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    Mixed convection heat transfer of ethylene glycol and water mixture based Al2O3 nanofluids: Effect of thermal conductivity models
    (Elsevier Science Bv, 2016) Ogut, Elif Buyuk; Kahveci, Kamil
    The effect of different nanofluid thermal conductivity models on the mixed convection flow and heat transfer in a lid-driven square enclosure heated from the left vertical wall and cooled from the top wall was investigated numerically in this study for various values of the governing parameters. The Al2O3 was assumed as nanoparticle and ethylene glycol-water mixture as the base fluid. Three different nanoparticle volume fractions were taken into consideration: 0%, 4% and 8%. Four different volume ratios of EG to water were considered: 0:100%, 40:60%, 60:40% and 100:0%. The Grashof number was assumed constant at a value of 104 and the Reynolds number was varied in a range so that the Richardson number takes values in the range of 0.1 to 10. The results show that the average Nusselt number has a linear dependency on the nanoparticle volume fraction for all the thermal conductivity models considered in this study. The results also show that the thermal conductivity models produce considerably different average Nusselt numbers. The results also indicate that the average Nusselt number from the highest to the lowest is for: Pak and Cho model, Yu and Choi model, Ghanbarpour et al. model, Maxwell model, and Timofeeave et al. model. The results finally show that Pak and Cho model yields considerably higher average Nusselt numbers than the other models. (C) 2016 Published by Elsevier B.V.
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    Mixed convection in a lid-driven and inclined square enclosure under a magnetic field
    (Inderscience Enterprises Ltd, 2009) Ece, Mehmet Cem; Ogut, Elif Buyuk
    Steady, laminar, mixed convection flow under the presence of a magnetic field of arbitrary direction in an inclined square enclosure with isothermally heated and moving side walls, and stationary and adiabatic horizontal walls was considered. The governing equations were solved numerically for the stream function, vorticity and temperature using the differential quadrature method for various Reynolds, Grashof and Hartman numbers and inclination angle of the enclosure. The results showed that the movement of the side walls of the enclosure has a significant effect on the flow and temperature fields. Magnetic field applied parallel to the side walls is more effective in reducing the heat transfer rate. Counterclockwise inclination of the enclosure increases the average Nusselt number while clockwise inclination reduces it.
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    Mixed Convection of Water-Based Nanofluids in a Lid-Driven Square Enclosure with a Heat Source
    (Begell House Inc, 2011) Kahveci, Kamil; Ogut, Elif Buyuk
    This study is concerned with mixed convection of water-based nanofluids in a lid-driven square enclosure with a constant heat flux heater. The governing equations are solved numerically using the differential quadrature method. The computational results are obtained for the heater lengths of 0.25, 0.50, and 0.75. The Grashof number is kept at a constant value of 10(4), and the Reynolds number is varied so that the Richardson number will have values in the range of 0.1 to 10. The nanoparticles volume fraction phi is varied as 0%, 5%, and 10% and the value of the ratio of the nanolayer thickness to the original particle radius eta is fixed to 0.1. The results show that the presence of nanoparticles in the base fluid causes a significant enhancement of heat transfer. The results also show that the heat transfer rate increases considerably with a decrease in the Richardson number and the length of the heater.
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    Mixed convection of water-based nanofluids in a square enclosure heated and cooled on adjacent walls
    (Inderscience Enterprises Ltd, 2014) Ogut, Elif Buyuk; Kahveci, Kamil
    This study examines the mixed convection of water-based nanofluids in a lid-driven square enclosure heated from one side and cooled from the stationary adjacent side while the other sides are kept stationary and adiabatic. The conservation equations are solved numerically for the stream function, vorticity, and temperature using the differential quadrature method. The Grashof number is kept at a constant value of 104 in the present study, and the Reynolds number is varied so that the Richardson number will have values in the range of 0.1 to 10. Nanoparticles volume fraction phi is varied as 0%, 5% and 10% and the value of 77 the ratio of the nanolayer thickness to the original particle radius, is fixed to 0.1. The results show that the motion of the side wall and nanoparticle usage has significant effects on the flow and temperature fields. A significant increase in the average Nusselt number is seen with an increase in the volume fraction of nanoparticles and a decrease in the Richardson number.
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    NATURAL CONVECTION OF ETHYLENE GLYCOL AND WATER MIXTURE BASED AL2O3 NANOFLUIDS BETWEEN VERTICAL CONCENTRIC CYLINDERS
    (Turkish Soc Thermal Sciences Technology, 2020) Kahveci, Kamil; Ogut, Elif Buyuk
    Natural convection of ethylene glycol (EG) and water mixture based AL(2)O(3) nanofluids between vertical concentric circular cylinders heated from the inner wall and cooled from the outer wall was investigated numerically in this study. The computations were carried for the Rayleigh numbers of 10(4), 10(5), 10(6), and 10(7), nanoparticle volume fractions of 0%, 4% and 8%, ethylene glycol (EG) to water volume ratios of 0:100 %, 50:50%, and 100:0%, the radius ratios of 2, 3 and 4, and aspect ratios of 0.5, 1, and 2. The Brinkman model was used to predict the viscosity and the Yu and Choi model for the thermal conductivity of nanofluid. The results show that the average Nusselt number shows a considerable increase with an increase in the Rayleigh number and radius ratio. The results also show that the average Nusselt number shows a medium increase with increasing nanoparticle volume fraction and a slight increase with increasing volume ratios of EG to water. Furthermore, the results show that the average Nusselt number experiences first an increase then a decrease with an increase in the aspect ratio except for the low Ra numbers. Finally, the average Nusselt number experiences a slight increase with the aspect ratio for the low Rayleigh numbers.