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Öğe Analysis of pressure distribution of turbulent asymmetric flow in a flat duct symmetric sudden expansion with small aspect ratio(Iop Publishing Ltd, 2004) Canbazoglu, S; Bozkir, OThis paper describes the pressure distribution of turbulent airflow through a flat duct containing one-dimensional symmetric sudden expansion in cross-sectional area encountered frequently in plate heat exchangers and other devices of practical importance. The pressure distributions of turbulent asymmetric airflow through constant width flat ducts having modest expansion ratios of 2, 2.5 and 3, aspect ratios of the expansion of 0.40, 0.26 and 0.20 and modest area ratios of the expansion of 1/3, 1/2.5 and 1/2 were investigated experimentally. The axial and vertical pressure distributions of the turbulent asymmetric flow with relatively small Reynolds numbers (Re-Dh = uD(h)/v = 12 000,4887 and 4125) in downstream cross section of the duct were analyzed. The variations of pressure coefficient with local Reynolds numbers were also investigated. Turbulent flow in flat ducts with symmetric sudden expansion has not sufficiently been studied contrary to axisymmetrical or two-dimensional case for which a large numbers of papers can be found in the literature. This experimental study fulfills this gap and shows that the flow is asymmetric as in a two-dimensional case. It also brings interesting data for numerical simulations for the presented flat duct configurations. These data,concern the axial and vertical distribution of pressure coefficient, the axial velocity in the duct and Reynolds numbers based on the hydraulic diameter, the step height or the local axial distance of the duct. The results obtained complement and extend the previous results, and show that the expansion ratio and Reynolds number affect the flow field. (C) 2004 Published by The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.Öğe Enhancement of solar thermal energy storage performance using sodium thiosulfate pentahydrate of a conventional solar water-heating system(Elsevier Science Sa, 2005) Canbazoglu, S; Sahinaslan, A; Ekmekyapar, A; Aksoy, IG; Akarsu, FThe time variations of the water temperatures at the midpoint of the heat storage tank and at the outlet of the collector in a conventional open-loop passive solar water-heating system combined with sodium thiosulfate pentahydrate-phase change material (PCM) were experimentally investigated during November and then enhancement of solar thermal energy storage performance of the system by comparing with those of conventional system including no PCM was observed. It was observed that the water temperature at the midpoint of the storage tank decreased regularly by day until the phase-change temperature of PCM after the intensity of solar radiation decreased and then it was a constant value of 45 degreesC in a time period of approximately 10 h during the night until the sun shines because no hot water is used. Heat storage performances of the same solar water-heating system combined with the other salt hydrates-PCMs such as zinc nitrate hexahydrate, disodium hydrogen phosphate dodecahydrate, calcium chloride hexahydrate and sodium sulfate decahydrate (Glauber's salt) were examined theoretically by using meteorological data and thermophysical properties of PCMs with some assumptions. It was obtained that the storage time of hot water, the produced hot water mass and total heat accumulated in the solar water-heating system having the heat storage tank combined with PCM were approximately 2.59-3.45 times of that in the conventional solar water-heating system. It was also found that the hydrated salts of the highest solar thermal energy storage performance in PCMs used in theoretical investigation were disodium hydrogen phosphate dodecahydrate and sodium sulfate decahydrate. (C) 2004 Elsevier B.V. All rights reserved.Öğe A model governing the stall characteristics of an isolated axial compressor rotor(Emerald Group Publishing Limited, 2005) Canbazoglu, S; Yilbas, BSPurpose - A stall model to predict the performance of a blade row operating under rotating stall conditions, is proposed. Design/methodology/approach - The experiments were carried out on an isolated rotor row of an axial flow compressor of a radius ratio of 0.66 hub/tip. Wall static pressure tappings were used for measurement of blade row pressure rise. The mass flow rate through the machine was determined from the pressure drop at the intake. Detailed flow measurements were made using a hot wire V probe and transducers. An online data acquisition system was used in which data sampling was phase-locked with respect to stall cell trailing edge. Findings - Measurements indicate that a pressure depression occurs in the stalled region. The assumption of uniform static pressure at the exit of a stalled blade row is not supported by the present work. The assumption of uniform static pressure at the exit of a stalled row together with the assumption that flow in unstalled regions operates at fixed point on the unstalled characteristic leads to the conclusion that total-to-static pressure rise during stalled operation is independent of blockage. This view is not supported by the experiments carried out on an isolated rotor. Research limitations/implications - Additional experimental studies for axial compressors having different rotor and blade geometries and rotor speeds, are required. Practical implications - The results can be used in the design and operation of axial compressor rotors. Originality/value - A new stall model is presented in which the behavior during stalled operation with large blockage is different from that during, low blockage.