Subtopic: Mechanics and energy requirement in size reduction of agriculture produce
Question Statement:
In a size reduction operation, the power required to crush 2 ton of feed material per hour is 7.2 kW. Eighty per cent of the feed and product material pass through 4.75 mm and 0.5 mm sieve openings, respectively. The work index of the material is
Options:
(A) 6.5
(B) 7.4
(C) 11.9
(D) 14.8
Official Answer Key:
C
Step-by-Step Solution & Explanation
By Bond's Law: Specific energy E (kWh/ton) = 10·Wi·[1/√P₈₀ − 1/√F₈₀] (P₈₀, F₈₀ in μm). Specific energy = 7.2 kW / 2 ton/h = 3.6 kWh/ton. F₈₀ = 4750 μm, P₈₀ = 500 μm: 1/√500 = 0.04472; 1/√4750 = 0.01451; difference = 0.03021. Wi = 3.6/(10×0.03021) = 3.6/0.3021 = 11.9, matching (C).
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