CFD validation of condensation heat transfer in scaled-down small modular reactor applications, Part 1: Pure steam

This study presented the state-of-the-art computational fluid dynamics (CFD) validation and scaling of the condensation heat transfer (CHT) models for passive containment cooling system (PCCS) of the small modular reactor (SMR). The STAR-CCM+ software with real 3D computational domains was used to validate the condensation models with a preliminary assessment of pure steam scaling performance. The boundary and appropriate physics conditions from the test data were applied. The condensation was modeled using the condensation-seed parameter as a source term for mass, momentum, and energy conservation equations. A small percentage of air (within 1%) was considered in the test section; hence, multi-component gas models were used. The implicit-unsteady numerical solver was applied to improve numerical stability. Mesh size, run time (duration), and time step sensitivity analyses were applied to obtain optimized simulation results. The test fluid parameters—temperature (at bulk steam-mixture, bulk coolant, inner and outer tube walls), condensation film thickness, mass fraction, and heat flux—were utilized to validate the CFD simulations. Finally, Nusselt number (Nu), as the dimensionless number heat transfer, was calculated for diameter scaled-up and scaled-down geometries. The heat transfer coefficient and Nu values were compared to evaluate the scalability performance of CHT models.