بررسي اثر زاويه و نسبت مشخصه بر ضريب انتقال حرارت جابجايي آزاد نانو سيالات نيوتني در يك محفظه بسته استوانه اي

چكيده انگليسي :

Investigation on the Effect of Slop Angle and Aspect Ratio of Closed Cylindrical Enclosure on the Natural Convection Heat Transfer Coefficient of Newtonian Nanofluid Hamid Moradi H Moradi@ce iut ac ir May 25 2011 Department of Chemical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language Farsi Supervisor Ahmad Moheb Ahmad@cc iut ac ir Seid GholamReza Etemad Etemad@cc iut ac ir Abstract Importance of heat transfer in the industry has been motive axis for improving methods of heat transfer and optimum use of it In recent decades the technology provides a way of making nanoparticles Nano fluid is considered as a new option for heat transfer Discussion on free convection heat transfer of Nano fluids studied by researchers and results in different publications have evaluated The published comparison results in the journals are not consistent with each other much so that the results prognosticate in some cases an increase in heat transfer and in some a decrease for the Nano fluids relative to the base fluid Thus it seems that more researches and investigation in these criteria are important In this study the effect of slope angle and the aspect ratio on free convection heat transfer characteristics of Nano fluids of water and aluminum oxide titanium oxide was investigated Used concentration of Nano fluids in experiments are 0 1 0 2 0 5 and 1 5 of volume percent These Nano fluids were prepared in two stages In this study the cylindrical diameter of 8 cm with variable height to evaluate the aspect ratio height to diameter was used The spec ratios of 0 5 1 and 1 5 for 0 2 concentrated aluminum oxide in water and 0 1concentrated titanium oxide in water were examined Low level of cylindrical test chamber placed under constant heat Flux and high level was kept at constant temperature by the cold water bath Meanwhile to prevent heat transfer through the walls of the cylinder with environment the chamber side walls were insulated For all tested concentrations the slope angle on free convection heat transfer coefficient was more effective in high concentrations Changing the slope angle of 0 degrees to 90 degrees Nusselt number increased after reaching a maximum value will decrease For all the tested concentrations free convection heat transfer coefficient was maximum in slope angle of 30 degrees This trend has been observed in all the Nano Fluid concentrations and intensified in higher concentrations Use higher concentrations of 1 0 volume percent aluminum oxide nanoparticles decreases free convection heat transfer coefficient In all investigated Rayleigh s number this decreasing trend was observed Results show that the inclination angle has effect upon free convection heat transfer for Nano fluid of water titanium oxide Trend of heat transfer depends on the concentration of nanoparticle of aluminum oxide So that for concentrations less than 0 1 volume percent of titanium oxide nanoparticles heat transfer increased with increasing slope angle from 0 to 90 degree after reaching a maximum value heat transfer decreased For Nano fluids of water aluminum oxide in slope angle of 30 degrees free convection heat was maximum But in higher concentration of 0 5 volume percent slope angle effect on heat transfer was less This behavior was observed in all investigated Rayleigh s number Keywords nanofluid free convection heat transfer inclined angle aspect ratio enclosure

مرادي، حميد

بررسي اثر زاويه و نسبت مشخصه بر ضريب انتقال حرارت جابجايي آزاد نانو سيالات نيوتني در يك محفظه بسته استوانه اي

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