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Radiation Model Issue

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Old   September 13, 2016, 10:24
Default Radiation Model Issue
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Devesh Baghel
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Hi guys.....

I am running a model of bulb, placed in a room.
I am using S2S radiation model along with Gray Thermal Radiation.
I need suggestions on below mentioned points:-

1. Do I need to model bulb as solid, so that we can give volumetric heat source Or can give surface heat flux as bulb surface, will be good approximation ?
2. Bulb is covered by a reflector body which has certain thickness. While defining reflection specularity, do we need to define on both solid and air interface ?
3. Constant property of air doesn't work well while using Ideal Gas model ?
4. Need some transmissivity, thermal resistance coefficient value for combination\pair of glass+plastic, glass+air, air+plastic.

Please let me know your suggestions.

Thank you
Dev
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Old   September 14, 2016, 02:32
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Gajendra Gulgulia
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Hi,

What you need to model depends on the objective of your simulation. If you are trying to simulate the temperature rise of air due to bulb shape, then surface flux would be a good idea.

1. If you are analyzing the power requirements of the bulb, then volumetric heat source would be a good idea.

2. Regarding your second question, I am not familiar with radiation in depth and the physics you mentioned above is not known to me.

3. For temperature rise of air, ideal gas model is recommended however when temperature rises, the gas properties will not remain constant for obvious reasons.

4. You need to have the heat transfer coefficients for air, plastic, glass (though I am not sure why would one use plastic for bulb because the high temperature in bulb filament doesn't permit plastic to be used as bulb cover, again I am not an expert on this. Just thinking critically.) Regarding transmissivity/reflectivity/opacity you can google up.
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Old   September 14, 2016, 10:45
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Devesh Baghel
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Hi guys.....still looking for some more opinion

Thank you Gajendra,
I was expecting some response from you as well.
Got to know few key points from your reply.

Can you please share your E-mail address or please drop me an e-mail at devesh.baghel@gmail.com.


Thanks
Devesh
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Old   September 15, 2016, 14:17
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Gajendra Gulgulia
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Hi Davesh,

Thanks for your reply.

I am sorry. I am not comfortable taking the discussion off this page to my private mail. However I am open to answer all your questions, within the ambit of my knowledge, on this forum.

Regards
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Old   September 23, 2016, 03:49
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Devesh Baghel
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Hi guys....

As shown above in query text (S2S radiation, grey thermal radiation, ideal gas model),
Does any have idea about the importance of "radiation temperature" in physics continua ?
By default it is 300 K.

Regarding transmissivity, I got values while googling. But still looking forward for thermal resistance values ?

Since air flow in and around the bulb is through natural convection, what should be convective heat transfer coefficient on outer surface of casing around the bulb ?

Please help...!!!!!
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Old   September 23, 2016, 07:09
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Gajendra Gulgulia
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Hi,

Radiation Temperature is the temperature at which your radiation models will activate. For eg. if you set the radiation tempt to 400K, radiation effects won't come into picture if the continua temperature is less than 400.

Thermal resistance values of glass I don't know sir. I think this should be available online or in CCM+ material database.

Prandtl number of air is 0.71. From that you can calculate other parameters.

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