A Two Unequal Fluids (TUF) model for thermalhydraulics analysis

TUF is an advanced two-phase flow computer code being developed at Ontario Hydro for analysis of thermalhydraulics transients in which the Homogeneous Equilibrium Model is not adequate, i.e., when the two phases (vapor and liquid) have Unequal Velocities (UV) and Unequal Temperatures (UT). The paper covers only one of the several development areas encompassed by TUF, namely its mathematical aspects. TUF's basic features include: numerical solution of mass-energy balance equations over fixed control volumes, semi-analytical solution of momentum equations at junctions (such that the solution is unconditionally stable and and has UV-UT choking and flooding limitations built-in). Two strategies are being developed: one based on the Porsching approach (for short-term use in an existing system code) and the other based on a two-step pressure field approach (computationally more efficient and unconditionally stable). Some simple test cases are presented