Signals features extraction in liquid-gas flow measurements using gamma densitometry. Part 1: time domain

Abstract

Abstract. The paper presents an application of the gamma-absorption method to study a gas-liquid two-phase flow in a horizontal pipeline. In the tests on laboratory installation two 241 Am radioactive sources and scintillation probes with NaI(Tl) crystals have been used. The experimental set-up allows recording of stochastic signals, which describe instantaneous content of the stream in the particular cross-section of the flow mixture. The analyses of these signals by statistical methods allow to determine the mean velocity of the gas phase. Meanwhile, the selected features of signals provided by the absorption set, can be applied to recognition of the structure of the flow. In this work such three structures of air-water flow as: plug, bubble, and transitional plug -bubble one were considered. The recorded raw signals were analyzed in time domain and several features were extracted. It was found that following features of signals as the mean, standard deviation, root mean square (RMS), variance and 4 th moment are most useful to recognize the structure of the flow.

Prospects for the application of radiometric methods in the measurement of two-phase flows

“…In order to perform automatic pattern flow recognition one may utilize artificial neuron networks or other methods of the so-called calculation intelligence. The particular applications were described in publications [36][37][38][39].…”

Application of ANN and PCA to two-phase flow evaluation using radioisotopes

“…Photons pass through the pipeline with flowing compound (5) and detector's collimators (3) before achieving probes (4). Two sets consist of linear 241 Am sources with an activity of 100 mCi and probes with 2'' NaI(Tl) scintillation detectors [19]. For flow velocity measurement, the sets are placed at a distance of L = 97 mm between them [20].…”

“…Detailed specification of experimental set-up presented in Fig. 2 is described in publications [19,20]. …”

“…For these structures of flow, the 300,000 sample signals were recorded in experiments denoted as: BUB6, BUB4, and BUB1 with a sampling rate of 1 kHz [19]: m / s, where ȣ W -velocity of water was measured by ultrasonic flowmeter Uniflow 990. Velocity of gas phase ȣ A was appointed using cross-correlation technique [21][22][23][24].…”

“…Based on the analysis of the data records registered in the experiments the following parameters (features) were calculated for the three types of the flow regimes (classes): "plug flow", "transitional plug -bubble flow", and "bubble flow": a) in the time domain: mean value, variance, standard deviation, 4 th order moment, root mean square (RMS), skewness, kurtosis [19]; b) in the frequency domain: maximum value of the autospectral density function (ADF), maximum value of the cross-spectral density function (CSDF) magnitude, sum and relative sum of the ADF in the selected frequency range, sum and relative sum of the CSDF in the selected frequency range, the maximum value of the sum of selected amplitudes of Short-Time Fourier Transform (STFT) spectrogram, and area and relative area under the graph of STFT spectrogram sum in the selected frequency range [25].…”