Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

Browse

Filters

2000 - 200942010 - 2019142020 - 20233

Settings

Subject: search.filters.subject.Heat transfer

Search Results

Now showing 1 - 10 of 21
  • Article
    Citation - WoS: 15
    Citation - Scopus: 17
    Effects of Nanosecond Laser Ablation Parameters on Surface Modification of Carbon Fiber Reinforced Polymer Composites
    (SAGE Publications, 2023) Martin, Seçkin; İplikçi, Hande; Barışık, Murat; Türkdoğan, Ceren; Yeke, Melisa; Nuhoğlu, Kaan; Esenoğlu, Gözde; Tanoğlu, Metin; Aktaş, Engin; Dehneliler, Serkan; İriş, Mehmet Erdem
    Removal of contaminants and top polymer layer from the surface of carbon-fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/?45/90]2s stacking of carbon/epoxy prepregs (HexPly®-M91), 100 mJ/mm2 generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition. © The Author(s) 2023.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    EXPERIMENTAL AND ANALYTICAL EXAMINATION OF THE EFFECT OF DOUBLE SKIN FAÇADE SYSTEM ON BUILDING THERMAL PERFORMANCE;
    (Turk Isi Bilimi ve Teknigi Dernegi, 2021) Hülagü,S.; Göksal Özbalta,T.; Başaran,T.
    In this study, heat transfer in conventional single skin façade and double skin façade system was studied experimentally and numerically by using one dimensional time dependent approach and the effects of the façade systems on building energy performance especially heating energy was investigated. In this context, a mathematical model considering user behavior and window aluminum frame element effect was build by zonal analysis method to calculate the heat transfer in single and box type closed cavity double skin façade systems, and build model was experimentally verified. Experimental study was conducted in office spaces having single and double skin façade systems in Ege University, Civil Engineering Building’s south façade in January 2017. Next, verified model was used to study the heat transfer in the façade systems for İzmir’s climatic condition by using monthly average daily data. The change in thermal performance of single and double skin façade systems due to the climatic condition during a year was investigated by using the 10 year average climate data of İzmir (Mediterranean climate). It was found that double skin façade system acts as an insulator preventing extreme indoor temperature values, thus contributing to the indoor comfort level against changing outdoor conditions. ©2021 TIBTD Printed in Turkey.
  • Article
    Interfacial Convective Heat Transfer for Randomly Generated Porous Media
    (Begell House, 2018) Uçar, Eren; Mobedi, Moghtada; Ahmadi, Azita
    Heat and fluid flow in 20 random porous media is investigated by using the Monte Carlo (MC) procedure. Each porous medium consists of long square rods distributed randomly in flow direction. The continuity, momentum, and energy equations are solved for a row of porous media representing the entire domain of a random porous medium. The microstructure properties of each random porous medium which are the mean and standard deviations of the Voronoi areas, the nearest neighbor distance and orientation are obtained. The rods in the domain are classified into three groups as blocker, active, and passive rods according to their effects on the penetration of heat in porous media. 'The interfacial convective heat transfer coefficients for each rod and entire porous medium are calculated and plotted for different Reynolds numbers. A characteristic length based on the microstructure properties of the generated porous media is defined, and three correlations relating to the upper limit, lower limit, and mean of the overall interfacial convective heat transfer coefficient are proposed.
  • Article
    Citation - WoS: 35
    Citation - Scopus: 38
    Heat Transfer Enhancement in a Microchannel Heat Sink: Nanofluids And/Or Micro Pin Fins
    (Taylor & Francis, 2020) Coşkun, Turgay; Çetkin, Erdal
    Here, we show that overall thermal conductance in a rectangular microchannel heat sink can be maximized with the combination of nanofluids and micro pin fins. We uncover the effect of micro pin fins and nanofluids both separately and simultaneously in order to uncover their effect on the thermal conductance (i.e., thermal resistance). Both nanofluids and micro pin fins decrease the overall thermal resistance due to increase in the average thermal conductivity of the flow system. In addition, they increase the heat transfer surface area of the solid interacting with the fluid. However, the pumping power (pressure drop) increases in both methods due to the increase in the resistances to the fluid flow. The results document what should be the nanoparticle volume fraction mixed into the base fluid and the micro pin fin volume in order to minimize thermal resistance. If the thermal conductivity of the nanoparticles and micro pin fins are the same, the thermal conductance becomes the maximum with 4% and 0.14% volume fractions for the nanofluid and micro pin fins, respectively. This result shows that inserting micro pin fins and using nanofluids with a given volume fraction ratio maximize the overall thermal conductance. © 2019, © 2019 Taylor & Francis Group, LLC.
