Thermal Management

2" Styrofoam is usually pretty good - wonder if it distorted in the low pressure? Also, there's not much air to conduct heat away (about 1% of pressure at ground level), so am I right in thinking heat's lost by radiation? Doesn't make sense if bubblewrap worked.

Puzzled, of Reading.

2" Styrofoam is usually pretty good - wonder if it distorted in the low pressure?

If it does it returns exactly as it left. We use molded boxes for like transporting transplant organs very tight fitting lids, and after returning everything still fits perfectly.

Also, there's not much air to conduct heat away (about 1% of pressure at ground level), so am I right in thinking heat's lost by radiation?

Yes probably 99% radiation,

Doesn't make sense if bubblewrap worked.

Puzzled, of Reading.

he he he us too.

Joe

You need a heat source in the styrofoam box....probably would go exothermic chemical type...they are small, light weight, cheap, and long lasting(7+ hrs)

http://www.warmers.com/Category.aspx?Cat=67

http://homechemistry.blogspot.com/2008/03/hand-warmers.html

Those chemical warmers do not function without oxygen, and up there there is no oxygen.

Thanks Tho.

Joe

Powdered oxygen...

http://www.amazon.com/Grotek-Oxy-Cal-Powdered-Oxygen/dp/B000WCQXAW

Thats interesting.. I wonder what would happen if one was to mix the two together?

Joe

True, but for a night launch one of these pouches would heat during the ascent in darkness.

True, but in 30 minutes it is already way below zero and already above 99% of any oxygen available.

There are the supersaturated solution type that require no oxygen but don't last as long, 3 hrs claimed....but you could probably figure out how to activate one every so often...

http://www.stevespanglerscience.com/experiment/instant-hot-ice

http://www.mikesenese.com/DOIT/2009/12/ez-heat-reusable-hand-warmer-supersaturated-solution-transforms-to-solid-gives-off-heat/

http://www.amazon.com/exec/obidos/ASIN/B000E90A3E/msdoit-20/

That is pretty cool,

will have to see whats involved in bending the metal thng,,,, I wonder if it is a snap and activates it by like ultra sound or something? Maybe?

Whats cool is could make it run, then when cold jettison it as ballast, and start a new one when needed.

I gave this a GA. Was going to say the same thing. Just put a heatsource in the box and if not checmical why not an electric one?

styrofoam should keep the heat in at least the same way it keeps it out.

Same remark as above the problem is the energy/mass ratio : it has to be high !

Batteries have a low ratio. Qualitative and quantitatve are not the same. One can be right from the qualitative point if view (idea) but not be good for the application when the "quantitative" aspect is as well considered.

I disagree. This is a classic thermodynamic equilibrium problem. NSS is looking for long term operation of the payload above a certain minimum temperature. So instead relying on extending the time constant of the exponential thermodynamic equation for the length of the balloon journey one should calculate an the internal watts dissipation through insulating material to meet a minimum temperature for the electronics to operate in equilibrium with the outside temperature. The previous tests that failed will help to determine the time constant the system takes to reach this equilibrium. Putting in any added insulation or phase changing media will lengthen the time for the electronics to freeze but they will eventually still freeze.

I say this because I believe that NSS is looking for months and not hours of operation time aloft. This is why I suggested the combination of battery and solar panel. Better insulation will minimize the internal heat needed to be released to achieve this thermal equilibrium.

The insulation is already very good, there is little to be done (k= 0.03 W/mK).

Of course if there is a very long time request the only solution will be the solar panel + energy accumulator but it has a weight penalty.

My basic though was that till now he made day tests and had the benefit of the solar radiation and that now he wants to do as well night tests and since it had not this incoming energy the interior was too soon cold and the components did not work properly.

Even if a solar panel will be used the energy accumulator could be a water container heated by the electric current. It would have the highest energy density accumulation capability. According to some estimations I made if water is at start heated up to 50°C and the outer temperature is -30°C for the kind of box he uses temperature is still >0°C after 1h from start for 0.4 kg water / m² internal box area.

The losses being about 30 W/m² with 20°C /-30°C about 40..50 W should be harvested with the solar panel. For about 200 w/m² solar incoming energy and an efficiency of 25% to cover the night cooling > 1. m²/m² internal area would be needed. The panels should not bring shadows on the box itself if they bring the power has to be higher to compensate reduction of direct sun effect.

By the way what you suggested I did before making the proposal of the water accumulator and this was the reason I assumed that the night flight was not OK because of the lack of sun energy.

This is, I believe, the optimal solution from several points of view if the travel has to be for several days and nights. I still believe that using an electric battery will be a bad solution from the dead load point of view and supplementary energy losses, water would be better since all harvested energy is converted in heat.

