Thermal performance analysis of the multi-layer insulation in radioisotope thermophotovoltaic systems

For the radioisotope thermophotovoltaic (RTPV) system, enhancing the temperature of the system's heat source is of great significance. Currently, multi-layer insulation (MLI) is commonly used as a thermal insulation material in the RTPV system. This study proposes its application to an RTPV system without considering PV cells, focusing on the thermal insulation effect. The fraction of input power not absorbed by the MLI is proposed as the key parameter for evaluating thermal performance. First, an RTPV system model with MLIs is designed and compared with the simulated results under the experimental operating conditions. At an input heating power of 240.9 W, the predicted heat source temperature reached 1099.5 °C, compared with a measured temperature of 1099 °C in experiments. Then, the temperature distribution of heat source and MLI are calculated. The temperature trends obtained from the experiments agree well with simulation predictions, implying that the temperature distribution on MLI surface is uneven. Additionally, the thermal performance of the RTPV system resulting from heat source power, number of MLI layers, and number of heat sources is discussed in detail. The results indicate that significant temperature rises occur inside the heat source, suggesting the advantages and effectiveness of the proposed novel structure configuration. As the number of MLI reflective layers n rises from 0 to 3, the heat source's temperature increases from 1114.3 °C to 1141.2 °C. This study provides important insights into the expanded application of RTPV systems with MLI as thermal insulation, as well as for thermal performance analysis under different conditions.