# How to calculate blender capacity

In pharmaceutical industries, different types of blenders are used for mixing granules and powders. Blenders are used in wet granulation, dry granulation and direct mixing of tablet manufacturing.

It is my common observation that in pharmaceutical industries about 90% of people working there consider that the capacity of a blender is taken in kilograms(kgs).

But it is not true because scientifically the capacity of a blender is described in terms of litres.

The capacity of blenders is described in litres not in kilograms because if we take the capacity of blenders in kilograms it does not remain the same for denser and lighter products.

Example

• If we assume that we have a double cone blender and its capacity is taken in kilograms e.g 300 kgs, then for all the products, the capacity of double cone blender should remain fixed i.e 300 kilograms.
• We know that the density of all products is not the same,Â  denser products like Mannitol will occupy less volume or less space in the blender and may be we can add up to 350 kilograms of Mannitol in a 300-kilograms double cone blender.
• Â Lighter or low-density products like Aerosil or fumed silica will occupy more volume and may be we can just add up to 100Â  kilograms of Aerosil in a 300 kilograms double cone blender.

We can understand from the above example that Fixed claim Capacity of a blender in kilograms(kgs) changes as the bulk density of a product is changed.

Capacity Calculation

To calculate the capacity of a blender we will have to findÂ  two things which are as follow,

• Volume of blender
• Bulk Density of product

The following formula is used to calculate the blender capacity

Â The volume of blender(Litres)Ã—Bulk density of the product

How to calculate VolumeÂ

• To calculate the volume of blender water is added into the blender.
• We can add a measured quantity of water by marking a container.
• For example, take a calibrated measuring beaker of 5 litres and add 10 beakers into a container and mark it 50 litres.
• Then add 50 litres filled container into the double cone blender to make it brimful. Say we add 6 containers to the brim full of double cone blender.

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 50Ã—6 = 300 liters

• So the brimful capacity of double cone blender in litres is 300 litres.
• The calibrated flow meter can also be used to note the brimful volume of double cone blender.

100 MCQs to revise your pharmaceutical knowledge.

How to Calculate Bulk Density

To calculate the bulk density of a product (powders or granules) the following formula is used.

Â Â Â Â Â Â Â Â Â Â Bulk density= mass/ volume

For bulk density, we have to find two things which are as follow,

• The mass of the product (granules or powders)
• The volume of the product (granules or powders)

Weigh some quantity of product (granules or powders) on a measuring balance say it’s weight is 300 grams.

Add this product in a measuring cylinder and note the volume occupied by the product( granules or powders) for example it is 400 ml.

Find bulk density by applying the above formula.

Â Â Â Â Â Â Â Bulk density=300gm/400ml

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â =0.75gm/ml

How to calculate blender Capacity

As we discussed above, for blender capacity calculation we use the following formula,

Â The volume of blender(Litres)Ã—Bulk density of the product

Put the values of volume and bulk density which are measured in the above section.Â  As we know Volume is 300 litres and bulk density is 0.75gm/ml

300Ã—0.75=225 kg

So Brimful capacity of double cone blender 300 litres in kilograms is 225 kgs, for a product having bulk density 0.75gm/ml.

Now if we have a product whose bulk density is 0.8 then the brim-full capacity of 300 litres double cone blender in kgs will be calculated as follow,

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 300Ã—0.8=240 kg

As we noticed that with an increase in bulk density of a product, the capacity of the same blender(300 litres) is increased in kilograms or kgs.

Maximum Working Capacity

• In the above example, 225 kgs is the brimful capacity of 300 litres double cone blender for a product with bulk density 0.75gm/ml.
• As a general rule, some space should be provided for the movement of product in the blender to ensure uniform mixing.
• We can not add product up to brim-full capacity.
• Usually, for maximum working capacity, we take 70-80% of brim-full capacity.
• So if we take 80% of 225 kgs then,

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 80/100Ã—225=180 kgs

180 kgs is Maximum working capacity of 300 litres double cone blender for a product having a bulk density ofÂ  0.75gm/ml.

Minimum Working Capacity

• Usually 30-40% is used for minimum working capacity.
• Minimum working capacity can be calculated by validating the results

Conclusion

The capacity of blenders should always be taken in litres, not in kilograms and the bulk density of every product is calculated to determine its actual filling weight in blenders.

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