mixing processes

Mixing Processes Explained


Usually a straight forward process, aiming to create a homogenous mixture of input materials to form a finished product or intermediate component. This often involves bringing together two liquids or dissolving/dispersing a powder in a liquid and the best result may well be achieved using a simple low speed propeller or “bow tie” type mixer

For less miscible liquids and powders, completely homogenisation is achieved using either a High Shear Disperser or a GM High Shear Homogeniser.

Choice of equipment depends on the process specification, particularly any vortex or aeration requirements to achieve the desired product properties.


Propeller, Axial flow Turbine, Radial Flow Turbine, Helical Ribbon Blade, Anchor Helical Scraper


Where two or more liquids are non-soluble and immiscible, a High Shear Mixer will produce smooth emulsion in minutes. A key objective in all instances is to reduce droplet or particle size and achieve a homogenous mixture. A high upward flow rate maintains the immiscible liquids in full circulation whilst they continue to pass through the mixer head where they are subjected to high shear action. This means excellent emulsions can be rapidly produced with minimum effort. Oil in water and water emulsions are rapidly produced even when thickening has occurred; a high flow rate ensures homogeneity and this permits any colouring to be added at the end of the batch process.


High Shear mixer, High Shear Disperser


This term applies to any fluid where a smooth, stable mixture is required regardless of the volume being processed. When conventional agitation or stirring does not offer these results, Greaves High Shear mixers will homogenise the mixture or emulsion without making any physical changes to the fluid properties


High Shear mixer, Pitch blade turbine


Some powders are difficult to disperse in water ( or other solvents) due to incomplete ‘wetting-out’. High shear mixers execute this task in impressive timescales. Typical applications might include Methyl Cellulose, Carboxy-Methyl Cellulose,Locust Bean Gums, Starch Ethers and Esters, Alginates and Crystal Gums for thickening and stabilising foodstuffs. Even for viscosities greater than 30,000 cps a High Shear Mixer will continue to circulate the fluid and disperse any lumps which may already have formed in the initial stages of mixing.


High Shear mixer, Pitch blade turbine


This typically involves blending of liquids to dilute products in let down tanks to produce a reduced concentration solution. Axial flow impellers are employed to circulate vessel contents until a uniform product is achieved. For less miscible products Greaves offer the GM range. In this type of application high shear impellers generate a strong vacuum and the resulting turbulence ensures any heavy pastes or sediments which may otherwise form are instantly dispersed.


High Shear mixer, disperser


Where particle size is inconsistent, the powerful action of a Greaves High Shear Mixer can offer an effective way to disintegrate larger particles and create a smooth, homogeneous dispersion or mixture.


High Shear mixer, High Shear disperser


When powders are introduced in the mixing process using simple agitators, agglomerates or lumps can often form. This is due to poor ‘wetting-out’ of the powders; usually the core of the agglomerate contains dry powder.

Use of High Shear Mixers ensures powders are rapidly dispersed into to fine particles, increasing the surface area available to the surrounding liquid, thereby allowing complete and uniform hydration.


High Shear mixer

Disolving & Dispersing

Many products dissolve or wet out particularly well within the vortex of simple agitation, increasing the flow around the vessel easily speeds up this process. Impeller design is key to optimising the process – this could be a conventional propeller, pitch turbine or bow-tie type. For other applications, optimum dissolving and dispersing is achieved with high shear mixers due to their intensity and speed. High speed impellers reduce particle size quickly ensuring solubilisation occurs effectively in minutes. By maintaining high flow rates around the vessel, the powders pass through the work head many times and therefore dissolve in minutes.


Propeller, Bow tie,high shear mixer


In many applications there is a requirement to store finished products in “bulk” tanks or vessels and it is clearly vital that product quality is kept consistent without any deterioration. This usually involves constant circulation to maintain temperature stability, physical consistency, and keep insoluble components fully in suspension.

When heating or cooling jackets are used, equalisation through agitation is important – for example hygienic storage of food/beverage products up to 150,000 litres.

Water treatment agitators perform a similar function with far greater volumes – typically up to 5,000,000 litres. Such large volumes require very high flow rates, usually achieved with high torque mixers.



“Powder into liquid” mixing presents a number of challenges. When powders are introduced to liquid clumps, lumps or “fish eyes” often become apparent. These agglomerates contain a dry powder centre surrounded by liquid. In general, only high shear applications address this issue very effectively, but other more soluble paste compounds can be achieved by unique high impact axial flow ‘bow-tie’ type impellers.


High Shear mixer, High Shear disperser, bow-tie impeller


In viscous products, aeration can cause unwanted effects on the product. Air pockets may cause discoloration, aroma and taste deterioration, chemical imbalances and preservation issues. For coating materials porous or pitted surfaces will appear if air is introduced to the product whilst processing. By taking care to avoid aeration during mixing, a more stable and durable product will result. Some hazardous products require complete elimination of oxygen during processing to prevent ignition. Aeration can also be avoided by mixing under vacuum or a nitrogen blanket.


Vaccum, low pressure vessel systems

Atmospheric Conditioning

Unstable products often require the regulation of temperature, pressure or vacuum during processing. Products which are very viscous at ambient temperature may need to be processed at high temperatures for ease of circulation/homogenisation and for complete reaction. Vacuum removes the associated issues of aeration and often reduces hazardous product ignition, especially once a nitrogen purge is employed too. Many resins and autoclave processes require a combination of temperature and pressure mixing. Products with low flashpoints and auto ignition temperatures often require nitrogen, vacuum and temperature control for the perfect result whilst maintaining an intrinsically safe process.


Pressure vessels, heating jackets, cooling jackets, temperature gradient control system

The Ultimate Mixing Solution

Greaves “Triple Action” processing units incorporate a versatile combination of high shear, blending, heating, cooling, pressure, vacuum and nitrogen purging techniques with remote operation if required, thereby delivering the ultimate fluid processing solution for the most sophisticated applications. Highly viscous products can be more rapidly discharged from the vessel by application of high pressure.


Triple action units typically incorporate High Shear heads for maximum mixing rate and minimum process time.