In the modern chemical industry, various processes of interaction of various chemical elements are carried out. These processes are:
- dissolution of crystalline compounds,
- fluid diffusion,
- decomposition or homogenization of a complex multi-component solution into components.
These chemical-technological processes can occur in a rather long period, and to increase the productivity and intensity of work in these processes, physical methods are used to influence the initial liquids. The most common and effective method of physical impact is mechanical mixing, which is divided into several directions:
- the addition of additional mechanical energy,
- turbulization of reacting components;
- grinding lumpy materials to increase the contact surface.
- homogenization of multicomponent mixtures;
- emulsification and emulsification of components;
- intensification of heat and mass transfer.
Often, the possibility of using mechanical processes determines the efficiency and profitability of the production process as a whole.
Thus, production technology in the chemical industry is inextricably linked to mechanical mixing. Mechanical mixing is carried out by the impeller of the mixer due to the rotation of the torque transmitted by the electric motor to the shaft. The fixing element of the mixer on the apparatus is a mounting flange, which is pulled together with a counter flange fixed in the apparatus in most cases by a bolt or hairpin connection. For mounting the shaft with a gear motor, to prevent running out, and to prevent leakage of gaseous or liquid components and pressure loss in the apparatus, the mixer is equipped with bearing housing and seals. Depending on the location of the bearing units, the presence of seals and a thrust bearing, the shaft is structurally divided into single-span or cantilever.
Application of paddle mixers in the chemical industry
Paddle mixer is most widely used in the chemical industry. The main features are:
- mixing mutually dissolved liquids;
- deep emulsification;
- weighing solid particles in liquids with a mass content of up to 90%;
- weighing of fibrous substances;
- agitation of light sediment;
- the slow dissolution of crystalline, amorphous or fibrous substances;
- temperature equalization;
- intensification of heat transfer and mixing in crystallization processes.
This type of mixer is easy to manufacture: it has only two blades mounted perpendicular to the direction of movement.
Principle of operation of a paddle mixer
The principle of operation of the paddle mixers as follows: when the blades move at their contact with the liquid, a thin-walled laminar layer is formed, the dimensions of which depend directly on the size of the blades and the properties of the mixed fluid (density and dynamic viscosity). Over time, there is an increase in the laminar layer, its deformation associated with the appearance of the separated flow and circulation zones (or the so-called turbulent wake). The beginning of the formation of separation zones indicates the emergence of a sharp resistance of the medium with the subsequent achievement of the minimum values.
The turbulent wake is not uniform along the entire length of the blade and increases at maximum distance from the shaft. Due to its heterogeneity and the appearance of a pressure gradient, interaction with centrifugal forces, a radial movement appears in the liquid, which characterizes the achievement of an acceptable mixing intensity.
The maximum intensity of fluid mixing is achieved using a paddle mixer with reflective partitions, which are vertically placed strips. When liquid flows around them, a zone of reduced pressure forms and a separated vortex flow arises, which has motion co-directed with the mixing apparatus. As a result, the resistance of the blades decreases and turbulization of the flow is added.
Thus, when using paddle mixers, centrifugal, vortex and radial flows arise, which, when interacting, transform the laminar motion of the fluid into turbulent and accelerate the flow of necessary chemical processes. Due to the interaction of all flows, energy consumption is reduced. In comparison with similar type mixers (turbine,frame and anchor ), power consumption with the same quality of mixing is lower by 25% on average.
Thus, paddle mixers will continue to hold primacy for their use in the chemical industry for a long time.