In this paper, a coupled volume-of-fluid and level set (VOSET) method is developed to simulate the two-phase flows. To improve the calculation accuracy of two-phase flows and reduce the cost of computer resources, the dynamically adaptive octree grids are used to refine the grids near the interface. For the deformation of a sphere, the numbers of cells and the CPU time are analyzed. The number of cells for the adaptive grid system is less than 550000. To keep the same resolution, the number of cells for the uniform grid system would be 4096000. The CPU time for the adaptive grids is less than 300 min, while it is 650 min for the uniform grids. The results demonstrate that using the adaptive octree grids takes less storage and time to achieve almost the same accuracy as employing the relevant uniform grids. A static drop in equilibrium without gravity is numerically simulated, and the results show that this method can accurately calculate the interfacial force. A rising gas bubble and the coalescence of two bubbles are simulated, and the results are in good agreement with the previous results.

A large amount of air need be transported into the reservoir in the deep stratum to supply oxygen to some microbes in Microbial Enhanced Oil Recovery (MEOR). Air-water two-phase flows downward along vertical pipeline during the air transportation. Base on the experiment data described in this paper, the characteristics of air-water two phase flow patterns were investigated. The flow pattern map of air-water two phase flows in the pipe with inner diameter of 65 mm was drawn, criterions of flow pattern transition were discussed, and the dynamic signals of the pressure and the differential pressure of the two phase flow were recorded to characterize the three basic flow regimes indirectly. The frictional pressure drop of downward flow in vertical pipe must not be disregarded contrast with upward two phase flow in the vertical pipe because the buoyancy must be overcame when the gas flows downward along pipe, and there would be a maximum value of frictional when the flow pattern translated from slug flow to churn flow.

Density Wave Oscillation (DWO) in tubes was usually studied by using the frequency domain method. However, in the conventional model, the heat storage of wall metal was usually neglected to simplify the complex solving process of transfer functions, which might cause unreasonable results when the tube wall had a thick wall or complex geometry structures. Hence, in the present paper, an improved mathematical model was proposed based on the frequency domain theory to theoretically study the DWO in tubes. The present model was an improvement of the conventional model. The most notable improvement in the present model was that the heat storage of the tube wall metal, the internal wall heat flux and the external wall heat flux were all considered as dynamic parameters. Based on the improvement, the prediction of the DWO in tubes by using the present model might be more accurate and reasonable than that by using the conventional model, and this was proved by the comparison of the results obtained with the two models to the experimental results gained from literature. In the present study, it was shown that both the present model and the conventional model could predict the DWO in tubes well when the tube wall was thin, and it was also found that the present model was more appropriate than the conventional model when the tube wall was thick. Both the thickness of the tube wall and the specific heat of tube wall metal play negative roles in the system stability.

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