Dry Ice payload testing


Michael Hojnowski
 

Hey Gang,

Does anyone have much experience in cold-testing payloads with dry ice?   A few students on our team tried to use dry ice for a test, and didn't have much luck.  The objective is to try and test the payload box in very cold exterior temperatures to see if the interior can be kept warm.  They have an experiment that won't tolerate cold very well.  The initial attempt was to use a small battery powered hand warmer (which has a thermostat to keep from getting too warm) inside the payload box to keep the temperature around 70f.  The "hoped for" outcome was that they would measure some very cold (-40ish) temps outside the payload box, but that the interior would remain toasty warm.   In practice, the test didn't work out so well.

I didn't see the test, but they apparently got 8 pounds of dry ice and put it in a large cooler.  They put the payload box in the cooler, and ran some thermocouples into the payload box and surrounding container.  The larger cooler was a snug fit around the payload box.

They left it closed for an hour, and the "outer cooler" temp only went down to about 7c.  Unfortunately, the payload box interior temp went down to just about the same during the test.  Apparently, the hand warmer failed at some point during the test.

They'd like to be able to create very cold conditions outside the payload box (colder than 7c) while they sort out the interior heating issue.

If anyone has some experience, war stories, or scars they can share, the team would appreciate it.

Thanks!
Mike


Hank Riley
 

How big is that payload box if it's a snug fit inside the large cooler?   How was the CO2 distributed?  All just at the bottom of the cooler (not too good), or some against all four vertical surfaces of the payload and maybe over the top as well (best)?

Offhand it seems that just a hour might not be nearly enough to realize a decent low temp. of the sort desired.

Just to be concrete, I'd suggest trying something more like 4 to 8 hours.


Dennis Klipa - N8ERF
 

As a research chemist, I used dry ice a lot to cool reactions to low temperatures,  -78°C.

I would suggest you set your payload in your cooler and then pour dry ice powder over it.

Dry ice comes in a block a couple inches or so thick as you know.  I would use a rubber mallet/hammer to break the block into a few large chunks and put the dry ice chunks into a heavy denim bag.  Gather the top of the bag and beat the dry ice chunks with the mallet.  The chunks will break up into a course powder resembling sleet that you can easily pour from the bag to surround and cover your your payload giving good contact with your payload  This should give you good heat transfer and a good test of your heater.  I am not sure 8 lbs will be enough, depending on the size of your payload and cooler.

Best Regards,
Dennis, N8ERF

On Mon, May 3, 2021, 1:35 AM Hank Riley via groups.io <n1ltv=yahoo.com@groups.io> wrote:
How big is that payload box if it's a snug fit inside the large cooler?   How was the CO2 distributed?  All just at the bottom of the cooler (not too good), or some against all four vertical surfaces of the payload and maybe over the top as well (best)?

Offhand it seems that just a hour might not be nearly enough to realize a decent low temp. of the sort desired.

Just to be concrete, I'd suggest trying something more like 4 to 8 hours.


Hank Riley
 

Mike,

Dennis and I are suggesting better contact of the dry ice with the payload than might have been accomplished.  (We don't know because you have not supplied that information)

As to the amount of dry ice, I have done a quick calc. based on a 12 inch cube (again, payload size is missing information).

Instead of me doing the middle school arithmetic for your students, I'd suggest you have them do this for themselves to determine if 8 pounds is enough to create a decent thickness (maybe an inch or more) surrounding at least 5 faces of the cube.

Surrounding the payload with a good layer of dry ice in good contact may not require the several hours of "soaking" I mentioned previously.

Hank


Bruce Coates
 

Hi Michael

Another trick you can use is to pre-chill the outer cooler, and ideally run the entire experiment, inside a standard chest freezer.   On its coldest setting, that would get the external temperature you down to around -20c making it easier for the dry ice to further chill the interior. 

73, Bruce - VE5BNC
SABRE


Joe WB9SBD
 

Something to remember,

While this test using Dry Ice is better than no test at all.

It is also very different set of conditions than what is happening at flight levels. Due to how heat is escaping the heat generating components.

Remember cold is NOT going INTO a component, the Heat energy is being REMOVED from the component.

And being in the near vacuum, two of the paths of heat energy is either gone or highly removed because of the lack of air.

Convection, and Conduction. You primary path of heat transfer is now Radiation. And dry Ice has no effect on that.

I have had repeaters overheat during flights. They would shut down. We suspected heat caused this because the behavior was exactly the same as when it would overheat when being testing at sea level. So one flight we had three temp probes running during the flight.

One outside,

One inside

and one on the heatsink for the final amps.

The air outside had a curve as expected.

