Abstract
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.
Highlights
Powders are the final or intermediate products of many food, chemical and pharmaceutical industries
It discusses the relationship between the ultrasonic velocity and attenuation measurements and tracking caking kinetics and the effective stiffness of powders
Published under licence by IOP Publishing Ltd alumina. They demonstrated that ultrasonic velocity can be related to the packing geometry of coarser powder particles
Summary
Powders are the final or intermediate products of many food, chemical and pharmaceutical industries. Powder strength can increase significantly in the process equipment and during storage in the pack This phenomenon is known as caking whereby free flowing powder is transformed into clumps or aggregates [1, 2]. Published under licence by IOP Publishing Ltd alumina They demonstrated that ultrasonic velocity can be related to the packing geometry of coarser powder particles. 2. Theory of ultrasonic wave propagation in powder The acoustic properties of granular materials under confining pressure can be extremely nonlinear compared to continuum elastic solids. Equation 2 shows that the effective stiffness of the caked powder can be calculated from measurements of sound velocity by assuming Z and ø do not significantly vary and determining ρdry from the received signal amplitude. This is because of the tortuous path of the propagated ultrasonic signal in the free flowing powder as shown in figure 1
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