The use of acoustic inversion to estimate the bubble size distribution in pipelines

Abstract

The most popular technique for estimating the gas bubble size distribution (BSD) in liquids is through the inversion of measured attenuation and/or sound speed of a travelling wave. The model inherent in such inversions never exactly matches the conditions of the measurement, and the size of the resulting error (which could well be small in quasi-free field conditions) cannot be quantified if only a free field code exists. Users may be unaware of errors because, with sufficient regularization, such inversions can always be made to produce an answer, the accuracy of which is unknown unless independent (e.g. optical) measurements are made. This study was commissioned to assess the size of this error for the mercury-filled steel pipelines of the target test facility (TTF) of the spallation neutron source at Oak Ridge National Laboratory, TN, USA. Large errors in estimating the BSD (greater than 1000% overcounts/undercounts) are predicted. A new inversion technique appropriate for pipelines such as TTF gives good BSD estimations if the frequency range is sufficiently broad. However, it also shows that implementation of the planned reduction in frequency bandwidth for the TTF bubble sensor would make even this inversion insufficient to obtain an accurate BSD in TTF.

Dolphin-Inspired Target Detection for Sonar and Radar

“…Humans have spent over a century researching this interaction for a range of applications (Ainslie, Leighton, 2009). These include attempts to derive beneficial effects from bubble acoustics, in fields as diverse as: climate science for air/sea transfer (Thorpe, 1992 ; the processing and monitoring of pharmaceuticals and food (Campbell, Mougeot, 1999;Skumiel et al, 2013), and of fuel and coolant (Leighton et al, 2012a); the generation of microfluidic devices (Carugo et al, 2011); ultrasonic cleaning (Leighton et al, 2005;Offin et al, 2014); and, in biomedicine, the provision of acoustic contrast agents and drug delivery vectors (Ferrara et al, 2007), and the use of cavitation as a therapy monitor (McLaughlan et al, 2010;Leighton et al, 2008a). Studies also include attempts to mitigate or exploit the detrimental effects of bubbles, for example in the cavitation erosion of turbines and propellers Szantyr, Koronowicz, 2006), ship noise and its environmental impact (Kozaczka, Grelowska, 2004;Parks et al, 2007;Grelowska et al, 2013), and the sonar clutter that oceanic bubbles can produce.…”

Investigation of a method for real time quantification of gas bubbles in pipelines

“…This is because the liquid and pipe are acoustically coupled 20,21 and because, over most of the frequency range of interest in some pipe systems (such as SNS), modal acoustic propagation occurs with distinct frequencydependent sound speeds and attenuations for each mode. The current authors 10 showed that errors of þ/À 1000% can occur when such an approach is followed in a pipe of similar dimension to that used in the SNS at Oak Ridge National Laboratory (ORNL). Further complications occur with the acoustic inversion techniques that are based on the bubble pulsation resonance since the pipe can alter the inertia, 17,[22][23][24] frequency, 25 and damping 26 of that bubble resonance.…”

“…7 Recently, detectors for helium bubbles in steel pipelines filled with liquid mercury have been investigated for a spallation neutron source (SNS). [8][9][10] The ability to control the bubble size distribution, and to generate and detect a broad range of acoustic frequencies with controlled and calibrated amplitude in order to measure the bubble population, is however more characteristic of the laboratory than of industry.…”

“…Here, the coupling between liquid and wall generates similar effects to the coupling seen in SNS TTF. 20,21 Having therefore (i) characterized the bubble-free baseline 20,21 and (ii) shown that application of the "free field" inversion method (when bubbles are added) can produce overcounts and undercounts of þ/À 1000% in bubble numbers, 10 a new inversion was produced that is applicable to data taken in pipes. 10 The plan to implement this inversion with a broadband acoustic source was, however, interrupted: mid-way through this study the new funding pressure on the sponsors made the planned 1-1000 kHz frequency range unaffordable.…”

“…The initial intention was to invert the measured sound speeds and attenuation across this frequency range to obtain an estimation of the bubble population. 10 The first stage of this was to characterize propagation in bubble-free pipelines at SNS TTF, which further showed that useful data could be taken on 1:1 scale model pipelines built of water-filled polymethylmethacrylate (PMMA) pipes (Fig. 1).…”