A compact compander is suitable for reverse Brayton air-cycle chillers with severe space constraints. In the present compact compander, the 114 °C compressor, the heat-generating permanent magnet synchronous motor (PMSM), and the -54 °C expander are arranged within an axial span of 300 mm inside the compander, resulting in about 2580 W of axial heat leakage to the expander. This leakage raises the expander-side refrigerant temperature by approximately 7 °C and reduces the chiller COP by about 30% compared with the case without axial heat leakage. However, studies that explicitly identify thermal interference in companders and provide thermal management strategies to mitigate it remain limited. In this study, two thermal management strategies are considered to address this thermal interference: thermal insulation near the expander and external housing cooling. While highly effective insulation suppresses heat leakage but aggravates internal overheating, requiring impractically strong external cooling. To quantify this trade-off and identify practical combinations of insulation thermal conductivity and thickness and external convective heat transfer coefficient (HTC), a lumped parameter thermal network (LPTN) model of the compander is developed and used to screen the thermal design space. The analysis shows that using a 20 mm PEEK insulation layer with a thermal conductivity of 0.23 W/m ⋅ K, together with external cooling that provides an HTC of about 200 W/m 2 ⋅ K, can limit COP degradation to within 3% while keeping the PMSM winding temperature below 130 °C, the thermal limit of the winding. In addition, a fin-equipped compander can further reduce the required HTC to approximately 30 W/m 2 ⋅ K. These results provide practical guidelines for managing the trade-off between COP degradation and winding overheating and demonstrate that the LPTN model is an effective tool for rapid design-space screening of thermally constrained compact companders. • The coupled thermal issues of COP degradation and winding overheating are addressed. • The LPTN model is 2600 times faster than FEM, with only 2.2% energy balance error. • Thermal insulation reduces COP degradation from approximately 30% to 3%. • With insulation and external air cooling, the winding is maintained below 130 °C.
Jeong et al. (Sun,) studied this question.