Nanofluids are suspensions of high thermal conductivity nanoparticles in a base fluid that offer a potential to enhance thermal conductivity and heat transfer performance of the base fluid. An experimental investigation of the thermo-physical properties (thermal conductivity, viscosity and specific heat), heat transfer performance and pressure loss characteristics of Aviation Turbine Fuel (ATF) based Al2O3, TiO2 , CuO and Multi-walled carbon nanotube (MWCNT) nanofluids has been described. The effects of volume concentration, size and material of suspended particles as well as the effect of the temperature of the nanofluid are explained. The experimental results of thermal conductivity and viscosity indicate influence of Brownian motion of nanoparticles in the base fluid. Two different numerical modelling approaches (a single phase fluid model with enhanced thermo-physical properties and an Eulerian-Lagrangian model called the "discrete phase model") are adopted for understanding the physics of nanofluid. Numerical results of two different modelling approaches are described in this book.