Learning Forum

[Mawkly]

Hi there i am new here.
Plz i am in desperate need of some help guys
I am doing a simulation on a power plant which is air enters and goes through until reaches the chimney then it goes up.
It moves because the radiation from sun will enter through the glass and heats the air by natural convection.
"" anything you can answer just answer it plz""
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1.
I used DO radiation model with two-bands , visible and infrared
I don't know the real values of them, is this true bellow?
Visible = 0.38-0.78 !
Infrared = 0.78-2 !
Is this correct?
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2.
I wanna put a solar radiation from sun as only 1000W/m2, so i did put that, but ? Why the visible and infrared need also radiation value in the glass boundary condition?? I have put 1000 for each, is it correct??
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3.
Plz what is difference between sun vectors that the solar collector gives it, and the beam direction in the glass boundary condition??

is it same values but different signs ?
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4.
Plz see in the materials i used glass, it needs absorption coefficient, i put it 0 is it correct?? Or it depends on the two bands? and if so,

how could i calculate it for each band ?

THANKS IN ADVANCE

[Rob]

1) No idea. Work out how much energy you want to add and work with that. Note, air doesn't absorb much radiation so the bulk of the heat transfer is through surface heating. 

2) Read the tutorials etc on the DO model and solar load. 

4) You need to define all material properties. 

[Juwelmojumder1]

HI Mawkly,

Range is varied a bit depending on the solar radiation. However, 0-0.4 um, 0.4-0.85um, 0.85-  0.85< is a nominal range for UV,visible and infrared respectively. 

An individual spectrum will be the sum of the fraction of the main spectrum. So you have to rationalize the fraction of incident radiation for individual bands. Hereby, with respect to that sense putting 1000w/m2 is not correct. 

Please see the help section, as there you may find a guide for the direction.  

Absorption, scattering and extinction coefficient are the main optical properties fluid.The absorption coefficient of any solar participating medium needs to defined according to the Raleigh optical model. 

Thanks

Juwel

 

[m.f.arefi]

hi there

I have a problem to find absorption and scattering coefficient of water and nanoparticles,I'm modeling nanofluid in a direct absorption solar collector .I found some data in a website https://refractiveindex.info/ but absorption coefficient of for eg. cuo is α = 7.3665e+5 cm-1  and its not logic,is it? can you recommend me a way to find these coefficients

thanx in advance
  

[Rob]

Why isn't it logical? 

 

[m.f.arefi]

because I think it means: α = 7.3665e+5 cm-1 =7.3665e+7 m-1   and its a big number and I saw a paper that has a table of nanofluid properties, and cuo/synthetic oil nanofluid absorption coefficient was 103 and I got confused about it.Because they were not in a same order.

somewhere I read that based on rayleigh scattering theory it can be calculated.

 I wanna know which one is correct?

best regards