Solar Load and fvDOM Radiation Modeling
 

Hello Everyone,


Currently, I am simulating a room which has a one glass wall through which solar radiation enters into the room. I am using an OpenFOAMv-1906.


I am able to give the correct input for solar load calculation which I can see its effects through q_primaryRadiation_0 variable and when I run this simulation along with fvDOM radiation model The surfaces on which solar radiation are falling showing the very less temperature compare to other unexposed surfaces, for reference I have attached the comparative T and Solar Load on the surface images.

I am using an externalWallHeatFluxTemperature boundary condition by which I can specify the flux on all Walls, on adiabatic walls q=0 and qr =qr similarly, on some other walls I specified q=x, qr=qr, where x is some value.

When we apply only Solar Load model alone the q_primaryRadiation_0 is equal to qr and it is a positive value and it gives very high temperatures on exposed surfaces. Whereas with Solar Load + fvDOM, the qr is negative and it gives the low temperature on exposed surfaces.

My main question is why the sun directs exposed surfaces showing ver less temperature when I choose Solar Load + Radiation Model?

For Reference purpose, I am attaching the T and radiationProperties and boundaryRadiationProperties files also.

Looking for your help and thanks in advance.

Regards
Shadab

Hello,
Could you find an answer to your problem?
cheers

Hi,

I have resolved that issue of showing very low temperature on sun direct exposed surfaces.

The flux/power what I am specifying by using externalWallHeatFluxTemperature BC is for convection transfer only, As we don't know on which faces sun radiation will fall and final load will be the sum of convention plus solar loads.

So I slightly changed the externalWallHeatFluxTemperature BC which consider the solar load by looking into solar load file which is generated by running the solar load radiation model. The solar load written on the boundary patches only and for inside the domain, it is zero.

Similarly, I changed the solver also which carry this solar load field with it, actually, once a solar field is generated it is acting as heat source field which is applied only on the boundaries and once the simulation becomes stable run it with radiation model. Because there will be a very high temperature on the boundaries.

Regards,
Shadab

Hello,

Thank you, I was asking you since I want to do something similar.
I am not specifically inserted in solar load, but a have a very hot source in my domain and I want to include mirrors and windows inside the domain (as baffles) to speculary reflect or transmit radiation, and I have seen that you use such things in your boundaryRadiationProperties.
I have been trying to use such file in my simulations but it seems to not be taken into account in the solver.
There is no tutorial in the source about such problem, so I was wondering if you could explain me a bit about that.
Thank you a lot in advance
Yann

Hi Yann,

To consider the radiation effects on your boundary condition use externalWallHeatFluxTemperature BC with (qr qr) instead of (qr none) when radiation is on.

You can't see the radiation effect on constant temperature and zero gradient type of boundary condition. So, if you want to specify adiabatic wall use flux or power mode and give zero value and make (qr qr) in BC. Be make sure heat flux or power what you specified is the steady heat transfer through that patch with a combination of both convection plus radiation.

Currently, OpenFOAM supports grey diffusive/non-grey diffusive walls only, it means you can see the effect of radiation emission and reflection from the walls but not transmit through it, which is available in fluent as the semi-transparent boundary condition. But by using the above boundary condition we can interact with the environment with available qr on the patch and can give heat through radiation mode also.

I hope it solves your problem!

Cheers
Shadab

Hello Shadab,


I am little bit confused, because in your case you use this entry:

or




Which if I understand well, should do speculat reflection or tramsmissivity, no?


I also have another question, I already use externalWallHeatFluxTemperature BC with (qr qr), but I don't really understand how the material properties of the heated wall taken into account?


Cheers
Yann

Hi Yann,

The type of radiation wall properties that I have specified in boundary radiation properties such as opaqueReflective and transparent are specifically used only with solar load model.

opaqueReflective : This boundary condition gives tranparent = 0, absorptivity= x and reflectivity = 1-absorptivty. another factor fd is there which decide how the reflective component distribute as diffusive or a specular.

transparent : complete transparent =1.

As solar load is not an alone radiation model it must be run with another radiation model such as P1, fvDOMor viewFactor. As I am not familiar with other models except fvDOM So, I can't comment much on it.


In fvDOM model when we discretize the domain into multiple solid angles then we solve RTE for multiple radiation intensity rays, for that we provide greyDiffusiveRadiation or nonGreyDiffusiveRadiation BC which is for only Opaque walls which absorbs and reflect only and it read the emissivity property (emissivity = absorptivity) from boundaryRadiationProperties file only. It performs transmissivity calculation only solar load is true otherwise it is a simple opaque wall BC. for more information visit the BC implementation.

So, with the best of my knowledge, you can't apply a transparent/semitransparent type of BC with fvDOM in OpenFOAMv-6/v1912 current versions.

Hope I have clear your doubts.


Cheers,
Shadab

Hello,


Thank you very much for your complete answer, I still don't understand how such BC can only be used for solar load if it uses fvdom as a radiation model anyway, but there is no big deal and I will consider that I can't use reflective walls in my simulations.
Regarding my other question, I still don't really understand how externalwallheatflux BC works, I put flux equal to zero as you suggested but the temperature goes really high (with qr=300W/m2), I looked deeper into the code and found something about relaxation and qrRelaxation but I don't really get their meaning and how it affects results.
Thank you again in advance
Yann

Dear Shadab,

I want to know that which solver you used for your problem?

Best regards

Chengan

Hello,

i am just starting out with the solar load feature of OpenFOAM and i was wondering if you could share your case files, because I am working with a simialar setup. Thank you very much.

Hi!

Thanks for explaining solar load radiation boundaries. Can you tell what does opaqueDiffuisve boundary condition do? Isn't it the same as opaque reflective since opaque reflective too has diffusive fd option?

THanks

Dear Shadab,
i'm inerested in your model, what solver did you use, is was BuoyantSimpleFoam?
I wanted to simulate a similar case in steady state with solar load only and I got very high temperatures (about 600 K), I thought it was because of the absence of the radiation model but 600 K is still a lot .
can you please give more information about your model, numerical methods and schemes.
could you please share your case file, it will be really helpful for me to do internal simulation of thermal comfort.
regards
Abbes

integration of an evaporative air cooler with a refrigeration unit to enhance the ind
 

integration of an evaporative air cooler with a refrigeration unit to enhance the indoor thermal environment and production of clean water in iraq
room 3m x4m and height 3m ,walls from hollow block and roof from curpy steel , with door and window in east wall, there is duct inside room two supply one to input cooled air from evaporative air cooler and other from refrigeration unit with return to refrigeration unit, i want simulate to this system with effect sun solar radiation with outdoor conditions on walls and roof daily and 3monthly (in summer) by any program and how to get on results from as indoor and outdoor conditions as temp. and relative humidity

Solar Load
 

Hello
I am also trying to simulate the same conditions as you.
I have a glass wall(defined as a solid surface) through which solar radiation enters the system and the system heats up which contains air ,2 solid and water flowing inside one of the solid.
I want to know about the boundary conditions you gave on your glass wall with complete explanation.
I am using OpenFoam 10 in which solar load isn't working i guess.
so I have coupled solar load with other radiation models which i read about in one of the forums.
But to my bad luck i am not getting any heat input.(solar load is not working at all).

If you still have your case with you ,sharing the case files can be helpful too.
I can learn it by my own and you wont be needing to waste your time explaining things to me.

Please please help me on this.