WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 14Citation - Scopus: 15Ultrafast High-Temperature Sintering (uhs) of Wc and Wc-Containing Zrb2(Elsevier Ltd, 2024) De Bona,E.; Karacasulu,L.; Vakifahmetoglu,C.; Sglavo,V.M.; Biesuz,M.WC and ZrB2 are refractory ceramics with excellent thermophysical properties and melting temperatures exceeding 2800°C. Both materials require the application of external pressure and long sintering times for their consolidation. In particular, commercially available ZrB2 powders are intrinsically difficult to sinter and usually need long pre-processing steps such as high-energy ball milling. Ultrafast high-temperature sintering (UHS) is a recently developed technique that enables the consolidation of bulk ceramics within minutes. In the present work, pure WC was efficiently densified to above 98% in just 3 min by UHS. Moreover, small WC additions enhanced ZrB2 densification by activating liquid phase sintering. Samples containing 5 and 10 vol% WC were sintered to 95 and 96%, respectively, in 2 min. All the WC initially present in the blend reacts to form a liquid phase during sintering and solidifies as WB and (Zr,W)C upon cooling. The formation of a ZrB2-(Zr,W)B2 core-shell structure was detected in all the sintered composites. The hardness of UHS samples reaches 15 GPa (WC - ZrB2 composites) and 21 GPa (pure WC), similar to that measured in materials obtained by slower and more sophisticated pressure-assisted sintering techniques. © 2024 The AuthorsArticle Citation - WoS: 14Citation - Scopus: 17Experimental Investigation on Heat Transfer and Air Flow Behavior of Latent Heat Storage Unit in a Facade Integrated Ventilation System(Elsevier Ltd, 2021) Pekdogan,T.; Tokuç,A.; Ezan,M.A.; Başaran,T.All-air central HVAC systems are widely applied to provide fresh and conditioned air, which is very important for users to lead healthy and productive lives. Decentralized systems are another mechanical solution to ensure indoor air quality and thermal comfort with a heat recovery ventilation system integrated into the building wall. These commercially available systems store sensible energy in the heat exchanger. In this study, an experimental real-size staggered tube bundled prototype with phase change material (PCM), which stores latent thermal energy, was proposed/designed and full-scale experiments were carried out in laboratory conditions. The experimental setup includes two spaces that simulate indoor and outdoor conditions that are separated by an insulated aerated concrete wall. In the prototype, two ducts embedded in the wall contain staggered tube bundles filled with PCM, which are positioned perpendicular to the airflow to recover heat for supply and exhaust ventilation modes. The thermal performance of this prototype is investigated for different operating times, namely, 15, 20, and 30 min. The average air energy change of the latent heat recovery ventilation system values is between 20 and 35 kJ approximately for the operating times. The supply mode efficiency result is an average of 50% and exhaust mode efficiency is 25%. © 2021 Elsevier LtdArticle Citation - WoS: 10Citation - Scopus: 12Transparent block copolymer thin films for protection of optical elements via chemical vapor deposition(Elsevier Ltd, 2018) Karabıyık, Merve; Ebil, ÖzgençIn this study, glycidyl methacrylate and 1H, 1H, 2H, 2H-perfluorodecyl acrylate copolymer p(GMA-co-PFDA) thin-films fabricated via Initiated Chemical Vapor Deposition (iCVD) were investigated as protective coatings on optical BK7 glass substrates and commercial optical filters. Durability tests based on military standards MIL-F-48616 and MIL-C-48497A were performed to evaluate performance of coatings for the protection of surfaces of optical elements. Cross-linked p(GMA-co-PFDA) copolymer coatings successfully passed all durability tests showing excellent mechanical properties and protection against humidity, salt water, swelling in water, and resistance to organic solvents while providing excellent adhesion to substrate. iCVD process enabled fine tuning of film morphology, mechanical properties and hydrophobicity by controlling the process parameters. Fabricated films were hydrophobic and highly transparent (>98%) in the wavelength range from 300 nm to 1000 nm. Optical transmittance measurements before and after coating process proved that while providing chemical and physical protection, p(GMA-co-PFDA) copolymer thin-films do not cause any detectable change in optical performance of commercial narrow band and wide band filters.Article Citation - WoS: 42Citation - Scopus: 55Processing of Clear and Turbid Grape Juice by a Continuous Flow Uv System(Elsevier Ltd, 2016) Kaya, Z.; Unluturk, S.The inactivation of inoculated (S. cerevisiae) and