Effective viscosity in a wave propagation model for ultrasonic particle sizing in non-dilute suspensions

Estimates of particle size distributions (PSDs) in solid-in-liquid suspensions can be obtained from measurements of ultrasonic wave attenuation. The technique is based on adaptively fitting theoretical wave propagation models to the measured data across a frequency range. These models break down at high solid concentrations and it is believed that this failure is due to the effective viscosity of the mixture in the vicinity of the particles being different from that of the continuous phase. This paper discusses PSD estimation when a number of different viscosity formulations are incorporated into the wave propagation model. The viscosity model due to Happel provides the best estimate of PSD in suspensions of medium concentration

Uncertainties in ultrasonic particle sizing in solid-in-liquid suspensions

Measurements of the frequency dependence of ultrasonic attenuation can be used as the basis for the estimation of particle size distributions (PSDs) in solid-in-liquid suspensions. The method requires matching the attenuation simulated by a candidate PSD in combination with a wave propagation model to the measured function in a fitting procedure. Uncertainty in the type of candidate PSD, whether based on fractional volume or fractional number of the dispersed particles, can cause errors in the overall estimation process, particularly for the median particle size. These uncertainties are investigated in the first part of this paper. The second part deals with uncertainties associated with the values for the physical properties of the suspended particles, seven of which are required in the simulation stage. It is shown that the particle sizing exercise is relatively insensitive to all of the physical properties except density, for which values are necessary to an accuracy commensurable with that required for the two principal parameters associated with the PSD – median size and standard deviation. The discussion is limited to small (less than 1 micron) silica particles dispersed in water. The results will have more general application

Ultrasonic wave propagation in powders

Powder clumps (cakes) has a significant effect on the flowability and stability of powders. Powder caking is mainly caused by moisture migration due to wetting and environmental (temperature and humidity) changes. The process of moisture migration caking involves creating liquid bridges between the particles during condensation which subsequently harden to form solid bridges. Therefore, an effective and reliable technique is required to quantitatively and non-invasively monitor caking kinetics and effective stiffness. This paper describes two ultrasonic instruments (ultrasonic velocity pulse and airborne ultrasound systems) that have been used to monitor the caking phenomenon. Also, it discusses the relationship between the ultrasonic velocity and attenuation measurements and tracking caking kinetics and the effective stiffness of powders

A novel high-resolution optical instrument for imaging oceanic bubbles

The formation of bubbles from breaking waves has a significant effect on air-sea gas transfer and aerosol production. Detailed data in situ about the bubble populations are required to understand these processes. However, these data are difficult to acquire because bubble populations are complex, spatially inhomogeneous, and short lived. This paper describes the design and development of a novel high-resolution underwater optical instrument for imaging oceanic bubbles at the sea. The instrument was successfully deployed in 2013 as part of the HiWINGS campaign in the North Atlantic Ocean. It contains a high-resolution machine vision camera, strobe flash unit to create a light sheet, and single board computer to control system operation. The instrument is shown to successfully detect bubbles of radii in the range 20-10 000 μm

Ultrasonic particle sizing in aqueous suspensions of solid particles of unknown density

Estimates of particle size distributions (PSDs) in solid-in-liquid suspensions can be made on the basis of measurements of ultrasonic wave attenuation combined with a mathematical propagation model, which typically requires seven physical parameters to describe each phase of the mixture. The estimation process is insensitive to all of these except the density of the solid particles, which may not be known or difficult to measure. This paper proposes that an unknown density value is incorporated into the sizing computation as a free variable. It is shown that this leads to an accurate estimate of PSD, as well as the unknown density

Ultrasonic attenuation measurements at very high SNR: correlation, information theory and performance

This paper describes a system for ultrasonic wave attenuation measurements which is based on pseudo-random binary codes as transmission signals combined with on-the-fly correlation for received signal detection. The apparatus can receive signals in the nanovolt range against a noise background in the order of hundreds of microvolts and an analogue to digital convertor (ADC) bit-step also in the order of hundreds of microvolts. Very high signal to noise ratios (SNRs) are achieved without recourse to coherent averaging with its associated requirement for high sampling times. The system works by a process of dithering – in which very low amplitude received signals enter the dynamic range of the ADC by 'riding' on electronic noise at the system input. The amplitude of this 'useful noise' has to be chosen with care for an optimised design. The process of optimisation is explained on the basis of classical information theory and is achieved through a simple noise model. The performance of the system is examined for different transmitted code lengths and gain settings in the receiver chain. Experimental results are shown to verify the expected operation when the system is applied to a very highly attenuating material – an aerated slurry

