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Öğe Forced convective two phase flow analysis in a circular tube equipped with twisted tapes(2012) Omeroglu G.; Comakli O.; Karagoz S.; Manay E.In forced convection boiling systems, it is important to know the dynamic behavior for understanding and predicting the local and global stability of the system. Besides this, the instability phenomenon in the industrial processes in which two phase flow takes part becomes more of an issue. So, the mechanisms of instabilities and the ways of decreasing the stabilities are of interest of the researchers for a long time. In this study, the effects of pitch ratio, inlet temperature and the mass flow rate on two phase flow instabilities in a horizontal circular tube are investigated. The experiments are conducted under constant system pressure, and a constant heat input of 24 kW is applied to the outer surface of the circular test pipe having constant exit restriction. The results of two different pitch ratios are also compared with the smooth tube. For all investigated cases, the results are evaluated in terms of pressure drop type and density wave type oscillations. The time dependent measurements of top wall temperature, bottom wall temperature, inlet pressure and mass flow rate variations are also presented. The boundaries of the oscillations are found for both twisted tape and smooth channel. It is found that the unstable region of the flow extends while the distance between boundaries increases. It is observed that the system is more stable in the case of the lowest pitch ratio, and the increase of the pitch ratio causes system to be less stable. By the decrease of the inlet temperature, the single phase liquid region extends in the test tube and thus the system becomes more stable. © Sila Science.Öğe Optimization of design parameters for heat transfer and friction factor in a heat sink with hollow trapezoidal baffles(Elsevier Ltd, 2019) Sahin B.; Ates I.; Manay E.; Bayrakceken A.; Celik C.The aim of this study is to optimize the design parameters of a heat sink on which hollow trapezoidal baffles are mounted on the bottom surface by using Taguchi experimental-design method. The Nusselt number and the friction factor are considered as performance parameters. An orthogonal array is selected as experimental plan for the six parameters: the corner angle (?), the inclination angle (?), the baffle height (H), the baffle length (L), the baffle width (S) and Reynolds number. First of all, each goal has been optimized, separately. Then, all the goals have been optimized together, considering the priority of the goals. The length of the baffle is found to be the most influential parameter on the friction factor. This can be attributed the enhanced effect of longitudinal vortices with baffle length in flow direction. Likewise, it is demonstrated that the most effective parameter on the heat transfer is Reynolds number. The results show that the baffle width (S) and the corner angle (?) have insignificant effect on Nusselt number. The maximum heat transfer was obtained at Re = 17,000, H = 36 mm, L = 45 mm, S = 26 mm, ? = 0°, ? = 0°. The inclination angle (?) and the baffle height (H) have nearly no effect on the friction factor. The minimum friction factor was obtained at Re = 17,000, H = 20 mm, L = 25 mm, S = 26 mm, ? = 16°, ? = 0°. The inclination angle (?) and the baffle height (H) have nearly no effect on the friction factor. It can be concluded that the higher heat transfer rates can be achieved with lower pressure drop penalty with this type of vortex generator in particular configurations. © 2019 Elsevier LtdÖğe The prediction of heat transfer and fluid characteristics for equilateral triangular bodies in tandem arrangement by artificial neural networks(2012) Manay E.; Güneş S.; Akçadirci E.; Özceyhan V.; Çakir U.; Çomakli O.The objective of this study is to investigate the effect of the spacing between equilateral dual triangular bodies symmetrically placed into the channel axis under steady state conditions on heat transfer and fluid characteristics by using artificial neural networks (ANN). The Back Propagation (BP) training algorithm was applied to train the model. The successful application proved that ANN model can be used for predicting the Nusselt number and skin friction coefficient as a convenient and effective method. The distribution of local Nusselt number, skin friction coefficient along the channel wall and overall enhancement ratio of all investigated cases are presented.Öğe A Taguchi approach for optimization of design parameters in a tube with coiled wire inserts(2011) Gunes S.; Manay E.; Senyigit E.; Ozceyhan V.This study presents the determination of the optimum values of the design parameters in a tube with equilateral triangular cross-sectioned coiled wire inserts. The effects of the design parameters such as the ratio of the distance between the coiled wire and test tube wall to tube diameter (s/D), pitch ratio (P/D), ratio of the side length of equilateral triangle to tube diameter (a/D) and Reynolds number (Re) on heat transfer and pressure drop were investigated by using Taguchi method. The Nusselt number and friction factor were considered as performance parameters. An L9(34) orthogonal array was chosen as experimental plan. The goal of this study is to reach maximum heat transfer (i.e. Nusselt number) and minimum pressure drop (i.e. friction factor). First of all, each goal was optimized, separately. Then, all the goals were optimized together, considering the priority of the goals. Contribution ratios for each parameter on the heat transfer and pressure drop were determined. Consequently, the optimum results were found to be s/D = 0.0357, P/D = 1, a/D = 0.0714 and Re = 19800. © 2011 Elsevier Ltd. All rights reserved.
