Question

A pipe is insulated such that the outer radius of the insulation is less than the critical radius. Now the insulation is taken off. Will the rate of heat transfer from the pipe increase or decrease for the same pipe surface temperature?

Answer 1

Answer:

the heat transfer from the pipe will decrease when the insulation is taken off for r₂< $r_{cr}$

where;

r₂ = outer radius

$r_{cr}$ = critical radius

Explanation:

Note that the critical radius of insulation depends on the thermal conductivity of the insulation k and the external convection heat transfer coefficient h .

$r_{cr} =\frac{k}{h}$

The rate of heat transfer from the cylinder increases with the addition of insulation for outer radius less than  critical radius (r₂< $r_{cr}$) 0,  and reaches a maximum when r₂ = $r_{cr}$, and starts to decrease for r₂< $r_{cr}$. Thus, insulating the pipe may actually increase the rate of heat transfer from the pipe instead of decreasing it when r₂< $r_{cr}$ .