摘要

A computational model has been developed at UW Madison which provides a simulation tool for the steady-state and transient analysis of one dimensional natural circulation flow of a supercritical fluid, and was applied for loop stability analysis. Several modifications and improvements were incorporated from past numerical schemes (Chatoorgoon, 1986) before applying it to investigate the transient behavior of two experimental loops, namely, the supercritical water loop (SCW) at UW-Madison (Jain et. al, 2002) and the supercritical carbon-dioxide (SCCO₂) loop at Argonne National Laboratories (Lomperski, 2003). Two types of boundary conditions were studied which included, a fixed heater inlet pressure and temperature boundary condition, which corresponds to the presence of a reservoir in the flow loop; the second boundary condition being the assumption of no reservoir in the system allowing the inlet temperature and pressure to vary with respect to time. The model predicted development of instabilities for a system with a large reservoir for both SCW and SCCO₂ loop in agreement with some previous work. The experiments conducted at SCCO₂ loop with a finite reservoir conversely exhibited stable behavior. The model with a closed loop boundary condition with no reservoir present, however, displayed instabilities that diminished in magnitude with the numerical time step used in the calculations. In order to distinguish between the numerical effects and physical processes, a linear stability approach was undertaken to compare to the transient model.