Numerical and experimental study on cooling enhancement of a high-power linear alternator for free-piston Stirling machines

Free-piston Stirling machines (FPSMs) require efficient thermal management of the high-power linear alternator (HPLA) to ensure stability and longevity under high-load operation. In this study, a combined numerical-experimental approach was adopted to investigate cooling enhancement strategies for a HPLA. Baseline CFD simulations revealed severe non-uniformity in internal gas flow, leading to local hot spots near coils and magnets. To address this, structural modifications including flow-blocking baffles, perforations, and asymmetric flow-control elements were proposed. The optimized design increased convective heat transfer coefficients of coil and magnet walls by over 10%, reducing their maximum temperatures by 32.5 K and 13.2 K, respectively. Quasi-one-dimensional modeling of SAGE, validated against CFD, enabled rapid parametric analysis of channel geometries and asymmetric pressure differentials, identifying an optimal unidirectional pressure difference of 1000 Pa that maintained gas temperature rise within 10 K at a marginal power cost of 12.3 W. Preliminary experiments further confirmed the effectiveness of the proposed strategy: although absolute temperatures were higher than predicted due to larger heat generation and housing thermal resistance, the modifications successfully homogenized the internal temperature field and prevented critical hot-spot risks. The results demonstrate a practical pathway for enhancing HPLA cooling, offering valuable guidance for the thermal design of high-power FPSMs. • A combined numerical and experimental approach was developed for thermal design. • Flow-blocking baffles and perforations reduced peak temperatures by up to 32.5 K. • Gas diodes induced unidirectional streaming to enhance cooling with low energy use. • Experiments confirmed nearly uniform temperature fields with <1 K variation.