Natural Convection Heat Transfer Enhancement using Functionalized Nanodiamonds in Transformer Oil

Efficient transformer cooling is an important factor in increasing the lifetime of transformer and reducing the associated maintenance costs. It has been reported that the lifetime of the transformer is increased by 10% with 1 °C decrease in the core temperature. The transformer oil which is a typically a mineral oil, used commonly in cooling of transformers has an inherent disadvantage of low thermal conductivity. This limits the amount of heat transfer from the core of the transformer to the surroundings. This research discusses the improvement of thermal conductivity of transformer oil by using functionalized nanodiamond (fND) particles in transformer oil. In this study, enhancement in natural convection heat transfer is studied by using two different concentrations (0.2 wt.% and 0.4 wt.%) of fND in transformer oil and compared with the base transformer oil. A tall container insulated from all sides and heated from one side is considered for the experiment's geometry. The natural convection is observed in the container and the experimental results are validated with the theoretical model. The observed enhancement in heat transfer coefficient for 0.2 wt.% sample was 41.7% and for 0.4 wt.% sample was 82.5%.