Learning Forum

[adlyna]

Hi all,nI needs help to determine solar heat flux if I have a value of solar radiation (w/m2) and solar absorptivity coefficient (alpha). Does it it have any formula? I want to assign at wall boundary condition in fluent. As I found in the paper, solar heat gain in wire qs = aplha x diameter x solar intensity. But, the unit is in W/m.nI hope whose are have experience using solar heat flux in fluent can share the knowledge. Thank for advanced.n

[Rob]

The absorption coefficient will determine how much radiation is absorbed on route to the walls: ie you may convert 20% of the energy into heat on the way through a column of water. Thus 80% of the initial load reaches the walls and is either absorbed (wall gets hot) or reflected (may hit another wall, warm the fluid up and/or leave the domain). n

[adlyna]

Sorry maybe I am not clear in explain my question. I want to put and used solar in my simulation to see the effect of temperature on my model. My model is a wire form as a cylinder and surrounding with air. All is assign as a opaque. I want to used solar load tracing but, I am not sure how fluent work with that. I just have value of direct solar (1200 w/m2). In my searching, another way, I should used solar heat flux at wire wall (if I not mistaken. Correct me if I am wrong). But, how to get the solar heat flux by just having value of direct solar (1200). Is there any formula to calculate it? As I now, the solar heat flux need to assign at my wire at thermal tab in boundary condition.I hope somebody can help me. Thank younn

[Rob]

I tend to apply the load to the outer boundary (with direction etc) and let Fluent work it out. What's set as opaque? n

[adlyna]

ya I set the boundary as opaque. The load you are mention is heat flux?n

[Juwelmojumder1]

Hi, Adlyna,nIf you are still looking for the solution of your problem, then I can share my understanding with you. nAs you are solving an opaque medium, you not require to calculate the RTE. So imply uncheck the radiation model i.e OFF your radiation model, and active your solar ray tracing from 'solar load'. Put your value i.e 1200 w/m^2 in 'direct solar irradiation' box. This is the equivalent of solar heat flux that you are looking for. You can add diffuse solar irradiation to make the model more realistic if you require, but not recommended in your case. You can adjust the direction, or simply can use the number 1/0 which you guide you to fix the direction. For example, if +1 is towards wall, then -1 would be the opposite of it. nThen go to the BC where you will find all necessary options for the wall i.e absorptivity, transmissivity.ThanksnJuweln