FLASHING LIQUID JETS IN LOW-PRESSURE ENVIRONMENT

Abstract

In the present paper, highly expanded flashing liquid jets in a low-pressure environment are studied experimentally, particularly focusing upon the physics associated with liquid flashing regimes. A long, straight stainless steel capillary with an inner diameter of 0.23 mm and a length of 17.0 mm is used as the nozzle, which is connected with a syringe. Through a solenoid valve, a test vessel is connected with a vacuum chamber with a volume about 800 times bigger than that of the test vessel, in order to keep constant pressure inside the test vessel throughout every experimental run. Distilled water of about 1 mL is filled into the syringe at first, while the syringe is open to the ambient. Then, opening the solenoid valve, the air inside the test vessel will be evacuated quickly, resulting in a quick depressurization and a low backpressure inside the test vessel. The water in the syringe is then driven by the difference between the ambient pressure and the backpressure to form a highly expanded flashing liquid jet into the test vessel. For the case of low initial temperature and high backpressure, there is no evaporation, and then the flow of the liquid jet from the nozzle exit section remains intact and follows a straight path. On the other hand, if the initial temperature is high and/or the backpressure is low enough to lead a superheated exit condition, evaporation will take place, irregular evaporation waves around the liquid core are visible, and the jet shattering occurs. On further decreasing the backpressure, the liquid jet shatters giving rise to a cloud of droplets with a spray angle usually bigger than 90°, indicating a large number of nucleation sites and rapid bubble growth. It is also shown that there is flow choking behavior as the flow rate becomes constant and is insensitive to pressure reduction below some backpressure threshold.