A Study on the Steady-State Flow Behavior of the Flashing-Driven Open Natural Circulation System

Abstract The steady-state flow behavior serves as an important indicator of a natural circulation system, since it directly reflects the flow and heat transfer capacity of the system. Many studies have been conducted into the steady-state behavior of high-pressure natural circulation, while a few have focused on the open natural circulation. The steady-state flow behavior of the open natural circulation is however more complex due to its low-pressure property, which increases the likelihood of flashing. The position of flashing front and the distribution of void fraction in the riser are never fixed. Furthermore, due to the nonlinear characteristic of flashing and nonzero integral result of accelerated pressure drop along the loop direction, it is difficult to obtain an accurate mathematical expression of the relationship between flowrate and heating rate by using the integral of momentum conservation equations. Therefore, relevant theoretical formulations are inadequate and unavailable. In this paper, a theoretical formula to determine the steady-state flow behavior of a flashing-driven natural circulation system was derived by using a quasi-linear flashing mode and a special formula processing of accelerated pressure drop integral result. The prediction results of the formula were validated by experimental data. Furthermore, the influence of geometric and thermal-hydraulic parameters on the steady-state flow behavior was studied through calculation and validated by experimental data. This paper aims at providing technical support for the design of open natural circulation systems.