  • 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: 15
    Citation - Scopus: 16
    A Pore Scale Analysis for Determination of Interfacial Convective Heat Transfer Coefficient for Thin Periodic Porousmedia Undermixed Convection
    (Emerald Group Publishing Ltd., 2017) Çelik, Hasan; Mobedi, Moghtada; Manca, Oronzio; Özkol, Ünver
    Purpose - The purpose of this study is to determine interfacial convective heat transfer coefficient numerically, for a porous media consisting of square blocks in inline arrangement under mixed convection heat transfer. Design/methodology/approach - The continuity, momentum and energy equations are solved in dimensionless form for a representative elementary volume of porous media, numerically. The velocity and temperature fields for different values of porosity, Ri and Re numbers are obtained. The study is performed for the range of Ri number from 0.01 to 10, Re number from 100 to 500 and porosity value from 0.51 to 0.96. Based on the obtained results, the value of the interfacial convective heat transfer coefficient is calculated by using volume average method. Findings - It was found that at low porosities (such as 0.51), the interfacial Nusselt number does not considerably change with Ri and Re numbers. However, for porous media with high Ri number and porosity (such as 10 and 0.51, respectively), secondary flows occur in the middle of the channel between rods improving heat transfer between solid and fluid, considerably. It is shown that the available correlations of interfacial heat transfer coefficient suggested for forced convection can be used for mixed convection for the porous media with low porosity (such as 0.51) or for the flow with low Ri number (such as 0.01). Originality/value - To the best of the authors' knowledge, there is no study on determination of interfacial convective heat transfer coefficient for mixed convection in porous media in literature. The present study might be the first study providing an accurate idea on the range of this important parameter, which will be useful particularly for researchers who study on mixed convection heat transfer in porous media, macroscopically.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 5
    Analytical Solution of Micro-/Nanoscale Convective Liquid Flows in Tubes and Slits
    (Springer, 2017) Kalyoncu, Gülce; Barışık, Murat
    Analytical solutions examining heat transport in micro-/nanoscale liquid flows were developed. Using the energy equation coupled with fully developed velocity, we solved developing temperature profiles with axial conduction and viscous dissipation terms. A comprehensive literature review provided the published range of velocity slip and temperature jump conditions. While molecular simulations and experiments present constant slip and jump values for a specific liquid/surface couple independent of confinement size, non-dimensional forms of these boundary conditions were found appropriate to calculate non-equilibrium as a function of flow height. Although slip and jump conditions are specific for each liquid/surface couple and hard to obtain, we proposed modeling of the slip and jump as a function of the surface wetting, in order to create a general, easy to measure methodology. We further developed possible correlations to calculate jump using the slip value of the corresponding surface and tested in the results. Fully developed Nu showed strong dependence on slip and jump. Heat transfer stopped when slip and jump coefficients became higher than a certain value. Strong variation of Nu in the thermal development length was observed for low slip and jump cases, while an almost constant Nu in the flow direction was found for high slip and jump coefficients. Variation of temperature profiles was found to dominate the heat transfer through the constant temperature surface while surface and liquid temperatures became equal at heat transfer lengths comparable with confinement sizes for no-dissipation cases. In case of non-negligible heat dissipation, viscous heating dominated the Nu value by enhancing the heating while decreasing the heat removal in cooling cases. Implementation of proposed procedure on a micro-channel convection problem from a micro-fluidics application showed the dominant effect of the model defining the slip and jump relationship. Direct use of kinetic gas theory resulted in an increase of Nu by an increase in non-equilibrium, while models developed from published liquid slip and jump values produced an opposite behavior.
