Modelling and validation of atmospheric expansion and near-field dispersion for pressurised vapour or two-phase releases

Secondly, both ATEX expansion options have been applied to known available experimental data for orifice releases. For these experimental data it was confirmed that the ATEX conservation-of-momentum option without a velocity cap provides overall more accurate concentration predictions than the isentropic assumption. However the existing default 'minimum thermodynamic change' option was found to mostly impose conservation of entropy (velocity cap not applicable) for two-phase releases and conservation of momentum (velocity cap applicable) for sonic gas jets. Rainout calculations for flashing two-phase releases are currently always based on the isentropic assumption, which is inconsistent with the recommended conservation of momentum; a further investigation is recommended.