Red–Green–Blue (RGB) colour system approach to study the segregation and percolation in a mixture of white wheat flour and bleached wheat bran

Abstract

SummaryIn this work, we applied a nonintrusive measurement method based on the Red-Green-Blue (RGB) image analysis system to study the segregation and percolation in a mixture of white wheat flour and bleached wheat bran. This method intended to quantify the presence of one or several colours in the surface of mixed ingredients. The mixing of flour particles with bleached and unbleached wheat bran was studied using a 90 mm closed rotating cube. This system forced the particles to roll relative to each other so as to favourite the segregation by percolation in order to hide one colour by another. The obtained results showed a possibility of obtaining homogeneous colour when the wheat flour was mixed with the bleached wheat bran at a volume ratio of 20/5%-10%. By increasing to ratio up to 20/15% (flour/bran), the RGB system showed a presence of two colours in the surface of the mixture. Moreover, the RGB method confirmed the presence of two heterogeneous colours when the wheat flour was mixed with the unbleached wheat bran whatever the ratio (20/5%, 10% and 15%).Keywords Percolation, segregation, static mixer, wheat bran, wheat flour. IntroductionThe mixing of solids, powders or granular materials is a key operation in many industrial fields such as pharmaceuticals, food powders and granular ingredients, agricultural powders, cement and plastics. This operation allows achieving the specifications and usage properties of the desired products. Moreover, mixing is largely responsible for the homogeneity of the final product. The mixing is an essential step during which many problems can occur which can have significant influence on the product quality because the notion of homogeneity of a solid mixture is very important.Unlike fluids, the powder mixing is still poorly understood. This is probably due to the mesoscopic nature of these environments and lack of models describing the behaviour of mixed powders. According to A€ ıt Aissa (2011), the powder differs from the liquid mixing by three aspects: (i) there is no relative movement of the solid particles without energy as for liquids or gases, (ii) the rate of powder homogenisation depends only on the particle flow properties, operating conditions and mechanical stresses imposed by the stirring device and (iii) although the molecules of a liquid in a mono-phase system may be different and diffuse at different speeds, they will always reach a state of perfect mixing. The homogenisation of solids is, however, often accompanied by a process of segregation, which often does not allow obtaining a perfect blend. Thus, the final state of the mixture is a balance between homogenisation and segregation. Finally, the size of a solid particle is always much higher than that of molecule of any liquid or gas. In fact, once the particles set in motion, they can also mix well or segregate according to the movement imposed on the system and the characteristics of the components.Segregation is an undesirable phenomenon in particle mixing because it significantly affects the blend qu...

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