Öğe A note on the flow coefficients of capillary tube and small orifice restrictors exposed to very low Reynolds number flow(Emerald Group Publishing Limited, 2005) Canbazoglu, S; Canbulut, FPurpose - The main objective of this study was to obtain the flow restricting capacity by determining their flow coefficients and to investigate the unsteady flow with low Reynolds number in the flow-restricting devices such as orifices and capillary tubes having small diameters. Design/methodology/approach - There is an enormous literature on the flow of Newtonian fluids through capillaries and orifices particularly in many application fields of the mechanical and chemical engineering. But most of the experimental results in literature are given for steady flows at moderate and high Reynolds numbers (Re > 500). In this study, the unsteady flow at low Reynolds number (10 < Re < 650) through flow-restricting devices such as orifices and capillary tubes having very small diameters between 0.35 and 0.70 mm were experimentally investigated. Findings - The capillary tubes have much more capillarity property with respect to equal diameter orifices. Increasing the ratio of capillary tube length to tube diameter and decreasing the ratio of orifice diameter to pipe diameter before orifice increase the throttling or restricting property of the orifices and the capillary tubes. The orifices can be preferred to the capillary tubes having the same diameter at the same system pressure for the hydraulic systems or circuits requiring small velocity variations. The capillary tubes provide higher pressure losses and they can be also used as hydraulic accumulators in hydraulic control devices to attenuate flow-induced vibrations because of their large pressure coefficients. An important feature of the results obtained for capillary tubes and small orifices is that as the d/D for orifices increases and the L/d reduces for capillary tubes, higher values C are obtained and the transition from viscous to inertia-controlled flow appears to take place at lower Reynolds numbers. This may be explained by the fact that for small orifices with high d/D ratios and for capillary tubes with small L/d ratios, the losses due to viscous shear are small. Another important feature of the results is that the least variations in C for small orifices and the higher variations in C for capillary tubes occur when the d/D and L/d ratios are smallest. This has favourable implications in hydraulic control devices since a constant value for the C may be assumed even at relatively low values of Re. Originality/value - To the authors' knowledge, there is not enough information in the literature about the flow coefficients of unsteady flows through capillary tubes and small orifices at low Reynolds numbers. This paper fulfils this gap.Öğe Performance and flow-induced vibration characteristics for conical-ring turbulators(Elsevier Sci Ltd, 2004) Yakut, K; Sahin, B; Canbazoglu, SIn the present study, the performance characteristics of the conical-ring turbulators are determined by means of the entropy-generation minimization method based on the second law and enhancement efficiency based on the first law of thermodynamics. The relations between these performance and flow-induced vibration characteristics have been examined. The maximum entropy generation, at the same Reynolds number, occurs in sequence by the conical rings with 10, 20 and 30 mm pitches, respectively. The conical rings are thermodynamically advantageous (N-s,N-a < 1) UP to 8000 Reynolds number with respect to entropy generation. The enhancement efficiency increases as the pitch decreases and varies between 0.86 and 1.16. The turbulators with 20 and 30 mm pitch, especially, produce vortices having low amplitudes up to a Reynolds number of 12,000. (C) 2003 Elsevier Ltd. All rights reserved.Öğe Reduction of peak amplitudes of pressure fluctuations in turbulent pipe flow using vortex generators and compliant boundaries(Taylor & Francis Inc, 2005) Canbazoglu, S; Yakut, KThe effects of vortex generators and compliant boundaries on the reduction of peak amplitudes of pressure fluctuations in a turbulent pipe flow were investigated experimentally. They had important effects on the reduction of peak amplitudes of pressure fluctuations in the model experimental pipe system containing two orifices. The vortex generators having an alternating angle were more effective than the compliant boundaries.Öğe Unsteady thermal performance analysis of a room with serial and parallel duct radiant floor heating system using hot airflow(Elsevier Science Sa, 2004) Bozkir, O; Canbazoglu, SIn this study, the unsteady thermal performance of a test room heated by circulating hot airflow under the floor was analyzed with a developed mathematical model based on heat transfer equilibrium among the air flow, the floor and the indoor air. The time variations in the indoor air temperature for the serial duct floor heating system were investigated theoretically and experimentally. The time variations in the floor surface and the indoor air temperatures were predicted theoretically for the parallel duct floor heating system. Experiments on the time variations of the dimensionless numbers such as Nu for the airflow in duct and the indoor air, Gr for the indoor air and the heat ratios of convection and radiation to total heat for the serial duct floor heating system were performed. The theoretical and experimental results showed a good agreement. (C) 2004 Elsevier B.V. All rights reserved.
