Non‐Invasive Size‐Control of Pneumatically Conveyed Particles

Abstract

Investigations on the size control of pneumatically conveyed coarse particles were carried out using a microphone which detects the structure‐borne sound caused by the impact of the particles on the pipe wall. Modes of eigenvibrations of the pipes are excited up to a maximum frequency, which decreases with increasing particle size. In an assembly of different sized particles, the lower frequencies are more stimulated as the fraction of larger particles increases. Changes in the particle size distribution are detected by analysing the intensities of the vibration modes which are set up in the walls of the tube by particle impact. One application is the monitoring of the upper range of a particle size distribution.

Non-invasive monitoring of the mixing of pharmaceutical powders by broadband acoustic emission

“…This observation is similar to that reported previously for the impact of various objects on different materials (e.g. steel ball bearings with a steel plate, 44 itaconic acid particles in toluene with a reactor wall, 30 powders with the wall of a mixing bowl, 38 and coal with a pipe wall 45 ) and from collisions between particles [33][34][35][36][37]46 and glass spheres [47][48][49] in a rotating drum. Similar trends were obtained with the WD transducer, and when mixing Avicel of different particle size ranges, although some variations were noted in the extent of the shift of intensity to lower frequencies.…”

System modelling and device development for passive acoustic monitoring of a particulate-liquid process

“…Note that the peak at 90 kHz corresponds to the resonance of the oil layer. The increase in the relative intensity of the signals in the lower frequency regions as particle size increased is in agreement with previously reported studies of the impact of objects with surfaces [7,17,[35][36][37][38]]. An increase in particle size causes an increase in AE magnitude and a decrease in AE frequency owing to a dependence on the particle surface area and impact time, respectively [33].…”

“…The amplitude of AE arising from collisions between a steel plate and a ball bearing increased as the number of impacting objects was increased, but as for collisions between spheres, the frequency of AE did not change [35]. During the pneumatic conveyance of coal, the maximum frequency of the vibrational modes of the structure excited on impact was found to decrease with an increase in particle size [36,37]. In studies of the mixing of dry powders [7,38] and particles in a liquid [17], the AE signal increased with an increase in the mass and size of particles, while the portion of AE at lower frequencies increased with particle size.…”

Factors affecting broadband acoustic emission measurements of a heterogeneous reaction

“…18,19 In comparison, when the size of an impacting object was increased, the emission frequency was found to decrease while the amplitude of the acoustic emission increased. 20 Where the source of acoustic emission was the impact of an object with a surface, e.g., in a powder mixing process, 21 during pneumatic conveyance of coal 22,23 or for steel ball bearings dropped onto a circular steel plate, 18 the emission frequency was inversely proportional to the size of the impacting object. The same relationship was also found for collisions between spheres in water, 20 steel balls, 24,25 spherical, [26][27][28][29] cylindrical 30 and irregular-shaped 31 particles, and glass spheres in an artificial sediment-water system 19,32 contained in a rotating drum.…”

“…The same relationship was also found for collisions between spheres in water, 20 steel balls, 24,25 spherical, [26][27][28][29] cylindrical 30 and irregular-shaped 31 particles, and glass spheres in an artificial sediment-water system 19,32 contained in a rotating drum. Other factors such as the shape 33 and velocity 20,22,23 of the impacting object have also been shown to affect the amplitude and/or frequency of acoustic emission generated.…”