Quick question about dry ice

Does dry ice absorb heat, or does it release cold (That sentence sounds weird). My friend had the idea of placing dry ice in front of his radiator intake to cool the air down. I haven't come in contact with dry ice in a while, but I could have sworn that the air surrounding the ice doesn't get all that much colder.

It depends on how much surface area the dry ice has in contact with the air flowing over it, and how fast it's flowing. If it's one big block of dry ice just sitting in front of a radiator with high airflow, it won't cool the air that much. If there's lots of surface area, (broken into little bits) and the dry ice is sitting in an intake duct, with a lower airflow, then the air will be substantially more cooled. In answer to your first question though, It absorbs heat and releases cold - if you see what I mean. The surrounding air warms the dry ice, and causes the vapour you see, and the vapour is cold because the energy it takes to sublimate the dry ice - or in other words, evaproate it, comes from the warm air. Kind of both and neither.

dry ice falls into a rare catagory in physics. Its one of the few pieces of matter that can be a gas/solid/liquid at the same time. However, regular dry ice when in solid form goes from a solid to a gas. Basically the air is boiling it. But the above poster is right. More surface area will cool the air down, but not much. Contact with dry ice can cause almost immediate frostbite. If you place it water is boils instatly, thus, dry ice an water have a better reaction than dry ice and air.

just so you know.. nothing releases cold... cold is simply a lack of heat.. things are either endothermic or exothermic meaning they absorb or emit heat energy.. but its true the air surrounding dry ice *frozen CO2* doesnt really get that much cooler *think fog*.. and if you put it in front of a fan it going to disappear pretty fast and be a waste of money...if you just temporarily want cold temps *like for a maximum overclock test* then stick it near an A/C duct if yours come out of the floor.. or you could submerge your radiator in an ice bath

ashenfang said:

dry ice falls into a rare catagory in physics. Its one of the few pieces of matter that can be a gas/solid/liquid at the same time. However, regular dry ice when in solid form goes from a solid to a gas. Basically the air is boiling it. But the above poster is right. More surface area will cool the air down, but not much. Contact with dry ice can cause almost immediate frostbite. If you place it water is boils instatly, thus, dry ice an water have a better reaction than dry ice and air.

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Hold the phone - lots of substances I know of can be a solid, liquid, and gas at a certain temperature and pressure. A material at its triple point will have solid, liquid, and gaseous material present and in equilibrium. What you have here is a case where CO2 DOESN'T have a liquid phase. It goes directly from a solid to a gas, as you mentioned. It's triple point is at a lower temperature than room temperature. Look at this link for more information.

Ken

doesn't every object have a temp, and when in contact with that temp the cold object takes heat and the hot object takes cold? or somethin like that. 8th grade sience goin right there

a few ways you can use Dry Ice better.

1. get a container, remove the fan and place your radiator in there. or your res...
get Ethanol or basically alot of Everclear as thats the closest thing to that... pour alot of that in there, till if covers your Rad.
get Bricks of Dry Ice, usually from a specialty food place, or something similar. it's about a dollar a pound usually.
place brick of dry ice in ethanol or everclear (acetone if your in a VERY well ventilated area can work too)
this will get the ethanol incredibly cold.

the idea is to not freeze solid like water does.
a super cold liquid is more effective then a solid block of water.
thats why you need something like ethanol or such.

I haven't figured out why anti freeze and water just kinda sucks for this, but it doesn't do as well as just ethanol alone, atleast not for me.
oh yeah, and once you place the dry ice in the ethanol, remember to open some windows, it's gonna do this rolling fog thing, it's actually kinda cool, but it's also sucking the air out of the room.
not a good idea....

I have been playing around with dry ice for about 2 weeks now, I have old Epox KT-333 and a duron 800 here that can do 1.4 ghz with dry ice.
it's not that great, but I wanna REALLY learn the do's and don'ts of this stuff before I play with it on some expensive hardware.

the cool thing about dry ice benchmarking, is it's incredibly cheap.

LilBuddy said:

doesn't every object have a temp, and when in contact with that temp the cold object takes heat and the hot object takes cold? or somethin like that. 8th grade sience goin right there

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Energy is always transferred from warmer objects to colder objects. This energy is what we call heat. If two objects are made of the same material and are at two different temperatures, the colder object simply has less heat energy than the warmer one. There is no such thing as "cold" that can be transferred.

Ken

Kunaak said:

a few ways you can use Dry Ice better.

1. get a container, remove the fan and place your radiator in there. or your res...
get Ethanol or basically alot of Everclear as thats the closest thing to that... pour alot of that in there, till if covers your Rad.
get Bricks of Dry Ice, usually from a specialty food place, or something similar. it's about a dollar a pound usually.
place brick of dry ice in ethanol or everclear (acetone if your in a VERY well ventilated area can work too)
this will get the ethanol incredibly cold.

Click to expand...

Be careful with the ethanol too. Most of the ethanol available commercially has been denatured with methanol or other poison to keep people from drinking it. The vapors from this can be dangerous in a poorly ventilated room as well.

the idea is to not freeze solid like water does.
a super cold liquid is more effective then a solid block of water.
thats why you need something like ethanol or such.

I haven't figured out why anti freeze and water just kinda sucks for this, but it doesn't do as well as just ethanol alone, atleast not for me.

Click to expand...

Are you measuring effectiveness by the temperature that the ethanol or water mixture reaches? If so, here's the reason the ethanol gets colder. It requires less heat energy to be taken away by the dry ice evaporating to get the same change in temperature. The cooling provided by both liquids should be the same or very close to the same, however. They will need to absorb the same amount of energy (the energy absorbed and removed by the evaporating dry ice) to reach ambient temp again.

Ken