Dr. Thomas Höhne
Phone: +49 351 260 2425

Phase Transfer on Free Surfaces

Gas-liquid two-phase flows have become increasingly important in engineering equipment and technology. Depending of mass flow rates, geometry and the fluid properties, different flow regimes may occur.

CFD simulation of TOPFLOW-PTS
Fig. 2: CFD simulation of the TOPFLOW-PTS steam/water experiment: condensation of the steam on subcooled water surface (the interface is shown by an isosurface (volume fraction=0.5)).

The current work focuses on stratified two-phase flows with mass transfer due to direct contact condensation on the interface in horizontal channels. In case of direct contact condensation (DCC), the resistance to condensation heat transfer is considerably lower compared to film-wise condensation. Therefore, DCC allows a considerably better heat exchange between the phases. Condensation phenomena depend on the turbulence in the liquid phase. DCC is used in a variety of heat transfer devices (such as direct contact condensers), which offer the possibility of increased performance. DCC has also been of major importance in connection with the analysis of nuclear reactor safety systems, in particular during two-phase pressurized thermal shock (PTS) scenarios. Hence, the modeling of direct contact condensation is a problem of considerable importance. Due to pronounced 3D effects and the necessity to consider local phenomena, this can only be done using CFD codes. Therefore, CFD methods may bring a real benefit. The project aims at the development and validation of CFD models for two-phase stratified flows with heat and mass transfer due to direct contact condensation on free surfaces.

Direct contact condensation is investigated by using a DNS-method and experiments (TOPFLOW-PTS experiments). Finally, a new CFD model for prediction of DCC will be developed and implemented into the Algebraic Interfacial Area Density model (AIAD).

The Lithuanian Energy Institute (LEI) test case deals with direct contact condensation (DCC) in the two-phase stratified steam-water flow (Fig. 3). The main goal of CFD simulations of these experiments is to compute new models of heat and mass transport from saturated vapour to liquid over a free surface and the temperature profiles across the liquid flow in a channel. Condensation occurs mainly on free surfaces for instance at PTS scenarios. The knowledge of the accurate coolant temperature is important for nuclear safety assessment.

LEI Comparison
Fig. 4 Water surface temperature, Comparison Experiment vs. different DCC models

Three different direct contact condensation models for the heat transfer within the AIAD framework at the free surface were formulated and tested. The AIAD model describes a consistent set of model correlations for the interfacial area density, the drag, the non-resolved disturbances of a free surface and the turbulence damping the interface. The calculated surface temperature profiles agree well with the experiment (Fig. 4). Further model development should focus on “CFD grade” experimental data and direct numerical simulations.


  • Höhne, T. , Gasiunas, S., Šeporaitis, M., Numerical modelling of a direct contact condensation experiment using the AIAD framework, International Journal of Heat and Mass Transfer, Volume 111, August 2017, Pages 211-222
  • Apanasevich, P., Lucas, D., Beyer, M., Szalinski, L., CFD based approach for modeling direct contact condesation heat transfer in two-phase turbulent stratified flows,
    International Journal of Thermal Sciences 95 (2015) 123-135
  • Apanasevich, P., Coste, P., Niceno, B., Heib, C., Lucas, D., Comparison of CFD simulations on two-phase Pressurized Thermal Shock scenarios,
    Nuclear Engineering and Design 266 (2014) 112-128
  • Apanasevich, P., Lucas, D., Seidel, T., Numerical simulations of condensing steam-water flow, 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-15),
    Pisa, Toscany, Italy, 12-17 May, 2013, paper 270
  • Deendarlianto, Höhne, T., Apanasevich, P., Lucas, D., Vallée, C., Beyer, M., Application of a new drag coefficient model at CFD-simulations on free surface flows relevant for the nuclear reactor safety analysis, Annals of Nuclear Energy 39 (2012) 70-82

  • Apanasevich, P., Lucas, D., Höhne, T., Numerical simulations of the TOPFLOW-PTS steam-water experiment, 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics
    (NURETH-14), Hilton Toronto Hotel, Toronto, Ontario, Canada, September 25-29, 2011, paper 362

  • Apanasevich, P., Lucas, D., Höhne, T., Pre-test CFD simulations on TOPFLOW-PTS experiments with ANSYS CFX 12.0,
    Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues (CFD4NRS), Washington D.C., USA, 14-16 September, 2010


The work is carried out as a part of current research projects funded by the German Federal Ministry of Economics and Technology, project numbers 150 1411.