Chemical Engineering - Heat Transfer - Discussion

A 10 cm dia steam pipe, carrying steam at 180°C, is covered with insulation (conductivity = 0.6 W/m.°C). It loses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from the surface to the surroundings.

Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cm, the rate of heat loss from this insulated pipe will be.

Answer A is perfectly right according to concept.

Upto critical radius HT increases, beyond that the resistance of the insulating material is dominant.

And also with increase in radius there is increase in thermal resistance and decrease in convective resistance here the h value greater than k.

Option A is correct.

Here 2 factors are acting. The desired answer depends upon the dominating one. The 2 factors are, 1st HT increases as the area for HT increases due to the insulating material, 2nd the insulating material itself impose a resistance to HT. Now it determines the critical thickness. Up to critical thickness HT increases due to the area of the insulating material. Beyond that resistance of the insulating material more dominant and HT decrease.

Please explain the answer clearly.

A must be the right answer according to the critical radius concept.

RC>RO so it is undesirable to have inaulatiin addition of insulation increses heat loss.

From the formula critical Radius = Thermal conductivity/heat transfer coefficient.

We can say that heat loss is minimum when it is insulated.

How? @ Vandana.

B is the correct option. I agree.

The correct answer is option : A.