Mixing and Agitation Techniques PDF

**Agitation** of liquids. The unit operation is **used to prepare liquid**--mixture by bringing in contact two liquids in a mechanically agitated vessel or container. Agitation refers to the induced motion of liquid in some defined may, usually in circulatory pattern and is achieved by some mechanic...

**Agitation** of liquids. The unit operation is **used to prepare liquid**--mixture by bringing in contact two liquids in a mechanically agitated vessel or container. Agitation refers to the induced motion of liquid in some defined may, usually in circulatory pattern and is achieved by some mechanical device Agitation is the **process of providing bulk motion to a liquid.** Agitation & Mixing of fluids - ppt download **Kneading** is a process in the making of [bread](https://en.wikipedia.org/wiki/Bread) or [dough](https://en.wikipedia.org/wiki/Dough), used to mix the ingredients and add strength to the final product. Kneading is the **process that brings the dough together, develops the strands of gluten and creates a silky and strong dough ready to be baked**.  **Mixing (or blending)** is a unit operation **in which a uniform mixture is obtained from two or more components**, by dispersing one within the other. Hence it is a process which involves manipulating a heterogeneous physical system, with the intent to make it more homogeneous. **Homogenization** is an **essential unit operation during the manufacture of a number of food and dairy products**. As a unit operation, homogenization performs multiple functions such as reduction of particle size, dissolution, mixing, dispersion, encapsulation, and emulsification. **Types of Agitators** ---------------------- 1. 2. 3. 4. 5. ### 1. **Turbine Agitators** These agitators have an axial input and the output is radial. Turbine agitators are very versatile; they are able to handle a wide variety of mixing operations because these agitators can create turbulent movement of the fluid due to the combination of rotational as well as centrifugal motion. They are popularly used in metal extraction industries and also for chemical reactions and have a very high blending efficiency. These are mostly used in chemical, pharmaceuticals, grease, cosmetics industries. Turbine Agitator ### 2. **Paddle Agitators** It is one of the most basic types of agitator. It contains blades which are paddle shaped; the blades stretch throughout the vessel and reach the walls of the vessel. They are primarily used in applications where a uniform laminar flow of the liquids and little shearing is desired. This type of agitator is especially used for viscous materials. These are mostly used in food, chemicals, pharmaceuticals, sorbitol etc industries  ### 3. **Anchor Agitators** As the name indicates the shape of the impeller resembles that of the anchor. These agitators also extend and spread throughout the vessel such that there is very less clearance between the blades and the walls of the vessel. These agitators are also used when laminar flow conditions are desirable. These impellers sweep the whole batch because the blades are almost in physical contact with the walls of the vessels. These agitators are used in ink, paint and adhesive industries. ### Anchor Agitators **4. **Propeller Agitators: These have impellers that similar to marine type propellers. They have blades which taper towards the shaft to minimize centrifugal force and to promote axial flow. It means when this agitator operates the motion of fluid is such that the inlet flow is parallel to the shaft and the outlet flow is also parallel to the shaft, the ideal flow is axial in nature. They are primarily used in applications to stir low viscosity liquids. They are used in pharmaceuticals industries and also other industries which use suspensions as the agitators don't let the solid particles settle. ###  ### 5. **Helical Agitators** ### The blades of the helical agitators are arranged in a structure of helix. The appearance is similar to how a threaded screw looks. The motion of the liquids in this type of agitator is also axial in nature due to the way the blades or the ribbons move while helical agitator is in operation. There is a vigorous motion of the fluids within the vessel when the agitator is in operation. It is used in polymer industries and other industries which require the use of quite viscous materials. Helical Agitators  **Flow Pattern based impeller:** The most common flow patterns in mixing are **axial** (down and up) and **radial** (side to side) flow. These flow patterns also describe the generic classes of impellers: axial and radial. ----------------- ---------------------------------------- Axial Impellers  ----------------- ---------------------------------------- ### 1. Axial Flow Impellers Axial (down and up) pumping is an important flow pattern because it addresses two of the most common challenges in mixing; solid [**suspension**](https://dynamixinc.com/mixing-101-the-basic-principles-of-mixing-and-impellers/#solid-suspension) and [**stratification**](https://dynamixinc.com/mixing-101-the-basic-principles-of-mixing-and-impellers/#stratification). In this process both the superficial and annular velocities can be calculated to determine and control the level of mixing. (If your axial impeller is causing swirling or vortexing, check out our previous [**Mixing 101 posting Baffled by Baffles**](https://dynamixinc.com/baffled-by-baffles)?) Here