‘Types of Stirrer in Reactor‘ is a very interesting and easy topic for everyone. Hi, my name is B.A. Kadam, and I am going to explain the ‘types of agitators in reactors’ briefly.
The design of a reactor is a primary responsibility for every design engineer working in the chemical industry. In reactors, we use stirrers for different purposes, so proper selection of a stirrer is very important. I have structured this article so that by the end, you will have a clear understanding of all types of stirrers, including their construction, design, selection, and much more. I’m expecting feedback from you to help improve this article for better performance.
This article covers what an agitator is?, the functions of an agitator in a reactor, types of agitators in reactors, details about each type of stirrer, selection of stirrers, factors affecting stirrer performance, an explanation of the power number, frequently asked questions, pro tips for interview preparation and stirrer selection, a conclusion, and recommended books for further learning.
Table of Contents
What is an Agitator? What is an Stirrer ?
An agitator or stirrer is a mechanical component of a reactor, consisting of a shaft with blades on it, used for various purposes in the reactor. Below is an example of stirrer in reactor.
Function of Agitator in Reactor
Primary functions of agitators are as below. Agitator mix the solute and solvent in reactor.
Mixing
As per experience mixing is first main function of stirrer.
Heat Transfer
Agitator helps to get proper heat transfer by circulating the fluid inside. If we stop the stirrer, proper heat transfer doesn’t happen. In reactor, because of mixing or circulation of fluid within the reactor, heat transfer between two fluids happens.
Mass Transfer
Third main function of agitator is mass transfer. Agitator does circulation of fluid and because of it, contact area gets increased.
Solid particle Settling Preventation
By agitation, fluid gets motion or gets circulated within the reactor, which helps to prevent solid particles from settling at the bottom of the reactor. This is particularly useful for non-mixing solutions.
Gas Dispersion
It help to disperse gases into the mixture.
Help Crystallization
In crystallization, mixing is very important. Agitator helps to mix the fluid, which aids in crystallization.
Types of Stirrer in Reactor
Now lets disuses the main types of agitator in the reactor.
Turbine Type Agitator
A typical turbine-type agitator contains a shaft with turbine blades on it. The shaft rotates the turbine blades, resulting in axial or radial mixing.
Types of Turbine Type Agitator Based on Blade
There are several types Depends on blade used in stirrer.
Pitched Blade Turbine (BPT)
In this type, there are pitched blades ( typically 45 degrees) placed on a centrally mounted shaft to create radial flow as well as axial flow in the reactor.
Flat Blade Turbine
In this type, there are flat blades placed on a centrally mounted shaft to create radial flow in the reactor. This is normally used for medium to low-viscosity fluids.
Curved Blade Turbine
It also called as Back Swept Blade turbine. In this type curved blade placed on shaft which produced radial flow with lower shear force than flat blade type.
Rushton Turbine
Rushton turbine has flat blades placed on a disc, which is on the central shaft. This type is normally used for gas-liquid applications in the reactor.
Anchor Type Agitator
Anchor-type agitator contains anchor shaped blades placed on a shaft, which are used to move material around the shell of the reactor. This type of agitator is used in crystallizers. The rotation speed is slower than other types, especially compared to turbine types.
Types of Anchor Agitators
Based on the number of anchors used, we can categorize it as.
- Single Anchor Agitator
- Double Anchor Agitator
Propeller Type Agitator
Propeller type agitator contains propeller-type blades mounted on a shaft. This is a high-speed mixer or stirrer. This type of stirrer creates axial flow.
Helical Type Agitator
It is also known as also known as a helical ribbon agitator or spiral agitator. Helical-shaped blades are mounted on a shaft, as shown in the image below. This is normally used for high-viscosity fluids.
Paddle Type Agitator
This is almost similar to a flat-blade turbine. In this, flat blades are mounted on a shaft, which is good for mixing applications.
Custom Type of Agitator
In a custom type of agitator, we customize it. As shown in the picture below, we use turbine and flat blades. Depending on process requirements, we can customize it.
Magnetic Stirrer
A magnetic stirrer is a type of stirrer that uses magnetic fields to stir or mix substances within the reactor without requiring a direct mechanical connection to the stirring element.
Main Features and Components
- Magnetic Drive Mechanism
- Stirring Bar or Magnetic Impeller
Selection of Stirrers
Based on my experience, I have generated the following table, which may help you choose the right one as per your requirements.
| Type of Agitator | Power Number (Np) | Type of Applications | Cost |
|---|---|---|---|
| Propeller Agitator | Low to Medium | Low-viscosity liquid mixing, gas-liquid dispersion | Moderate to High |
| Turbine Agitator | Medium to High | Rapid mixing, crystallization, and gas absorption | Moderate to High |
| Paddle Agitator | Low to Medium | Solid-liquid mixing, gentle blending, and suspensions | Low to Moderate |
| Anchor Agitator | Low to Medium | High-viscosity liquids, pastes, and creams | Moderate |
| Helical Agitator | Medium | Viscous fluids, slurries, and thermal processes | Moderate to High |
| Custom Agitator | Varies | Specialized applications with unique mixing requirements | High |
Factors Affecting Stirrer Performance
- Stirrer design and type selection
- Speed and power input
- Viscosity of fluid
- Geometry of tank
- Impeller position in reactor
- Baffles in Reactor
- Gas or solid addition
- Temperature and pressure
- Scale of operation
- composition of fluid
- Power number
- Shaft diameter
- Tips speed
Power Number
The power number is a vital parameter for a stirrer, providing insight into the power required for stirring in relation to selecting the type of stirrer in a reactor. It is a dimensionless number. In this article, we will explore more about it, covering its definition, formula, and a general overview.
The power number is a dimensionless number that provides insight into stirrer efficiency and power consumption. The simple formula is.
where:
- P = Power input to the stirrer (W)
- ρ = Fluid density (kg/m³)
- N = Stirrer rotational speed (revolutions per second, s⁻¹)
- D = Stirrer diameter (m)
Tips Speed
Tip Speed is linear speed at the tip of rotating stirrer or blade in the reactor.
to calculate we can use below formula.
Tip Speed=π*D*N
where,
D = Diameter of the impeller (m)
N = Rotational speed (rotations per second or per minute)
π = 3.14
During the scale-up of a reactor, it is very, very important to maintain the tip speed for proper scaling of the stirrer in the reactor.
Frequently Asked Questions
What is a stirrer shaft?
A stirrer shaft is a long, cylindrical rod or shaft that connects the impeller or stirring blades to the motor or drive system in a reactor.
What is the function of a stirrer in a reactor?
All types of stirrers in a reactor provide fluid mixing for different purposes, such as reactions and uniform distribution.
What is the principle of a stirrer?
The rotation of the stirrer generates shear forces or motion, which results in mixing or dispersion.
Pro Tips
Now, let’s come to our main content. Having knowledge about stirrer construction and types, along with scale-up, is very, very important for a process engineer or chemical engineer. So if you want growth, you should have knowledge about it. Prepare for all types along with their selection criteria.
Whatever stirrer you use in the lab or industry, try to collect data on them. Make drawings, check the type, check tip speed, power number, think about why it was selected for the application, and ask senior engineers about the selection. This strategy will help you gain knowledge about the types of stirrers in reactors.
Conclusion
All types of agitators in a reactor play a main role, such as mixing. Based on the application, we can select the stirrer. Types of stirrers include propeller stirrers, anchor stirrers, turbine stirrers, paddle agitator, and custom stirrers.
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