I’m thinking of an idea, probably ill-conceived, but it’s an idea nonetheless
If I buy a block of dry ice and keep it in my car during the day, will that keep my car cool when I drive home in the afternoon after work? Is there anything not feasible about this idea? I figured if I can get a block of dry ice to the right size that would evaporate in about 9 hours in a hot car, I shouldn’t worry about that thing jostling around when I drive home
Also, where does one get dry ice? Can I buy it from a stock like regular ice? Is it expensive?
I think the size of block required to keep a hot car cool in the summer would take up the entire back seat. And then, you’d have to get all the CO2 out of the car before you could drive it again.
Look in the phone book under “Ice”. Many places that sell block ice will also sell dry ice. It’ll work, but it’s not an efficient (or safe) way to cool your car.
CO2 is heavier than air, so it’ll pool around your feet as you drive. When I got in, I’d open the door and give it enough time to air out, then drive with the window down. As long as your head is above the level of the window, you should be OK, though it still doesn’t sound terribly clever. And that’s ignoring the fog effect filling your car with opaque vapor. And the condensation coating every interior surface.
Although I’m sure the car isn’t sealed tight enough, I can still imagine the giant pop as the expanding gas blows out the windows and sends all the doors flying off the car.
It is fun to try with a hunk of dry ice in a water bottle with a small amount of water to speed the process.
As one who got a snoot full of CO2, you’ll know it because burns like hell. Ever burp through your nose after drinking a soda? Imagine acid in your nasal passages (which probably is the case).
Buy a good car cover; its cheaper in the long term.
I’ve driven around with dry ice in a cooler in my car, but I’ve never had any problems with C02. But the amounts were much smaller than you are proposing and they were insulated so as to not sublimate quickly.
Some modern cars come with these new-fangled things called air conditioners that do this.
Even if you started your car and let the AC run for 5-10 minutes before driving off, I think that would still cost less than buying the large chunk of dry ice that would be needed.
Dry ice freezes at -70ºF, about 100 degrees F colder than water ice. Thus it would use up a considerable more amount of heat to melt than a similar block of water ice.
Dry ice sublimates rather than melts under the usual amospheric pressure. That phase change requires about 240 Btu /lb. Water requires about 143 Btu/lb to melt from the solid to the liquid state. That’s close enough to 2:1 that some people say “One kg of dry ice has the cooling capacity of 2 kg of ordinary ice.”
So if it takes 50g of ice to cool your sodapop to 4°C, it’ll only take 25g of dry ice to do the same.
Now dry ice’ll cool your pop faster than regular ice*, and if you add too much, it’ll cool it til it’s much cooler, but that’s just a consequence of CO[sub]2[/sub] having such a low vaporization temperature. Another consequence of that is that your car’ll cool much more quickly with vaporizing dry ice, than it will with melting water ice.
As a practical matter, the cheapest, best way to cool your hot car interior with dry ice, might be to buy a pound of the stuff, pulverize it into little granules, then throw it into the car by handfuls immediately before climbing in yourself. You’d best wait until the asphyxiating gas dissipates before entering, and try to avoid getting any of the stuff on heat shockable surfaces, such as glass and some plastics. You’d get the fastest cooling this way, and no messy residue like you’d have if you attempted the same thing with frozen water.
*All other things being equal, the greater the temp differential, the greater the heat flow.
That doesn’t follow. Most of the cooling effect of ice comes from the heat of the phase transition, not from the fact that ice is colder than what is being cooled. According to Squink, dry ice cools about twice as much per mass as water ice–not much more, from my point of view–not primarily because its phase transition happens at a lower temperature, but because it involves a larger enthalpy change.
Another way to go is the http://en.wikipedia.org/wiki/Icy_Ball. It would have to be a much larger version than shown in the link. It uses liquid ammonia, but its in a closed container. You could start the cycle with engine heat.
BTW: you can make your own dry ice using the rapid expansion of liquified gas, like propane. Then you can use the CO2 from the dry ice to extinquish your flaming body.
My son and his friends have plans to fill a VW van with dry ice fog, so they can pile out in front of their high school, wreathed in a suspicious cloud …
To recreate the scene from Fast Times At Ridgemont High.
Airlines use Dry Ice for cooling the drinks trolley, it is also good for removing chewing gum from carpets and seats.
Those pop videos with smoke are using dry ice, which is comical as it means the performers will have cold feet.
Humans are pretty sensitive to even small concentrations of CO2, the Vagus nerve starts blasting signals at pretty low concentrations, which is why holding ones breath is so difficult.
IIRC in Philip K Dick’s Do Androids Dream … the androids had a difference in the Vagus that enabled them to commit suicide by holding their breath. Presumably the OP is not an Android, so he would be pretty safe unless the car suddenly became airtight and ‘locked’.
The main advantage of Dry Ice is that it is clean, it just evaporates, unlike water.
Personally I would go for the freezer blocks, they are reuseable, and probably a lot more practical in the long run. But not as much fun
dry ice does go from solid to gas. it will in a moist environment condense water vapor and freeze it, so it will create water ice where there was none. a large amount of dry ice, if not sublimed rapidly, may leave a big puddle of water.