  • Conference Object
    Citation - WoS: 3
    Citation - Scopus: 3
    Performance Assessment of a Near Room Temperature Magnetic Cooling System
    (Elsevier Ltd., 2017) Ekren, Orhan; Yılancı, Ahmet; Ezan, Mehmet Akif; Kara, Salih Murat; Bıyık, Emrah
    In this study, performance of a near room temperature magnetic cooling system was investigated experimentally in terms of temperature span. The current setup has a permanent magnet pairs (0.7 Tesla), a magnetocaloric material (Gadolinium) and a heat transfer fluid (water, ethylene glycol and 10% ethanol-water mixing) furthermore solar energy was used as a power source of liner motion of the magnetic system. The obtained results showed that ethanol-water was the best heat transfer fluid and also that optimum magnetization-demagnetization period for the system was found 10 s. © 2017 The Authors.
  • Article
    Citation - WoS: 33
    Citation - Scopus: 35
    Experimental and Numerical Investigation of Constructal Vascular Channels for Self-Cooling: Parallel Channels, Tree-Shaped and Hybrid Designs
    (Elsevier Ltd., 2016) Yenigün, Onur; Çetkin, Erdal
    In this paper, we show experimentally and numerically how a plate which is subjected to a constant heat load can be kept under an allowable temperature limit. Vascular channels in which coolant fluid flows have been embedded in the plate. Three types of vascular channel designs were compared: parallel channels, tree-shaped and their hybrid. The effects of channel design on the thermal performance for different volume fractions (the fluid volume over the solid volume) are documented. In addition, the effects of the number of channels on cooling performance have been documented. Changing the design from parallel channels to tree-shaped designs decreases the order of pressure drop. Hence increase in the order of the convective heat transfer coefficient is achieved. However, tree-shaped designs do not bathe the entire domain, which increases the conductive resistances. Therefore, additional channels were inserted at the uncooled regions in the tree-shaped design (hybrid design). The best features of both parallel channels and tree-shaped designs are combined in the hybrid of them: the flow resistances to the fluid and heat flow become almost as low as the tree-shaped and parallel channels designs, respectively. The effect of design on the maximum temperature shows that there should be an optimum design for a distinct set of boundary conditions, and this design should be varied as the boundary conditions change. This result is in accord with the constructal law, i.e. the shape should be varied in order to minimize resistances to the flows.
  • Article
    Citation - WoS: 13
    Citation - Scopus: 19
    Effect of Pore To Throat Size Ratio on Interfacial Heat Transfer Coefficient of Porous Media
    (The American Society of Mechanical Engineers(ASME), 2015) Özgümüş, Türküler; Mobedi, Moghtada
    In this study, the effects of pore to throat size ratio on the interfacial heat transfer coefficient for a periodic porous media containing inline array of rectangular rods are investigated, numerically. The continuity, Navier-Stokes, and energy equations are solved for the representative elementary volume (REV) of the porous media to obtain the microscopic velocity and temperature distributions in the voids between the rods. Based on the obtained microscopic temperature distributions, the interfacial convective heat transfer coefficients and the corresponding Nusselt numbers are computed. The study is performed for pore to throat size ratios between 1.63 and 7.46, porosities from 0.7 to 0.9, and Reynolds numbers between 1 and 100. It is found that in addition to porosity and Reynolds number, the parameter of pore to throat size ratio plays an important role on the heat transfer in porous media. For the low values of pore to throat size ratios (i.e., β = 1.63), Nusselt number increases with porosity while for the high values of pore to throat size ratios (i.e., β = 7.46), the opposite behavior is observed. Based on the obtained numerical results, a correlation for the determination of Nusselt number in terms of porosity, pore to throat size ratio, Reynolds and Prandtl numbers is proposed.