Institute for Neutron Physics and Reactor Technology (INR)

The Porous Media Two-phase Flow Code TwoPorFlow


TwoPorFlow (TPF) is a thermal-hydraulics simulation code under development at the Karlsruhe Institute of Technology (KIT). It has the capability to simulate single- and two-phase flow in a structured or unstructured porous medium using a flexible 3-D Cartesian geometry. TwoPorFlow calculates the transient or steady state solution of the mass, momentum and energy conservation equations for each fluid phase with a semi-implicit numerical procedure based on the implicit continuous Eulerian (ICE) method. Several closure correlations are implemented in order to model the heat transfer between solid and coolant, boiling condensation, wall friction as well as liquid-vapor momentum coupling.

Recently, models for turbulent mixing models were implemented into the momentum and energy equations (vapor and liquid) for more physical simulations of two-phase flow. TPF is extended with different critical heat flux (CHF) correlations  for safety-relevant analysis of reactor cores.

Application scope

TPF potential applications may be the simulation of simple 1-D geometries like heated pipes, fuel assemblies resolving the sub-channel flow between rods or a full BWR core using a coarse mesh 3D approach. Potential applications are also nuclear spent fuel pools.


Present validation uses data provided by international benchmarks e.g. NUPEC PSBT and BFBT (pressure drop, void fraction, critical power) as well as Becker CHF tests.  

Key-features and physical models

  • Forced convection porous body approach
  • Sub-channel fuel assembly simulations
  • Steady state and transient solution
  • Conventional closure correlations from standard literature (heat transfer and pressure loss)
  • Coarse Cartesian grids
  • 3D-conservation equations for two interpenetrating fluids
  • Implicit Continuous Eulerian method (ICE)
  • Water and steam properties: IAPWS-97 formulation
  • 3D-Heat conduction for porous body, 2D for fuel rods
  • Direct pressure solver (LU with pivoting) for small problems
  • Iterative BiCGSTAB pressure solver for large problems
  • Completely programmed in Fortran 95



Current validation:


  1. V. Jauregui Chavez, U. Imke, V. Sanchez-Espinoza; TWOPORFLOW: A two-phase flow porous media code, main features and validation with BWR-relevant bundle experiments. NED 338 82018) 181-188.
  2.  V. Jáuregui Chávez, U. Imke, J. Jiménez and V. Sánchez-Espinoza; Implementation And Validation of CHF models in the two-Phase Flow porous media Code TwoPorFlow. Paper ID : 20248. 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17), September 3-8, 2017, Xi'an, Shaanxi, China.
  3. J. Jiménez, N. Trost, U. Imke, V. Sánchez; Recent developments in TWOPORFLOW, a Two-phase Porous Media Code for Transient Thermo-hydraulic Simulations. Annual Meeting on Nuclear Technology. Frankfurt, Germany, May 6-8 2014
  4. Nico Trost, Javier Jiménez, Victor Sanchez and Uwe Imke; Parallelization of TWOPORFLOW, a Cartesian grid based two-phase porous media code for transient thermo-hydraulic simulations. Joint International Conference on Supercomputing in Nuclear Applications and Monte Carlo 2013 (SNA + MC 2013). La Cité des Sciences et de l’Industrie, Paris, France, October 27-31, 2013.