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Thermal Activated Cooling System  (Source: Oregon State University)
Device may eventually be used on a car exhaust for cooling and power

Today, about half the energy produced by cars, factories, and power plants is wasted as heat that escapes into the atmosphere.

Engineers from Oregon State University have made a major step towards addressing one of the most common wastes of energy today by recapturing some of the heat generated by a motor and using that energy to produce power. The engineers have successfully completed a prototype machine that can be attached to the exhaust pipe of automobiles, diesel generators, factory, and utility machinery that produces waste heat. The prototype system is being perfected at the university right now.

"This could become a very important new energy source and way to improve energy efficiency," said Hailei Wang, a research associate in the School of Mechanical, Industrial and Manufacturing Engineering at OSU. "The prototype shows that these systems work as well as we expected they would."

The researcher says that over half the heat generated by industrial activities is currently wasted. Even the most efficient plants according to Wang only convert about 40% of the energy produced into electricity. Combustion engines inside vehicles are even less efficient converting only 25-40% of the energy they produce.

The system that the team in Oregon has produced is called the thermally activated cooling system. The system is able to combine a vapor compression cycle with an organic Rankine cycle, which is an existing conversion technology. Using the prototype, the team at the university was able to turn 80% of every kilowatt of waste heat into a kilowatt of cooling capability. However, the efficiency wouldn't be as high at about 15-20% efficiency if the goal was to produce electricity.

"This technology would be especially useful if there's a need to have cooling systems where heat is being wasted," Wang said. "That's one reason the research has been supported by the Department of Defense, because they see it being used to provide needed air conditioning for electronics and other purposes when they are using generators in the field."

The team is looking at the system to power air conditioning systems in a hybrid auto and recharge the batteries at the same time. German scientists have previously developed a system that is able to generate power from wasted heat that can be turned into electricity. Researchers at the ORNL have also worked on a system that captures the water that is in the exhaust from diesel engines to provide drinking water for soldiers in the field.



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RE: Would be good if this works
By AnnihilatorX on 6/15/2011 5:24:20 AM , Rating: 2
quote:
Absolutely. I'm surprised it's efficiency is so low...15%? I mean something is better than nothing, but honestly, this shouldn't be marketable until its at least near 50%.


You need to read up on the law of thermal dynamics
Absolute maximum efficiency = 1-Tout/Tin
where Tout and Tin denote temperature of sink and source in Kelvins respectively, for a device which converts thermal energy to other form of energy (heat engine).

If exhaust temperature is 60 degrees Celsius (333K), outside temperature is 22 degrees Celsius (295K), the maximum efficiency for any energy conversion system, regardless of sophistication is 1-295/333 = 11.5%
So that's about 15% depending on what they take as temperatures.

You can achieve better on a cooling system however, since that's not strictly an energy conversion system.


RE: Would be good if this works
By FishTankX on 6/15/2011 8:21:28 AM , Rating: 2
Exhaust temperatures if I'm not misinformed actually exhaust at arouund 200C. Maybe much higher.

This article (http://www.sciencedaily.com/releases/2008/06/08060... says around 700 degrees. That's PLENTY of difference to work with to get 15% energy out of the system.


RE: Would be good if this works
By AnnihilatorX on 6/16/2011 3:32:37 AM , Rating: 2
Well you also need to consider a efficient heat pathway from your heat source to environment, along with inevitable efficiency loss during conversion. The thermal efficiency law I quoted is theoretical maximum, real device may get 40% out of that.

So if we take 200deg C, That gives about 40% theoretical max.
Then you are lucky if your energy converter itself achieve 50% of that. That gives 20% efficiency overall.


By AnnihilatorX on 6/16/2011 3:38:06 AM , Rating: 2
As for the 700 deg C, it must be a big truck! After reading the article, I believe that it says the exhaust pipe can reach 700 deg C, but if you start extracting energy from it, my guess is that it won't sustain the temperature. 200 is a better guess.


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