Experimental Visualization of Cryogenic Backflow Vortex Cavitation with Thermodynamic Effects

摘要

The world's first test facility that allows the visualization of cavitation on a rotating inducer in both cryogen and water was used for comparing the cavitation features in liquid nitrogen at 77.9 K and water at 292.5 and 333.5 K. The test inducer was a triple-threaded helical one with a diameter of 65.3 mm and a rotational speed range of 3500-6000 rpm. The backflow vortex cavitation on the rotating inducer was quantitatively measured in the considered fluids. From the results, it was inferred that the backflow vortex cavitation orbital rate and its orbital diameter around the inducer axis depend on the head coefficient but are almost independent of the cavitation number and kind of fluid. Furthermore, the diameter of each backflow vortex cavitation column depends on the head coefficient, cavitation number, and kind of fluid. At the same head coefficient and cavitation number, the diameter in liquid nitrogen is 2.4 times smaller than that in water because of the thermodynamic effects. Moreover, the appearance of the cavitation is "foggy" in nitrogen and "foamy" in water. This difference can be explained by the maximum stable size of cavitation bubbles derived from the critical Weber number theory. Based on this theory, each cavitation bubble at the tip vortex regions in nitrogen is four times smaller than that in water.