Mixing pasty products - Characteristics of an agitated system

Today's agri-food sector is increasingly faced with the need to market or produce rheologically complex products (ready meals, seasonings, yoghurts, etc.). Consumer tastes and choice criteria are directly responsible for this state of affairs. To give an idea of the scale of the problem, over 80% of fluids processed in the food industry today have a non-Newtonian rheological behavior.

These new products are very often obtained by bringing the various substances required for their production (ingredients, thickeners, colorants) into contact in mechanically agitated tanks.

The main purpose of mechanical agitation of the system is to provide mechanical energy to the medium, and thus to promote intimate contact between the different substances or phases, in order to achieve optimum conditions for the transfer of matter or heat.

In recent years, agitation has progressively moved from being an "art" to a "science", thanks in particular to advances in experimental techniques (laser velocimetry, particle image velocimetry PIV, tomography, ultrasonic techniques) and numerical techniques (computational fluid dynamic CFD).

The first question to be asked when tackling a stirring-mixing problem is what type of stirrer can be used to meet the objectives of the mixing operation, particularly when dealing with rheologically complex and/or highly viscous media.

In this dossier, we propose to present the various types of mixing equipment for viscous fluids. We will then report on the main characteristics of mechanically agitated systems, in particular power consumption, mixing and circulation times, and heat transfer within these agitation systems.

In the second part will cover the performance of agitation equipment.

For more information on the rheology, texture and texturing of food products, please refer to [F 3 300] .