Chemical Engineering - Heat Transfer - Discussion
Discussion Forum : Heat Transfer - Section 1 (Q.No. 50)
50.
A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be
Discussion:
15 comments Page 1 of 2.
Debasish said:
7 years ago
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.
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.
(1)
Neethu said:
5 years ago
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.
And also with increase in radius there is increase in thermal resistance and decrease in convective resistance here the h value greater than k.
(1)
Omprakash said:
1 decade ago
Radius of insulation is less than that of critical radius. Hence heat loss from ins pipe is more than that in without insulated pipe.
Deekshant said:
1 decade ago
k/d = 0.75 mts.
So critical radius = 75 cm.
But here the radius is 7 cm.
So, ans A must be right.
So critical radius = 75 cm.
But here the radius is 7 cm.
So, ans A must be right.
Nihar said:
1 decade ago
The concept is if the insulation exceeds (rc) critical radius of insulation then the insulation not worthy i.e. we are wasting money. And here if at all the thickness is less than the rc but still it is obvious thing that heat transfer is less in a insulated pipe as compared to non-insulated.
Suraj said:
9 years ago
Also calculated by the formula.
1) without insulation.
2) with insulation.
1) without insulation.
2) with insulation.
Amit shah said:
8 years ago
Explain the formula.
Vandna said:
7 years ago
The correct answer is option : A.
Arindam said:
7 years ago
How? @ Vandana.
B is the correct option. I agree.
B is the correct option. I agree.
Vamsi said:
7 years ago
From the formula critical Radius = Thermal conductivity/heat transfer coefficient.
We can say that heat loss is minimum when it is insulated.
We can say that heat loss is minimum when it is insulated.
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