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Study On Electrical Capacitance Tomography And It's Application In Parameter Measurement Of Two-phase Flow

Posted on:2004-07-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:L WangFull Text:PDF
GTID:1118360122471278Subject:Control Science and Engineering
Abstract/Summary:PDF Full Text Request
Two-phase flow has a wide range of application in industry. The research on two-phase flow is developing rapidly. The subject on two-phase flow has been one of the frontier subjects concerned deeply in the world. The measurement of two-phase flow is difficult, owing to the complexity of the characteristic of two-phase flow. In many cases, the two-phase flow measurement technique has been one of the factors that bottleneck the study in the field of two-phase flow.Electrical capacitance tomography (ECT) is a kind of process tomography techniques that are widely studied. ECT is fast, non-invasive, low cost, safe and widely applicable. It has become one of important techniques for two-phase flow parameter measurement. But there are some problems and difficulties in ECT designs and ECT applications. The topics of this dissertation are small capacitance measurement that is a key part in ECT designs and ECT applications, high-speed data acquisition system design and ECT applications in two-phase flow parameter measurement. The main works are listed as follows:(1) The small capacitance measuring circuit for ECT based on the charge amplification principle was deeply analyzed and improved. The stray-immunity and the charge injection effect of this circuit were deeply analyzed. The influence of the charge injection effect was eliminated by practical time sequences and circuit structure differential. The mathematics model of this circuit was improved. Capacitance data acquisition speed was increased by optimization measures of software and hardware. Test results showed that the data capture rate of 600 frames/second can be achieved without real-time image reconstruction.(2) Based on the ECT sensor and the geometry of two-phase flow regimes, a new method was proposed for gas-liquid two-phase flow regimes identification. Four experience formulae were obtained from mass experiments data. The static and dynamic test results showed that the new method is effective and the identification results of stratified flow, annular flow, core flow and plug flow are satisfied for the requirements of theindustrial operation online.(3) Based on ECT sensor and pattern recognition theory, a new method was proposed for voidage measurement of gas-liquid two-phase flow. One of three template databases was selected by flow regime classification. The voidage was obtained by template matching with Euclid distance measure. The advantages of this method were that the measurement results weren't affected by flow regime and the speed was faster than the conventional voidage measurement method by reconstructed ECT image. Test results showed that the method is effective and the maximum error of measurement is less than 5%.(4) According to the characters of large rectangular pixels of ECT reconstructed images, a new method was proposed to obtain contour line of pixel gray. The four sidelines of ECT reconstructed images pixels were labeled as three classes by the different adjacent cases of pixels. The original contour line was formed by the first and third class sidelines. Based on B-spine function, the original contour line was smoothed and fitted. This method was successfully used to monitor the solid concentration in gas-solid fluidized bed.
Keywords/Search Tags:capacitance, tomography, sensor, two-phase flow, regime, voidage, measurement
PDF Full Text Request
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