Cavitation flow instability of liquid nitrogen in converging-diverging nozzle flow.


 Cryogenic fluids such as liquid hydrogen (20 K), liquid oxygen (90 K), and liquid nitrogen (77 K) are expected for use in a variety of fields, including as propellants for rockets and other aerospace equipment, and refrigerant for superconducting equipment.

 Research on cavitation has been carried out at many different facilities. Most of this research, however, has used water and other liquids at room temperature, and there are few detailed reports on cavitation in cryogenic liquids because of the difficulties involved in designing appropriate experimental equipment, and in conducting the experiments themselves.

 Cavitation experiments were performed using converging-diverging (C-D) nozzles with a throat diameter of 1.5 or 2.0 mm, and cavitation instability mechanisms for liquid nitrogen under saturated and subcooled conditions were investigated [28, 29]. Considering that throat flow velocity is limited by the speed of sound in a single-component vapor-liquid two-phase flow, the relationship between choked flow phenomena and cavitation behavior was elucidated.
 Cavitation was observed to change from continuous mode to intermittent mode when the temperature of liquid nitrogen at the throat was reduced to 76 K, as shown in the above figure.

 At a throat diameter of 1.5 mm, flows were observed that showed the intermittent cavitation continuously occurring during a very short time-period. These flows were accompanied by a very high oscillation pressure of 70 kPa at a temperature of 74 K, as shown in the figure below.

Correlation between oscillation pressure and liquid nitrogen temperature at the throat.