Energy Measures of Efficient Mixing

Abstract

Abstract Several significant developments have taken place recently in the understanding of elastomer behavior in the internal mixer. An elastomer must be treated as a viscoelastic solid rather than a viscous fluid. The material behavior is recognized as transient instead of steady state. Elongational deformation plays an important role and the rate of such deformation is fast. Relevant fundamental properties are the viscoelastic properties at large deformations and ultimate properties. Views on the mechanisms of mixing have also changed recently. Instead of the laminar flow model, which accepts steady state shear flow, a comminution and lamination model has been proposed to represent large deformation, rupture, and recovery of the elastomer during mixing. With the comminution model and the fundamental measurements of rupture energy, a theoretical minimum mixing energy was estimated. The difference between the actual energy spent for mixing and the theoretical energy required is substantial. This suggests that there is room for saving energy through process improvements. Two examples of energy saving have been reported recently; one is the use of warm water cooling with an efficient heat transfer and another is a new configuration for four-wing rotors. The optimum processing temperature can be estimated from fundamental measurement of the ultimate properties of the elastomer. This points towards the use of warm water cooling. The new rotor design avoids impinging streams, which result in wasting energy for mixing viscoelastic material, although it mixes low viscosity fluids efficiently.