Insights into the dynamics of supercritical water flow using a two-phase approach
Piyush Mani Tripathi, Saptarshi Basu
Abstract
A two-phase approach has been proposed to study the supercritical flow with heat transfer deterioration (HTD) phenomena so that an analogy can be derived between subcritical flow boiling and supercritical heat transfer. The volume of fluid multiphase model has been used to analyze the flow, and the simulation result reasonably predicts the wall temperature peaks. Moreover, the velocity and turbulent kinetic energy profiles at different axial locations explain the occurrence of HTD. The parametric study of the thermophysical properties revealed that the density variation is the primary cause of HTD in supercritical flows. Leaning onto this observation, the current study focuses on the forces generated due to the density variation. It suggests that for no HTD, buoyancy and inertia forces have to be of comparable magnitude throughout the flow. Mapping of volume fraction variable reveals a sudden jump in the lighter phase thickness near the wall at the site of HTD, which is also reflected as a maximum in the plot of nondimensional two-phase interface distance from the wall (P). However, this observation is only restricted to HTD caused by buoyancy. This can be used to draw analogy with the phenomenon of film boiling in subcritical fluids. In the end, a theoretical expression has been conceptualized for computing the phase boundary distance from the wall (h), which can serve as a fundamental length scale in supercritical flows as it marks the region of highest property gradient near the wall.