Natural Draft Direct Dry Cooling System Performance at Various Application ScalesUnder Steady and Transient Conditions

The natural draft direct dry cooling system (NDDDCS) combines the advantages of traditional forced draft air-cooled condensers (ACCs) with those of indirect natural draft dry cooling systems, providing reduced complexity, lower auxiliary power consumption, and enhanced thermal efficiency through direct condensation. This study examines the transient cold start-up and operational performance of NDDDCSs under no-wind and crosswind conditions at two scales: a large-scale coal-fired power plant (900 MWt) and a medium-scale (100 MWt) concentrated solar power (CSP) plant, both equipped with vertically arranged heat exchanger bundles. Addressing a significant gap in the literature, a co-simulation approach is used, integrating a transient 3-D computational fluid dynamics (CFD) model via FLUENT for the air-side analysis with a transient 1-D Python-based numerical model for the steam-side, coupled through the PyFLUENT architecture. The 1-D and 3-D model components are validated, based on the foundations of previously validated steady-state 3-D CFD and 1-D transient models.