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Hello Davide,

I don't how inflow heat flux is working but have you tried heat flux (=> convective heat flux => heat transfer coeff.)? I assume that you need to define boiler walls/convective tubes?

Best regards

Tero Hietanen

Hi Tero,

Yeah I tried everything but I don't know why is not working. I guess there is also some kind of problem with the water because it is not heated that much.
I'll try to figure out what the issue is and I'll keep you posted if you are interested.

Thanks for your reply,
- Davide

Hi

If you have a constant temperature of your inflowing fluid, just put a constant Temperature boundary in the HT and a Inlet in the fluid section + a velocity condition for the fluid (on the same "inlet boundary".

The Inflow Heat Flux is rather for convective exchange if you look at the formulas, it assumes a "virtual" domain with the temperature T at the virtual far boundary and it exchanges with your defined boundary via the heat coefficient term, and any inflow heat exchange q0

Well the nice thing with COMSOL it's easy to make a simple "test model", see below

still the strange thing is that:

1) First try with only 1 Heat inflow with q0=0 and T=T0+2/3*DT did NOT give the expected result

2) by adding in the total heat flux q0=1.24E5[W] as found for a constant Temperature input I do not get the same results, I must add a T=T0+2/3*DT/4, why "/4" ? to have the same as for a constant T BC

3) by adding a second Heat Inflow node and this time setting q0=0 and T=T0+2/3*DT I do get the expected results ?

=> is there something wrong ?, perhaps worth to repeat with a fresh model from scratch and/or ask support

============
update, I tried again with a fresh model, this time it works as expected: see HTtst2 (v5.1)

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Good luck
Ivar

Hi Ivar,

Thanks a lot for your help.
I can't see the model 'cause I'm using an older version of Comsol. I'll try to figure out what you did exactly and try to repeat.
Thanks again, your suggestions have been very useful.

- Davide

Hey Ivar,

So I'm trying to do the model as you did but there is something unclear.
1 - what is DT in the expression of the temperature?
2 - where did you add the second heat inflow node?
Also, would you mind creating a very simple model like HTtst2 in an older version of COMSOL? (I'm using 4.3b) So I can import the model and see all the settings that you used.
That would be very useful for me.

Thanks a lot for your help,
- Davide Ivaldi

Hi

DT is a delta Temperature step in [K]

OK I tried it again in V4.4 => failure to converge and to include correctly the temperature of the fluid inflow, as well with a T=cte BC as for the heat influx !?
but it works in the V5.1 by insisting a bit, both as T=cte BC and as inflow with no extra Q but only a T

I would suggest that you get "support" to explain

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Good luck
Ivar

Hi Ivar,

Thanks a lot for your help. I will try to ask for support.
As always, your help has been very useful.

Cheers,
- Davide

Hi
I am trying to model a cone with other cone inside. There is a small part that will be heated up inside the smaller cone. Everything is ok, just i do not know why in the equation window, for my inlet and outlet (which I defined constant temperature for them) and for all the boundaries, the ht.q0 (Inward heat flux) is equal to zero. Even when I define some inflow heat flux, it is still zero. Could you please tell me what is the exact meaning of the Inward heat flux here?
How can I see the COMSOL algorithm, which is used to solve my case?