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    Effects of using vortex tubes on events during cold start of a direct injection diesel engine
    (Amer Inst Physics, 2013) Celik, Adem; Ceviz, Mehmet Akif; Yilmaz, Mehmet; Oner, Ilhan Volkan; Karagoz, Sendogan
    Vortex tubes use a compressed gas flow and separate it into low and high temperature regions without using any moving mechanical parts. Cold and hot exhaust flows of vortex tubes can be used for different purposes. In this study, a vortex tube was used to improve the cold start performance of a six cylinders, four stroke and direct injection diesel engine of a truck. To increase the engine intake air temperature, hot exhaust of vortex tube was introduced to the engine intake manifold. Pressured air was supplied to the vortex tube from the air tank of the compressed-air brake system of the truck. Variation in the cold starting events was observed by both in cylinder pressure data and revolution of engine crank shaft. Experiments were started when the ambient air and engine cooling fluid temperatures were at 0 degrees C, which is a critical temperature for cold-starting diesel engines. Experimental results showed that the cold starting performance of the engine can be successfully improved by using vortex tubes. Durations of engine starting-cranking, cranking-idling, and idling-stabling were decreased due to the increase in the intake air temperature. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4798489]
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    Performance and entropy production analysis of angle blade turbulators used to increase heat transfer
    (Springer, 2023) Firat, Ilker; Karagoz, Sendogan; Yildirim, Orhan; Yilmaz, Mehmet
    In this study, the effects on thermal performance and entropy production of new type turbulators with different blade angles and numbers, which are placed in a circular shaped pipe and manufactured in a 3D printer, were investigated experimentally. According to the experiments performed in the Reynolds number (Re) range of 7007-13,982, the Nusselt numbers of the 60 degrees, 70 degrees and 80 degrees fin angle turbulators are, respectively, compared to the supported plain pipe; increased by 82.09%, 98% and 105.83%. Due to the increase in the blade angle, the maximum thermal performance was obtained as 1.542 for the 80 degrees blade angle turbulator for Re = 12,538. The thermal performance factors of the 80 degrees and 70 degrees blade angle turbulators were found to be 1.048 and 1.039 times higher than the 60 degrees blade angle turbulators, respectively. It was determined that the thermal improvement factor of the 80 degrees blade angle turbulator is 1.008 times higher than the 70 degrees blade angle turbulator. In terms of the second law, the maximum entropy production increase of the finned turbulators compared to the supported plain pipe was 153.96% at Re = 8387, in 3 turbulators with 80 degrees fin angles. It has been determined that 1 turbulator model with 60 degrees blade angles is more advantageous compared to the turbulators with 70 degrees and 80 degrees blade angles, since it produces the lowest entropy. In addition, it has been concluded that the most suitable turbulator model in terms of thermal performance is 3 turbulators with 80 degrees blade angles.