are some of the most common axial impellers: +-----------------------------------+-----------------------------------+ | #### A. Marine-type Propellers | Marine-Type Propellers | | | | | [**Viscosity**](https://dynamixin | | | c.com/mixing-101-the-basic-princi | | | ples-of-mixing-and-impellers/#vis | | | cosity): | | | 0 -- 5,000 cps | | | | | | Commonly used on marine boats, | | | the propellers are often used in | | | small portable direct drive mixer | | | applications because they're | | | economical and efficient. | | | However, in larger applications | | | they're seldom used because of | | | their price and weight. | | +===================================+===================================+ | #### B. Pitch |  | | **[Viscosity](https://dynamixinc. | | | com/mixing-101-the-basic-principl | | | es-of-mixing-and-impellers/#visco | | | sity):** 0 | | | -- 50,000 cps | | | | | | The pitch blade impeller is the | | | most versatile impeller and was | | | the standard until the | | | development of the airfoil. | | | They're useful in blending two or | | | more liquids and are effective in | | | low bottom clearance with less | | | liquid submergence. | | +-----------------------------------+-----------------------------------+ | #### C. Dynaflow^TM^ (Hydrofoils) | Hydrofoil Impellers | | | | | **[Viscosity](https://dynamixinc. | | | com/mixing-101-the-basic-principl | | | es-of-mixing-and-impellers/#visco | | | sity):** 0 | | | -- 3,000 cps | | | | | | The camber of the blade increases | | | the efficiency of the impeller, | | | reducing its power / pumping | | | ratio. A more technical benefit | | | is the laminar flow created by | | | the camber of this impeller. This | | | camber reduces turbulence (shear) | | | substantially. That is why it is | | | selected for shear-sensitive | | | applications as well. | | +-----------------------------------+-----------------------------------+ ### 2. Radial Flow Impellers ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Unlike axial impellers, radial impellers are commonly selected for low level mixing (known as a tickler blade) or elongated tanks. They typically give high shear rates because of their angle of attack. They also have a relatively low pumping number, making them the most sensitive to viscosity. Radial impellers do not have a high tank turnover flow like axial flow impellers. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ **FLOW PATTERN** **Axial flow** is the most efficient flow for bulk blending. With axial flow, the individual blades on the propeller are angled downward. When the blade spins, it pushes the mixture down towards the bottom of the tank. As the mixture hits the bottom of the tank, it bounces off and moves towards the sides of the tank. The continued force of the moving blade moves the mixture up the sides of the tank, and then begins to recirculate as the spinning blade pulls in the mixture from above. This type of flow provides great mixing for a wide range of conditions. Also, if you are looking for a way to suspend solids in a liquid mixture (think of suspending sugar in hot tea in order to give it time to melt) this is the kind of flow you'll want. **Radial flow** pushes the mixture out towards the side of the tank. Part of the mixture hits the side of the tank and moves downward, while the other part hits the side of the tank and moves upward. Radial flow mixing is great for intense mixing needs like when you need to break down the molecular bonds of the items that you are mixing. Also, radial flow generally has a slower blending time than axial flow. **Rotational flow** is usually avoided or limited. With rotational flow, the mixture moves around the shaft of the mixer without really getting mixed. If you dropped a ball into a tank mixing water with a rotational flow, the ball would essentially orbit the shaft of the mixer without moving up or down in the container. Rotational flow spins liquids around the without mixing them. However, rotational flow can break the surface tension of the mixture by creating a vortex. This can be used helpful for adding other liquids and solids into the mixture. **Prevention of Swirling and Vortex Formation ** There are three methods for the prevention of swirling and vortex formation:   (i) Off-centre mounting of the impeller.   (ii) Use of baffles.   (iii) Use of diffuser ring with turbines.   Vortex Formation - In small vessels, the impeller can be mounted off-centre - In large vessels with vertical agitators, the most common method of reducing swirling is to install baffles along the side of the vessel, which hinder rotational flow  without disturbing radial or longitudinal flow.   - In an unbaffled vessel, there are strong tangential flow currents and vortex formations at moderate speeds but in the presence of baffles, the vertical flow currents are  increased and there is more rapid mixing of the liquid.  - With side entering, inclined and off-centre propellers, baffles are not needed Fig. c : Propeller‚ off-centre and angular (unbaffled) **Propeller‚ off-centre** **and angular (unbaffled)**  **Side entering propeller** Flow pattern with turbine impeller in baffled tank **Flow pattern with** **turbine impeller in baffled tank** #### Horizontal Mixers A horizontal mixer gives you a clear advantage when you're trying to mix thousands of pounds of dough in a very short amount of time. Medium-to-large-sized bakeries and factories depend on this type of machine because of its sheer size and capability. **Horizontal Mixers** consists of ribbon, plough and paddle mixers, which are designed for consistent batch and continuous blending of powder and granules with capacities ranging from 35 -- 60,000 litres. This type of mixer is perfect for the mixing of things like short doughs, tortillas, fillings, pie doughs, health breads, cheesecakes, muffins and many other things. Horizontal mixers come with a selection of mixing arms that allow you to customize based on the type of dough you are mixing. They also allow for continuous mixing, meaning once the mixed dough comes out, exiting easily into a trough, the next batch can go into the machine on the other end. The **disadvantage** to this choice is that heat generation is a concern. The friction from the dough rubbing on the sides of the mixing chamber causes the dough temperature to rise, which can be damaging to some types of dough. It is important to take this into consideration when choosing the right mixer, especially if you plan on mixing mostly bread doughs.  -------------------------------------------------------------------------------------------------------------------- Operations ---------- The horizontal mixer provides a superior uniform mix of a wide range of materials from free flow material to high density wet material such as plastics chemicals liquids molasses, minerals and detergents, live stock feed for poultry and cattle adding premixes and vitamins. Its \"U\" shape body is manufactured in a robust heavy-duty construction in painted carbon steel or stainless steel. The effective speed and the specially designed agitator gives the Horizontal mixer a fast time of mixing with 100% accuracy and homogenity. The discharging of the mixer is either done Manually or Pneumatically through operated outlet or slide gate. Mixers are equipped with either a low speed Gearbox motor attached to the main shaft with a chain and sprocket or a speed reducer driven by a motor with a V belt drive. Side bearings holding the main shaft are either bolted to the sides of the mixer directly or away from the sides with a special stuffing boxes installed for preventing ingredients getting into the bearings. The Horizontal mixer is manufactured in various capacities and sizes from small SH, medium MH, and large LH. Horizontal mixers are equipped by either a Ribbon or a Paddle agitator.The Ribbon Agitator consists of a set of inner and outer helical ribbons that circulates the material from end to end inside and outside, it is recommended to be used for the mixing of free flow material. moreover Ribbon agitator are designed for center discharge or multiple side discharge position. The Paddle agitators uses a lifting and tumbling circulation of materials from end to end and its is recommended to be used with heavy resistant material for both wet or dry ingredients. They are also designed for center or side discharge position. Both Agitators are manufactured to result a fast yet efficient and accurate blending. Common Applications ------------------- - - - - - - **Video link for visualization:** **Planetary Mixer** **Video link for visualization: ** **Sigma Blade Mixer** In mixers managing very viscous materials, it is essential to support both tangential and oblique motion of the substance. The geometry and profile of the sigma blade is intended such that the glutinous mass of substance is pull, shear, dense, knead, and fold by the exploit of the blade next to the walls of the mixer trough. The amount to which this happen depends on the exploit of the blades - peripheral or overlap and the ratio of the speed of replacement of the blades. The twist angle of the blade can be customized depending on the necessary shearing. **Operation of Sigma Blade Mixer** In process, substance is loaded from side to side the top of the container to characteristically 40 to 65 percent of the mixer\'s total volumetric capability. The replacement of the blades is through serious duty drive system characteristically consisting of a motor, gearbox, coupling, and gears. The tip haste of the sigma blender is normally incomplete to 60 metres per minute. Mixing may be approved out at ambient temperature or under unnatural temperature situation. The blender trough can be providing with jackets for transmission of hot or cold media to continue the obligatory temperature situation within the mixer. The release of the material from the blender container is also by leaning of the mixer or from side to side an extruder / screw positioned in the lower segment between the two trough compartments. The mixer may be capable of with some one of these free activities. The orientated discharge understanding is mainly common. The tilting understanding of the container may be intended for physical process or may be developed using mechanical or hydraulic understanding. Materials of inferior thickness, the base free valve may be providing on the blender trough. Intend outline of the valve should be flush with the blender furrow to keep left from any dead or straight pockets of substance). The extruder/screw release has a benefit that supplies can be straight discharge, extruded, in the obligatory shape or size for additional dispensation. In adding, the screw intends eliminate operative experience to hot materials if the integration process are approved out at high temperature and/or with supplies that are toxic in character. **Video link for visualization:**