JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Pharmacy II Year PHARMACEUTICAL ENGINEERING Previous Question Paper (August/September-2022 - R17)

The energy required for size reduction is governed by three primary laws, which relate the energy input to the change in particle size:

1. Rittinger's Law: States that the energy required is proportional to the new surface area created. It is most applicable to fine grinding where the change in surface area is significant. The formula is
   E = K_R(1/D_2 - 1/D_1)
   where E is energy, K_R is Rittinger's constant, and D is particle diameter.
2. Kick's Law: States that the energy required is proportional to the ratio of the reduction in size (the change in volume). It is primarily used for coarse crushing. The formula is
   E = K_K ln(D_1/D_2)
   where K_K is Kick's constant.
3. Bond's Law: Acts as an intermediate theory, stating that the energy required is proportional to the square root of the surface-to-volume ratio. It is widely used for industrial grinding calculations. The formula is
   E = K_B(1/√D_2 - 1/√D_1)
   where K_B is Bond's constant.

Principle: Operates on the principle of attrition and impact between particles suspended in a high-velocity gas stream.

Construction: Consists of a hollow oval or circular pipe loop with nozzles at the bottom. It includes a feed inlet, a classifier section at the top, and a product collector.

Working: Compressed air or steam is introduced through nozzles at high pressure, creating a high-velocity turbulent stream. Material is fed into this stream. Particles collide with each other at high speeds (attrition) and against the walls of the mill (impact), causing size reduction. The finer particles are carried by the air stream to the classifier, where only particles of the desired size exit, while larger particles are returned for further grinding.

Uses: Used for ultra-fine grinding of heat-sensitive materials like antibiotics, vitamins, and specialized chemicals.

Advantages: Produces extremely fine particles (1-20 microns); no heat generation (suitable for thermolabile substances); no contamination from grinding media.

Disadvantages: High energy consumption; high initial cost; not suitable for fibrous or sticky materials.