Studies Of Gas-liquid Two-phase Flow Measurement Based On A Slot Venturi Device

The gas-liquid two-phase flow phenomena are common in industries such as petrol, power, chemical, metallurgy, pipeline transport, medical and refrigeration. It is of great importance to research on hydrodynamics mechanisms and accurate detection of parameters in two-phase flow.On the basis of the study about the Venturi tube and U tube, a new gas-liquid two-phase flow metering system based on a slot Venturi device was proposed, and the two-phase flow metering with flow pattern recognition was implemented.The mainly research works of this thesis are as follows.1. Based on the homogenous and separated flow theory, a new H-S model was put forward. Inheriting the merits of homogeneous correlation and separated correlation, The H-S model can predict Venturi over reading accurately both under high and low pressure with the prediction error less than±6.5%. A model based on artificial neural network(ANN) was also presented, and the error of ANN model is within±5%2. A new gas-liquid two-phase flow measurement system based on slot Venturi device was proposed. Theory analysis shows that the effect of the friction pressure drop can be reduced by a symmetry structure; the gravity differential pressure measuring, which vertical to the flow direction in slot segment, can avoid the effect of the frictional resistance.3. The gravity differential pressure fluctuation signal and the time averaged signal were firstly used to analyze the characteristics of gas-liquid two-phase flow. The gravity differential pressure signal relates to the void fraction directly, and reflects the interaction between the gas phase and the liquid phase. Under different flow patterns, the gravity differential pressure fluctuation signal and the time-averaged signal compensate each other, and the flow pattern can be recognized accurately by combining these two signals.4. The differential pressure characteristics of the slot Venturi were investigated under two-phase flow condition. Study shows that the performance of the slot Venturi with its symmetry structure is consistent with the separate flow assumption due to the reduction of the friction pressure drop. The measurement models under different flow condition conditions were presented according to the differential pressure features, and the prediction errors are within±5%.5. The metering models about gas quality fraction and liquid volume fraction were put forward under different two-phase flow conditions and were proved by experiments. Under the gas dominated flow condition, the gas quality fraction has a linear relationship with the ratio of the acceleration pressure drop and the friction pressure drop. The slopes of the curves were affected by the static pressure and the gas froude number. The error of fitting correlation was within±12.5%. While Under the liquid dominated flow condition, the liquid volume fraction can be calculated according to the relationship between the gravity differential pressure and the void fraction, where the error was within±5%.6. A non-diverter metering program was implemented based on slot Venturi, and two-phase flow measurement with flow pattern recognition was investigated. Three types flow patterns were identified with time-averaged signals of the gravity differential pressures; the gas and liquid flow rate can be solved with different measurement models under different flow patterns. The results show this method is available.