Silly question - what can you really do with liquid nitrogen at home? I can think of cooking applications but I’m pressed to think of something else.
We concluded we'd need several cubic meters of ice, and the thing would be impossible to transport outside the river, so it would have to be built in-situ, and the obvious choice for that much cooling was liquid nitrogen. Unfortunately we ran the specific heat numbers and concluded it would cost several thousand pounds to buy that much LN2 off the shelf, so there the project ended.
Given a homebrew LN2 supply, lots of fun (and dangerous) possibilities will present themselves.
(I've also been to a make-your-own-icecream festival in a wood which was done with LN2; blend ingredients, add LN2, stir frantically)
2. Freeze off warts
Heck, when I was at Intel we used to do that in the lab. A copper cup full of liquid N is a great heat sink!
And tradeshows; it’s always kind of fun to see in an absurd way.
E.g. fitting bushings into excavator pivots or caterpillar track bearings. Great footage shown on site on an Australian series: Mega Machines?
So.... a business application, but also home :)
Dunno how well liquid N2 compares to Dry ice. Less toxic, but probably can’t take as much advantage of phase changes? Either way, -125C ice packs will perform better than -18C ice pack.
Your CO2 is going to sublimate straight from a solid to a gas. The heat moved is going to be "latent heat of sublimation" which is 199kJ/kg. This is only going to be around -78°C and also has a specific heat around 1kJ/kg, so about another 78kJ/kg.
Ok, that seems suspicious, the phase change energies are the same, but it appears to be a total coincidence.
So… if we can hold on to the gas and warm it up before releasing it, then liquid nitrogen wins with about 400kJ/kg compared to 280kJ/kg.
…but depending on our insulation and volume, we may find that we are making a lot more gas than will fit in the cooler so we can't make use of the gas, in which case both choices are about 200kJ/kg.
If you could just keep CO2 from sublimating it would be a huge winner at combined melting and evaporating energy of about 840kJ/kg… but that's why it would rather sublimate.
In the boring category though, water really rocks at 334kJ/kg to melt, so if you supercool your water ice to liquid nitrogen temperatures before leaving you will win.
For safety: Liquid nitrogen needs some special care. If you put your cooler in a small tent, and evaporate off a couple kilograms of liquid nitrogen over night you may not wake up in the warning. The higher nitrogen content of your stuffy little tent will displace oxygen and your body doesn't have a "low oxygen" detector built in. You just die. In contrast, your body does have a "high CO2" detector built in and you would likely have trouble breathing and open the tent flap.
Was hoping sublimation worked like melting+evaporation, but nowhere close :(
On toxicity, my thinking was you would need a lot more N2 to displace enough atmospheric O2 to cause a problem.
Whereas the sublimating CO2 does displace O2, the CO2 itself is toxic and would probably kill you first. But maybe not in the tent scenario.
Dunno if the DIY N2 has a lot of liquid O2 in it anyway?
That has a pretty significant effect in favour of plain old water.