dry-ice freezers

[abcdefg1675]

what refridgerants do the freezers use that hold dry ice? and at what temperature does Carbon dioxide become ice?

[aenigma]

Hmmm good question.
Dry ice freezes at -56.6c i believe.
Cold freezers

[Dan]

I really could be way off here, but I don't think dry ice is held by refrigerating devices. A well insulated container is not a bad thing to put dry ice in, however. Liquid carbon dioxide tanks are refrigerated with normal refrigeration duty condensing units as are other high pressure gases. I believe that dry ice is a product of a process and that after that.... IT is considered a refrigerant.

Saying all that, I think I will poke about the web to see how wrong I am.

[aenigma]

Maybe,but I remember my friend telling me how when he lived in arizona they kept dry ice in freezers.

Maybe if kept under pressure it stays frozen?Hmmm,I am sure some kind of refrigeration is needed....
Let us know what you find

[Dan]

I doesn't appear that dry ice is kept in mechanically refrigerated containers. I think my original post still stands after searching around.

Dry ice is made by expanding liquid CO2 through an orifice to atmospheric pressure and catching the snow it makes and putting it under pressure to compact it. Then it is cut with a band saw, wrapped and stored in well-insulated containers. You can make your own dry ice with a small tank of CO2 and a catching bag on the nozzle - but compacting it is the trick.

Think of it this way: If you had a freezer that could keep dry ice from evaporating, why would you need the dry ice in the first place? I once had a few pounds of dry ice that lasted 2 days in a styrofoam cooler that I put in my side-by-side freezer and it disappeared by morning.

In an insulated conainer with no air movement it lasted longer than in a -10 deg F freezer with air movement. Ironically, I heated up the dry ice in the freezer (by moving warmer air over it) whereas the dry ice held equilibrium in the styrofoam cooler because it surrounded itself by undisturbed air temperatures increasingly closer to its surface temperature, and the insulation impeded heat transfer.

A cold wall freezer with no air movement is basically a styrofoam cooler with refrigeration tubing wrapped around the interior wall. But the refrigeraion tubing is warmer than the dry ice, by design. If you filled such a freezer with dry ice, it should never turn on. The dry ice is the refrigerant.

But an interesting question pops into my mind after this line of speculation.. let's just say your Arizona friend puts 5 pounds of dry ice on top of his frozen food, as opposed to filling the freezer with dry ice.

Would the dry ice last longer in your friend-from-Arizona's freezer than it would in a styrofoam cooler? I would guess only slightly so.

[aenigma]

hahaha I didnt say i was right
I said that a store he went to in arizona kept dry ice in the freezer.I am sure your right about it not needing refrigeration.

But IF it needed refrigeration,I am sure the freezer used would get below the freezing point of fry ice...I think around -56c

Build a cascade freezer and test it

[Dan]

LOL! But if we hav the cascade freezer, why do we need the dry ice?

[aenigma]

I have never used it.

Dry ice is small,you can use it in little coolers,it is portable etc. etc.
But what do you use it for?
I wouldnt need dry ice because I have a dual phase cascade system

[Argus]

Hmmmmm....

My recollection is that dry ice is solidified CO2 that returns to the gaseous state at atmo pressure by sublimation. Therefore it just needs to be kept in a sealed, insulated container. It will sublimate sufficiently to fill the space in the container to its saturation limit and, losses permitting, it will last for days.

The only use I ever had for it was in the dim and distant past when I worked on big chillers, Centrifugals and the like, that suffered a broken tube.
It was delivered in insulated boxes and I used to keep it in plastic bags in an old domestic chest freezer.
Drying a flooded chiller to a servicable condition was a marathon job.
We used to blow out the worst of the water from the shell with N2, but the real work was the evacuation that could often take weeks. To keep the (expensive) Vacuum pump oil from saturating with water and to save time on ballast mix, we rigged a knock out pot to get rid of the water.
It consisted of a closed steel vessel with an open hollow pot inside it with the CO2 / R11 mix in it.
This was placed in the return pipes to the Vac pump and the moisture laden air/krud mixture would freeze in the pot. Periodically we would melt the frozen ice/krud and throw it away.
You did that until the chiller came through dry. For the last stage of evacuation you could discontinue the dry ice. It took a lot of time and CO2. Never had any other use for it.
If I had to do that job again I would probably construct a small heat exchanger and hermertic compressor, but dry ice was cheap.
In those days you could use R11 like that and stay out of jail. Now, we know better, don't we?
________
Honda 70

[abcdefg1675]

i have seen very large freezers that hold dry ice at safeway, or some store like that. they hold the dry ice for a long time. the size of the freezer is 6 or 7 of your home fridges sitting side-by-side. the interior of the freezer wasnt quite big. I guess the bulk of it is insulation.

[Argus]

Very Interesting - what do the supermarkets sell or use it for?
________
Ducati 749

[Dan]

Dry ice is ideal for mobile ice cream vendors. I have used it for picnics to keep ice cream and novelties frozen. As a contractor we occasionally buy several hundred pounds during remodels to keep the product intact in tub cases and reach ins during extended downtimes.

Also, supermarkets will use it during power outages to retain product integrity in the walk-ins. I can't comment on its effectiveness in walk-ins, but it does help out with the tub cases and reach-in freezers, properly spread out.

[Argus]

Thanks Dan.
That's interesting. Not seen it used for quite those purposes too much in this part of the world.
Isn't there a danger of asphyxiation in enclosed coldrooms?
________
make a vaporizer

[Dan]

Regarding the danger of asphyxiation:

My thoughts exactly. Which is why we don't do it nor recommend it. But the danger is no worse than when you have a refrigerant leak in a cold storage room, if you think about it. We don't recommend leaks in cold storage rooms for the same reason.

[superheat]

I would say that dry ice keeps longer in a cooler than a freezer because the air is saturated with CO2 in the cooler. You get less evaporation. A freezer is larger and has more air to saturate. Door opening would not help either.
The size of the box might help increase the load as well. Small styrofoam cooler is less space to keep very cold.

[Argus]

Very valid point, Dan. ALL joints should be brazed, in my opinion.
Especially in enclosed rooms and spaces.

They problem with all heavier-than-air, odourless compounds is that the asphyxiant qualities are completely unoticed.

I am an advocate of the Ban-all-Flare-Joints point of view.
What other gas-based system allows the use of a joint that relies on the distortion of the wall of the pipe for it's leakage integrity?
The problem is compounded when they are taken apart and reassembled, leaving behind a twice work hardened seat. Get rid of Schraeder valves too! They're another source of leaks.
________
Escort RS 1700T

[abcdefg1675]

the store stocked it occasionally during the summer, and filled up the freezer and put it on sale during halloween.

[Dan]

Get rid of Schraeder valves too! They're another source of leaks.

LOL. I don't think we should go that far, Argus. We should simply attend to our Schraeder valves.... such as insuring they are capped, that the O-ring is in place, that the core is tightened, etc.

the store stocked it occasionally during the summer, and filled up the freezer and put it on sale during halloween.

I forgot to mention that aspect. I would bring ice cream and popsicles and such to picnics as a plausible excuse for the children to eat the damn ice cream and get in trouble playing with the dry ice.....Fog in mom's soda cup....the haunted toilet.... foggy bubbles in the lake.

The bubbling cauldron in B movies. That is a very important aspect of dry ice. It being close to Halloween, why not get some dry ice and play with it?

If you feel guilty, just have a child with you for support.