spoilage microorganisms, i.e. yeasts and lactic acid bacteria (LAB), in clear and turbid grape juice was investigated using a pilot scale UV system. The biodosimetry method was used for UV dose prediction in a continuous flow UV reactor. Weibull model was applied for fitting the inactivation data. The flow rates (774, 820 ml/min) in this system were very close to the ones used in fruit juice processing. S. cerevisiae in clear juice was reduced by 3.39 ± 0.04 at 65.50 mJ/cm2 of UV dose. 1.54 ± 0.04 and 1.64 ± 0.03 log CFU/ml reductions were obtained for spoilage yeasts and LAB in turbid juice at UV dose of 78.56 and 67.97 mJ/cm2, respectively. The soluble solids (°Brix) and pH of grape juice samples were not affected by UV-C treatment (p > 0.05). Although the color parameters slightly were changed after irradiation, the color of PCGJ and FSTGJ did not show visual difference compared to the untreated samples. Industrial relevance: UV light has a potential to reduce the levels of microbial contamination in liquid foods. Although grape juice has many beneficial health effects, it has a fairly short shelf life. Therefore, pasteurization is required. But the thermal pasteurization has some undesired effects on the juice quality. Consumer demands for high quality fruit juice with fresh-like characteristics have markedly expanded in recent years. In the current study, the microbial inactivation efficiency of a pilot scale UV system for non-thermal treatment of clear and turbid grape juice was evaluated under conservative conditions. Most of the physicochemical properties of grape juice samples were not significantly affected from UV-C treatment (p > 0.05). This would be a major advantage in the processing of nutritious juice products. © 2015 Elsevier Ltd. All rights reserved.Article Citation - WoS: 93Citation - Scopus: 6Natural Gas Fueled Compression Ignition Engine Performance and Emissions Maps With Diesel and Rme Pilot Fuels(Elsevier Ltd, 2014) Imran, Shahid Mohammed; Emberson, David Robert; Díez, Alvaro; Wen, Dongsheng; Crookes, Roy James; Korakianitis, Theodosios P.When natural gas is port/manifold injected into a compression ignition engine, the mixture of air and the natural gas is compressed during the compression stroke of the engine. Due to the difference in the values of specific heat capacity ratio between air and natural gas, the temperature and pressure at the time of pilot fuel injection are different when compared to a case where only air is compressed. Also, the presence of natural gas affects the peak in-cylinder (adiabatic flame) temperature. This significantly affects the performance as well as emissions characteristics of natural gas based dual fueling in CI engine. Natural gas has been extensively tested in a single cylinder compression ignition engine to obtain performance and emissions maps.Two pilot fuels, diesel and RME, have been used to pilot natural gas combustion. The performance of the two liquid fuels used as pilots has also been assessed and compared. Tests were conducted at 48 different operating conditions (six different speeds and eight different power output conditions for each speed) for single fueling cases. Both the diesel and RME based single fueling cases were used as baselines to compare the natural gas based dual fueling where data was collected at 36 operating conditions (six different speeds and six different power output conditions for each speed). Performance and emissions characteristics were mapped on speed vs brake power plots. The thermal efficiency values of the natural gas dual fueling were lower when compared to the respective pilot fuel based single fueling apart from the highest powers. The effect of engine speed on volumetric efficiency in case of the natural gas based dual fueling was significantly different from what was observed with the single fueling. Contours of specific NO<inf>X</inf> for diesel and RME based single fueling differ significantly when these fuels were used to pilot natural gas combustion. For both of the single fueling cases, maximum specific NO<inf>X</inf> were centered at the intersection of medium speeds and medium powers and they decrease in all directions from this region of maximum values. On the other hand, an opposite trend was observed with dual fueling cases where minimum specific NO<inf>X</inf> were observed at the center of the map and they increase in all direction from this region of minimum NO<inf>X</inf>. RME piloted specific NO<inf>X</inf> at the highest speeds were the only exception to this trend. Higher specific HC and lower specific CO<inf>2</inf> emissions were observed in case of natural gas based dual fueling. The emissions were measured in g/MJ of engine power. © 2021 Elsevier B.V., All rights reserved.