Non-dimensional parameters for static instability in supercritical heated channels

A study of supercritical flow stability in vertical channels has been undertaken to develop and assess relevant non-dimensional parameters governing the static instability mode. As in two-phase flow, two types of flow instabilities have previously been identified: static and dynamic. However, in supercritical flow, it was found that static instability and dynamic instability occurs in different temperature ranges. For a given fluid and system pressure, below a certain temperature only a static instability is possible, while above that temperature only a dynamic instability is possible. In down-flow, the static mode is more prevalent, while the dynamic mode was found to be more prevalent in up-flow. The examined fluids were H2O and CO2. This paper proposes and assesses new non-dimensional parameters for static instability in supercritical fluid flow, as well as assesses the non-dimensional parameters of Ambrosini. Different inlet temperatures, inlet and outlet K factors and systems pressures were examined. Insights into how the instability can be delayed or circumvented were obtained and are discussed. This study was undertaken using an in-house linear instability program.