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newbie · 12-11-2001, 08:00 PM

redleader is almost right. The energy transition takes place entirely at 0 degrees, not 0 to 1 degree C.

It takes 80 calories/gram to change ice into water. It takes 600 calories to make a gram of liquid water vaporize. It takes 1 calorie to raise 1 gram of water 1 degree C. The phase change coolers I've seen go for the 600 calorie transition by boiling water. Water coolers move 600 times as much liquid water as vapor change coolers do to achieve the same cooling effect.

Since water boils at 100 degrees centigrade at sea level pressure, you would think the cpu would melt. The trick to a phase change cooler is they lower the pressure inside the cooler to about 1/4 atmosphere so that the water boils around 25 degrees C. It still takes 600 calories to change the water from a liquid to vapor but it happens at a lower temperature due to the lower pressure.

Besides being able to absorb lots of heat quickly, water-based phase change coolers have the advantage of being able to move heat away from the source. When water vaporizes, the molecules take the heat of vaporization along with them. Since they're vapor instead liquid, they can move much faster and hence, they can move heat faster and further. If you look at a thermal picture of a phase change cooler vs. a block of copper, you'll see an even distribution of heat in the former and a hot spot where the cpu is in the later.

There's a lot more info at [url =http://www.thermacore.com ] Thermacore.[/url] If you're not scared of math, try this paper on cooling lasers with heat pipes Skip the section on lasers and focus on the heat pipe discussion. Good stuff.

12-11-2001, 08:00 PM	#5
newbie Cooling Neophyte Join Date: Dec 2001 Location: salinas Posts: 12	redleader is almost right. The energy transition takes place entirely at 0 degrees, not 0 to 1 degree C. It takes 80 calories/gram to change ice into water. It takes 600 calories to make a gram of liquid water vaporize. It takes 1 calorie to raise 1 gram of water 1 degree C. The phase change coolers I've seen go for the 600 calorie transition by boiling water. Water coolers move 600 times as much liquid water as vapor change coolers do to achieve the same cooling effect. Since water boils at 100 degrees centigrade at sea level pressure, you would think the cpu would melt. The trick to a phase change cooler is they lower the pressure inside the cooler to about 1/4 atmosphere so that the water boils around 25 degrees C. It still takes 600 calories to change the water from a liquid to vapor but it happens at a lower temperature due to the lower pressure. Besides being able to absorb lots of heat quickly, water-based phase change coolers have the advantage of being able to move heat away from the source. When water vaporizes, the molecules take the heat of vaporization along with them. Since they're vapor instead liquid, they can move much faster and hence, they can move heat faster and further. If you look at a thermal picture of a phase change cooler vs. a block of copper, you'll see an even distribution of heat in the former and a hot spot where the cpu is in the later. There's a lot more info at [url =http://www.thermacore.com ] Thermacore.[/url] If you're not scared of math, try this paper on cooling lasers with heat pipes Skip the section on lasers and focus on the heat pipe discussion. Good stuff.