A review is made of the various models and basic equations of gas-liquid two-phase flows which are indispensable for accurate analyses of the phenomena. As the most detailed model, a local instantaneous representation of mass, momentum and energy conservation is shown. Then, averaging procedures for the various physical quantities and their derivatives of two-phase flow are described with a particular attention to the existence of the interface. Based on the local instantaneous formulation and averaging methods, the averaged formulations of basic equations of two-phase flow are stated. Two-types of formulations based on mixture models and two-fluid models are shown. The mixture model is further divided into homogeneous model, a slip model and a drift flux model depending upon the treatment of velocity differences between phases. Approximations, assumptions and limitations of applications of the basic equations based on each model are described.
This paper is concerned with the effects of fine particle concentrations in a carrier fluid on the pressure fluctuation and water hammer phenomena in coarse solid-liquid flows. When fine particles were mixed with the carrier fluid, pressure fluctuations were reduced. This is due to the suppression of fluid turbulence. However, there was little effect of the fine particles on the reduction of pressure fluctuations at lower velocities because the movement of dunes dominated the pressure fluctuation, considerably suppressing the fluid turbulence. It was discovered from a power spectral density function that the existence of fine particles in the carrier fluid reduced the frequency of pressure fluctuations. The maximum surge pressure, due to water hammer, increased in relation to additions of the fine particle concentrations, resulting from the increase in mixture density. It is advantageous to the reduction of pressure loss and pressure fluctuations to mix fine particles with the carrier fluid. However, the maximum surge pressure increases when fine particles are mixed with the carrier fluid. Therefore, the concentrations of fine particles should be determined by taking into account both of the above mentioned effects.
The Profile of the velocity of a diesel spray, which is a liquid-gas two phase flow with high velocity, is a significant phenomenon to analyze the mixing and combustion processes in a diesel engine. It is impossible to measure the velocity because a large number of droplets and entrained air exist in the spray. In the experiments presented here, the composed velocity of droplets and entrained air was calculated by using a model built under certain assumptions, using the droplet area density measured with the laser light extinction method and the momentum flux measured with a newly developed probe. The validity of the model was examined by comparing the velocity profile with the measured data and that predicted by the numerical calculations based on the well-known KIVA code for diesel spray. As a result, the profiles of droplet density, momentum flux and velocity in a diesel spray are very similar to those in unsteady gas and water jets.