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Demir Aydin M.,Ataturk University | Akpinar S.,Technical University of Erzurum
International Journal of Adhesion and Adhesives | Year: 2014

In this study, mechanical properties of different T-joint configurations with embedded or non-embedded supports, subjected to tensile loading, were investigated experimentally and numerically. For this purpose, experimental studies were conducted on two different types of T-joint samples produced by using an adhesive film. Stress analyses in the T-joints were performed with a three dimensional non-linear finite element method by considering the geometrical non-linearity and non-linear material behaviors of both adhesives (FM73) and adherend (AA2024-T3). In conclusion, it can be stated that the variation of the geometry of the bonding zone, where the support was embedded, changed the stress distributions on the adhesively bonded joint. Accordingly, these variations had a strong impact on stress concentrations, the load bearing capacity and prolonged performance of these joints. © 2013 Elsevier Ltd. Source

Omeroglu G.,Bayburt University | Comakli O.,Ataturk University | Karagoz S.,Ataturk University | Sahin B.,Technical University of Erzurum
The Scientific World Journal | Year: 2013

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. Source

Omeroglu G.,Bayburt University | Comakli O.,Ataturk University | Karagoz S.,Ataturk University | Manay E.,Technical University of Erzurum
Energy Education Science and Technology Part A: Energy Science and Research | Year: 2012

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. Source

Akpinar S.,Technical University of Erzurum
Composites Part B: Engineering | Year: 2014

Peel stresses developing at the edges of the overlap area of the adhesively bonded single lap joints subjected to static tensile loading have a profound effect on the damage of the joint. The reduction in the stress values formed at the edges of the overlap area or the transfer of these stresses to the middle part of the overlap area increase the strength of the joint. In this study, mechanical properties of the single lap joint (SLJ), one step lap joint (OSLJ) and three step lap joint (TSLJ) subjected to tensile loading were examined experimentally and numerically by keeping the bonding area same for all samples examined. In the samples produced for experimental study, AA2024-T3 aluminum alloy was used as adherent, while a flexible adhesive SBT9244 and a stiff adhesive DP460 were applied separately. After experimental studies on the three different joint types were conducted, stress analyses in the joints were performed with a three-dimensional finite element method by considering the geometrical non-linearity and the material non-linearities of the adhesive and adherend. As a result, it was observed that one-step lap geometry reduces the stress concentration developing at the edges of the overlap area while the highest decrease occurred in the three-step lap geometry. Additionally, the amount of reduction in the stress values supports the increase in the experimentally obtained load carrying capacity of the joint. © 2014 Elsevier Ltd. All rights reserved. Source

Sahin B.,Ataturk University | Gultekin G.G.,HIGH-TECH | Manay E.,Technical University of Erzurum | Karagoz S.,Ataturk University
Experimental Thermal and Fluid Science | Year: 2013

In this study, the steady state turbulent convective heat transfer and pressure drop characteristics of Al2O3-water nanofluid inside a circular tube were investigated experimentally. The effects of the volume fraction and Reynolds number were determined under constant heat flux. The results of the heat transfer and pressure drop characteristics with respect to appropriate variables were presented. It was observed that the heat transfer increased with the increase of Reynolds number. The heat transfer increased with an increase in the volume concentration With the exception of the particle volume concentrations of 2 and 4vol.%. The highest heat transfer enhancement was achieved at Re=8000 and f{cyrillic}=0.005. © 2013 Elsevier Inc. Source

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