Experimental study on flow and heat transfer characteristics of the core rod bundle region in a space gas-cooled microreactor based on similarity analysis method

In the design process of space gas-cooled microreactors, it is essential to investigate the flow and heat transfer characteristics of fuel rod bundles to ensure the rationality and feasibility. Helium-xenon gas mixtures are commonly employed as coolants in such reactors. However, existing studies about helium-xenon gas mixture flow and heat transfer characteristics were mainly performed with circular, annular, or rectangular cross-sectional channels, while few with rod bundle regions. Furthermore, current studies predominantly rely on numerical simulations, while few on experiments due to the high cost of helium-xenon gas mixture. In order to obtain the experimental data, an experiment is designed using air instead of helium-xenon gas mixture based on similarity analysis between air and helium-xenon gas mixture. Consequently, in this paper, a similarity analysis method by differential equation analysis method for the flow and heat transfer of air and helium-xenon gas mixture is established. According to the boundary conditions obtained from the similarity analysis theory, the flow and heat transfer experiment is conducted under different operating conditions to obtain the temperature distribution and the pressure drop variations within the core. Through analyzing the experimental results of helium-xenon gas mixture converted from air by similarity theory criteria, a set of semi-empirical correlations for helium-xenon gas mixture flow and heat transfer is proposed by using a six-rod average methodology, demonstrating errors within 10 %. The derived correlations exhibit conservatism, ensuring reliability in engineering applications. This study can validate the reactor core structural design and provide critical experimental references for the design of space gas-cooled microreactors.