It has been found that vapour bubble behaviour changes radically depending on the liquid is superheated or subcooled, and the phase change kinetics is of great significance in these phenomena.
On the basis of this model, two other mathematical models have been constructed to analyse the evolution of a vapour bubble ensemble after changing external pressure. Within the framework of the cell model, the ensemble-averaged pressure in the liquid phase has been calculated both for boiling and cavitation. The rate of growth or collapse of the bubbles in these phenomena is found to control the average pressure change. Another model is intended for analyses of micro-flow patterns in liquid phase between the bubbles and allows a detailed description on a microscopic scale both pressure and velocity fields within the ensemble.
A qualitatively new modelling approach is proposed to analyse both stationary and non-stationary flashing flows. This approach, which is completely based on the above ensemble model, treats two-phase bubbly flows in a channel as evolution of a vapour bubble ensemble in time and in space due to pressure difference at the both ends of the channel. On this basis an original mathematical model has been developed, which spreads all over every possible mode of steam-liquid bubbly flows, critical flow included, and takes into account all the non-equilibrium effects such as temperature, pressure and chemical potential differences between both phases. A great deal of attention is given to applications of this model in the description of critical flow regimes.
All the models mentioned have the advantage of possessing a high degree of physical visuality. They are accurate enough for practical design calculation and enable the computation time to be reduced significantly.
Comparison of the numerical results predicted by these models with a variety of published experimental data on the bubble dynamics in boiling and cavitation phenomena, as well as with data on flashing flow behavioural patterns, showed fair agreement. In all cases the models proved to be essentially superior to other known models.
The numerical investigations on bubble dynamics performed in this research with using the models in view enable obtaining a great deal of useful information and reveal some new features of which many are unaware.
Key words: intensification, energy saving, mathematical models, heat and mass transfer, phase change, bubble dynamics, steam-water systems, boiling, cavitation, flashing flows.