Dynamics of annular two-phase flow
A basic understanding of various hydrodynamic phenomena in annular two-phase is essential to develop mechanistic model for the prediction dryout. The major objective of this investigation was to perform experimental and theoretical analysis of the important hydrodynamic phenomena such as droplet entrainment, droplet deposition, and liquid film interfacial waves in vertical annular two-phase flow. Towards this end, adiabatic air-water and organic fluid (Freon-113) annular flow experiments have been conducted in 1 cm diameter test sections at pressures up to 6 and 8.5 bar, respectively. The organic fluid experiments simulated high pressure steam-water conditions representative of dryout in the Advanced Boiling Water Reactor (ABWR). A liquid film extraction method was applied for the measurement of entrainment fraction, droplet entrainment rate, and droplet deposition rate. Instantaneous liquid film thickness was measured in the air-water experiments using ring shaped conductance probes and properties of interfacial waves were estimated from the statistical analysis of the film thickness measurement. Detailed analysis of the experimental data revealed several inadequacies of the existing annular flow correlations available for the predictions of entrainment fraction, droplet entrainment rate, and droplet deposition rate including their inability to predict the limiting conditions observed under high gas phase velocity. Based on the detailed analysis of the air-water data, a new, non-dimensional and explicit correlation was developed for the prediction of entrainment fraction. The new correlation accounted for the existence of an upper limit on entrainment fraction as well as for the existence of critical liquid and gas velocities below which no entrainment is possible. Additionally, an improved correlation was proposed for the estimation of minimum liquid film flow rate at the maximum entrainment fraction. The newly developed entrainment fraction correlation successfully predicted the organic fluid experimental data obtained in this study and the several other data sets available in literature. The correlation is applicable to annular mist flow conditions in the test sections having the inside diameters smaller than 32.0 mm. Liquid film thickness measurements in the air-water experiments gave valuable information on the behavior of liquid film and interfacial waves in annular mist and annular wispy flow. The film thickness data was processed following the objective, statistical data analysis approach in order to estimate the interfacial disturbance wave frequency, wavelength, velocity and amplitude. Detailed analysis of the wave data was carried out in order to study the effect of flow rate and pressure conditions. Existing correlations for the prediction of disturbance wave velocity and frequency failed to predict the high pressure data. A new, non-dimensional correlation was developed for the prediction of disturbance wave frequency and successfully predicted the new data as well as the data available in literature. The liquid film thickness data in annular wispy flow regime revealed a significantly different nature of the interfacial waves in this flow regime. Further studies of the entrainment mechanisms and wave characteristics in this flow regime are essential for the development of entrainment correlations.
Ishii, Purdue University.
Chemical engineering|Mechanical engineering|Nuclear engineering
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