Question Bank • QB_EXP_APE_SZR_001 NAT • 2 Marks

Section 6: Agricultural Process Engineering

Size Reduction Mechanics & Energy Laws

Subtopic: Rittinger law power scaling

Question Statement:

A hammer mill requires $10.0\text{ kW}$ of power to crush agricultural feed from an initial size of $10\text{ mm}$ to $2\text{ mm}$. According to Rittinger's law ($E = K_R [1/d_2 - 1/d_1]$), the power required to grind the same feed from $10\text{ mm}$ to $1\text{ mm}$ at the same throughput capacity is ________ $\text{kW}$ (round off to two decimal places).

Answer Key:

22.50

Step-by-Step Solution & Explanation

From Rittinger's law: $\frac{P_2}{P_1} = \frac{\frac{1}{d_3} - \frac{1}{d_1}}{\frac{1}{d_2} - \frac{1}{d_1}}$ $\frac{1}{d_3} - \frac{1}{d_1} = \frac{1}{1.0} - \frac{1}{10} = 1.0 - 0.1 = 0.9$ $\frac{1}{d_2} - \frac{1}{d_1} = \frac{1}{2.0} - \frac{1}{10} = 0.5 - 0.1 = 0.4$ $P_2 = 10.0 \times \left( \frac{0.9}{0.4} \right) = 10.0 \times 2.25 = 22.50\text{ kW}$
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