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

Methods of acoustic gas flux inversion-Investigation into the initial amplitude of bubble excitation

Passive acoustic inversion techniques for measuring gas flux into the water column have the potential to be a powerful tool for the long-term monitoring and quantification of natural marine seeps and anthropogenic emissions. Prior inversion techniques have had limited precision due to lack of constraints on the initial amplitude of a bubble's excitation following its release into the water column ( _R). _R is determined by observing the acoustic signal of bubbles released from sediment in a controlled experiment and its use is demonstrated by quantifying the flux from a volcanic CO₂ seep offshore Panarea (Italy), improving the precision by 78%.

Acoustic backscattering observations from non-spherical gas bubbles with ka between 0.03 and 4.4

The study of gas bubbles in liquid media is of importance in many areas of research. Gas bubbles are often studied using in situ measurement techniques; however, acoustic inversion techniques have also been used to extract physical properties of gas bubbles. These inversion techniques rely on existing analytical scattering models; however, these models often assume that the gas bubbles are spherical in shape and have an equivalent bubble radius, a, that is small compared to the incident acoustic wavelength (ka ≪ 1), which is not always valid. This study aims to understand how the departure from these assumptions affects the acoustic backscattering cross section, σ_bs, of non-spherical gas bubbles. Experimental estimates of σ_bs of non-spherical gas bubbles of different sizes, with ka values ranging between 0.03 and 4.4, were compared to four commonly known analytical σ_bs models. All models performed equally at predicting σ_bs for ka smaller than 0.5; however, there was no model that better predicted the experimental estimates of σ_bs for ka larger than 0.5, regardless of bubble shape. Large variabilities in the experimental estimates of σ_bs are observed for ka larger than 0.5, which are caused by the variability in bubble shape and size, as well as the bubble's orientation.

Extraction of bubble size and number data from an acoustically-excited bubble chain

The passive-acoustic measurement of bubbly flows could potentially deliver data useful to many industrial and environmental applications. However, acoustic interactions between bubbles complicate interpretations of measured frequencies in terms of the bubble sizes that are of practical interest. Experiments were undertaken on the emissions of a bubble chain when a just-formed bubble at one end of the chain created a sound pulse. This is an idealised paradigm for many applications. The chain was a one-dimensional line of bubbles fixed with known bubble sizes and inter-bubble spacings. Frequencies naturally emitted by the chain were measured for various bubble sizes and spacings, including cases such that the bubbles were close to touching. Semi-empirical fits were found relating the bubble size and number to the lowest and highest-measurable peak frequencies. It was found that all data collapsed onto two curves, one for the lowest-peak and one for the highest-peak frequency. This was confirmed by running numerical simulations for wider ranges of parameters than available experimentally. The results suggest that for a bubble chain, measurements of two peak frequencies could be used to determine the bubble size and also the number of interacting bubbles.

Determination of bubble size distribution in gas-liquid two-phase systems via an ultrasound-based method

Over the past few years, ultrasonic techniques are increasingly used to determine bubble size distribution in gas-liquid two-phase systems. However, the development of a precise and efficient measuring system is very challenging because bubbles are dynamic and unstable relative to time and space in a moving fluid, thus hindering an accurate validation of the measuring system. Therefore, this study examined the possibility of using artificial bubbles to establish an ultrasonic measuring system. The main concept for this study involved developing an ultrasound-based measuring system with the aid of a certain type of artificial bubbles. The developed system was subsequently adapted to the bypass pipeline of a propagator to demonstrate the reliability of this concept. The results indicated that the established system could measure a microbubble size distribution with a root mean squared error of validation that corresponded to 0.1243 % v/v. Additionally, the estimates of real bubble measurement agreed well with the reference method. Thus, this study demonstrated that the developed system could be a potential method to determine bubble size distributions in gas-liquid two-phase systems.