Numerical Static Instability Analysis of Supercritical Water Flowing Upward in a Vertical Channel

Abstract

Numerical analysis of supercritical water flowing upward in a vertical heated pipe is carried out using a RANS model in the CFD ANSYS CFX v14.5 code. Four cases with different inlet temperatures and outlet local pressure drop coefficients, but identical operational pressures and heat fluxes, are modeled. Threshold of static instability is determined using the CFD code. The CFD results are for 2-D axisymmetric up-flow using the k-ε and the SST turbulence models. Results are compared with 1-D non-linear code solutions. Also, Chatoorgoon's and Ledinegg's conditions for approximating the static instability threshold are assessed and discussed. In addition, two different constant turbulent Prandtl numbers (Prt) are used to study the effect of Prt on the instability threshold. Results show relatively good agreement between the results of the k-ε and the SST turbulence models on the instability threshold. Also it is concluded that the results of instability threshold are not very sensitive to the value of Prt used. However, further studies are needed to draw a final conclusion on the effect of the Prt on instability margins.