Due to their potential use as an insulating oil as well as an improved thermophysical heat transfer fluid, nanofluids have attracted a lot of attention in recent years. Modern power networks rely heavily on mineral oil, which is employed as insulating and heat-transfer fluids.Nanofluids based on transformer oil are being investigated as an alternative to regular mineral oil. In this case Multi-Walled Carbon Nano Tubes are considered to study enhanced thermophysical properties of transformer oil, IS 335. Properties at four different concentrations for MWCNT will be studied for flow rate varying from 0.5 lpm to 1.25 lpm (Natural Convection). Results of this project can be used to develop a new class of transformer fluid for ONAF power transformers. Set up of this project is designed to help further studies in oil based nanofluid for various cooling applications. This report discusses the results of mathematical model for oil based nanofluid and they are compared with the results obtained by the CFD model and experimental trials.