Compared to a conventional liquid and conventional two-phase mixture, the nanofluid has higher thermal conductivity, does not block flow channels, and induces a very small pressure drop. Solid particles are added as they conduct heat much better than a liquid. In this paper, theoretical prediction and experimental values of nanofluids thermal conductivity, which has been filled by TiO2, SiO2, and Al2O3, has been compared. However, nanoparticle of SiO2 was synthesized by plasma, but TiO2 and Al2O3 were synthesized by a chemical vapor deposition process. Thermal conductivity of nanofluids was measured with a transient hot wire method, which is one of the most accurate methods for determining thermal conductivity of fluids. The result has shown, the surface-to-volume ratio of nanoparticles is a principle factor in determining thermal conductivity of nanofluids. In addition, the thermal conductivity of SiO2 nanofluids is almost linearly increased with increasing particle volume fraction. Moreover, the thermal conductivity enhancement of water-based SiO2 nanofluid is increased up to 23% at a volume fraction equal four

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