The influence of thermal radiation on the free convection inside enclosures

• Published in: Nuclear engineering and design 2019-01, Vol.341, p.176-185
• Main Authors: Dehbi, A., Kelm, S., Kalilainen, J., Mueller, H.
• Format: Article
• Language: English
• Subjects: Aerodynamics; Air flow; Atmosphere; Atmospheric circulation; Atmospheric models; Blowdown; Computational fluid dynamics; Computer simulation; Convection; Energy balance; Free convection; Heat conductivity; Heat transfer; Induction heating; Large eddy simulation; Low temperature; Nuclear engineering; Radiation; Steam; Temperature effects; Thermal radiation; Thermal stratification; Turbulence; Turbulent flow
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2018.10.025

•Thermal radiation may have a significant influence on containment flow fields.•Paper addresses two cases: participating and non-participation media.•CFD simulations are conducted to highlight the importance of radiation.•Including radiative heat transfer improves the agreement between CFD and data. Natural convection is the dominant flow regime inside containments following the short-term blowdown phase. To simplify CFD computations in such flows, thermal radiation has traditionally been ignored due to the modest containments temperatures expected in typical severe accident scenarios. Recently, however, some reduced scale experiments have shown that radiation may have profound effects on the flow field even at relatively low temperature levels and differences. We will summarize two series of computations conducted with CFD tools. The first exercise consists of simulating turbulent air flow inside the DIANA cubical differentially heated cavity at PSI (Switzerland). A large eddy simulation (LES) is performed with and without wall-to-wall radiation modeling. Including radiation significantly improves the prediction of the flow field, correctly displaying a reduced level of thermal stratification and an enhanced level of turbulence. Secondly, the technical scale THAI (Becker Technologies, Germany) natural circulation test TH24 is analyzed. In this experiment, a stratified air-steam atmosphere is remobilized due to a natural circulation flow induced by wall heating in the lower part of the facility and steam condensation inside the stratified cloud. An unsteady RANS model is applied with and without consideration of the gas radiation heat transfer within the steam rich atmosphere. The comparative evaluation clearly highlights the effect of gas radiation on the overall energy balance as well as the natural circulation and mixing process. In comparison to the experimental data, a significantly improved consistency is obtained if gas radiation is considered.