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Measuring Heat Content
Posted Jun 1, 2017, 7:31 a.m. EDT 3 Replies
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Hi,
I have a 2D model of a seabed with a cable in it, which produces heat. I have a heat source implemented for this. I would like to know how much heat is stored in the volume around the cable in a stationary case.
So the heat source produces a constant amount of heat, which is very slowly transfered through the soil to the ocean water above. In a stationary case the temperature in the seabed reaches a certain value which is higher than without the heat source of course.
How can I measure the amount of heat "stored" in the seabed in comparision to a undisturbed case without heat? In J/m³ for example for the volume of 5m distance from my heat source?
Hope to hear from you :-)
BR, Madlen
I have a 2D model of a seabed with a cable in it, which produces heat. I have a heat source implemented for this. I would like to know how much heat is stored in the volume around the cable in a stationary case.
So the heat source produces a constant amount of heat, which is very slowly transfered through the soil to the ocean water above. In a stationary case the temperature in the seabed reaches a certain value which is higher than without the heat source of course.
How can I measure the amount of heat "stored" in the seabed in comparision to a undisturbed case without heat? In J/m³ for example for the volume of 5m distance from my heat source?
Hope to hear from you :-)
BR, Madlen
3 Replies Last Post Jul 4, 2017, 4:42 p.m. EDT
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Posted:
7 years ago
Updated:
7 years ago
Hi Madlen,
just set up an integration on the seabed domain. If rho is the specific heat capacity in J/m3 and T0 the start ambient temperature:
Wth is the stored heat and V is the seabed domain. You can set up the integration in the definitions section and use the integration operator to set up a global variable, or you can do it in post processing in case your model is already solved.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
just set up an integration on the seabed domain. If rho is the specific heat capacity in J/m3 and T0 the start ambient temperature:
Wth is the stored heat and V is the seabed domain. You can set up the integration in the definitions section and use the integration operator to set up a global variable, or you can do it in post processing in case your model is already solved.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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Posted:
7 years ago
Hi Edgar,
sorry for the late replay and thanks for the answer. I have now tried it but didnt succeed yet.
I added an integration node (named intop1) to my component definitions and selected the domain for it. Where in Comsol can I add the formula you gave earlier?
I also tried in the post processing but am not sure if I should take a surface or volume integration. My model is in 2D, but in total I would like to obtain a value for the heat content of the sediment in J along the whole cable which is some kilometers long in reality.
And one question about the formula: For me the heat capacity is Cp in J/kgK. Shouldn't I add also the densitiy (rho) which is in kg/m³ to the integration formula? Then after the integration the unit that remains would be only J.
Thank you for answering these beginner questions,
Best Madlen
sorry for the late replay and thanks for the answer. I have now tried it but didnt succeed yet.
I added an integration node (named intop1) to my component definitions and selected the domain for it. Where in Comsol can I add the formula you gave earlier?
I also tried in the post processing but am not sure if I should take a surface or volume integration. My model is in 2D, but in total I would like to obtain a value for the heat content of the sediment in J along the whole cable which is some kilometers long in reality.
And one question about the formula: For me the heat capacity is Cp in J/kgK. Shouldn't I add also the densitiy (rho) which is in kg/m³ to the integration formula? Then after the integration the unit that remains would be only J.
Thank you for answering these beginner questions,
Best Madlen
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Posted:
7 years ago
Updated:
7 years ago
Hi Madlen,
You can do it in postprocessing of course. The volume integral in 2D is just the surface integral multiplied by the model length, that is typically set in the physics top node.
And you are right, the
in my formula has to be the gravimetric density multiplied by the heat capacity. Both can be a function of the spatial variables.
You can also define a variable:
heat = intop1(Cp*rho*(T-T0))
To get the heat in the volume you can again multiply by the model length.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
You can do it in postprocessing of course. The volume integral in 2D is just the surface integral multiplied by the model length, that is typically set in the physics top node.
And you are right, the
in my formula has to be the gravimetric density multiplied by the heat capacity. Both can be a function of the spatial variables. You can also define a variable:
heat = intop1(Cp*rho*(T-T0))
To get the heat in the volume you can again multiply by the model length.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com