Abstract
This paper addresses the issues of slug detection and characterization in air-water two-phase flow in a vertical pipeline. A novel non-invasive measurement technique using continuous-wave Doppler ultrasound (CWDU) and bandpass power spectral density (BPSD) is proposed for multiphase flow applications and compared with the more established gamma-ray densitometry measurement. In this work, analysis using time-frequency analysis of the CWDU is performed to infer the applicability of the BPSD method for observing the slug front and trailing bubbles in a multiphase flow. The CWDU used a piezo transmitter/receiver pair with an ultrasonic frequency of 500 kHz. Signal processing on the demodulated signal of Doppler frequency was done using the Butterworth bandpass filter on the power spectral density which reveals slugs from background bubbles. The experiments were carried out in the 2” vertical pipeline-riser at the process system engineering laboratory at Cranfield University. The 2-inch test facility used in this experiment is made up of a 54.8 mm internal diameter and 10.5 m high vertical riser connected to a 40 m long horizontal pipeline. Taylor bubbles were generated using a quick-closing air valve placed at the bottom of the riser underwater flow, with rates of 0.5 litres/s, 2 litres/s, and 4 litres/s. The CWDU spectrum of the measured signal along with the BPSD method is shown to describe the distinctive nature of the slugs.
Highlights
Multiphase flows are common in many industries such as nuclear, chemical, and petroleum, and are often required to be measured under harsh surroundings, access difficulties, and strict safety restrictions
The measurement of multiphase flow is essential in oil and gas production for monitoring, reservoir management, well testing, and production allocation
Slug flow is one of the multiphase flow regimes and it is considered the most pervasive flow pattern conditions in vertical, horizontal, and inclined pipelines [1,2]. It is known as an irregular flow with a succession of liquid slugs, each accompanied by elongated gas bubbles above a thin liquid film layer [3,4]
Summary
Slug flow is one of the multiphase flow regimes and it is considered the most pervasive flow pattern conditions in vertical, horizontal, and inclined pipelines [1,2]. It is known as an irregular flow with a succession of liquid slugs, each accompanied by elongated gas bubbles above a thin liquid film layer [3,4]. The occurrence of slug flow may cause a serious problem in the piping systems and may cause large bubbles for the constant mixture velocity in the individual liquid and gas flow delivery systems.
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