Which will boil faster?

  • #1

Homework Statement


upload_2016-6-1_20-0-36.png

Case 1: Which will boiling faster the container having steel ball dipped in it or container having only water?

Case 2: Which one will attain thermal equilibrium faster? Consider balls are just in middle of the container.

every condition of each the cases have same volume of water

Homework Equations


Q=mc*dT

The Attempt at a Solution


It is different than boiling stone; As we are heating simultaneously water and the steel ball.
In 1st case; as volume of water is same that means container with steel ball would require extra energy that means it will boil late.
In 2nd case; we could apply transient head transfer but how could we compare "h" for both the cases.
 

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Answers and Replies

  • #2
BvU
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In 1st case; as volume of water is same that means container with steel ball would require extra energy that means it will boil late
On the other hand, conductivity of the contents will effectively improve, perhaps offsetting the little bit of extra heat required ?
For case 2 it isn't clear to me what the system under consideration is and what thermal equilibrium would mean here. The whole lot at 20 C ?
 
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  • #3
CWatters
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I agree with your answer for case 1.

For case 2 you aren't given the relative masses of the ball and water so you can't calculate the final temperature or estimate the heat that has to flow into or out of the ball. Perhaps consider what happens if the ball is the size of a grain of sand? Or the water just one droplet?
 
  • #4
For case 2 it isn't clear to me what the system under consideration is and what thermal equilibrium would mean here. The whole lot at 20 C ?
Thermal equilibrium means; heat transfer will stop between ball and water. Equilibrium temperature would be something between 100 c to 30c
 
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  • #5
On the other hand, conductivity of the contents will effectively improve, perhaps offsetting the little bit of extra heat required ?
Bulk temperature need to attained faster. What is the role of conductivity of ball here?
 
  • #6
I agree with your answer for case 1.

For case 2 you aren't given the relative masses of the ball and water so you can't calculate the final temperature or estimate the heat that has to flow into or out of the ball. Perhaps consider what happens if the ball is the size of a grain of sand? Or the water just one droplet?
I am pretty much sure that heat capacity (m*c) of ball is low. Water's mass is much more than the ball.
 
  • #7
BvU
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Bulk temperature need to attained faster. What is the role of conductivity of ball here?
Depending on how the heat is brought to the contents, it has to be transported (or not -- like in microwave oven) by conduction and/or convection.
 
  • #8
BvU
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Thermal equilibrium means; heat transfer will stop between ball and water. Equilibrium temperature would be something between 100 c to 30c
Like very close to 30 in one case and very close to 100 in the other ? And all transport mechanisms for heat are to be considered ?
What is the context of this exercise? Where does it come from ?

So many questions...
 
  • #9
Like very close to 30 in one case and very close to 100 in the other ? And all transport mechanisms for heat are to be considered ?
What is the context of this exercise? Where does it come from ?

So many questions...
Yeah you got it right
You can neglect radiation
It was just asked in BARC interview
 

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