Nanofluid is a novel heat transfer fluid prepared by suspending solid nanoparticles in a traditional fluid. The most important feature observed in nanofluids is an abnormal rise in thermal conductivity, far beyond expectations and much higher than any theory could predict [1]. The thermal conductivity of nanofluids is a strongly increasing function of temperature, much more than that of pure liquids. The large surface area of nanoparticles allows for more heat transfer. Also, the mobility of the particles attributes to the tiny size, increases heat transfer. The abnormal increasing the thermal conductivity of nanofluids with a rise in temperature may be attributed to the above reasons. Research on the abnormal enhancement of thermal conductivity of nanofluids has been carried out experimentally and theoretically [2-5]. In the present work, we have prepared the ZnO nanofluids in 2-propanol as a base fluid. The effects of temperature and volume fraction of nanoparticles on the thermal conductivity of these nanofluids have been investigated.

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