This paper investigates the enhancement of heat transfer coefficient and Nusselt number of a nanofluid containing nanoparticles\n(?-AL2O3) with a particle size of 20nm and volume fraction of 0.1%ââ?¬â??0.3% (V/V). Effects of temperature and concentration of\nnan oparticles on Nusselt number changes and heat transfer coefficient in a double pipe heat exchanger with counter turbulent\nflow are investigated. Comparison of experimental results with valid theoretical data based on semiempirical equations shows an\nacceptable agreement. Experimental results show a considerable increase in heat transfer coefficient and Nusselt number up to\n19%ââ?¬â??24%, respectively. Also, it has been observed that the heat transfer coefficient increases with the operating temperature and\nconcentration of nanoparticles.
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