Visualization Methods Of Two-phase Flow Based On Electrical And Ray Tomography

The two/multi phase flow process is not only frequently encountered in natureand human being life, but also occurs widely in the energy, petroleum, chemical,metallurgical, refrigeration, aerospace, pharmaceutical, food and other modernindustrial processes. Measuring the process parameters of the two/multi phase flow isnot only very important to the development of the national economy, but also of greatsignificance to human resources being efficiently used. However, because of thedifferent flow characteristics and complicated instantaneous change interface betweentwo phases, precise measurement of the process parameters of two phase flow hasalways been a hotspot and difficult point in scientific research and industryapplication. Therefore, the purpose of this research is, on the basis of the conceptionof visualization measurement of multiphase flow, to investigate and analyze the mainvisualization measurement methods, especially tomography techniques, and todevelop new visualization measurement sensors for measuring and analyzingmultiphase flow. The research has been conducted by four steps as follows:1. New digital electrical resistance tomography system based on FPGA andCompactPCI industry standard bus has been built. By using the CompactPCI industrystandard bus protocol, the new system has the advantages of excellent operationalstability, high-speed data transportation, good extended performance, etc. Because ofthe application of FPGA chips, the digital demodulation and other signal digitalmodules have easily been realized, hence the speed of the data acquisition system hasbeen improved substantially. The imaging experiment result showed that the systemhad a high data acquisition speed which was above1300frames per second, a signalto noise ratio which was above60dB and an outstanding image reconstructionperformance. The new system could meet the measurement needs of most industrialprocesses with continuous conductive materials.2. The axial step exciting method of segmented electrodes based on thecapacitance measurement principle has been developed. The simulation experimentsproved that the characteristics of the processed dataset obtained by the excitingmethod could directly identify the flow pattern. In addition, the data characteristics ofstratified flows with different liquid levels proved to be very obvious. The method is mainly used to investigate the response of the capacitance materials whenmeasurement fields are extended from the local to the global.3. Based on the electrical capacitance measurement principle, an annular fieldfocusing capacitance sensor has been developed. The sensor has been used for thevisualization of two phase flows in the annular flow field. The performance analysisof the sensor showed good sensitivity. The imaging simulation proved that the signalof the sensors could be used to obtain images of the two phase distribution in theannular flow field directly without any complicated imaging reconstruction algorithm.To sum up, a visualization method for the two phase flow in an annular pipe has beenestablished.4. Based on the combination of the Wire-Mesh and ultra fast X-ray tomographysensors, the co-current vertical gas-liquid flow experiments, especially the bubbly andslug flow measurement experiments, have been executed. After processing andanalyzing the tomography data, the radial cross-section gas fraction and velocity aswell as the bubble size distribution of the two phase flows have been extracted andcalculated. The experiment results showed that, because of the high space and timeresolution of the sensors, the combination of the wire-mesh sensor and ultra fast X-raytomography sensor could provide an effective method for measuring the dynamicparameters of the high-speed transient two-phase flow. The maximum deviation of thegas fraction profiles was4%, which indicated very good agreement. The gas phasevelocity radial profile could be evaluated by using the cross-correlation of the gasfraction from the two sensors. With the gas fraction and velocity data, the bubblescould be identified and the bubble size, bubble equivalent diameter and bubble sizedistribution could be extracted. When measuring bubbly flow using the two sensors,the bubble size distributions indicated good agreement.