N. S. Khabeev

Simulation of vapour explosions

Vapour explosions, also called thermal detonations, occur when a liquified gas comes into contact with water. During the contact of the two liquids with considerably different temperatures, intensive boiling of one of them takes place which is accompanied by an explosive increase in pressure. A similar phenomenon also arises in the cooling systems of nuclear-power stations, when, as a result of some accident, the heated particles of the nuclear fuel settle in the cold water. This leads to the explosive boiling of the liquid and to a rapid increase of the pressure. This paper presents analytical and numerical modelling of the behaviour of small-scale single drops of liquified gas in water.

Acoustics of boiling solutions

The possibility of an anomalous effect of the component composition on disturbance propagation in boiling solutions has been established. A criterion defining the cases in which the monotonic behavior of binary systems with respect to concentration is disturbed during sound propagation in them has been derived.

Oscillations of a gas-vapor bubble in an acoustic field

It is shown that at large vapor contents, as a result of the combined action of phase transitions and capillary effects, the small radially symmetric oscillations of gas-vapor bubbles in an acoustic field are unstable in amplitude. The critical vapor concentration in the bubble separating regions of qualitatively different bubble behavior in the acoustic field is determined. Expressions are obtained for the decay rate of the radial oscillations of the gas-vapor bubble and the growth rate characterizing the rate of increase of oscillation amplitude in the region of instability. It is shown that adding only a slight amount of gas to the vapor bubble leads to a marked decrease in the growth rate. It is found that in the particular case of a vapor bubble the tine growth rate characterizing the development of the instability is of the same order as the second resonance frequency of the vapor bubble. This may serve to explain why in the case of vapor bubble oscillations the second resonance effect, which has been established in a number of theoretical studies and is widely discussed in the literature, has not yet been experimentally confirmed. The problem of spherically symmetrical processes around gasvapor bubbles was posed in [1], and their small oscillations are investigated in detail in [2–4].

Towards the problem of droplet injection in a vapor with the aim of reducing the pressure

As applied to the analysis of sprinkler systems which inject droplets into a vapor in the case of emergency pressure increases, the process of vapor condensation on a single droplet is considered. For the specification of the intensity of interphase heat and mass transfer, the solution of an unsteady heat conduction problem is used. Approximate formulas describing the laws of the pressure drop in a vapor-droplet system due to the condensation of the vapor phase are obtained.

Some characteristics of the propagation of sound in binary bubble media

The effect of the composition and thermophysical properties of binary vapor-liquid bubble systems on the propagation characteristics of small disturbances, the stability of the media and the rate of development of instability is investigated.

Gas solubility effects associated with the propagation of small perturbations in bubbly mixtures

The effect of gas solubility on the oscillation characteristics of bubbles in an acoustic field, the propagation and damping of perturbations in bubbly mixtures and, moreover, the stability of such media is analyzed.