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Heat Transfer Problem

Posted 03.02.2013, 22:58 GMT-5 Fluid & Heat, Heat Transfer & Phase Change, Mesh Version 4.2 3 Replies

Gary Yu
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Hi everyone,

I found my heat transfer problem is taking too long to solve even in stationary.

The problem is about a pair of thin pipes embedded in soil. pipe diameter 25mm, 20m long each. There is fluid flowing through inside the pipes. One pipe is the inlet with the temperature of 40deg C and the other is the outlet 35 deg C. I would like to find out the temperatures in the soil surrounding the pipes.

I have attached two different files:

SMALL SCALE with (0.5m x 1m x 1m length of pipes) soil block, which I think is successful and provides reasonable results, without taking long to solve.

LARGE SCALE is where my issue is: (0.5m x 1m x 20m length of pipes) soil strip, which is taking too long solve and I aborted it after it ran for 2 hours. Everything is the same as SMALL SCALE, except for the length increased by 20 times.

Is it something to do with the meshing, element size, number of elements? I tried to play around with the maximum and minimum element sizes, in order to minimise the element quantity, but no luck.

I am looking forward to hearing some advice, thanking you all in advance.





3 Replies Last Post 04.02.2013, 20:45 GMT-5
Nithin
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Posted: 1 decade ago 04.02.2013, 00:28 GMT-5

Hi everyone,

I found my heat transfer problem is taking too long to solve even in stationary.

The problem is about a pair of thin pipes embedded in soil. pipe diameter 25mm, 20m long each. There is fluid flowing through inside the pipes. One pipe is the inlet with the temperature of 40deg C and the other is the outlet 35 deg C. I would like to find out the temperatures in the soil surrounding the pipes.

I have attached two different files:

SMALL SCALE with (0.5m x 1m x 1m length of pipes) soil block, which I think is successful and provides reasonable results, without taking long to solve.

LARGE SCALE is where my issue is: (0.5m x 1m x 20m length of pipes) soil strip, which is taking too long solve and I aborted it after it ran for 2 hours. Everything is the same as SMALL SCALE, except for the length increased by 20 times.

Is it something to do with the meshing, element size, number of elements? I tried to play around with the maximum and minimum element sizes, in order to minimise the element quantity, but no luck.

I am looking forward to hearing some advice, thanking you all in advance.


Mine is also a similar model. I too, am getting the same problem. Gary Yu, kindly help me if you get the solution.
[QUOTE] Hi everyone, I found my heat transfer problem is taking too long to solve even in stationary. The problem is about a pair of thin pipes embedded in soil. pipe diameter 25mm, 20m long each. There is fluid flowing through inside the pipes. One pipe is the inlet with the temperature of 40deg C and the other is the outlet 35 deg C. I would like to find out the temperatures in the soil surrounding the pipes. I have attached two different files: SMALL SCALE with (0.5m x 1m x 1m length of pipes) soil block, which I think is successful and provides reasonable results, without taking long to solve. LARGE SCALE is where my issue is: (0.5m x 1m x 20m length of pipes) soil strip, which is taking too long solve and I aborted it after it ran for 2 hours. Everything is the same as SMALL SCALE, except for the length increased by 20 times. Is it something to do with the meshing, element size, number of elements? I tried to play around with the maximum and minimum element sizes, in order to minimise the element quantity, but no luck. I am looking forward to hearing some advice, thanking you all in advance. [/QUOTE] Mine is also a similar model. I too, am getting the same problem. Gary Yu, kindly help me if you get the solution.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 04.02.2013, 01:01 GMT-5
Hi

I understand from your reading that you should use the physics from the pipe flow module, CFD is interested in the details of the flow, locally, else you need a horrible large amount of RAM and time to solve, while Pipe flow applies "engineering" formulas, just as precise but not giving the details of the flow.

Rewriting the pipe flow module by equations is possible but quite some work

--
Good luck
Ivar
Hi I understand from your reading that you should use the physics from the pipe flow module, CFD is interested in the details of the flow, locally, else you need a horrible large amount of RAM and time to solve, while Pipe flow applies "engineering" formulas, just as precise but not giving the details of the flow. Rewriting the pipe flow module by equations is possible but quite some work -- Good luck Ivar
Gary Yu
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Posted: 1 decade ago 04.02.2013, 20:45 GMT-5
Thanks for your advice, Ivar. I will try to use Laminar Flow (nitf) then.

Thanks for your advice, Ivar. I will try to use Laminar Flow (nitf) then.

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