Nanofluid is a fluid mixing nanometer-sized particles, called nanoparticles. These fluids are engineered colloidal suspensions of nanoparticles in a base fluid. Nanoparticles which are commonly used in nanofluids are made from numerous materials such as oxide ceramics (Al2O3,CuO),nitride ceramics (AlN ,SiN),carbide ceramics (SiC,T iC),metals (Cu,Ag,Au),semiconductors (T iO2,SiC),carbon nanotubes; and composite materials such as alloyed nanoparticles, Al70Cu30 or nanoparticle core-polymer shell composites. In addition, nonmetallic, metallic, and other materials for nanoparticles, completely new materials and structures may also have desirable characteristics. Common base fluids include water (H2O), ethylene glycol (EG), engine oil (EO), pump oil and glycerol have been used as host liquids in nanofluids. Enhancing thermal conductivity of liquids, concepts of nanofluids, modeling on suspensions are the most recent approach in more than a century of work. The low thermal conductivity of conventional heat transfer fluids (HTFs)is a serious constraint in improving the performance and compactness of engineering equipment. The notion of particles which can convert from millimeter to micrometer sized in the late 19th century has become a part of the modern adventure into the new realm of the very small: the world of nanoparticles. Particularly, nano fluids are a new noble class of nanotechnology-based heat transfer fluid that are engineered by stably suspending a small amount, 1 volume % or less of particles with lengths on the order of in traditional heat transfer fluids. In the commencement of 1990s, Choi had anticipated the impression of the emergence of novel class of fluid and the term 'nanofluids' (Choi ). The working together of two things to produce an effect greater than the sum of their individual effects is the key to success of nanofluids. The result is a matching set of remarkable thermal properties that have motivated students, scientists, and engineers around the world to undertake the challenge of exploring the possibilities of these captivating fluids.