Experimental and numerical study of rhomboidal mixing sections

The rhomboidal mixing section is becoming very popular among processors to provide distributive mixing. Currently, several different designs are used but the details of the flow behavior and mixing efficiency is not well unde rstood. This information is needed to be able to design and find the most e fficient rhomboid geometry. In this investigation nine different geometries with various pitches (helix of rhomboids) were analyzed using a 3-dimensio nal boundary element method (BEM). The geometries were compared according t o mixing efficiency, pressure and energy consumption. The results were comp ared to experiments performed with a conventional single screw extruder tha t was fitted with three different rhomboidal mixing sections. The investiga tion led to the conclusion that the most effective distributive mixing sect ions were those with neutral rhomboids (pineapple mixer). However, the neut ral rhomboidal mixing section consumes the most pressure in the extruder. I t was also concluded that rhomboidal mixing sections deform the material by shear, making them poor dispersive mixing sections.