An integrated sensor platform for food reassurance

Given the increasing pressures on the global food system to produce more from the planet’s diminishing resources, the need to produce food that is safe to consume and reflects the information declared on pack is becoming ever more difficult to achieve as shown by the recent ‘horsemeat’ scandal. The salutary lesson that emerged from this latest food scandal was the vulnerability of the highly complex food supply networks that we rely on. For example, the wafers in the popular KitKat are ‘glued’ together with plaster-of-Paris which is sourced from India. These convoluted food networks increase the potential for product contamination through either physical, chemical or microbial means, with potentially life threatening consequences. Recent issues include the 2005 Sudan Red dye scandal, in which food products were contaminated with the potentially carcinogenic dye, and the 2013 worldwide recall of dairy products manufactured by Fonterra, because whey products suspected of being contaminated with botulism-causing bacteria were found during safety tests. It is important to remain vigilant in identifying and solving emerging challenges in global food networks to ensure a high level of consumer trust in the supply chain and food sold for consumption

Automated processing of oceanic bubble images for measuring bubble size distributions underneath breaking waves

Accurate in situ measurements of oceanic bubble size distributions beneath breaking waves are needed for a better understanding of air–sea gas transfer and aerosol production processes. To achieve this goal, a novel high-resolution optical instrument for imaging oceanic bubbles was designed and built in 2013 for the High Wind Gas Exchange Study (HiWinGS) campaign in the North Atlantic Ocean. The instrument is able to operate autonomously and can continuously capture high-resolution images at 15 frames per second over an 8-h deployment. The large number of images means that it is essential to use an automated processing algorithm to process these images. This paper describes an automated algorithm for processing oceanic images based on a robust feature extraction technique. The main advantages of this robust algorithm are it is significantly less sensitive to the noise and insusceptible to the background changes in illumination, can extract circular bubbles as small as one pixel (approximately 20 μm) in radius accurately, has low computing time (approximately 5 seconds per image), and is simple to implement. The algorithm was successfully used to analyze a large number of images (850 000 images) from deployment in the North Atlantic Ocean as part of the HiWinGS campaign in 2013

Novel approaches to ultrasonic particle sizing in suspensions with uncertain properties, and to the design of ultrasonic spectrometers

Ultrasonic spectrometry is now recognised as an effective approach to monitoring chemical processes online, an important application being measurement of the particle size distribution (PSD) in suspensions. The ultrasonic method is based on adaptively fitting a model of wave propagation to measured attenuation. This requires seven physical properties for each of the dispersed and continuous phases, some of which may be unknown and difficult to measure. The sensitivity of the model to these physical parameters is established, with a view to using approximate values for them. This leads to novel approach to PSD estimation; it is based on a combination of "guessing" some parameters and fitting more than two when running the model adaptively. The current wave propagation model uses as its viscosity input the value for water; it breaks down at high solids concentration. Various viscosity models have been applied in the wave propagation model to better simulate local viscosity in the vicinity of suspended particles. The current particle sizing algorithm is relatively slow. Improvements in the algorithm speed have been achieved by the use of a two step fitting procedure which permits rapid adaption of the model and thereby much faster PSD estimation. Conventional ultrasonic spectrometers generate high excitation pulses of 50- 200 V. A novel ultrasonic spectrometer for highly attenuating media has been designed which operates at low transmitted voltage and over a wide frequency bandwidth whilst preserving workable signal to noise ratios (SNRs). The new spectrometer is based on pseudo random binary sequences (PRBSs).EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Towards omni-directional and automated imaging system for measuring oceanic whitecap coverage

Accurate measurements of the oceanic whitecap coverage from whitecap images are required for better understanding the air-gas transfer and aerosol production processes. However, this is a challenging task because the whitecap patches are formed immediately after the wave breaks and are spread over a wide area. The main challenges in designing a whitecap imaging instrument are the small field of view of the camera lens, processing large numbers of images, recording data over long time periods, and deployment difficulties in stormy conditions. This paper describes the design of a novel high-resolution optical instrument for imaging oceanic whitecaps and the automated algorithm processing the collected images. The instrument was successfully deployed in 2013 as part of the HiWINGS campaign in the North Atlantic Ocean. The instrument uses a fish-eye camera lens to image the whitecaps in wide angle of view (180º)