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Melting ice below rock using deforming mesh but without Lagrangian. Is there a way?

Posted 21 juil. 2014, 03:44 UTC−4 Heat Transfer & Phase Change, Mesh, Studies & Solvers Version 4.3 4 Replies

Jordan Mertes
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Hello,

I have a question about the setup similar to the melting tin model. I have block with two layers, one on top of the other. The upper layer is granite, the lower layer is ice. On the upper surface I have a prescribed heat flux, in the middle I have a set temperature at the melting point of ice and at the lower surface I have a set temperature a few degrees below freezing. The model is setup exactly the same as the melting tin model and does work. Using the assumption that any phase change from ice to water allows the water to leave the system. However, I realized while watching the results, that by using the set middle temperature and the weak constraints which give me the Lagrangian which I use to calculate the mesh velocity, the ice cannot cool. So while I am able to send heat to the boundary and melt the ice, I cannot remove heat across the boundary and cool the ice.

I am wondering what other methods are possible in COMSOL to perform the same task, yet allow for removal of heat from below the melt interface. I have been reading through the forum but don't see anything similar to this problem. I was thinking maybe I'd have to calculate the heat flux at each node along the boundary, for each timestep and then feed that into the model. This, however, is so far beyond me (I'm still a bit of a newbie).

I'm just curious if anyone out there might have any suggestions as to how to do this. Any help would be appreciated.

Also, I should apologize for sending a private message to a forum guru. I realized after sending it that the whole point of the open forum is so that everyone can see the discussions and get help where they can find it. Hopefully this question will be answered and help others as well.

Cheers,

J
4 Replies Last Post 29 juil. 2014, 06:07 UTC−4
Pieter Westerik
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Posted: 1 decade ago 25 juil. 2014, 05:57 UTC−4
How can the water disappear? It might take heat with it as it flows away.
How can the water disappear? It might take heat with it as it flows away.
Jordan Mertes
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Posted: 1 decade ago 27 juil. 2014, 04:05 UTC−4
Fair point. I was assuming the deforming mesh, which they say should be used in the case of adding or removing material, would "remove the water". If this isn't the case, then perhaps I should try and just set the boundary between the rock and ice to only have a maximum temperature of 273.15K but allow it to be cooled, thus simulating proper heating and forgo the deforming mesh all together. I could then look at the heat flux to the boundary and calculate the melt from that.

However, now I am encountering problems trying to set a maximum temperature of 273.15K on the boundary. I have read a "Tips and Trick" from 3.5, but I still don't quite understand. I was hoping I could set the boundary temperature to if(T>=273.15, 273.15,T) and hope it would adjust itself but it doesn't.

Anyone have better instructions on how to set a maximum temperature on a boundary?

Cheers
Fair point. I was assuming the deforming mesh, which they say should be used in the case of adding or removing material, would "remove the water". If this isn't the case, then perhaps I should try and just set the boundary between the rock and ice to only have a maximum temperature of 273.15K but allow it to be cooled, thus simulating proper heating and forgo the deforming mesh all together. I could then look at the heat flux to the boundary and calculate the melt from that. However, now I am encountering problems trying to set a maximum temperature of 273.15K on the boundary. I have read a "Tips and Trick" from 3.5, but I still don't quite understand. I was hoping I could set the boundary temperature to if(T>=273.15, 273.15,T) and hope it would adjust itself but it doesn't. Anyone have better instructions on how to set a maximum temperature on a boundary? Cheers
Pieter Westerik
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Posted: 1 decade ago 28 juil. 2014, 03:59 UTC−4
For me the question remains: where does the water go? Is the rock porous and does it flow through it? Then it will also cause some heat transport from the ice to parts of the rock that are further away from the interface. And maybe it evaporates at the top surface of the rock? Then you will also lose heat there.
For me the question remains: where does the water go? Is the rock porous and does it flow through it? Then it will also cause some heat transport from the ice to parts of the rock that are further away from the interface. And maybe it evaporates at the top surface of the rock? Then you will also lose heat there.
Jordan Mertes
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Posted: 1 decade ago 29 juil. 2014, 06:07 UTC−4
Well, alot of times in melt modeling you "assume" what water is produced runs off. We know that this is not correct and that there is a amount of heat that is absorbed, transported and even released through phase changes and soil moisture content. However, this may be asking a lot of the model. I haven't had time to explore the modules for fluid/heat in porous media. It would be great to try it out, but it may have to wait for now.
Well, alot of times in melt modeling you "assume" what water is produced runs off. We know that this is not correct and that there is a amount of heat that is absorbed, transported and even released through phase changes and soil moisture content. However, this may be asking a lot of the model. I haven't had time to explore the modules for fluid/heat in porous media. It would be great to try it out, but it may have to wait for now.

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