Browsing by Author "Salem, T. K."

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Effect of polymer coating on vapor condensation heat transfer
(ASME, 2020-04-01) Budaklı, M.; Salem, T. K.; Arık, Mehmet; Donmez, B.; Menceloglu, Y.; Mechanical Engineering; ARIK, Mehmet
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.
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An experimental and theoretical analysis of vapor-to-liquid phase change on microstructured surfaces
(Elsevier, 2020-09) Budakli, M.; Salem, T. K.; Arık, Mehmet; Mechanical Engineering; ARIK, 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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An experimental study on the heat transfer and wettability characteristics of micro-structured surfaces during water vapor condensation under different pressure conditions
(Elsevier, 2021-01) Budaklı, M.; Salem, T. K.; Arık, Mehmet; Dönmez, B.; Menceloglu, Y.; Mechanical Engineering; ARIK, Mehmet
In this study, condensation characteristics of water vapor on micro-structured surfaces at different pressures and subcooling temperature has been investigated experimentally. This work represents a basic study in order to design a secondary evaporator section in a refrigeration cycle. A set of surfaces has been manufactured over copper substrates with one sample used as unstructured (smooth) reference surface and two micro-structured surfaces with longitudinal grooves having V-shape and square cross-sections. As the second step, the surfaces have been modified by using a polymer coating to achieve stronger hydrophobicity at the surface and hence to influence wettability such that increased heat transfer rates should be reached. The polymer coating has been created with a dip coating process by applying a mixture of perfluoroalkyl triethoxysilane. Concerning the wettability, a high-speed flow visualization study has been performed for the interpretation of heat transfer results. Experimental results showed that an increase in the droplet contact angle by applying the polymer coating over surfaces, while the largest droplet contact angle was obtained (130.9°±2.0°) for the surface with V-shaped micro-structuring compared to other surfaces. The comparison of heat transfer performance reveals an enhancement in heat transfer coefficient for the coated version of unstructured, square-grooved and V-grooved surface by 34.5%, 61.8%, and 73.4%, respectively.
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Impact of functional nanofluid coolant on radiator performance
(ASME, 2019-08) Salem, T. K.; Nazzal, I. T.; Arık, Mehmet; Budakli, M.; Mechanical Engineering; ARIK, Mehmet
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.