- #1
JeffEvarts
- 74
- 7
Oh you who are wise in the ways of Physics, I beg a moment of your time.
I've poked around wikipedia and found my way to PV=nRT and Thermal Mass and some other basics, and Googled "compressed air" "ice" "expansion" and similar, but can't quite find anything that helps me answer my question, so I have come back to my colleagues here at PhysicsForum.
We "all know" that if you take a can of compressed air (say, a keyboard de-duster) and spray it out slowly through a straw into a cup of water, ice will form.
As the air leaves the can, the pressure decreases to ambient (1atm), the volume of the bubbles increase as they pass upward through the water, and the air itself absorbs heat from the water to cover the difference. This thermal transfer takes place at some level off real-world efficiency, and the air will be slightly cooler than ambient air when the bubble bursts at the water's surface. Once enough heat has been removed from the water, ice begins to form. Also, as anyone who's done the experiment will attest, the can gets colder as well.
Suppose
-Jeff Evarts
I've poked around wikipedia and found my way to PV=nRT and Thermal Mass and some other basics, and Googled "compressed air" "ice" "expansion" and similar, but can't quite find anything that helps me answer my question, so I have come back to my colleagues here at PhysicsForum.
We "all know" that if you take a can of compressed air (say, a keyboard de-duster) and spray it out slowly through a straw into a cup of water, ice will form.
As the air leaves the can, the pressure decreases to ambient (1atm), the volume of the bubbles increase as they pass upward through the water, and the air itself absorbs heat from the water to cover the difference. This thermal transfer takes place at some level off real-world efficiency, and the air will be slightly cooler than ambient air when the bubble bursts at the water's surface. Once enough heat has been removed from the water, ice begins to form. Also, as anyone who's done the experiment will attest, the can gets colder as well.
Suppose
- I have 1000L of air at a pressure of 1.09 atm, which is at 20°C.
- I allow this to bubble out of the tank (into the STP environment) through an expansion valve that is immersed in 1 liter of water which starts at 20°C.
- The thermal mass of air is approximately 1/4 that of water.
-Jeff Evarts