Features and scope of mixing devices of frame type

The alteration of similar and different substances by the state of aggregation is widely used in various fields: chemical, food, construction and other industries. This process helps to accelerate the interaction of mixing substances.

There are a large number of mixing methods such as:

  • the use of mechanical energy,
  • use of thermal energy,
  • mixing using compressed gases and other methods.

In all cases, the mixing device should provide maximum performance with minimal time costs. In this ratio, mixing takes the lead with the use of mechanical energy transfer. The above method is divided into many options, but the most energy-efficient at the moment is the method of using mixing devices(mixers).

There are 12 basic types of these devices, which are referred to the Guest 20680-75. They differ significantly in design but have the same principle of operation, which is reduced to repeated relative movement of the working body (hub) in the volume filled with the substance. Due to the transfer of mechanical energy, the substance begins to move and the motion vectors of the mixer can be decomposed into three types: radial, tangential and axial displacement.

The most widely usedpaddle mixers, due to its versatility. But, as you know, science does not stand still, and to achieve maximum performance and reduce energy consumption based on paddle mixers, the following were developed:turbine mixers open and closed, three and six-blade,anchor and frame, sheet.

Each of the above types specializes in specific applications.

Frame and anchor mixers are used for mixing inviscid, medium and viscous liquids (with a viscosity of up to 100 Pa*s), in terms of density these liquids can be classified as light, medium and heavy, as well as in mixing substances where it can be deposited on the surface of the tank. This type of mixing device is a leader in the intensification of heat transfer and heat transfer of the mixed fluid and is also used for suspending viscous media.

This type of mixer belongs to a slow-moving subclass and has a small number of revolutions it does not exceed 60 rpm, and its working body (impeller), on the contrary, is the largest among the mixers used in a turbulent fluid motion. According to RD-26-01-90-85, the optimal ratio of the diameter of the container to the diameter of the impeller is from 1.1 to 1.3. Recommended peripheral speed for liquids with low and medium viscosity can reach up to 8.0 m/s, in viscous media up to 4.0 m/s according to MN 5874-66.

According to practical data obtained by the Tula Mashiny plant, the average peripheral speed of the frame and anchor mixers is from 2 to 5 m/s.

The distinctive features of frame and anchor devices include their design, which repeats the shape of the container in which it is located. Due to this impeller design, this type of mixing device can prevent overheating of the liquid with a jacket.

In the case of mixing very viscous liquids, the frame and anchor mixers are provided with additional transverse or vertical elements.

Also, features of this type of mixers include their use in turbulent, laminar and transient mixing of liquids, which significantly expands their scope.

The design of the impellers of the frame and anchor mixer

a) for containers with a conical bottom; b) for containers with a flat bottom; c) for a tank with an elliptical bottom

When moving, anchor and frame mixers create mainly tangential fluid motion (along the tangent to the circle described by the end of the mixer), if necessary, reflective ribs are installed in the tank to increase the turbulence of the fluid motion. To eliminate stagnant zones, the location of these ribs should be above the impeller level by a distance from 0.1 to 1.0 of the length of the ribs.

Based on the foregoing, and despite the high energy consumption compared to its prototype — paddle mixers — the frame and anchor mixer in the ratio of energy consumption/performance play a significant role in processes where it is necessary to produce high-quality and fast heat transfer or to prevent the material from building up on the walls of the tank.

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