Project ForgeHeat Transfer
Conduction
GATE 2011
Medium
A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and surroundings is 5 W/m²K. It is proposed to reduce the heat loss from the pipe by adding insulation having a thermal conductivity of 0.05 W/mK. Which one of the following statements is TRUE?
- AThe outer radius of the pipe is equal to the critical radius.
- BThe outer radius of the pipe is less than the critical radius.
- Adding the insulation will reduce the heat loss.
- DAdding the insulation will increase the heat loss.
Explanation
Critical radius rc=k/h=0.05/5=0.01m=10mm. The pipe's outer radius is 12.5mm, which is already GREATER than rc=10mm — past the critical radius, adding more insulation only increases thermal resistance, so it reduces heat loss.
Source: GATE ME 2011 (2011)
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