Heat transfer in satellite components

[rlara]

Hi all:

A component inside a satellite enclosure needs to disipate Y amount of power through radiation.

If I need to determine X amount of surface area needed to disipate Y amount of power through radiation is it a good estimate to assume that all power is disipated in to an black body? and use q=A*sigma*E*(Ts^4-Te^4)

I assuming the ambient temperatuere(Te) that surrounds the component to be of 5 kelvin, is this correct for space enviorment?

I know there must me other issues that are not covered like the effects of shading, radiation from other components, etc. what other issues should i be concerned with?

Any direction would help, thanks

 

[IRstuff]

What class is this for?

TTFN

 

[rlara]

IRstuff:

No class just want to get more detail in to thermal analysis i am just starting out so my questions may seem pretty basic.

The problem may seem like a book problem, the way im setting it up is just to make it easier to post.

I want to get a general knowledge of what effects i should look for in space enviorment. Mostly simple calculations to get estimates, and better understanding.

Help or direction would be greatly appreciated.

thanks

 

[vpl]

rlara:

I think you're overlooking some things:

You first need to account for how the heat from the component is transferred to the outside skin of the satellite. Assuming that your component is a separate entitity inside your satellite, you will have some conduction between the component and the satelite. You might also have some convection issues, depending on whether the component is discrete from the satelite body (ie surrounded by air inside the satellite.)

Once you get to the outside skin of the satellite, then you can work on disipating the heat to space. And I wouldn't assume a black body by any means. You need to look at the material and shape of the satellite and determine the relative emissivity.

Like IRstuff, I'm having a hard time seeing this as a practical application. I can see no reason to design a satellite to remove heat from a component.

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[rlara]

Patricia:

The component it self is a passive microwave antenna that is machined out of aluminum. There is certain amount of power going in to it to transmit a signal. Most of the power will be passed through the antenna and released as microwave energy, but because the antenna is not perfect it will have some loss. This loss will be transformed in to heat, which I want to get rid off because there is a temperature range the antenna can handle (mostly due to material restrictions).

The two modes of heat transfer I have are radiation and conduction (don’t see where convection would come into if its in space at high vacuum levels). Until now I do not have any information regarding what my component will be connected to, meaning I don’t know what the interface temperatures will be, so my assumption is that I can only radiate.

If the only mode of heat dissipation is radiation, then I would need to increase the surface area of the unit. As a fast calculation with out having all the details of the component surroundings, I needed to determine how much surface area I would need to dissipate this heat.

With that said I wanted to see if the approach was correct just for getting a rough estimate.

Hopefully this gives more insight in to the problem.

Thanks

 

[IRstuff]

patricia,

welcome back, it's been a while ;-)


rlara,

I suggest that you get "Space Mission Analysis and Design" by Wertz and Larson, or something similar:

http://www.springer.com/sgw/cda/fro...SULTS_PER_PAGE%3D10%26resultStart%3D0,00.html

The paperback versions are a lot cheaper; $54.95 at the Stanford book store.

TTFN

 

[davefitz]

Rlara:
another useful text,, mostly based on NASA space engineering techniques, is Siegel and Howell's Thermal Radiation Heat Transfer.

Its been a while since I used that text, but I recall specific examples similar to the one you cited. One method involves using a heat pipe ( wicks) to transfer heat to the satellite surface, and the satellite surface facing deep space would have a selective emittive surface- the emissivity in the long wavelength range centered at the design surface temp would be high, while the emissivity at smaller wavelengths would be low.

 

[rlara]

All:

Thanks for your opinions, I looks like the question should have been, "Book recomendations for Spacecraft thermal Analysis".

I also found this book wonder if you have any coments on it.

Spacecraft Thermal Control Handbook: Fundamental Technologies
by David G. Gilmore

Looks like its a good overall book for themal analysis of spacecraft components.

Thanks again

 

[chicopee]

I used to design VHF and UHF microwave antennae for television stations back in the 70's. These antennae were emitting VHF and UHF frequencies and had outputs of the orders of 25kw to 100 kw . I dont remember heat to be a problem or a factor on the design of parasitic elements and coaxial cables on these antennae. So I am wondering as to what temperature values you expect to dissipate. Also radiation losses(here back on earth with warmer ambient temps.) from lets say bare steam pipes may not be significant if pipe surface temperature is around 350 degree F. or less.