| The gas-liquid two-phase flow is widely encountered in many industrial fields,such as petroleum,chemical,power,and metallurgy industries,and its online and non-separation flow rate measurement has important scientific and engineering significance.Detecting the parameters of the gas-liquid two-phase flow is very difficult because of the inherent complexity of this flow,and the online and non-separation flow rate measurement is a problem that has not been well resolved at home and abroad.Especially in the petroleum industry,the product obtained during the process of oil extraction is a three-element and two-phase mixture of oil,gas and water.The flow rate and ratio of each phase are the main parameters for monitoring the operating status of oil wells and the dynamic characteristics of oil and gas reservoirs.Accurate measurement of these parameters is of great significance for the comprehensive development of oilfields and energy conservation.In view of this problem and the huge difference in the heat transfer capacity of the gas and liquid phases with the heat exchange surface,this dissertation studies the temperature response of the pipe wall to the gas-liquid two-phase flow in the pipe during the heat exchange process,and proposes a new gas-liquid two-phase flow measurement method based on thermal diffusion:the flow characteristics of the fluid in the pipe are inferred by detecting the temperature response of the pipe wall during the heat exchange process with the gas-liquid two-phase flow,and the flow rates of the gas and liquid are further calculated,so as to realize the real-time online,non-separation,non-contact measurement of gas-liquid two-phase flow.A fully developed gas-liquid two-phase slug flow can be constructed in the vertical pipe with a suitable pipe diameter,and the flow rate is measured under this flow pattern.First,the temperature fluctuation law of the pipe wall in the heat exchange process with gas-liquid two-phase flow under different flow patterns is studied.The temperature fluctuation characteristics are characterized by four fluctuation parameters including temperature fluctuation velocity,intensity,frequency and temperature difference,and the correlations between these fluctuation parameters and flow patterns are obtained;based on these correlations,a method for identifying gas-liquid two-phase flow patterns according to temperature signal analysis is proposed for the first time,and the accuracy of flow pattern recognition in the experiment can reach 95%by combining these four fluctuating parameters.Then,in the slug flow state,the correlations between the temperature fluctuations and flow characteristic parameters(the velocity and length of the Taylor bubble and liquid slug,the liquid film thickness,and the void fraction in the liquid slug)are developed through the study of the one-to-one correspondence between the rise/fall of the temperature curve and the passage of Taylor bubble/liquid slug;the average relative error in the measurement of average velocity and length for the Taylor bubble and liquid slug are 2.28%and 4.65%,respectively.On the basis of the flow characteristic parameters,a flow rate calculation model is further established to calculate the volumetric flow rates of the gas and liquid in the gas-liquid two-phase flow,and their average relative errors are 3.45%and 5.51%,respectively.In addition,for the gas-liquid two-phase slug flow in which the liquid phase is incompatible with two components,the applicability of the drift flux model and the Taylor length correction equation is verified by experiments,and the liquid film thickness is also corrected according to the viscosity of the liquid phase at the same time;the average relative errors of the gas and liquid flow rates are 3.38%and 4.19%,respectively,therefore,the feasibility of the thermal diffusion measurement method within the range of fluid physical properties in the experiment is further proved. |
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