Near-field thermal radiation for enhanced heat transfer: Classification, challenges, and prospects

Near-field thermal radiation has garnered significant attention in recent years due to its advantages, including a high heat transfer rate and environmental friendliness, making it highly promising for engineering applications. This study summarizes and discusses the computational and experimental studies reported on heat transfer via near-field thermal radiation over the past decade. These computational and experimental studies were categorized based on configurations, materials, solution methods, systems, and domains. It was observed that computational studies significantly outnumber experimental studies because of the significant challenges in controlling gap distances at the nanoscale level, making experimental operations extremely difficult. However, notable progress has been achieved in experimentally measuring near-field thermal radiative heat transfer in recent years owing to advances in micro- and nanomanufacturing technologies and materials science. Nonetheless, experimental configurations such as nanoprobes or sphere-plate structures have limited applications in near-field thermal systems because of their very small heat transfer areas. For the plate-plate configuration, various factors affect the detection of near-field heat radiation, including the heat transfer distance, flatness of the plate, and proportion of heat conduction through the separating medium. Consequently, the measurement accuracy of near-field thermal radiation faces numerous challenges, necessitating the development of novel measurement methods. Finally, this review briefly summarizes the key challenges in near-field thermal radiation research and analyzes their potential applications.