Chemical Engineering - Heat Transfer - Discussion
Discussion Forum : Heat Transfer - Section 8 (Q.No. 10)
10.
A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions ? Assume that the conductive heat transfer co-efficient is infinitely large.
Discussion:
6 comments Page 1 of 1.
Pramita ghosh said:
3 years ago
For sphere time proportional to r^2.
So,
20/x = (0.1/0.05)^2,
x = 5 min.
So,
20/x = (0.1/0.05)^2,
x = 5 min.
(3)
Albaz said:
4 years ago
I think 10 min is the correct answer.
(2)
Papulu said:
9 years ago
Answer is 10, as time promotional directly radius.
H.A.t / dens.V.C proportiona Temp.
So, A/V proportional to 1/t.
t proportional to d.
H.A.t / dens.V.C proportiona Temp.
So, A/V proportional to 1/t.
t proportional to d.
(1)
Akash Varma said:
8 years ago
Yes. The answer is 10.
While doubling the radius of the sphere, it takes double the time to cool down to the same temperature.
As, Radius of the sphere is directly proportional to the time it takes to cool down to the same temperature, of course under identical external conditions.
While doubling the radius of the sphere, it takes double the time to cool down to the same temperature.
As, Radius of the sphere is directly proportional to the time it takes to cool down to the same temperature, of course under identical external conditions.
(1)
Osama said:
8 years ago
Yes, the answer should be 10 min.
Sujit P said:
4 years ago
From transient mode heat transfer equation with same temperature effect we get time(t) is directly proportional to volume/area(V/A) (i.e split mass = density * volume).
And for sphere t is directly proportional to r.
So, the answer is D 40 min.
And for sphere t is directly proportional to r.
So, the answer is D 40 min.
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