NONSTATIONARY OUTFLOW AND RAREFACTION WAVES IN FLASHING LIQUID

The outflow of high pressure liquid (in particular, water) to the atmosphere from a closed tube (of length a few metres and diameter more than a few centimetres) because of sudden destruction of one bottom is theoretically investigated. Evaporation takes places on the nucleus bubbles. The number of nuclei depends on the quality of the liquid or its purification. The process involves flashing evaporation of the liquid. There are two rarefaction waves at the initial stage. The velocity of the first wave (elastic forerunner) is sound speed in the one phase liquid and equals about 1000 m s(-1). After the elastic forerunner the liquid becomes superheated because the pressure drops and evaporation begins. The velocity of the second rarefaction wave is about 1-10 ms s(-1). There is intensive bubbly evaporation on and after the second wave. Intensity of the outflow is determined by the intensity of evaporation on the interface of the bubbles and by intensity of fragmentation of the bubbles because of their relative slip velocity in the liquid (0.1-1 m s(-1)). The fragmentation of the bubbles significantly intensifies the evaporation because of augmentation of the bubbly interface. The degree of non-equilibrium or superheating behind the forerunner in water grows with the increasing initial temperature T-0. For T-0 < 530-540 K this superheating is negligible and the process may be described by an equilibrium scheme. For T-0 above 0.95T(cr) approximate to 605 K homogeneous nucleation is possible. After forerunner reflection from the closed bottom, intense evaporation is initiated near the bottom. Then the equalization of the pressure along the tube occurs (quasi-static homobaric stage). There is good correlation with experimental data.