Question Bank • QB_SUB_DFE_CON_002
MCQ • 1 Mark
Section 7: Dairy and Food Engineering
Steady-State Conduction & Shape Factors
Subtopic: Critical radius of insulation concept
Question Statement:
Adding insulation to a bare cylinder will increase the total rate of heat loss as long as the outer radius of insulation is:
Options:
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(A) Less than the critical radius $r_{cr} = k/h$
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(B) Greater than the critical radius $r_{cr} = k/h$
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(C) Equal to zero
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(D) Infinite
Step-by-Step Solution & Explanation
For cylindrical geometries, adding insulation increases conductive resistance but reduces external surface convective resistance. When $r < r_{cr} = k/h$, convective resistance decreases faster than conductive resistance increases, maximizing heat loss at $r = r_{cr}$.
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