Dong Feng

Two methods for measurement of gas-liquid flows in vertical upward pipe using dual-plane ERT system

In modern industrial processes, the accurate measurement of two-phase flow is an important task. Process tomography can provide a distribution information of a two-phase pipe flow. In order to carry out instantaneous flowrate measurements of the gas-liquid two-phase flow in a vertical upward pipe, a dual-plane electrical-resistance-tomography (ERT) system is combined with a cross-correlation technique to measure the gas-liquid two-phase flow, in which the continuous phase is a conductive liquid. A pixel correlation method and a feature-value-correlation method are applied to estimate the disperse-phase velocity. Two methods are used to estimate the local void fraction and the disperse velocity distribution by reconstructing the image pixel gray value distribution. Estimates of the mean void fraction and the disperse-phase mean velocity are obtained by extracting the feature value of the measured data at the dual-plane ERT boundary. The variation in the disperse-phase distribution with changes in time is considered, and the estimated values for both the disperse-phase void fraction and velocity have been experimentally obtained, which are used in the calculation of the instantaneous flowrate. The air-water two-phase flow experiments are designed to evaluate the validity of the two methods used in estimation. The experimental results agree with the theoretical methods for obtaining the disperse-phase velocity and instantaneous-flowrate measurement in the vertical upward pipeA dual-plane Electrical Resistance Tomography (ERT) system is employed to combine ERT with cross correlation technique to measure the gas phase volumetric flowrate in gas-liquid flows in vertical upward pipe. According to the uniformity of the local void fraction distribution and the velocity distribution of gas phase, pixel-correlation method and eigenvalue-correlation method are put forward to estimate the gas phase volumetric flowrate. This paper compares the two estimate methods and makes preliminary study of the applicability of the two methods. Two experiments were designed to evaluate the validity of those two estimate methods. Experimental results were presented to analyze their characters respectively.

Research on electrical resistance tomography and cross-correlation technique to measure the two-phase flows

In the two-phase flows measurement, Electrical Resistance Tomography and cross-correlation technique have both been proved available and promising. So in our investigation, the dual-plane ERT system is founded after combining the two techniques, and we proposed pixel correlation method to achieve the parameters of velocity and void fraction which are important to the measurement of two-phase flowrate. The experimental results of single bubble experiment and its analysis are also presented in this paper.

Dynamic performance improvement of ERT system [electrical resistance tomography]

Electrical resistance tomography (ERT) is the embranchment of process tomography (PT). In this paper, the bottleneck of system real-time performance is analysed. The dynamic performance of the system can be improved by increasing the signal frequency, placing the band pass filter (BPF) parallel and replacing the low pass filter (LPF) used to obtain the amplitude information by a digital measurement method. Based on these analyses, an improved ERT system is designed, and a method of peak value measurement used to obtain the amplitude of the measurement signal is put forward.

Performance evaluation and structure optimization of an inner-outer electrical resistance tomography sensor

Electrical resistance tomography is a useful visualization technique to imaging the conductivity distribution inside a closed pipeline from the boundary measurements. Due to its advantages of high speed, low cost and high safety, the technique has been successfully applied in the measurement of many industrial processes. However, since the mathematical model is highly non-linear and ill-posed, the spatial resolution of ERT is low, especially in the center of the objective domain. To overcome the problem, an inner-outer ERT sensor structure was proposed. The structure is consisted by the internal and external electrodes, and can provided more independent measurements for high resolution image reconstruction. To test the performance of the inner-outer sensor structure, six inner-outer ERT sensors are designed, and the influences of the size, number and distribution of the internal electrodes are discussed. After several numerical tests, the inner-outer ERT sensor is proved having the ability of enhancing the spatial resolution of ERT, especially in the area near the internal electrodes.