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Spac3manspif (Aerospace) (OP)
4 Apr 12 8:14
I am currently working on a thermal analysis for a satellite in ANSYS.  I have been able to generate the satellites thermal flux that it will receive from the suns, earths, moons, etc radiations.  I have this working through matlab code to determine heat flux for all sides of the satellite.

My question comes in when applying radiation to the problem using ANSYS mechanical.  I have tried applying surface to ambient radiation on the outer surfaces of the satellite, with an ambient temperature of 4K.  This resulted in a steady temperature drop, even in direct sunlight... which doesn't make sense.

I figured maybe there must be an issue with having heat flux and radiation to ambient on the same surfaces.  Is this true, or should this not be an issue for ANSYS?

so I turned off ambient radiation into space,

I then applied interior surface to surface radiation, with an emissivity of .96 and an ambient temperature of 4K.  This gave me some results that seemed similar to other satellite analysis' I have seen.

My main question comes when I am trying to apply a temperature controlled heater.  This is to simulate the heater for the battery, turn on when the temperature is at 0 C and turn off when it hits 5 C. I have found some code that seems to simulate a heater, but I am having trouble figuring out the code... which nodes are checking for temp, and basically how to understand the code.


http://my.fit.edu/itresources/manuals/fluent14/help/ans_vm/Hlp_V_VM159TXT.html

here is the link I have to the heater example, if you can help me that would be great! Thanks!
Jetgirl8 (Aerospace)
4 Apr 12 12:35
I think you might get faster/better help if you post in the Finite Element Analysis Forum instead.

When the future's architectured
By a carnival of idiots on show
You'd better lie low

IRstuff (Aerospace)
4 Apr 12 12:55
"This resulted in a steady temperature drop, even in direct sunlight... which doesn't make sense"

Why not?  You've not indicated what incoming and outgoing fluxes are, so there might not be anything wrong.  What temperature does it stop at?  If the stopping point is 4K, then there probably is something wrong.  Assuming a 0.1 absorptivity and 1.0 emissitivity, a two-sided object should have thermal equilibrium at about 186K in Earth orbit.

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Hansmeister (Aerospace)
5 Apr 12 14:02
Perhaps a bit old school, but I thought spacecraft thermal analysis used Trasys/Sinda software to determine temperatures.  The resultant temperatures are then transferred to the mechanical model for analysis.
cloa (Petroleum)
22 Apr 12 3:49
Even better post in the ANSYS forum.  
Spac3manspif (Aerospace) (OP)
5 May 12 12:10
Sorry I didn't add the emissivity, .35, and absorptivity, .1.

I have found that most small satellites have the temperature range of -80C to 80C, obviously this depends on the orbit.

I believe my problem is with my ambient temperature, I am setting it to 4K, but this isn't always true if your looking at the side facing the sun and the side facing the earth correct?

I was thinking maybe using the equilibrium equation to obtain the ambient temperature for each side,

Te = (Ain/Aout*alpha/epsilon*So/sigma)^(-4)

this comes from equation 5.9,
http://www.space.aau.dk/cubesat/documents/psu/Chapter5.pdf

but I am unsure if it would be a correct assumption to say the ambient temperature is equal to the equilibrium temperature.

It gave me a reasonable answer for temperature fluctuations over a few orbits.


 
Spac3manspif (Aerospace) (OP)
5 May 12 22:07
sorry, made a mistake when I was writing out the equation, its supposed to be
Te = (Ain/Aout*alpha/epsilon*So/sigma)^(1/4)
 

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