Investigation of Velocity and Droplet Size Distributions of Flash Boiling LN2-Jets With Phase Doppler Anemometry

For a detailed experimental investigation of superheated cryogenic fluids the new cryogenic test bench M3.3 with a temperature controlled injection system was built at the DLR Institute of Space Propulsion in Lampoldshausen. After a first test campaign with high-speed shadowgraphy of flash boiling liquid nitrogen sprays a Phase Doppler Anemometry system was set-up to investigate the dependence of droplet velocities and diameters on the injection conditions at different positions in the spray. The local velocity distributions show their maximums close to the injector exit before they decrease to values around zero. The droplet diameters show an evolution from bigger structures with an inhomogeneous distribution close to the injector to a monodisperse spray with increasing axial and radial distances. Two droplet populations with different mean velocities were found at most of the spray positions