EvMick proposes a "cold' engine (opposite of a heat engine):
> How about if we go about it backwards?
> How much "Coldth" can be concentrated in a mobile source? Is a solid
> nitrogen brick possible?
> Assume it is (or something like it).....could usable amounts of electricity
> be developed using "thermocouple technology"? Or merely by letting the
> nitrogen boil off and powering "steam" engines?
You could probably do something like this, give a car a reservoir of something
cold and run an engine off the heat differential.
The problem is that hot and cold objects by themselves don't store much
energy compared to what we can get with chemical reactions. That's why
your car runs on gas rather than by being loaded with hot bricks.
When you're trying to diet, you learn that protein and carbohydrates have
5 Calories per gram, and fat has 9 Calories per gram. Gasoline, according
to my reference, has about 11 Calories per gram.
That's enough to heat a gram of water 5000, 9000, and 11000 degrees
respectively! So to have the same energy storage capacity as a fuel
as energetic as food, you'd have to have a heat reservoir stored at
thousands of degrees, which is not very practical (or safe).
Or to get the same effect with cold, it would have to be thousands of
degrees below zero, which you can't do because it doesn't get that cold.
Chemical energy is really amazingly efficient. Other energy storage
systems have been proposed; springs, flywheels, etc., mostly because they
might be more efficient at feeding energy in and then getting it out.
But if you just want the one-way process to be efficient and portable,
chemicals are the way to go.
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