Comparison of Bubble Size Distributions Inferred from Acoustic, Optical Visualisation, and Laser Diffraction

Abstract

Bubble measurement has been widely discussed in the literature and comparison studies have been widely performed to validate the results obtained for various forms of bubble size inferences. This paper explores three methods used to obtain a bubble size distribution—optical detection, laser diffraction and acoustic inferences—for a bubble cloud. Each of these methods has advantages and disadvantages due to their intrinsic inference methodology or design flaws due to lack of specificity in measurement. It is clearly demonstrated that seeing bubbles and hearing them are substantially and quantitatively different. The main hypothesis being tested is that for a bubble cloud, acoustic methods are able to detect smaller bubbles compared to the other techniques, as acoustic measurements depend on an intrinsic bubble property, whereas photonics and optical methods are unable to “see” a smaller bubble that is behind a larger bubble. Acoustic methods provide a real-time size distribution for a bubble cloud, whereas for other techniques, appropriate adjustments or compromises must be made in order to arrive at robust data. Acoustic bubble spectrometry consistently records smaller bubbles that were not detected by the other techniques. The difference is largest for acoustic methods and optical methods, with size differences ranging from 5–79% in average bubble size. Differences in size between laser diffraction and optical methods ranged from 5–68%. The differences between laser diffraction and acoustic methods are less, and range between 0% (i.e., in agreement) up to 49%. There is a wider difference observed between the optical method, laser diffraction and acoustic methods whilst good agreement between laser diffraction and acoustic methods. The significant disagreement between laser diffraction and acoustic method (35% and 49%) demonstrates the hypothesis, as there is a higher proportion of smaller bubbles in these measurements (i.e., the smaller bubbles ‘hide’ during measurement via laser diffraction). This study, which shows that acoustic bubble spectrometry is able to detect smaller bubbles than laser diffraction and optical techniques. This is supported by heat and mass transfer studies that show enhanced performance due to increased interfacial area of microbubbles, compared to fine bubbles.

Fluidic Oscillators Mediating Generation of Microbubbles (Survey)

“…Its design was specifically adapted to the conditions prevailing microbubble generating aerators- Figure 7. The new oscillator version is of two-sided relaxation type, in principle following the one-sided oscillator design of Zalmanzon [22], the earliest known fluidic oscillator but very little is known. The feedback effect is obtained by filling compressed air into its two accumulation chambers C 1 , C 2 in this particular design is connected to the middle of the attachment walls.…”

“…The sum of mass transport surfaces increases, of course, with increasing the number of bubbles (and hence decreasing their mean diameter) generated from the same gas volume. From the fundamental patent [2], the basis of further developments, is shown in Figure 8 a picture of a typical configuration used in the tests [21,22] with a simple bioreactor (at right-hand side of the picture) and the oscillator (in picture centre). For the photosynthetic growing of primitive organisms [25][26][27][28][29], the reactor walls are transparent and the water inside illuminated by spectrally suitable light.…”

Numerical Analysis of an Electroless Plating Problem in Gas–Liquid Two-Phase Flow

“…The bubble size distribution was not measured and it ought to be done in the future and combined with numerical simulations as in [37]. The measurement of the bubble densities in the experiment is possible by means of acoustic, optical, and laser diffraction approaches [38]. However, these techniques are hard (or expensive) to be adapted on a microfluidic scale.…”

Numerical Characterization of Acoustic Cavitation Bubbles with Respect to the Bubble Size Distribution at Equilibrium

“…The authors suggested a procedure based on L-Surface analysis and applied to log-normal size distribution of bubbles in water. Desai et al [28] examined the bubble size distribution using three different techniques, namely optical detection, laser diffraction, and acoustic inferences. Their comparative study mainly demonstrated that acoustic methods provide a real-time size distribution for a bubble cloud, whereas for other techniques, appropriate adjustments or compromises must be made in order to achieve robust data.…”