Learning Forum

[merveala01]

I am doing analysis in laminar flow and energy equations on. It is so simple. I know hot water and cold water inlet temperature values. Hot water varies between 25 and 55 degrees and cold water inlet is 20 degree as constant. and want to calculate outlet temperatures but I can not get sensible results about cold water outlet. for example even hot fluid water is 55 degree, the cold water outlet is 25 degree. I defined all the variables as parameter set. specific heat, viscosity, mass flow rate and density are other variables. Finally, I decided to write an equation for the walls. Because for an inlet temperature of 55 degrees, the outlet temperature should be around 45 degrees. But I don't know how to write the UDF function when I have so many parameter variables.

[Rob]

In CFD we'd tend to set the inlet value and calculate the outlet condition. So, in your case you can't force a fixed dT but instead need to understand why it might differ from the experiment. In your case I suspect there is no connection between the hot & cold zones so revisiting the geometry to apply "share topology" might be a good place to start. 

[merveala01]

I followed that video and it applies share topology. What else can ı do?

https://youtu.be/rFQisXCwLXI?si=cvkXZJVprKOWpakL

[Rob]

What setting have you applied to the wall & shadow pairs? 

[merveala01]

I didnt set any setup for wall they were default

[Rob]

OK, and what is the heat flux (Flux Report) through those walls?

[merveala01]

well ı didnt get specific heat flux for walls, ı just got that results, there total heat transfer rate for hot water and cold water inlet and outlets. 

[Rob]

In Fluent please report the flux on the wall & shadow pair. If you aren't getting results you expect you need to investigate in the solver, not just check the few monitors you have in Workbench. 

[merveala01]

I reported and all of them are zero :(

[Rob]

Please post a screen shot. And one of the wall bc panel. 

[merveala01]

Here wall boundary conditions they are all default. Do ı need user define function? My hot inlet temperature is variable so ı can not define a constant heat flus value or another heat generation rate.

[Rob]

That middle image - the wall setting is not the default. That should be coupled and then set the material & thickness in one or other of the pair. Otherwise Fluent has no way to pass heat between the two sides, and that's likely why your hot channel isn't cooling & the cool channel isn't warming. 

[merveala01]

I give 0.001m thickness both intermediate walls and side walls. But there isn't much more difference. maybe 0.05 change value. I need more

[Rob]

Have you switched the interior walls back to coupled?