What is the critical radius of insulation (cms) for a metallic cylinder, if the convective heat transfer co-efficient with the ambient atmosphere is 5 W/m2. °K? Thermal conductivity of metal and insulation material are 40 and 0.1 W/m.°K respectively ?
Correct answer: A. 2
- A. 2
- B. 8
- C. 10
- D. 40
Explanation
For a cylinder, the critical insulation radius is r_c = k_insulation/h = 0.1/5 = 0.02 m, or 2 cm. The metal conductivity is not used in this critical-radius expression.
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