I agree that the enthalpy of water freezing does have advantages here and could be the heat reservoir of choice. I'm apprehensive though of the complications of freeze expansion that comes with using water. This is why I still advocate that likely a heater is needed in some fashion. I also agree that the thermal conduction of Styrofoam seems to be up to the task.

More than a heater, I strongly advocate more telemetry on the thermodynamics. If the three regions of circuitry, inside and outside insulation temperatures identically track in time then the insulation is some how getting bypassed. Possibly the Styrofoam gas pockets pop during ascent. Remember it is the trapped gas that slows the heat transfer. Removing the gas might make the foam less insulating than expected here at ground level. Getting temperature telemetry of the three regions and analysing what is actually happening instead of speculating will identify how to proceed.

The Styrofoam is doing its job of slowing down of heat transfer in both directions. I would consider adding external to the Styrofoam solar cells and a LI-Ion rechargeable battery with a heater element internal to the Styrofoam. I realize that this will consume some of your lifting payload mass but controlling your heat loading will take more equipment.

This would add a little weight so it might be DOA, but since you stated " We use molded boxes like for transporting transplant organs with very tight fitting lids" I'll toss out the idea.

As far as I know the black boxes for commercial aircraft have the electronics potted in a synthetic wax that has a very high thermal index (proper term?). A lot of thermal energy must be transferred to have a small change in temperature. If your electronics were embedded in this wax then the wax block would effectively be a thermal mass and act as a low pass filter for your temperature.

If this idea works it might not be good enough for a full low altitude orbit, but it should give you more time than you currently are getting.

hmmm, Interesting,, I wonder where someone would get some to test with?

Joe

I suspect that paraffin would be good enough to research/experiment with the idea. The web site http://en.wikipedia.org/wiki/Paraffin has some interesting items. They state that it is an excellent material to store heat. They provide the specific heat and heat of fusion for paraffin. They talk about paraffin in drywall storing heat during the day and releasing the heat at night. An interesting point somewhat related to your application was "Paraffin wax phase change cooling coupled with retractable radiators was used to cool the electronics of the Lunar Rover".

If you find a substance that will melt at a temperature your electronics can tolerate then you could launch with liquid wax and have the added benefit of having the latent heat of fusion delay the cooling of your electronics.

hmmm I wonder what the vapor pressure might be, can't have it boiling off in the vacuum ya know?

It is important for this application to have the lowest additional weight.

Paraffin wax has a c=2.14-2.9 kJ/kgK and a fusion heat of 200-220 kJ/kg specific mass 0.9

Water has c= 4.2 kJ/kgK abd a fusion heat of 334 kJ/kg for specific mass of 1.

The comparison shows a nett advantage for water.

Plastic makes a good radiation block....

or you could go with something more effective....

http://www.nvenergysolutions.com/Energy/SPI/SuperThermInfo2.pdf

What you neglected is the energy brought by the sunlight.

Let us assume an internal temperature of 20°C (293K)and an outer temperature of -30°C(243K). The foam has a conductivity of 0.03 W/mK. If there is no sunlight with the wall temperature -30°C the heat loss = 30 W/m². I cannot estimate how long it takes to go to 0°C since I have no knowledge of the box content.

If there is sun light the wall outer temperature will be 293°K if the input power is only 170 W/m². Which means there is no heat loss. If the power input is higher there is even a content heating although it will take a long time. It can be assumed that during the day sun bring at least 200 w/m² so that your electronic is safe.

In fact it is not loss by radiation which leads to the problem but lack of radiated energy!

What you need is an internal temperature around 0°C since usual components work still at this level. I think that using for instance hot water could be a solution since water has a high specific heat and a quite important transformation heat from water to ice. You should compute the time if, for instance, you start with water at 50-60 °C till the internal temperature goes down to zero. Due to the low heat conductivity of the box it could be enough to solve your problem even with a small water quantity.

nick name,

have a E-Mail address I could use? I do have a thought and was gonna try it, but haven't yet. but it is very similar to what you were talking about here. We can discuss this in greater details off list, on on if everyone wishes?

Joe

CR4 ADMIN - email address removed

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Have you considered phase-change materials used for solar thermal storage such as eutectic salts or this wax/aluminum mixture?

http://www.arpnjournals.com/jeas/research_papers/rp_2009/jeas_1209_278.pdf

Just boil and pour into the space between two nesting insulating containers (covered with bubble wrap?). As an alternative how about a dual wall container with a vacuum between the walls like a Thermos bottle.

Another thought comes to mind about the anomalous behavior you have observed. Are you always using the same container? As the following paper points out, some foams are great at minimizing convective loss but are nearly transparent to radiation losses. If so why not try lining the walls with aluminum foil as a radiation block?

http://deepblue.lib.umich.edu/bitstream/2027.42/37305/1/690050413_ftp.pdf

We have done both ways.

with a foil layer and without. not a lot of difference

The sexy see-through solution: Aerogel.

hmmmmm..

