

Water evaporation-driven toy motor - trimble-alum
http://www.theguardian.com/science/2015/jun/16/scientists-build-toy-car-propelled-by-evaporating-water

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FiatLuxDave
I was the only poster to the previous thread about this at:
[https://news.ycombinator.com/item?id=9732609](https://news.ycombinator.com/item?id=9732609).

Here is what I wrote:

I also work in this space, so the headline caught my attention. This is far
from the first. Some other evaporation driven engines include:

[https://en.wikipedia.org/wiki/Drinking_bird](https://en.wikipedia.org/wiki/Drinking_bird)

[https://en.wikipedia.org/wiki/Energy_tower_%28downdraft%29](https://en.wikipedia.org/wiki/Energy_tower_%28downdraft%29)

[https://en.wikipedia.org/wiki/Barton_evaporation_engine](https://en.wikipedia.org/wiki/Barton_evaporation_engine)

The solar updraft tower and vortex engine also operate in a similar space,
meaning that all of them operate using the temperature difference between
ground and tropopause which feeds the water cycle.

It is my personal opinion that evaporation-driven engines (or something quite
similar) are the most promising energy source (on this planet). Essentially,
they are an alternative source of solar energy which doesn't have the problem
of needing the sunlight to be present to work.

The main issues, as with most new energy sources, are efficiency and cost. The
Columbia motor costs $5 for 50 microW, or $1x10^5 dollars per watt. You
generally want something nearer 1$/watt for primary energy use. The efficiency
in terms of water or thermal energy is not stated, but is likely similar to
drinking birds, which have a thermal efficiency around 0.01%. The
theoretically possible efficiency for the evaporative half of the water cycle
is on the order of 12%, so there is a lot of room for improvement.

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vixen99
“(Water)has a desire to evaporate". I wonder what other previously
unappreciated emotions it has.

~~~
JonnieCache
Even better, the subtitle reads: "Researchers at New York’s Columbia
University harness the element’s natural process"

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Animats
Aw. Anyone still have a drinking bird?[1] Same principle.

[1]
[https://www.youtube.com/watch?v=Yk71GY02diY](https://www.youtube.com/watch?v=Yk71GY02diY)

~~~
david-given
I used to have one, but I lived in a hard water area, and the felt evaporator
scaled up and is stopped working.

IIRC a sipping bird is powered by the heat differential caused by cooling of
the evaporator. This thing seems to be powered by centre-of-gravity changes
caused by motion of hygroscopic material.

I _suspect_ that IRL it would very quickly stop working due to gunk in the
water affecting the hygroscopic material, but it's a very neat hack
nevertheless.

I wonder if you could build a passive humidifier out of one of these? Float
one in a container of (clean) water and attach some fan blades. As it spins,
it pushes water into the air. At the very least it'd make a fun executive toy.

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murbard2
See also the rubber band heat engine, e.g.
[https://www.youtube.com/watch?v=dBXL93984cQ](https://www.youtube.com/watch?v=dBXL93984cQ)

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f00barbazb00
They're using difference in humidity... wow, inventive.

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sova
Wow this is amazing. I'm actually blown away.

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rootlocus
How much power can these motors produce? Can they be used for practical
purposes, or are they simply a cool experiment?

~~~
leoedin
The fact they don't give any hard numbers is a pretty big sign that this is
nothing more than a neat toy. Powering LEDs takes very little energy - 1 mA at
2V (2 mW) is enough to make it visible. Making it flash reduces that power
again.

The concept of using bacterial spores as a means of producing motion is pretty
neat, though it's obviously a long way from being practical. The suggested use
case (low power remote floating sensors) seems pretty suitable for solar
power, which has the advantage of maturity and no moving parts.

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spiritplumber
It looks like those discs-and-marbles perpetual motion machines... maybe
that's how those work (for a while).

