Investigation of Compressible Flow in Natural Circulation Loops With a Non-Boussinesq Algorithm

Abstract Natural circulation loops are adopted in various engineering fields, including thermal systems, nuclear reactors, and renewable energy systems, whose simplicity, reliability, and energy efficiency are crucial. Understanding and optimizing the performance of natural circulation loops are essential for enhancing heat transfer efficiency and overall system reliability. In present study, an innovative methodology noted as the Decoupled and Stabilized Lattice Boltzmann Method (DSLBM) is used to the research the compressible physical characteristic of natural circulation loop. It enables the concurrent treatment of pressure, density, and temperature, ensuring the precise retrieval of the entire compressible Navier-Stokes (NS) equation with a constitutive relation at the second-order level. By integrating the equation of state, the temperature equation, and the full NS equation, this method effectively addresses singlephase flow perturbations induced by gravity, pressure fluctuations, and temperature-induced density changes, without relying on the Boussinesq assumptions. This holistic approach offers a comprehensive depiction of the physical mechanisms governing natural circulation loops. On this basis, the paper analyzes the compressible relationships among heating power, cooling power, flow rate, driving head, and Nusselt number under different working conditions in single-phase natural circulation loops. Through velocity distribution, temperature distribution, and other parameters, the flow characteristics and heat transfer mechanisms of single-phase natural circulation loops can be revealed. The results provide a new insight for the design and optimization of nuclear reactors based natural circulation.