خواص رئولوژي نانو سيالات حاوي نانو لوله هاي كربني در مخلوط اتيلن گليكول و پروپيلن گليكول

چكيده انگليسي :

Rheological behavior of nanofluids containing MWCNTs in binary mixture EG and PG Samira Dadi Email samiradadi@yahoo com 22 11 2010 Department of Chemistry Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Y Ghayeb E mail ghayeb@cc iut ac ir E Keshavarzi Email Keshavrz@cc iut ac ir Abstract The object of this research is studying the viscosity of nanofluids and the effective factors on it such as temperature shear rate concentration of nanotubes sonication time and the composition of base fluid We know that mainly applications of nanofluids associated with their heat transfer properties However the most benefit nanofluids for these applications are the nanofluids with higher heat transfer coefficient Since carbon nanotubes have high thermal conductivity in this project have been used for synthesis of nanofluids with binary mixture of ethylene glycol and propylene glycol Nanofluids have prepared with chemical and mechanical methods containing chemical treatment and ultrasonic homogenization To prepare more stable nanofluids samples are sonicated for optimum sonication time The results show that the viscosity of the nanotube suspension first increased with sonication time until it reached a maximum and then decreased Whereas this increase and decrease in viscosity is due to breaking the aggregates of MWCNTs and bricking of them respectively optimum sonication time has the maximum value of viscosity Because with bricking and shorting of nanotubes the aspect ratio of them decreases that caused to decrease in thermal conductivity of nanofluids In these experiments we have seen that with increasing the concentration of nanotubes not only the viscosity of nanofluids increase but also the optimum sonication time increases Viscosity measurements of nanofluids afterwards that sonication stopped until one month show that the stability of nanofluids decreases with loading of nanotubes Viscosity measurements of nanofluids in different concentration of nanotubes with increase temperature show that nanofluids viscosity increased considerably with the nanotube loading but clearly decreased with temperature that is due to decrease in shear stress that cussed to the fluid s layers move easily therefore the viscosity of fluids decreases This results show that in low concentration of nanotubes the relative viscosity of nanofluids is independent of temperature but with increase in concentration of nanotubes dependence of viscosity to temperature increase too In high concentration of nanotubes relative viscosity of nanofluids decreases with temperature We have studied also effect of shear rate on the viscosity of nanofluids This studies show that the viscosity of base fluid is invariant with shear rate But it is notable that at a fixed concentration of CNT viscosity of nanofluids decreased with shear rate that is due to the decrease in shear stress However nanofluids have been shown a shear thinning behavior Therefore the non Newtonian behavior of nanofluids arises from the aggregation of CNTs in the samples Moreover these results show that with increase in concentration of nanotubes dependence of viscosity to shear rate increase In addition we have studied viscosity of these nanofluids with composition of base fluid Our results show that the viscosity of nanofluids increase with volume fraction of PG in the base fluid Also Because of the decreasing in polarity of base fluid at high volume fraction of PG dispersibility of CNTs decreased and therefore the optimum sonication time increased Moreover it has been found that dependence of viscosity to shear rate and temperature increase at high volume fraction of PG in base fluid These results also show that nanofluids with high volume fraction of PG are more stable Key Words nanofluid nanotube propylene glycol ethylene glycol viscosity

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خواص رئولوژي نانو سيالات حاوي نانو لوله هاي كربني در مخلوط اتيلن گليكول و پروپيلن گليكول

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