Countless manufacturing and processing operations depend on efficient mixing of solids, gases or liquids, (and combinations like slurries and foams). The objectives of mixing vary – sometimes it’s to optimise chemical reactions, sometimes to disperse heat, or produce products consistent in colour, texture or flavour.
While simple in principle, mixing technology is critical. Modern societies rely on it for manufacturing, water purification and food production. As scales increase, mixing efficiency becomes ever more important, enabling higher production, lower costs and better product quality.
The term “blending” is sometimes used for gentler degrees of admixing. Although maximum homogeneity is the usual objective, in some cases, lower degrees of blending are preferable. For example, overworked pastry gives a harder, less desirable, baked result, and levels of irregularity in concretes alter their structural qualities.
Types of mixing equipment
Solid powders usually require a different approach to that used to mix viscous fluids. Dynamic stirrers and tumbling equipment are power driven, whereas with fluids, static mixers are often a better option, with the energy to perform the mixing imparted by the flow of the fluid, driven by pumps or blowers (occasionally by gravity or convection) over mixing rods or profiles in continuous process pipelines and ducts.
The former group includes solid/solid mixing equipment, like tumble and double cone blenders, vertical screws, plough and paddle mixers, and fluid/fluid agitators, including flow impellers, and pitched blade turbines.
Static mixers include pipe, channel and duct mixers, gas dispersion units and heat exchangers. One advantage of mixing in pipelines is that samplers and injectors can constantly monitor and tune the results achieved at different points in the line.
In gases and liquids of moderate viscosity, flow turbulence is a key factor in how the blades induce mixing. In heavier fluids, viscous drag equations are often used. However, not all fluids exhibit simple Newtonian behaviour, which means that flow calculations can be complex. Specialist advice is available from statiflo.com.
In the chemical industry, thorough mixing is required to ensure top quality end products like polymers, fertilisers, explosives, ceramics, and rubber compounds for car tyres.
In the pharmaceutical industry, the blending of drugs with stabilisers and bulkers, like cellulose or lactose, is a common requirement.
In food production industries, good quality mixing is important for the dispersal of spices and additives, and in the preparation of dough and cake mixes.