Mixing of solids in liquids

Defining the type or degree of mixing required in proper manner is critical to mixer selection, says C C Tipnis

The most common mixing or agitation applications involve the suspension of solids in water or water like liquids. Correctly defining the type or degree of mixing required is critical to mixer selection.

Since the horsepower needed for a particular mixing job can vary dramatically defining the degree or amount of suspension required is a subject worthy of attention.

Complete uniformity: This implies that the percent suspension at any point is 100 per cent. The upper layer of liquid in the tank is the most difficult to bring to 100 per cent suspension. It is difficult to get particles with settling velocities about 6 feet/min suspended uniformly in the upper two per cent of the tank volume. Since the primarily horizontal flow pattern at this point cannot keep high-settling velocity solids in suspension.

Complete off-bottom suspension: This is defined as all particles moving up off the tank bottom. It does not have any further requirement for a particular percent suspension at any other point in the tank.

Complete motion on tank bottom: This means that all particles are either suspended off the tank bottom or are rolling around on the tank bottom. No statement is made concerning the percent uniformity in the vessel.

Filleting permitted but no progressive build-up: A fillet is a stationary or stagnant deposit of solids most commonly at the outside periphery of the bottom where it joins the tank wall, but it could exist at any other part of the tank bottom depending on the fluid flow pattern.

Height of suspension: The liquid height in the tank to which solids are suspended may be used to describe the operation. It is most commonly expressed as the percent solids of each of the various particle size fractions at various liquid heights off bottom. This can also be expressed as the particle size distribution in samples taken at various points.

Time and again companies specify mixers as the “standard” equipment for their processes, in industries as diverse as food, pharmaceuticals, cosmetics, chemicals and petrochemicals.

Advantages

High shear mixers improve quality plus increase production, rapidly blend, emulsify, homogenise, solubilise, suspend, disperse and disintegrate. The rotor/stator design is the solution for full production. Batch and in-line designs available. Rent before you purchase.

What are the uses of mixer?

Unsurpassed speed and efficiency in day-to-day laboratory work.

• Unrivalled versatility allowing any machine to be quickly adapted to perform the widest range of mixing applications - mixing, emulsifying, homogenising.
• Disintegrating, dissolving, dispersing, blending, particle size reduction and de-agglomeration.
• Constant and repeatable results, time after time.
• Accurate in forecasting the performance of large machines under full-sale working conditions.
• Excellent for small scale production work.
• Robust, simple construction, easy-to-use, easy-to-clean.

The writer is with Kunal Consultancy Services, Mumbai. Tel: 22-25904974/ 25923690/55974080.
Fax: 022-25904974. E-mail: kunalconsultancy@hotmail.com