A cooling system comprises an electronics module and a duct. The electronics module produces more heat at a first location than at a second location, and is rated to a safe operating temperature. The duct surrounds the electronics module, and has a shaped baffle with a constricted region near the first location and an open region near the second location. The expanded region has greater cross-sectional flow area than the constricted region. Airflow through the duct cools both the first location and the second location to within an efficiency margin below the safe operating temperature.