Yazar "Salem, Thamer Khalif" seçeneğine göre listele

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    An experimental and analytical study on the influence of superhydrophobic micro-textured surfaces on liquid wetting phenomena
    (Elsevier Science Bv, 2018) Salem, Thamer Khalif; Budaklı, Mete; Şahan, Oğuz; Arık, Mehmet
    Controlling dust, particle, gas or liquid attachment or motion over the surfaces is attracting many researchers to reduce losses or reach mission-specific goals. Therefore, researchers have been developing novel surfaces so that performance increase, such as heat transfer, or reduction of energy losses, such as pressure loss, will be achieved. One of those approaches is hydrophobic surfaces that are widely used in order to increase liquid repellence commonly by controlling the liquid-solid contact angle. To ensure desired contact angles between the surface and liquid, these micro-nano-textured surfaces are fabricated by using advanced manufacturing technologies and methods like etching, electrospinning, and chemical vapor deposition. While, these fabricated surfaces can be used for a variety of purposes, such as protecting the material e.g. from corrosion, changing the surface property to avoid deposition or preventing icing on aircraft wings; hydrophobicity is also a key parameter for heat transfer systems such as heat exchangers, refrigerators, and industrially used condensers, as the focus of current study. In this work, a set of experimental and analytical studies has been conducted to investigate the influence of micro-nano-textured surfaces on the liquid wetting phenomena. Since the liquid-wall interaction is a key parameter in terms of droplet formation, the present work represents an essential contribution to our major research focused on heat transfer performance of heat pipe condenser. Copper samples with three different surface topographies at micro-scale (unstructured-smooth, square-grooved and v-grooved) have been subjected to a chemical treatment process by applying commercially available nano-particles using dip-coating and spraycoating techniques. These types of surfaces have been chosen to understand the effect of micro-structuring/coating on wettability, droplet formation and their dynamics. Before and after the coating procedure, measurements have been performed with de-ionized water in order to determine the difference in droplet contact angle at the surfaces to be used. In the analytical part, capillary Laplace equation with available analytical correlations from the literature has been used to predict the contact angles and surface energies on the surfaces to be investigated. The experimental results have been validated with the analytical approaches. When bare surface experimental results are compared with uncoated samples, it is found that the average water contact angle (WCA) increases by 34.5% and 52.5% for the square-grooved and v-grooved surface. Analytical calculations compared to experimental results show a reasonable deviation of 2.3% and 4.1% for both square-grooved and v-grooved surface, respectively. Moreover, analytically validated results clearly show that the coated square-grooved surface has a larger average contact angle than the v-grooved surface by 4.6%.
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    An experimental and theoretical analysis of vapor-to-liquid phase change on microstructured surfaces
    (Pergamon-Elsevier Science Ltd, 2020) Budaklı, Mete; Salem, Thamer Khalif; Arık, Mehmet
    In this work, an experimental and a theoretical study was carried out on condensation heat transfer on vertically aligned bare unstructured, micro V-grooved and square-grooved copper substrates. During the experiments, dropwise condensation and drop-film-wise condensation modes were achieved. The surface wettability was recorded by using a high-speed camera, while the overall thermal performance has been evaluated through determining heat flux and heat transfer coefficients. Experimental results show that although the condensation surface area increased by 50% utilizing micro-grooves, the thermal performance is approximately 30% lower than the unstructured surface. Additionally, experimentally measured data has been compared with two correlations for filmwise condensation and one correlation proposed for dropwise condensation as classical benchmarks found in open literature. The comparison for the unstructured surface on which dropwise condensation has been visually monitored reveals that the benchmark for dropwise condensation agrees well for the subcooling ranging between 7.5-10 K and 35-40 K. Beyond this range, the correlation either overestimates or underpredicts the heat flux values. Two other correlations show similar trend but exhibit weak agreement with the experimental data. In case of microstructured surfaces, predictions of correlations for filmwise condensation are found to be the best for square-grooved surface than for V-grooved surface. Furthermore, new correlations have been proposed for all three surfaces based on the experimental data obtained in the present study. The proposed correlations show rather a good agreement for the unstructured surface over the full range of sub-cooling, while for those developed for microstructured surfaces, accordance up to 93-95% has been reached.
