Question

........... law propose that the final particle size to be the one for which 80 per cent of the product passes through 100 micron size sieve.

• A. Fick’s
• B. Kick’s
• C. Rittinger’s
• D. Bond’s

Hint:

Mnemonic for Size Reduction: Kick (Coarse), Bond (Intermediate/80% pass), Rittinger (Fine). Bond is the "bridge" between the two extremes.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks about size reduction laws in food engineering, specifically identifying the law that utilizes the "80% passing" criteria to define characteristic particle size.
Key Formula or Approach:
Bond's Law is expressed as: \[ E = 100 W_i \left( \frac{1}{\sqrt{D_{p2}}} - \frac{1}{\sqrt{D_{p1}}} \right) \] Where \(E\) is energy, \(W_i\) is the Work Index, \(D_{p1}\) is initial size, and \(D_{p2}\) is final size.

Step 2: Detailed Explanation:

• Size reduction is a process used in the production of flours, spices, and powders. The energy required for this process is estimated using various empirical laws.

• Bond's Law (also known as the third theory of comminution) suggests that the work required to form particles from very large feed is proportional to the square root of the surface-to-volume ratio of the product.

• A unique feature of Bond's Law is the definition of the characteristic size. It defines the "size" of the material as the aperture size through which 80% of the mass passes (\(d_{80}\)).

• This 80% passing rule is practical for industrial applications where particle sizes are not uniform and a representative "top size" is needed for calculations.

• Comparing other laws: Rittinger’s law states that energy is proportional to the new surface area created (valid for fine grinding). Kick’s law states that energy is proportional to the size reduction ratio (valid for coarse crushing).

• Bond’s theory occupies an intermediate position between Rittinger’s and Kick’s theories and is generally more accurate for most industrial grinding operations.

Step 3: Final Answer:
Bond’s law uses the 80 per cent passing criteria for particle size definition.