Spray System Trials in the Icing Research Tunnel

The spray bar system introduces water droplets into the Icing Research Tunnel’s air stream at the National Advisory Committee for Aeronautics (NACA) Lewis Flight Propulsion Laboratory. The icing tunnel was designed in the early 1940s to study ice accretion on airfoils and models. The Carrier Corporation designed a refrigeration system that reduced temperatures to -45° F. The tunnel’s drive fan generated speeds up to 400 miles per hour. The uniform injection of water droplets to the air was a key element of the facility’s operation. The system had to generate small droplets, distribute them uniformly throughout the airstream, and resist freezing and blockage. The Icing Research Tunnel’s designers struggled to develop a realistic spray system because they did not have access to data on the size of naturally occurring water droplets. For five years a variety of different designs were painstakingly developed and tested before the system was perfected. This photograph shows one of the trials using eight air-atomizing nozzles placed 48 feet upstream from the test section. A multi-cylinder device measured the size, liquid content, and distribution of the water droplets. The final system that was put into operation in 1950 included six horizontal spray bars with 80 nozzles that produced a 4- by 4-foot cloud in the test section. The Icing Research Tunnel produced excellent data throughout the 1950s and provided the basis for a hot air anti-icing system used on many transport aircraft.