during lane changing. The authors also state that this entropy framework governs the lane changing behavior in traffic flow in accordance with the long-range vehicular interactions and traffic safety. Methods: The nonadditive entropy framework is the new generalized theory of thermostatistical mechanics. Vehicular interactions during lane changing are considered within this framework. The interactive approach for the lane changing behavior of the drivers is presented in the traffic flow scenarios presented in the article. According to the traffic flow scenarios, 4 categories of traffic flow and driver behaviors are obtained. Through the scenarios, comparative analyses of nonadditive and additive entropy domains are also provided. Results: Two quadrants of the categories belong to the nonadditive entropy; the rest are involved in the additive entropy domain. Driving behaviors are extracted and the scenarios depict that nonadditivity matches safe driving well, whereas additivity corresponds to unsafe driving. Furthermore, the cooperative traffic system is considered in nonadditivity where the long-range interactions are present. However, the uncooperative traffic system falls into the additivity domain. The analyses also state that there would be possible traffic flow transitions among the quadrants. This article shows that lane changing behavior could be generalized as nonadditive, with additivity as a special case, based on the given traffic conditions. Conclusions: The nearest and close neighbor models are well within the conventional additive entropy framework. In this article, both the long-range vehicular interactions and safe driving behavior in traffic are handled in the nonadditive entropy domain. It is also inferred that the Tsallis entropy region would correspond to mandatory lane changing behavior, whereas additive and either the extensive or nonextensive entropy region would match discretionary lane changing behavior. This article states that driver behaviors would be in the nonadditive entropy domain to provide a safe traffic stream and hence with vehicle accident prevention in mind.
  • Article
    Citation - WoS: 100
    Citation - Scopus: 106
    Determination of Kozeny Constant Based on Porosity and Pore To Throat Size Ratio in Porous Medium With Rectangular Rods
    (Taylor and Francis Ltd., 2014) Özgümüş, Türküler; Mobedi, Moghtada; Özkol, Ünver
    Kozeny-Carman permeability equation is an important relation for the determination of permeability in porous media. In this study, the permeabilities of porous media that contains rectangular rods are determined, numerically. The applicability of Kozeny-Carman equation for the periodic porous media is investigated and the effects of porosity and pore to throat size ratio on Kozeny constant are studied. The continuity and Navier- Stokes equations are solved to determine the velocity and pressure fields in the voids between the rods. Based on the obtained flow field, the permeability values for different porosities from 0.2 to 0.9 and pore to throat size ratio values from 1.63 to 7.46 are computed. Then Kozeny constants for different porous media with various porosity and pore to throat size ratios are obtained and a relationship between Kozeny constant, porosity and pore to throat size ratio is constructed. The study reveals that the pore to throat size ratio is an important geometrical parameter that should be taken into account for deriving a correlation for permeability. The suggestion of a fixed value for Kozeny constant makes the application of Kozeny-Carman permeability equation too narrow for a very specific porous medium. However, it is possible to apply the Kozeny-Carman permeability equation for wide ranges of porous media with different geometrical parameters (various porosity, hydraulic diameter, particle size and aspect ratio) if Kozeny constant is a function of two parameters as porosity and pore to throat size ratios.
  • Article
    Citation - WoS: 20
    Citation - Scopus: 26
    Effect of Urban Geometry on Pedestrian-Level Wind Velocity
    (Taylor and Francis Ltd., 2014) Arkon, Çelen Ayşe; Özkol, Ünver
    The orientation of the streets and the height of continuous buildings cut off summer breezes and the prevailing wind in Izmir, Turkey. Compared with the northern parts of Turkey, the summer period in Izmir is relatively hot, humid and long. Due to the dense urban structure and the expansion of hard surface materials, the temperature in the city centre is higher than this centre's surroundings and this effect is called the urban heat island. Consequently, pedestrian comfort in the city drops dramatically especially in locations where the wind flow is obstructed by buildings. In addition, natural ventilation through the building façades is weakened due to the low average wind speed in the streets. For better outdoor and indoor comfort the citizens in Izmir should benefit from the prevailing wind and summer breezes locally named imbat in the sea-land direction. Therefore, the existing situation is examined through the field study in order to understand the natural ventilation potential at the pedestrian level in the selected main streets in Izmir.
  • Article
    Shear Strength of Pultruded Composite Pins With External Confinement
    (Taylor and Francis Ltd., 2014) Beylergil, Bertan; Aktaş, Alaattin; Pekbey, Yeliz
    Weight reduction using composites has gained increasing attention in recent times. In this study, pultruded composite pins (unconfined and confined) were manufactured and tested by using a custom double shear testing fixture. Different configurations were applied for confinement of the composite pins, including weft-knitted fabrics (plain, 1 × 1 rib, and Milano), woven fabrics and E-glass 130 tex fibers/adhesive cloth. They were externally wrapped and bonded to the unconfined composite pins. In each case, five identical specimens were tested, and shear strength data were analyzed by using two-parameter Weibull statistics. The results showed that the maximum shear strength took its highest value in the unconfined case for both average values of the test results and for 99% reliability under Weibull distribution. The confinement had a negative effect on the average shear strength of the unconfined pins. It was also seen that the 99% reliability values of shear strength were approximately equivalent to the 0.7 average value of the shear strength.
  • Article
    Citation - WoS: 12
    Citation - Scopus: 13
    Using of Bejan's Heatline Technique for Analysis of Natural Convection in a Divided Cavity With Differentially Changing Conductive Partition
    (Taylor and Francis Ltd., 2013) Koca, Ahmet; Öztop, Hakan Fehmi; Varol, Yasin; Mobedi, Moghtada
    The issue of laminar natural convection and conduction in enclosures divided by a partition with different thicknesses is investigated numerically. The partition is accepted as conductive at different thermal conductivity ratio. The cavity is filled with air, and it is heated differentially from vertical walls while horizontal walls are adiabatic. The problem is solved for different values of Rayleigh number (103 ≤ Ra ≤ 106), thickness ratio of the partition, and thermal conductivity ratio (0.1 ≤ k ≤ 10.0). It is found that both heat transfer and flow strength strongly depend on the thermal conductivity ratio of the solid material of partition and Rayleigh numbers.