Conjugate Heat Transfer Transient Model not Working

Posted 15 août 2024, 11:34 UTC−4 Fluid & Heat, Computational Fluid Dynamics (CFD), Modeling Workflow Version 6.0 2 Replies

Sayee Srikarah Volaity

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Hello all,

I am modeling a heating device placed inside a room using conjugate heat transfer module with k-ε turbulence model.

The simplified geometry consists of three cubes (figure attached), the smallest cube represents the device, which is placed inside the room very close to two walls. The air inside the room is defined using the second cube, and the difference between the biggest cube and the second cube is defined as a brick wall. The heating device is at a constant temperature of 100 degC, and there is a constant air inlet (mass flow rate defined) from the top face of the device. To make it a stable system, an opening is made in the roof (as seen in the attached picture).

Mentioned below are the specified boundary conditions. Heat transfer in solids and fluids: - Air inside the room and the brick wall are initially at 25 degC - The device is initially at 100 degC - Constant temperature of the domain is defined using a pointwise constraint - The exterior surfaces of the brick walls are convecting with the external air at 25 degC - An "outflow" condition is specified at the exterior surface of the window

Turbulent flow: - Initial and reference pressure levels at 1 atm for the whole model - Weakly compressible flow with no gravity effects - Inlet at the top surface of the device (mass flow rate defined) - The surfaces of the device (other than the inlet) are defined as walls - The internal surfaces of the brick wall are defined as walls - An "outlet" condition is specified at the exterior surface of the window - Used a pressure point constraint set at 1 atm at one of the point on the external surface of the window

For the multiphysics coupling, viscous dissipation is enabled.

With the above set of boundary conditions, a stationary model is working well and is giving reasonable results. But the same model when run using a time-dependent study is giving several errors. It initially gave an error of inconsistent initial values, following which I used step function to ramp up the transition of the device's temperature, inlet. and convective coefficient. This time, I am getting an error that says

"Time-Dependent Solver 1 (sol3/t1) Repeated error test failures. May have reached a singularity. Time: 3.2249932802768407e-06 s. Last time step is not converged".

I have tried changing the solvers and mesh resolution too, but nothing seems to work. Would be great if anyone could help me with this.

Attachments:

Geometry.png

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2 Replies Last Post 18 déc. 2024, 03:12 UTC−5

COMSOL Moderator

Hello Sayee Srikarah Volaity

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一帆宋

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Posted: 4 weeks ago

Hello, I have the same problem, have you found a solution to this problem?

Sayee Srikarah Volaity

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Posted: 1 week ago

Hello, I have the same problem, have you found a solution to this problem?

Hello,

The issue with it was that the solution was not converging as there were no adequate inputs defined to govern where the fluid would go in the turbulent flow module. You could use a pressure point constraint or define an outflow condition to make it work.

Hope that helps.

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