# Heat Transfer and Combustion

Question:

A pipe of outside diameter 200 mm is lagged with an insulating material of thermal conductivity 0.06 W m–1 K–1 and thickness 75 mm. The pipe carries a process fluid at a temperature of 300 °C and the average temperature of the outer surface of the lagging is 45 °C.

(a) Estimate the rate of heat loss per metre length of pipe.

(b) Explain why the thermal resistance of the pipe wall can be ignored.

Relevant Equation:

Φ=2πLk(T −T ) 12 / in (r2/r1)

Solution:

Should I be calculating the heat loss per metre of the insulation? The pipe has no dimensions provided e.g. wall thickness. So, I assume this is the case. Any feedback is appreciated.

Or, should I treat this as the outer wall is r2 and the outer insulative later is r3.

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Hello T,

You can assume some material and thickness for the pipe (dn200, probably), but the wording of the exercise makes one guess it shouldn't matter much. Your
treat this as the outer wall is r2 and the outer insulative later is r3
sounds like a good idea to me. See what comes out.
And yes, if (a) says per meter of pipe, then that is also per meter of insulation; both lengthwise.

• Chestermiller