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Öğe Experimental research of dynamic instabilities in the presence of coiled wire inserts on two-phase flow(2013) Omeroglu G.; Comakli O.; Karagoz S.; Sahin B.The aim of this study is to experimentally investigate the effect of the coiled wire insertions on dynamic instabilities and to compare the results with the smooth tube for forced convection boiling. The experiments were conducted in a circular tube, and water was used as the working fluid. Two different pitch ratios (H / D = 2.77 and 5.55) of coiled wire with circular cross-sections were utilised. The constant heat flux boundary condition was applied to the outer side of the test tube, and the constant exit restriction was used at the tube outlet. The mass flow rate changed from 110 to 20 g/s in order to obtain a detailed idea about the density wave and pressure drop oscillations, and the range of the inlet temperature was 15-35°C. The changes in pressure drop, inlet temperature, amplitude, and the period with mass flow rate are presented. For each configuration, it is seen that density wave and pressure drop oscillations occur at all inlet temperatures. Analyses show that the decrease in the mass flow rate and inlet temperature causes the amplitude and the period of the density wave and the pressure drop oscillations to decrease separately. © 2013 Gokhan Omeroglu et al.Öğe The merrifield-simmons indices of 2-methyl alkanes and 1-methyl bicyclo(Editura Academiei Romane, 2017) Gültekin I.; Sahin B.In this paper the Merrifield-Simmons indices of the 2-methyl alkanes and the 1-methyl bicyclo [X.1.0] alkanes are obtained. After that, the Merrifield-Simmons index of the binary compositions of these molecules which are connected with a single carbon atom are obtained. © 2017 Editura Academiei Romane. All Rights Reserved.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 Ltd
