Estimation Of Gas/liquid Two-Phase Flow Void Fraction Based On Flow Regimes Identification

The two-phase flow systems are very common in many industry fields, such as petroleum, chemistry engineering, metallurgy, energy power, pharmacy and so on. Because of its complexity and variability, the real-time parameter measurement of two-phase flow becomes a difficult issue in the field of engineering and science. Therefore, the advanced sensor and modern information processing techniques are combined to provide the new measurement method of two-phase flow.As an on-line measurement technique with the advantages of visualization, non-invasion, low cost, and non-radiation, Electrical Resistance Tomography (ERT) based on the principle of electrical sensitivity is playing an increasingly-important role in the field of two-phase flow. In this paper, by combining the ERT technique with the modern information processing techniques, the identification of flow regimes and the estimation of void fraction were achieved.The main achievements in this paper are as follows:1. The real-time experiments were conducted using ERT system in oil/gas/liquid three-phase flow laboratory of Tianjin University, and the data with different flow regimes of gas/liquid two-phase flow in vertical upward pipe were obtained.2. According to the real-time experiments, the soft-sensor model of gas/liquid two-phase flow in vertical pipe has been established. Three features in amplitude domain are extracted by time series statistical analysis, and the features of multiple scales wavelet energy percent are derived by discrete wavelets transform. All the features constituted the feature quantities database of soft-sensor model. The Support Vector Machine (SVM) theory is adopted as the classification model to identify the three typical flow regimes. By comparing the two methods, the results indicate that the method of multi-feature information fusion which combined the two feature extraction methods could better express the essential information of gas/liquid two-phase flow, and achieve a higher identification rate of flow regimes.3. Based on the accurate flow regimes identification of gas/liquid two-phase flow, a new method for estimating the void fraction of gas/liquid two-phase flow has been brought forward. By using ANSYS simulating software, the simulation model of ERT system has been established and a lot of experimental data of different two-phase distributions in measured cross-section were obtained. The simulation data of three typical phase distributions (single-air-bubble distributing, two-air-bubble-separated distributing and many-air-bubble-mixed distributing) are analyzed, and the method for estimating the void fraction of gas/liquid flows, which is based on the feature extraction of measured voltage data from ERT system, has been presented and realized. This method can achieve a relative higher precision on void fraction prediction under some certain circumstances.