Project ForgeA 10 mm diameter electrical conductor is covered by an insulation of 2 mm thickness. The conductivity of the insulation is 0.08 W/m-K and the convection coefficient at the insulation surface is 10 W/m²-K. Addition of further insulation of the same material will
- Aincrease heat loss continuously
- Bdecrease heat loss continuously
- increase heat loss to a maximum and then decrease heat loss
- Ddecrease heat loss to a minimum and then increase heat loss
Explanation
Critical radius of insulation rc=k/h=0.08/10=0.008 m=8 mm. The current insulation's outer radius is (10/2)+2=7 mm, which is still less than rc=8 mm. Since the outer radius hasn't yet reached rc, adding more insulation continues to INCREASE heat loss (because the added surface-area benefit outweighs the added conduction resistance) until r=8 mm is reached (maximum heat loss), after which further insulation would start to decrease heat loss.
Source: GATE ME 2015 (Session 1) (2015)
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