Ice will melt faster which case -- over or below hot block?

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Discussion Overview

The discussion centers around the heat transfer mechanisms involved in melting ice placed either above or below a hot metal block. Participants explore the roles of conduction and convection in this context, considering both theoretical and practical implications of the setup.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants express confusion about the role of convection in heat transfer, particularly since ice is solid and convection typically occurs in liquids and gases.
  • One participant argues that heat transfer will primarily occur through conduction when the ice and metal blocks are in contact, regardless of their positioning.
  • Another participant suggests that ice placed on top of the metal block will melt faster due to the direct contact and heat transfer dynamics.
  • Some participants note that the flow of melt water and steam may significantly influence heat transfer, while simple air convection could be a minor factor.
  • There is a discussion about the presence of a layer of melt water between the ice and the metal block, and how this layer may affect heat transfer as melting progresses.
  • Participants question whether the positioning of the blocks makes a difference in the melting rate and explore the implications of temperature gradients between the blocks and the surrounding air.
  • One participant asserts that conduction is the predominant mechanism of heat transfer, while acknowledging that convection may also play a role due to liquid water and air movement.

Areas of Agreement / Disagreement

Participants generally agree that conduction is a significant mechanism for heat transfer, but there is no consensus on the extent to which convection contributes or on the overall impact of block positioning on melting rates. Multiple competing views remain regarding the relative importance of these mechanisms.

Contextual Notes

Some participants highlight the need to consider the actual physics involved, including the effects of temperature gradients and the flow of melt water, which may not be fully resolved in the discussion.

Ravi Singh choudhary
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Natural convection always occurs opposite of gravity due to buoyancy; but I am confused as ice is solid so how could possibly convection even contribute to the heat transfer. I doubt about air movements nearby block that may contribute to greater heat transfer rate in case of hot block placed below the ice.

Pls help
 

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Your drawing shows the ice and hot metal blocks are in contact. So most heat will be transported by conduction not convection. It will not make much difference which one is on top.

Ravi Singh choudhary said:
as ice is solid so how could possibly convection even contribute to the heat transfer

Convection only occurs in liquids and gasses, NOT in solids like ice.

If you look what happens at the edges...

If the metal block is below the ice it will heat up the air causing the air to rise past the edges of the ice.
If the metal is on the top that energy is carried away into the room without going past the edges of the ice.

Convection.jpg
 
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I am talking about even the negligible difference between the timing of melting of ice.
I think ice on top of metal block will win the race.
 
I agree.
 
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Ravi Singh choudhary said:
Natural convection always occurs opposite of gravity due to buoyancy; but I am confused as ice is solid so how could possibly convection even contribute to the heat transfer. I doubt about air movements nearby block that may contribute to greater heat transfer rate in case of hot block placed below the ice.

Heat transfer is almost entirely determined by flow of melt water and steam . Simple air current convection will probably only be be a minor contributor .

Try thinking about the actual physics of what is happening .
 
Nidum said:
Heat transfer is almost entirely determined by flow of melt water and steam . Simple air current convection will probably only be be a minor contributor .

Try thinking about the actual physics of what is happening .

I think steam would not be there as metal block is at 50 degree Celsius only.
 
In between the ice block and the metal block there must be a layer of melt water .

What happens to this layer of water as the melting of the ice block progresses ?
 
Last edited:
Nidum said:
In between the ice block and the metal block there must be a layer of melt water .

What happens to this layer of water as the melting of the ice block progresses ?
I think water will flow down between the edges of block
 
Yes - water will flow out continuously while the melting process is active .

So :

(a) What is the main mechanism of heat transfer between the blocks ?

(b) Is there any additional mechanism of heat transfer involving the external flow of the melt water ?

(c) Back to the original question - does it make any difference which block is on top ?
 
  • #10
Nidum said:
Yes - water will flow out continuously while the melting process is active .

So :

(a) What is the main mechanism of heat transfer between the blocks ?

(b) Is there any additional mechanism of heat transfer involving the external flow of the melt water ?

(c) Back to the original question - does it make any difference which block is on top ?
Yeah that water would be at just more than zero degree Celsius. That means we have a gradient between atmosphere and water flowing. So somehow it will drop the temperature nearby air. If Ice would be on top; it will decrease the metal block temperature side wise also. In the meantime the gradient between metal block and ice will reduce consequently it would reduce the heat transfer. But if Ice would be below the metal block, then water will just fall to the ground.
 
  • #11
What is the answer to (a) ?
 
  • #12
Nidum said:
What is the answer to (a) ?
Conduction only
 
  • #13
Is that correct ?

What do other PF members think ?
 
  • #14
Nidum said:
Is that correct ?

What do other PF members think ?
I must say conduction is predominant. Convection would be there due to liquid water flowing and air movement also. Magnitude of both will decide, in which case ICE will melt fast?
 
  • #15
Ravi Singh choudhary said:
I must say conduction is predominant. Convection would be there due to liquid water flowing and air movement also

Seems about right for the problem you originally described . At higher temperature differences convection would probably become more active .

That's it for now .
 
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