Stability analysis of single-phase thermosyphon loops by finite-difference numerical methods

Abstract

In this paper, examples of the application of finite-difference numerical methods in the analysis of stability of single-phase natural circulation loops are reported. The problem is addressed here for its relevance to thermal-hydraulic system code applications, with the aim to point out the effects of truncation error on stability prediction. The methodology adopted for analyzing in a systematic way the effect of various finite-difference discretization can be considered the numerical analogue of the usual techniques adopted for PDE stability analysis. Three different single-phase loop configurations are considered involving various kinds of boundary conditions. In one of these cases, an original dimensionless form of the governing equations is proposed, adopting the Reynolds number as a flow variable. This allows for an appropriate consideration of transition between laminar and turbulent regimes, which is not possible with other dimensionless forms, thus enlarging the range of validity of model assumptions.