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When gas is introduced from the bottom of bed of solid particles, the gas moves upwards and move through the spaces between the solid particles. If the velocity of gas is low then the aerodynamic drag on the particles is also low and the solid bed will be in a fixed state.

When the velocity is high the aerodynamic drag force will be greater than the gravitational force and causes the bed to expand in volume. When the velocity is further increased it will reach a critical velocity where upward forces become equal to gravitational forces. This causes the particles to become suspended. This state is called as a "Fluidized State." This state is called so because here the entire solid particles behave as fluids.[1][2]

In this state, all the particles remain suspended in the air stream.

Fluidization depends upon-

  • Particle size
  • Particle density
  • Velocity of air

Disadvantages of Fluidization -

  • Erosion of vessel internals
  • Attrition of solids.

Advantages of Fluidization -

Enhanced mixing with less temperature gradient

All solid particles cannot be fluidized. Based on this particles can be divided into the following classes.[3]

Types of Fluidization -

Particulate fluidization: Fluidization of sand with water.

Aggregative or bubbling fluidization: Fluidization of solid particles with air.

Applications of Fluidization -

Fluidized bed dryer[4] - With the principle of fluidization, drying can be carried out. In a fluidized bed dryer, hot air stream at high velocity is passed from the bottom of a perforated basket containing the material to be dried.

Fluid energy mill[6] - Size reduction can also be carried out by fluidization as the main principle by fluid energy mills. In these mills, high velocity air is allowed to enter the milling chamber through tangential nozzles. Along with the air, the particles will also raise. Due to attrition in between the particles milling is accomplished.

Fluid granulator[7] - Granulation of powders can be done by following fluidization. A granulating solution is sprayed on to the fluidized ingredients by which granulation is accomplished.

Fluidized bed Coater[5] -Here coating solution is sprayed on to the fluidized powders, microspheres etc

Fluidized bed Combustion

Fluidization -



  1. en.wikipedia.org/wiki/Fluidization -
  2. www.msubbu.in/ln/fm/Unit-IV/Fluidization.htm
  3. ttp://dissertations.ub.rug.nl/FILES/faculties/science/2004/c.dechsiri/c2.pdf
  4. http://www.kason.com/fluidbed/principle.php
  5. http://www.cjtech.co.kr/Technical%20Process%20Fluid%20Bed%20Coating.htm
  6. http://www.cn-pharmaceuticalmachinery.com/product/Product-200.html
  7. http://www.cjtech.co.kr/Technical%20Process%20Fluid%20Bed%20Granulation.htm



About the Author

Navya Sai's picture
Author: Navya Sai


Siva Mavuduru's picture

Hi Navya Good blog but why are you considering attrition as disadvantage? its important principle in size reduction principle. isn't it? What is fluidized bed combustion?
Navya Sai's picture

thank u for your query. 1. Because of attrition the size of the solids may further reduce which cause the entrapment of solids with fluid. 2.fluidized bed combustion means conversion of solids to fluid by passing air stream.the bed material contains sand,coal,ash or limestone. references: 1.www.britannica.com/EBchecked/.../fluidized-bed-combustion 2.www.msubbu.in/ln/fm/Unit-IV/Fluidization.htm -


Navya sai

K Rajakrishna's picture

Hello navya, its a very good presentation. Can you through some light on the internal lining of the fluidised unit. Most of them will be abration free. How can you say that it will corrode the internal surface.
Nandini's picture

Its a good and simple presentation. Can you tell me what are the major parameters for the validation of the fluidized units.

with regards Nandini. TEAM ASSIMILATORS.

Radha Krishna's picture

nandini, do you mean process validation or equipment validation. i can expalin based on the type of validation you would like.


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Nandini's picture

respected ramakrishna sir, thank you for payiing attention to my query. i would like to have more knowledge on process validation. can you also give the citation where in i can get more information about other process too!.

with regards Nandini. TEAM ASSIMILATORS.

Radha Krishna's picture

as for process validation is concerned i can share with you certain presentations.


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Narmadha's picture

Hello navya that was a good one. Can you explain weather a step of granulation is carried out in granulator or the end granules come out of it. What is the range of sizes of granules that can be obtained.

With regards, Narmadha  

Radha Krishna's picture

narmadha, granulation in carried out in FBG or fluidized bed granulator or FBP fluidized bed processor. at end granulate comes out of the equipment. the size of the granules depend on the particle size of the material and the rate, amount granulating liquid used for sparaying. also other process parameters that allow mass buildup. rama


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Sravani kompella's picture

It is a nice presentation navya. 1)can you tell me wat is the influence of inter particle forces on fluidisatio? 2)How are cohesive particles fluidised?
A.R.Khan's picture

You explained in simple way with sound pictures. I am glad to see pictures by your team. Have you guys made on your own ? How did you do that? If i were you, i would include on more section like "Usful Links for Further reading on fluidization".... That way your reader will be 100% staisfied ...what do you say ?
Sudha Thamarapalli's picture

Hello Sir, Thanks a lot for your comments... This will help us in experimenting some more methods to attract the readers. Yes, these pictures are made by me. I am constructing the pictures in Microsoft Powerpoint by using the shapes there and iam saving them as jpeg pics. And thank you so much for suggesting us to add links... Your suggestions mean a lot for us. We will definitly implement you suggestion.



Amol Malpani's picture

Quite catchy last part with moving pictures. I think you attached powerpoint slide with animation????? Nice way to present the process. Keep the good work. Can u give a definition of fluidisation in complete sense? Regards,

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