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Article Citation - WoS: 27Citation - Scopus: 31Experimental Investigation of Surface Roughness Effects on the Flow Boiling of R134a in Microchannels(Elsevier Science inc, 2016) Jafari, Rahim; Okutucu-Ozyurt, Tuba; Unver, Hakki Ozgur; Bayer, OzgurThis study experimentally investigates the effect of surface roughness on the hydrodynamic and thermal performance of microchannel evaporators. Three micro-evaporators of the same dimensions and different surface roughness have been fabricated by micro-WEDM. Each micro-evaporator consists of forty rectangular microchannels of 700 mu m height, 250 mu m width, and 19 mm length. A microscale vapor compression refrigeration cycle has been constructed to carry out the experiments. R134a is used as the refrigerant. Heat transfer coefficient, pressure drop and COP results are presented at variously imposed heat fluxes, and at mass fluxes of 85 and 200 kg/(m(2)s). The results demonstrate up to 45% enhancement in the two-phase heat transfer coefficient at low to moderate heat flux values as the surface roughness increases. Considering the surface roughness effect of the microchannel walls, a new correlation is developed to predict the heat transfer coefficient of R134a boiling in microchannels. (C) 2016 Elsevier Inc. All rights reserved.Article Citation - WoS: 37Citation - Scopus: 43Slot milling of titanium alloy with hexagonal boron nitride and minimum quantity lubrication and multi-objective process optimization for energy efficiency(Elsevier Sci Ltd, 2020) Osman, Khaled Ali; Yilmaz, Volkan; Unver, Hakki Ozgur; Seker, Ulvi; Kilic, Sadik EnginThe implementation of sustainable manufacturing techniques to make machining processes more eco-friendly is a challenging topic that has attracted significant attention from the industrial sector for many years. As one of the dominant manufacturing processes, machining can have a considerable impact in terms of ecology, society, and economics. In certain areas, this impact is a result of using certain cutting fluids, especially during the machining of difficult-to-cut alloys such as titanium, where a large amount of cutting fluid is wasted to ease the cutting process. In such scenarios, identifying suitable machining conditions to supply cutting fluids using eco-friendly techniques is currently a major focus of academic and industrial sector research. In this study, effects of minimum quantity lubrication with different concentrations of hexagonal boron nitride nanoparticles on the surface roughness and cutting force of slot-milled titanium alloy is investigated using analysis of variance and response surface methodology. The results reveal that all responses are sensitive to changes in the feed per tooth, cutting depth, and cutting fluid flow rate. The regression functions generated were combined with particle swarm optimization in order to improve energy-efficiency, as well. Possible sectorial scenarios were generated for wider industrial adoption. With this study, it was proven that utilizing minimum quantity lubrication with hexagonal boron nitride nanoparticles can reduce both cutting force and surface roughness, which makes it to be a promising alternative as a nanoparticle augmented minimum quantity lubrication method for machining titanium alloys. (C) 2020 Elsevier Ltd. All rights reserved.Article Citation - WoS: 19Citation - Scopus: 20A Framework for Energy Reduction in Manufacturing Process Chains (e-Mpc) and a Case Study From the Turkish Household Appliance Industry(Elsevier Sci Ltd, 2016) Uluer, Muhtar Ural; Unver, Hakki Ozgur; Gok, Gozde; Fescioglu-Unver, Nilgun; Kilic, Sadik EnginEnergy is a major input in the manufacturing sector. Its security and efficiency are of supreme importance to a nation's industrial activities. Energy consumption also has serious environmental impacts in terms of Greenhouse Gas (GHG) emissions. In order to use energy more efficiently, simply designing parts and planning manufacturing processes with an energy-aware mindset is insufficient; it is also necessary to model and assess the energy efficiency of a process chain from a holistic point of view. In this work, we propose an integrated energy reduction framework and the internal methods to implement it. Our framework builds on three pillars. Creating an energy profile of a process chain is the first step in characterizing a manufacturing system in terms of energy demand. Energy-aware part designs and process plans are based on ISO/STEP 10303 AP224 standards in order to estimate the embodied energy of a mechanical part. Finally, using discrete event simulation methods, the energy consumption of a process chain is assessed and reduction scenarios are generated based on design or operational alternatives. A data collection and analytics system visualizing measures and key performance indicators (KPIs) also must be implemented in order to measure real consumption values and track improvement results over time. The energy reduction in manufacturing process chains (E-MPC) framework is unique in that it provides a structured method which enables the embodied energy of a part to be estimated during early design stages and further enables the evaluation of design impacts on process chains, thereby recognizing the dynamic nature of systems. A pilot case study of the framework was implemented at the largest household appliance manufacturer in Turkey, Arcelik A.S. In order to evaluate its usefulness and validity, we performed a detailed implementation on a fully automated crankshaft manufacturing line in Arcelilc's refrigerator compressor plant. The results reveal that design improvements estimated gains would reach 2%, whereas operational improvements yield up to 10% energy savings per produced part. (C) 2015 Elsevier Ltd. All rights reserved.
