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This study introduces a measurement technique for simultaneous phase-separated velocity in two-phase bubbly flow. The non-invasive technique, based on an Ultrasonic Velocity Profiler (UVP), is used in order to obtain an instantaneous, separate velocity profile for both liquid and bubble. The aim of this paper is to measure each phase velocity at the same time and position it using only a single resonant frequency. To achieve this aim, extended signal processing of the Short-Time Fourier Transform (STFT) is proposed, combining with amplitude classification to analyze Doppler signal influenced from the bubbly flow. The use of developed algorithms allows the instantaneous separation of liquid and bubble velocity profiles. In this work, the developed technique is used to measure the velocity profile of bubbly flow in the vertical pipe, demonstrating the classification of liquid and bubble velocity. To confirm the accuracy of each velocity profile phase, the Particle Image Velocimetry (PIV) method is used for comparison. The results clarify that the proposed method is in good agreement with the PIV measurement. Finally, the effect of void fraction against velocity measurement of both phases was demonstrated. [ABSTRACT FROM AUTHOR]

Two-phase air-water bubbly swirling flow through a pipe is a complex turbulent flow and its prediction is still challenging. The present paper describes the experimental investigation of the air-water bubbly swirling flow in vertical co-current flow. Swirling flow is induced by a twisted tape in a 20 mm inner diameter pipe. The flow is investigated using Ultrasonic velocity profiler (UVP), which allows the measurement of liquid and gas velocities simultaneously. Furthermore, simultaneous measurement of void fraction is performed using Wire mesh sensor (WMS). The experimental results reveal that swirling flow has significant impact on bubbles' distribution. In low liquid flow rate, the average bubble velocity is fairly uniform along the radial position and void fraction increases in the near wall region. However, increasing liquid flow rate at constant gas flow rate leads to increase in void fraction in the core region, this is mainly due to drift velocity which is affected by centrifugal force. Experimental findings and parametric trends based on the effects of swirling flow are summarized and discussed. [ABSTRACT FROM AUTHOR]

Abstract: An ultrasonic velocity profile measurement system has been realized that can measure velocities in a very slow flow. The system implements a novel phase difference method that overcomes the low velocity limitation in a conventional signal processing algorithm for the Doppler method. The measurement system consists of pulser/receiver, transducer and digitizer only with all signal processing carried out on a personal computer. The measurement limitation at a very low velocity was examined using signals reflected from a wall which are collected by moving transducer at speeds less than 10−2 mm/s. For velocity profiling, real-time profile measurements were performed, which demonstrated successful results for the flow inside a rotating cylinder. [Copyright &y& Elsevier]

This paper presents a new estimationmethod to determine the optimal number of transducers using an Ultrasonic Velocity Profile (UVP) for accurate flow rate measurement downstream of a single elbow. Since UVP can measure velocity profiles over a pipe diameter and calculate the flow rate by integrating these velocity profiles, it is also expected to obtain an accurate flow rate using multiple transducers under nondeveloped flow conditions formed downstream of an elbow. The new estimation method employs a wave number of velocity profile fluctuations along a circle on a pipe cross-section using Fast Fourier Transform (FFT). The optimal number of transducers is estimated based on the sampling theorem. To evaluate this method, a preliminary experiment and numerical simulations using Computational Fluid Dynamics (CFD) are conducted. The evaluating regions of velocity profiles are located at 3 times of a pipe diameter (3D) for the experiment, and 1 and 5D for the simulations downstream of an elbow, respectively. Reynolds numbers for the experiment and simulations are set at 4 × 104 and 5 × 106, respectively. These results indicate the efficiency of this new method. [ABSTRACT FROM AUTHOR]

Abstract: This study proposes a new method that determines the number of transducers for accurate flow rate measurements using the ultrasonic velocity profile (UVP) method downstream of double elbows. Because the UVP method can measure velocity profiles over a pipe diameter and integrate them to obtain the flow rate, it is also expected to obtain an accurate flow rate using multiple transducers under asymmetric flow conditions formed downstream of elbows. The new estimation method employs the wavenumber of velocity profile fluctuation along a circle on a pipe cross-section, obtained by fast Fourier transform (FFT). The number of transducers was determined as twice the wavenumber at the foot of maximum Fourier amplitude, on the basis of the sampling theorem. The method was evaluated by a preliminary experiment and numerical simulations using computational fluid dynamics (CFD). The experimental and simulated velocity profiles were located at three times the pipe diameter (3D) and 1D downstream of the second elbow, respectively. Reynolds numbers for the experiment and simulations were set at 4×104 and 5×106, respectively. Using the number of transducers estimated by FFT, the standard deviations of flow rate errors were less than 1% or 2%, verifying the efficacy of the new method. [Copyright &y& Elsevier]