Convective heat transfer analysis of a laminated flux focusing magnetic gearbox

Abstract

Magnetic machine designers must consider a variety of mechanical and thermal aspects, particularly as the size increases and the air-gaps between rotors and stators decrease. In these instances, increased losses due to eddy currents can create elevated temperatures, which in turn create significant thermal deformation of components that compromises component positioning or magnetic material degradation. Lump capacitance and conduction methods are traditionally used in magnetic machines, but the fluid behavior is ignored. A coupled (conduction/convection) approach, where both convection and conduction heat transfers are considered in the domain, in a 3D flow and conjugate heat transfer analysis, is developed for the fully laminated magnetic gearbox, (1:4.25 gear ratio) to numerically investigate the effect of fluid properties on the thermal results. The numerical results are validated using experimental measurement data. The comparison between the coupled and conduction methods with experimental results shows higher accuracy for the coupled method compared to the conduction method, as the air trapped in the gaps is modeled as a fluid, which is more realistic way compared to the approximation of it with a solid part. This results in the coupled conduction/convection method over-predict the outer rotor temperature by only 2.5 K on average (over 29–123 rpm rotational velocity range), compared to the 5.5 K average over-prediction for the simple conduction method. The eddy current losses created by the travel of magnetic field in the conductive materials inside the active region of a magnetic gear corresponds for the main source of losses in these systems. A detailed loss analysis on the components, followed by the analysis of the structural deformation caused by temperature rise provides the designers with an insight into the material selection and structural design criteria to avoid off-the-range thermal stresses, temperatures and corresponding deformations in such systems.