Single droplet drying of detergents:Experimentation and modelling

This study evaluates the single droplet drying(SDD)of detergents.Experimental data are used to validate a theoretical multistage model.The experiments are carried out in an acoustic levitator analysing six different detergent formulations at 393 K.The work is completed by developing a model based on conservation equations.The model is composed of the three stages observed in the drying curve.In the first stage,an external surface drying stage occurs until the surface is saturated and the crust is formed.In the next stage,the drying rate is governed by diffusion through the pores.At the same time,the particle heats up until boiling conditions are achieved in the core of the particle.At this point,the third stage begins.In the final stage,the droplet core is in boiling conditions which are governed by the pressure drop through the crust and the concentration of salts.This model has been evaluated for the different formulations being flexible to predict the drying of different mixtures with good accuracy.

An experimental and numerical study of packing, compression, and caking behaviour of detergent powders

This paper presents an experimental and numerical study of the packing, compression, and caking behaviour of spray dried detergent （SDD） powders with a two-fold aim： an experimental process of observation and evaluation of the packing, compression and caking behaviour of SDD powders, and a numerical approach based on discrete element modelling （DEM）. The mechanical properties, including the stress-strain response and the corresponding porosity change as a function of consolidation stress in a confined cylinder, the stress-strain response during unconfined shearing and the cake strength as a func- tion of consolidation stress, were evaluated and compared for different SDD powders using an extended uniaxial tester （Edinburgh Powder Tester - EPT）. The experiments using EPT showed excellent repro- ducibility in the measurement of packing, compression and caking behaviour and were therefore very useful for describing the handling characteristics of these powdered products including screening new products and different formulations. It was found that the sample with higher moisture had lower bulk porosity but higher compressibility and cake strength. The porosity, compressibility and cake strength were found to vary across different size fractions of the same sample. The larger sieve-cut samples had higher initial bulk porosity, compressibility and cake strength. It is revealed that moisture plays a sig- nificant role in packing, compression, and shearing behaviour of the powder. Three-dimensional DEM modelling using a recently developed elasto-plastic adhesive-frictional contact model showed that the contact model is able to capture the detergent behaviour reasonably well and can be used to model complex processes involving these powders.

CFD-DNS simulation of irregular-shaped particle dissolution

A coupled approach between the conventional computational fluid dynamics platform COMSOL and an in-house-developed direct numerical simulation code DigiDiss is presented to study the dissolution kinetics of an irregular-shaped particle in a stirred cuvette.The complex flow dynamics from COMSOL were imported into DigiDiss as an initial flow condition.A digitised 3D particle structure scanned and reconstructed by X-ray micro-tomography was used in the dissolution simulation.A quantitative assessment of the simulation results was made using as a reference experimental data and a theoretical calculation based on the shrinking spherical model with different flow velocity profiles near the particle.The comprehensive agreement demonstrates the coherence of the simulation method in reproducing the experimental behaviour and is seen as a step closer towards developing a computer software design aide to help with formulation development.