Hassall, Guy (2011)
Eng.D. thesis, University of Birmingham.
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Most granular laundry detergents are manufactured through spray drying. One drawback of this process is wall build-up, which negatively effects process operation, safety and product quality.
Macro and micro-scale observations showed the amount and micro-structure of deposits changed significantly across the dryer. These changes were linked to changes in particle
properties during drying. Measurements of deposition ranged from 1 - 10 kgm-2, or 2 - 10% of the total slurry sprayed, depending on location, operating conditions and slurry/powder properties. Wall deposition appeared to be time dependent.
Wall deposition was broken down into two critical steps; collision frequency, describing how many and how often particles hit the wall and, collision success rate which describes particle’s behaviour upon contact with the wall. Collision frequency was investigated using Particle Imagine Velocimetry (PIV) to measure both fluid and particle dynamics. Finding both to be time dependent, and to vary with position and operating conditions.
To investigate collision success rate, particle physical and mechanical properties were studied, revealing mutual dependence of all properties on both formulation and particle size. Impacting these particles at a range of velocities and angles found that the fraction of particles that broke ranged from 0 - 100% and restitution coefficients from 0.1 - 0.8.
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