Evaluation of a Zonal Model for Large Enclosures Using Computational Fluid Dynamics

摘要

A temperature-based zonal model for large enclosures with combined stratification cooling and natural ventilation, proposed in a previous paper by Gao et al, is evaluated using the CFD (Computational Fluid Dynamics) method in this study. The CFD method adopted in this study using the RNG k-ε model with a differential viscosity is able to represent the non-isotropic thermally stratified flows encountered in the large enclosures. It is used to determine a key parameter, the heat transfer factor between adjacent zones in the zonal model due to temperature difference and turbulent penetration, and also to verify the zonal model for the prediction of thermal stratification in large enclosures. In order to avoid the poor representation of surface heat transfer by empirical/semi-empirical expressions suggested for conventional room enclosures, this study feeds a CFD-based coefficient to the zonal model. This treatment also gains an advantage over the experimental method, which is proved to fail in keeping the similarities of thermal buoyancy and surface convection based on the scale modeling. Furthermore, it responds to the influence of detailed information of local flows on the coefficient. Finally, comparison between the zonal model and CFD is carried out for the enclosure conditioned with the combined stratification cooling and natural ventilation, or single stratification cooling. It is found that the results calculated by the zonal model agree considerably well with those by the CFD.