Yazar "Kiliç, Mustafa" seçeneğine göre listele

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    Effects of lubricant fluid with nanoparticle additive on the load capacity of a hydrostatic journal bearing
    (TUBITAK, 2020) Dal, Abdurrahim; Kiliç, Mustafa; Akyüz, Ali Özhan; Tuncer, Azim Doğuş; Gungor, Afsin
    Hydrostatic journal bearings are recommended for supporting shafts operating at high speeds and under heavy loads in the industry. In the journal bearings, lubricant viscosity decreases with increasing temperature at high rotation speeds and hence, the fluid between the surfaces should be circulated using a pump to cool the lubricant. However, the lubricant supplying between the surfaces at the high flow rate causes the whirl instability and vibrations problems in the bearing-shaft system. These instability problems give rise to significant damage on the system during operating at the high speeds and under heavy loads. As a solution to this problem, it could be suggested to control the variation of the lubricant viscosity concerning the temperature by adding nanoparticle. In the present work, the effects of the lubricant with nanoparticle additives on the load carrying capacity of a hydrostatic journal bearing are theoretically investigated. The fluid film flow between the bearing and rotor surfaces are modelled with Reynolds equation and the viscosity term in Reynold’s equation is defined as a function which depends on the nanoparticle properties. Then, the pressure distribution is obtained with solving the film flow equation and the load capacity is calculated for different nanoparticle parameters using this pressure distribution. The results show that the usage of the lubricant with nanoparticle increases the load performance of the hydrostatic journal bearing and the influences of the nanoparticle size on the load performance is more dominant for high volumetric ratio. © 2020, TUBITAK. All rights reserved.
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    NUMERICAL INVESTIGATION OF ENHANCING MIXED CONVECTION HEAT TRANSFER BY USING SEMI-CYLINDRICAL OBSTACLES IN A VERTICAL CHANNEL
    (Turk Isi Bilimi ve Teknigi Dernegi, 2022) Özdemir, Sedat; Kiliç, Mustafa; Çalisir, Tamer; Başkaya, Şenol
    In this study; effects of mixed convection on heat transfer and flow properties was investigated numerically for a vertical channel which has semi-cylindrical obstacles with heat flux. Effects of distance, location and number of these semi-cylindrical obstacles on heat transfer and flow properties have been examined. The effect of one semi-cylindrical obstacle, two semi-cylindrical obstacles located one under the other and two semi-cylindrical obstacles on opposite sides were investigated in the study. As a result; it is obtained that increasing the ratio of the obstacle diameter to the channel width (BR) causes an increase on heat transfer. Increasing BR ratio from 0.15 to 0.75, depending on the increase of Ri number from 50 to 200 causes an increase of 58.3% on average Nu number. Increasing L/D ratio, which represents the distance between obstacles, causes generally an increase in the average Nu number. Increasing L/D ratio from 0.25 to 1.5 results in an increase of 25.2% on the average Nu number. The highest Nu number can be obtained for L/D = 1 and Ri = 300. For the case of two semi-cylindrical obstacles on opposite sides; it was seen that increasing the BR ratio causes an increase in the average Nu number depending on the increase in the Ri number. Increasing BR ratio from 0.15 to 0.30 yields an increase of 36.3% for a low Ri number (Ri=50) and an increase of 23.1% for a high Ri number (Ri = 200) in the average Nu number. Moreover; it has been shown that numerical results can well represent the temperature distribution and flow properties by comparison of these results with experimental results in the literature. © 2022 TIBTD Printed in Turkey.
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    Numerical investigation of heat transfer using impinging jets on triangular and square ribbed roughened walls
    (Turkish Society for Thermal Science and Technology, 2017) Calisir, Tamer; Caliskan, Sinan; Kiliç, Mustafa; Başkaya, Şenol
    This paper presents a heat removal study on triangular and square ribbed surfaces under an array of impinging air jets. The investigation was carried out using nozzles with a 7x3 rectangular array of circular jets. The effect of Re number, jet-to-plate distance, and rib arrangement on heat transfer and fluid flow characteristics was examined numerically. Two arrangements have been studied. Arrangement A considers the situation when the cooling jets are directed towards the ribs, while arrangement B considers the situation when the jets are directed towards the centre line of the cavity between two ribs. Wall jets of neighboring jets have a stronger interaction with increasing Reynolds number. The lowest and highest local heat transfer for all rib geometries was obtained for H/d=8 and H/d=4-6, respectively. On triangular ribbed surfaces the stagnation point Nusselt number values for arrangement A are significantly higher than the stagnation point Nusselt numbers for arrangement B. © 2017 TIBTD Printed in Turkey.