Impact of thermal radiation on containment phenomena at medium scale: Experimental and CFD investigations in the LINX facility

Recent studies have emphasised the significance of incorporating thermal radiation in simulations of large-scale containment phenomena. This assertion is substantiated by experimental findings in the PANDA facility and their corresponding CFD benchmark analysis, which demonstrated that radiative heat transfer can be substantial even at low steam concentrations. The present study extends this investigation to medium-scale enclosures conducted in the LINX facility at the Paul-Scherrer-Institute (PSI). Two experiments (LR1 and LR2) with varying steam concentrations (0.1% and 2.5%, respectively) were conducted in the medium-scale LINX facility, which consists of a vessel with a diameter of 2 m and height of 4 m (1/10th the volume of the PANDA drywell). The experiment involved the compression of a steam/air mixture by means of helium injection from the top at a mass flow rate of 1 g/s for a duration of 1200 s, which was then followed by a decay phase. This process resulted in the formation of a helium layer at the top, which displaced the steam/air mixture downward and created a high-temperature region. The development of a 0D model was undertaken to facilitate the estimation of energy balances and heat losses, with experimental data being utilized as inputs. Furthermore, CFD simulations of both tests were performed using ANSYS Fluent, employing the k–ω SST turbulence model along with either the P1 or Discrete Ordinate (DO) models to account for thermal radiation. The experimental findings demonstrated that the LR1 test yielded a substantially higher peak temperature in comparison with the LR2 test. CFD simulations without thermal radiation overpredicted the temperature profiles, but good agreement with the experimental data was achieved when the radiation model was applied. The estimated total heat transfer to the wall indicated that the presence of steam increased the total heat loss rate to 0.57 kW during compression phase, which 7% higher than in the dry test. The evaluation of CFD heat loss revealed that radiative heat transfer contributed approximately 25% of the total heat loss rate in LR2 during the compression phase, which increased significantly in the decay phase. The findings demonstrate the significance of incorporating thermal radiation when modeling naturally driven flows in steam-containing atmospheres, even at smaller scales.