Convective heat transfer in liquid metal flows with non uniform and time varying magnetic fields

One of the most effective ways to improve the efficiency of a gas turbine cycle is to increase the Turbine Inlet Temperature (TIT). Nowadays, commercial gas turbines employ air-cooling techniques to fulfill this aim and to keep the blades material under acceptable level for thermal and mechanical resistance. Since air has poor heat transfer properties, a better cooling is achievable using liquids. Among all, liquid metals have been studied in the past and deemed to have the highest heat transfer potentials, capable to reach even the highest values of TIT. However, past researches were abandoned due to different problems encountered in practical applications. This work focuses its attention on the further characteristic of liquid metals of being electrically conducing media. This peculiarity might be exploited to provide a heat transfer enhancement in the cooling channels. Indeed, if subjected to the action of a magnetic field, a liquid metal can show alterations in the flow field that cause modifications in the temperature field and, consequently, in the heat transfer. In particular, this thesis work analyzes the heat transfer effects produced by means of a non-uniform and time-varying magnetic field. The magneto-hydrodynamics of a liquid Lithium flow is studied through the use of an academic code initially developed at the Delft University of Technology and subsequently modified to account for a time-varying magnetic field. The code simulates a flow of liquid lithium between two heated and electrically insulating parallel plates, which is subjected to a nonuniform magnetic field with a sinusoidal law in time. Ideal AC current-carrying wires generating this field are located under the lower plate. A parametric study is conducted, showing the effects of frequency and of the Stuart number on heat transfer. A critical evaluation of results in terms of Nusselt number profile and friction factor is performed and results are compared to the ones obtained with the use of a steady magnetic field.