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    Effect of polymer coating on vapor condensation heat transfer
    (Asme, 2020) Budaklı, Mete; Salem, Thamer Khalif; Arık, Mehmet; Dönmez, Barca; Menceloğlu, Yusuf
    Condensation heat transfer coefficients (HTCs) are rather low compared to thin film evaporation. Therefore, it can be a limiting factor for designing heat transfer equipment. In this work, heat transfer characteristics of water vapor condensation phenomena were experimentally studied on a vertically aligned smooth copper substrate for a range of pressures and temperatures for two different liquid wettability conditions. The heat transfer performance is dominated by the phase change process at the solid-vapor interface along with the liquid formation mechanism. Compared to heat transfer results measured at an untreated copper surface, heat transport is augmented with a thin layer of perfluoro-silane coating over the same substrate. In this work, the effect of saturation pressure on the condensation process at both surfaces has been investigated by analyzing heat transfer coefficients. The results obtained experimentally show an increase in contact angle (CA) with the surface coating. A heat transfer augmentation of about 26% over uncoated surfaces was obtained and surfaces did not show any degradation after 40h of operation. Finally, current results are compared with heat transfer values reported in open literature.
  • Küçük Resim
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    Impact of functional nanofluid coolant on radiator performance
    (Asme, 2019) Salem, Thamer Khalif; Nazzal, İbrahim Thamer; Arık, Mehmet; Budaklı, Mete
    While a number of liquids are preferred in many heating and cooling applications, their thermal capacity can be a limiting factor in many thermal systems. Therefore, a series of methods such as use of mixtures of two or more fluids, emulsions, phase change materials, and more recently nanoparticle enriched fluids have been proposed. The impact of adding aluminum and copper nanoparticles to water in a closed-loop radiator has been investigated analytically and numerically. Heat transfer performances of different working fluids are studied under the same boundary conditions. The analytical and numerical models including external and internal flow domains of the radiator have been developed, and free convection air cooling has been considered over external surfaces of a radiator. Both plain and nanoparticle added fluid cases are analyzed individually to differentiate the impact over heat transfer. The results indicate that the presence of nanoparticles effectively raised the convective heat transfer coefficient and thus the performance of the radiator system increased by 2.1% and 0.6%, respectively, in comparison to plain water operating condition. Furthermore, the radiator tube length has been shortened by 2.0% and 0.75% for both Al and Cu nanoparticle filled fluid, respectively, to obtain the same thermal performance at a single tube. The total required heat transfer surface area is also reduced by 2.0% and 1.15% for Al and Cu, respectively. Finally, a comparison between analytical and numerical models has been found to be in a good agreement of heat transfer coefficient and Nusselt number.
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    Numerical and experimental analysis of a heat-pipe-embedded printed circuit board for solid state lighting applications
    (Taylor & Francis Inc, 2019) Salem, Thamer Khalif; Khosroshahi, Ferina Saati; Arık, Mehmet; Hamdan, Mohammad Omar; Budaklı, Mete
    Thermal management is one of the main issues for electronics cooling especially for tightly packaged PCBs that experience local heat generation. Thus, theoretical and experimental investigations have been conducted to predict thermal performance of a novel heat-pipe-embedded-PCB. First, plain heat-pipe is experimentally tested under various inclination angles and validated by theoretical and numerical calculations. Flattened heat-pipes have been embedded into PCB prototypes made of polymer and aluminum and have been tested for similar experimental parameters; they have shown a decrease in compared with conventional heat pipe. Accordingly, reduction of approximately 50% is achieved for both embedded PCB prototypes.