You need these guys to make you some 'helium-cell' instead of the 'aircell'

http://www.kingspaninsulation.com.au/Products/Kingspan-AIR-CELL.aspx

"Fish dont know they're underwater.......think."

How do you know what fish think? Just curious....

Off topic, but never mind.

I dont know if fish think or not, although it is my assumption that they must to some degree. They live in this world we call water, and that is all they know. It doesn't mean the rest of the planet doesnt exist just because they dont know its there, or have no comprehension of it. Same goes with everything.

Just because my feeble mind cant comprehend alot of the things in the universe, doesnt mean they are not possible, or not there. I just dont know about them, or havent yet evolved enough to fathom them or pick up on them.

For all we know there could be another dimension, but we arnt able to access it. If all humans were all born without eyes and all the other animals that have eyes were, then there would no such thing as 'seeing' simply because we didnt give it name, even though it would still exist. (we probably would have become extinct a long time ago to mind you )

Maybe we haven't yet come up with some sort of revolutionary device that defies the laws of physics, because we have already been taught and all believe the laws of physics cannot be defied.

Probably goes against the basics of science abit, but makes sense to me.

That make sense to you? Or am I off with the fairies? haha

As I am not an expert in fish cognitive powers, I will defer to someone with a valid opinion...

"According to Culum Brown from Macquarie University, "Fish are more intelligent than they appear. In many areas, such as memory, their cognitive powers match or exceed those of 'higher' vertebrates including non-human primates."^[1]"

^{http://en.wikipedia.org/wiki/Fish_intelligence}

"Scientists are starting to learn more and more about our finned friends, and their discoveries are fascinating.

Fish and Fisheries cited more than 500 research papers on fish intelligence, proving that fish are smart, that they can use tools, and that they have impressive long-term memories and sophisticated social structures. The introduction said that fish are "steeped in social intelligence … exhibiting stable cultural traditions and cooperating to inspect predators and catch food."

link...

I finally remembered the name: CT-TEXAS Home Page.

It's a ceramic filled paint.

that looks cool!

They sent me some cured samples about a year ago. Sorry to say, I can't find them.

Maybe paint the inside of your present box with it?

I have no idea if they'd give you a sample, they wouldn't give me any uncured paint to play with. But, we both knew I was not a potential customer, so I don't blame them.

Good luck.

Here's another source thin coat insulating systems using nanotechnology as a infrared radiation blocking technology:

http://www.nansulate.com/thermal_insulation_data.htm

http://www.nansulate.com/pdf/Nansulate_Solar_Manufacturer_brochure.pdf

Thanks!

Joe

This is interesting. Thanks for posting.

I have a few ideas for your consideration...

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Bubble wrap vs Styrofoam.

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-There are several reasons that bubble wrap could offer better performance than solid Styrofoam blocks.

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1. As previously mentioned Styrofoam distorts under pressure. It is probably experiencing significant growth as the ambient pressure drops, and returning to normal as pressure increases upon descent (the reverse happens Scuba diving 16 oz Styrofoam cups become miniature teacup-size on deep dives, only to regain normal size when brought back up).

The changes in the shape are probably creating gaps in the insulation... when the gaps are significant, the foam won't make up for it, no matter how thick.

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2. Effective seals are easier to make and maintain using a bubble wrap/bag type material than solid foam.

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3. A bag /bubble wrap type enclosure can be made with room to expand so that air (and the heat and insulation value therein) accompanying the equipment can stay with the equipment for a longer period.

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4. Even when most of the air that accompanied the equipment has been lost, bubble wrap keeps gas in sealed pockets surrounding the equipment. This is important not only for insulation, but also because it is a small source of heat in the increased UV (and other types of radiation) in the thin upper atmosphere.

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Leverage the surroundings

....speaking of radiation. Sending a tied off balloon or condom with a very small amount of something like Potassium permanganate or hydrogen peroxide sealed inside (leaving room for expansion) could provide a small, light weight heat source. UV radiation will cause an exothermic reaction liberating O₂ from either substance. Further incident radiation should cycle through the O₂ - O₃ cycle and provide a small amount of heat when the atmosphere is thin.

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...similarly, clear bubble wrap coated on the interior with a cheap dark selective surface would probably help a lot.

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Try to use every bit of what you send

If your electronics are freezing up before your batteries are truly out of juice, or even if your batteries are what is failing due to the temps, running an extra resistor in parallel to draw a little extra current to keep the equipment and or batteries warm makes sense. Ideally your batteries should be totally drained upon return.

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Start hot

Take as much heat with you as you can. At release the whole platform should be at the maximum service temperature.....electric blanket and hair driers on the launch pad.

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I hope you find some of that useful.

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Share some more pics as things progress?