Uniformity Index as a Universal Air-Cooled Condenser Fan Performance Metric
E1 Methods and Instruments for Transient Phenomena
Air-cooled condensers (ACCs) use axial fans to force airflow through finned tube heat exchangers and facilitate the heat transfer required to condense steam in a Rankine cycle. Distortions in the fan inlet airflow reduce volumetric flow rate (volumetric performance) through the axial fans and increase the dynamic loading of the fan blades. Severe dynamic blade loading can result in fan blade and motor gearbox damage, unit trips and related reductions in annual performance. One of the main contributing factors to distorted inlet airflow is ambient wind.
Literature relating to ACC fans and wind effects includes numerical and experimental studies that tend to focus on either volumetric performance or dynamic blade loading due to the difficulties related to determining the former in experimental work and the latter in numerical work. That these performance metrics are related is implicit since they are both affected by the same phenomena (distorted inflow). However, due to the lack of comprehensive studies examining both metrics, the relative sensitivities of these metrics to wind effects are not understood.
This study used a numerical approach to simultaneously investigate ACC fan volumetric performance and dynamic blade loading under windy conditions. Based on the numerical results, a fan inlet airflow uniformity index was identified as a single metric that can be used to estimate the severity of both the reduction in fan volumetric performance and the increase in dynamic blade loading under windy conditions. A proportional relationship between uniformity index and both fan volumetric effectiveness and dynamic blade loading was observed. The same proportional relationship was observed in experimental data from on-site ACC testing. Thus, suggesting uniformity index can be used in numerical or experimental work to allow for a qualitative investigation of wind effects and wind effect mitigation mechanisms.