A heat exchanger assembly includes first and second annular ducts, first and second airflow pathways, and heat exchanger. The first airflow pathway is configured to transport a first airflow and is disposed within the first annular duct. The second annular duct is disposed radially outward from the first annular duct. The second airflow pathway is configured to transport a second airflow and is disposed between the first and second annular ducts. The heat exchanger includes inner and outer portions. The inner portion is disposed radially inward of the first annular duct and is fluidly connected to the first airflow pathway. The outer portion is disposed between the first and second annular ducts and is fluidly connected to the second airflow pathway. The heat exchanger is configured to cool a third airflow with both of the first and second airflows from the first and second airflow pathways.