Influence of the Thermophysical Model on the CFD Analysis of Oil-Cooled Transformer Windings

A disc-type winding of an oil-immersed power transformer is modeled with Computational Fluid Dynamics. Different approaches are implemented to evaluate the feasibility of the Boussinesq approximation: (i) constant fluid properties, (ii) variable viscosity and thermal diffusivity and (iii) temperature-dependent fluid properties. Temperature and flow distributions are reconstructed and put into relation with physical phenomena and model assumptions. Their comparison suggests that numerical results are fairly sensitive to the thermophysical model as long as the buoyancy force is a relevant component of the flow. Nonetheless, all the cases converge to very close predictions of the hot-spot value and location, with possibly positive implications for the use of reference parameters when deriving flow and heat transfer correlations for this topic.