Discussion Forum

Hi,

I recommend to study the example of Free Convection, which can be found in the Model Library.

Regards,
Andrzej

Hi Andrzej,


How could i put that the temperature at the entrance would be the same that the temperature at the outlet??I mean,i have a fluid entering at 293K which is exposed to a heat flux,then is cooled because it transfers heat to a storage,and i would like to have this temperature fluid at the entrance,and the same process during the simulation,like a circulating fluid.

Thanks,

Carlos

Hi

I believe there is a "fan" BC in CFD now in 4.2a but I havent used it, do not know if it works for fluids

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Good luck
Ivar

Hi,

Previously it seemed to me that in your system there is free convection. This is not so.

Do you want to assume that the inflow temp of oil is the same as outflow temp of oil?
In this case, when the heat flux entering your system is constant, the temperature of the system will grow without bound!

Regards,
Andrzej

Andrezj!!

What i want to do is:

At the beginning of the simulation i will have a fluid entering at 293K.This fluid will "received" the heat flux,it will be heated(imagine 400K),and then it will pass through the storage,giving his heat and loosing temperature,so imagine it goes out at 300K.

I want to repeat this process but with the new inlet temperature(300K)........i want to simulate the fluid circulating,like if the inlet and the outlet were connected.Th fluid at the outlet will go another time to the inlet and will be heated another time.

Do you understand me??I hope so.

Hi
you can map the temperature of one boundary over to another with a coupling operator, then you add a few degrees for the DT value, particularly if it is constant.
But be aware, you have quite some "positive feedback" in your model like that, you will end up with a Temperature of a few millions degrees if you go on for long ;)

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Good luck
Ivar

Hi,

What is a coupling operator,??

I dont want to add degrees to the inlet temperature,i just want the inlet temperature to be the same that the one at the outlet at every time step in the simulation

Hi

check the Definition - Model couplings - and look up the help and doc for the 4 first in the list ;)

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Good luck
Ivar

Hi,


I think i have to use BOUNDARY SIMILARITY.I have define the operator name,the source boundary(outlet),the destination boundary(inlet)......but i think i should put something in the TEMPEARTURE BOUNDARY....what do i have to do?

Hi

that is one possibility, you have also the possibility to define an average operator on the output edge, and get the average output temperatre, then use this scalar value as input for the inflow temperature (by adding whatever you need as offset). Or you can se a mapping operator to map the temperature T(s) where s=0 to 1 along the output edge low region onto the input edge, such that you can use the mapping of T on the input to add to the output + whatever offset you want.

So there are many possibilities, all depends what you desire to model

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Good luck
Ivar

Hi,

please i am new to comsol, need to do some modelling for some parts of my thesis.

what i am trying to do is two fold

1 - flow in 2D through an idealized porous medium (since we have validation data for this). The medium is a periodic array of cylinders. But to do this, we define one grid cell (a square) with an obstacle in the center of the grid (a circle) and then set the boundaries of the square to be periodic and open to flow, while the boundaries of the circle are impermeable to the fluid flowing but could have some kind of slip boundary condition.

2 - the same idea as in 1 but this time in 3D using a cube instead of a square and a sphere in the center of the cube instead of a circle.

So far I am starting off on the 2D case. I have created a square using the square button and put a circle in the middle of the square after which I subtracted (boolean operation - difference) the circle from the square. My major challenge now is how to pick the boundaries of the circle to be different from the boundaries of the square since they both select as one object in the model.

Subsequently, I would need to know how to also allow fluid flow through the square boundaries and also make this one grid cell periodic.

I hope I can get some pointers in the right direction with this, any help is very much appreciated.

Thanks in advance

Hi Ivar,


Im doinf a 3D simulation,but it doesnt run because it says there is an "error:problem setting up multigrid"

How can i overcome that???


Thanks,

Carlos

Hi,

In trying to use the boundary similarity in a 3D design, but it doesnt run--> "Try to specify a mapping"

What should i do???