The "AIR" inside probe but not touching anything, was somewhat surprising. it had a very similar curve as the outside curve, it was just about 15 minutes behind, this was with 2" thick Styrofoam, with foil covering.

But the probe on the heat-sink when on the ground (with lots of dense air) would reach a max about 20 to 30 degrees above ambient temp.

But at altitude, WOW! The "AIR" temp in the payload could be well below zero. But the heatsink was was well above 100 deg, at times exceeding 140 degrees!

Because the heatsink only had radiation as a way to dump heat. And the payload being foil lined, any radiation that did escape the heat-sink was reflected back onto it.

Joe WB9SBD


On 5/3/2021 8:06 AM, Bruce Coates wrote:
Hi Michael

Another trick you can use is to pre-chill the outer cooler, and ideally run the entire experiment, inside a standard chest freezer.   On its coldest setting, that would get the external temperature you down to around -20c making it easier for the dry ice to further chill the interior. 

73, Bruce - VE5BNC
SABRE


Michael Hojnowski
 

Yes, I've seen similar with cameras that run hot inside the payload box.  They have nowhere to dissipate the heat at altitude.

The team does have access to nitrogen chilled vacuum chamber as well.  Unfortunately, it's pretty small so it's not possible to test this payload with it.  As you say, it's better than no test at all, but we're aware of the limitations.

Thanks to you, and all, for the suggestions.  I've passed them onto the team members.

Mike / KD2EAT

On 5/3/2021 9:35 AM, Joe WB9SBD wrote:
Something to remember,

While this test using Dry Ice is better than no test at all.

It is also very different set of conditions than what is happening at flight levels. Due to how heat is escaping the heat generating components.

Remember cold is NOT going INTO a component, the Heat energy is being REMOVED from the component.

And being in the near vacuum, two of the paths of heat energy is either gone or highly removed because of the lack of air.

Convection, and Conduction. You primary path of heat transfer is now Radiation. And dry Ice has no effect on that.

I have had repeaters overheat during flights. They would shut down. We suspected heat caused this because the behavior was exactly the same as when it would overheat when being testing at sea level. So one flight we had three temp probes running during the flight.

One outside,

One inside

and one on the heatsink for the final amps.

The air outside had a curve as expected.

The "AIR" inside probe but not touching anything, was somewhat surprising. it had a very similar curve as the outside curve, it was just about 15 minutes behind, this was with 2" thick Styrofoam, with foil covering.

But the probe on the heat-sink when on the ground (with lots of dense air) would reach a max about 20 to 30 degrees above ambient temp.

But at altitude, WOW! The "AIR" temp in the payload could be well below zero. But the heatsink was was well above 100 deg, at times exceeding 140 degrees!

Because the heatsink only had radiation as a way to dump heat. And the payload being foil lined, any radiation that did escape the heat-sink was reflected back onto it.

Joe WB9SBD


On 5/3/2021 8:06 AM, Bruce Coates wrote:
Hi Michael

Another trick you can use is to pre-chill the outer cooler, and ideally run the entire experiment, inside a standard chest freezer.   On its coldest setting, that would get the external temperature you down to around -20c making it easier for the dry ice to further chill the interior. 

73, Bruce - VE5BNC
SABRE



steve potter
 

I would also like to chime in and say a small battery powered fan would likely increase the distribution of the cold air, even in a cooler there will be a difference in temperature from the top to the bottom of it, some kind of circulation would likely help.


On Sun, May 2, 2021, 8:57 PM Michael Hojnowski <kd2eat@...> wrote:
Hey Gang,

Does anyone have much experience in cold-testing payloads with dry
ice?   A few students on our team tried to use dry ice for a test, and
didn't have much luck.  The objective is to try and test the payload box
in very cold exterior temperatures to see if the interior can be kept
warm.  They have an experiment that won't tolerate cold very well.  The
initial attempt was to use a small battery powered hand warmer (which
has a thermostat to keep from getting too warm) inside the payload box
to keep the temperature around 70f.  The "hoped for" outcome was that
they would measure some very cold (-40ish) temps outside the payload
box, but that the interior would remain toasty warm.   In practice, the
test didn't work out so well.

I didn't see the test, but they apparently got 8 pounds of dry ice and
put it in a large cooler.  They put the payload box in the cooler, and
ran some thermocouples into the payload box and surrounding container. 
The larger cooler was a snug fit around the payload box.

They left it closed for an hour, and the "outer cooler" temp only went
down to about 7c.  Unfortunately, the payload box interior temp went
down to just about the same during the test.  Apparently, the hand
warmer failed at some point during the test.

They'd like to be able to create very cold conditions outside the
payload box (colder than 7c) while they sort out the interior heating
issue.

If anyone has some experience, war stories, or scars they can share, the
team would appreciate it.

Thanks!
Mike