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#1 2017-09-27 01:20:51

From: UK
Registered: 2008-03-24
Posts: 3,486

Evaporation energy … l#comments

I hadn't heard of this evaporation energy technique before now.  Sounds intriguing.  Would presumably need domes on Mars to work.

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#2 2017-09-27 19:39:39

From: New Hampshire
Registered: 2004-07-22
Posts: 12,010

Re: Evaporation energy

A miniature version of the engine was first developed by scientists in 2015
It could be scaled up to cover 70% of the US's energy production from that year
It could yield between 2W and 10W per square metre, three times wind power

In a 2015 paper, Dr Sahin showed how this basic process can be exploited to do work.

In their 2015 paper, the researchers unveiled the first rotary engine and even a tiny car powered by humidity.

It works using bacterial spore that expand when they become humid to drive an engine.
Inside the bacterial spores, water is confined to nanoscale cavities and depending on the humidity, large pressure changes are induced.

When water is applied, the tape changes its curvature in moist and dry conditions.

When multiple tapes are assembled in parallel they can lift weight against gravity.

The engines start and run autonomously when placed at air–water interfaces.

They generate rotary and piston-like linear motion using specially designed, biologically based artificial muscles responsive to moisture fluctuations.

The bacteria spore and moisture pus any heat to cause motion to happen within a near operating temperature range I would supect....


#3 2017-11-03 06:41:08

From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Evaporation energy

Towards the polar regions of Mars, huge quantities of dry ice are present - about as much as is present in the existing atmosphere.  These could be melted and then boiled to drive gas turbines, using solar or geothermal heat.  Solid CO2 is kind of like a Martian fossil fuel - one that actually regenerates itself.

The energy content of liquid CO2 heated and expanded at 300K, is about 800KJ/kg.  This is substantially lower than diesel or coal here on Earth (40MJ/kg and 25MJ/kg, respectively).  However, is should be possible to use mild geothermal heat at polar regions to melt the dry ice in a sealed vessel at 5.1bar and -50C.  The liquid can then be piped through low-carbon steel pipes to solar thermal power plants closer to the equator or a geothermal hotspot, where it would be expanded to release its stored energy.  The mining of dry ice would be open cast and the power source could come from the liquid CO2 itself, expanded using some a stored heat source.

The potential for using condensed CO2 as both a primary energy source and an energy storage medium on Mars, continues to impress me.  I was initially sceptical that native solar power would provide sufficient EROI.  However, I am coming to realise that solutions are available on Mars that would not work on Earth.  Energy storage in liquid CO2 makes solar power a lot easier to use, as we do not need to rely on energy expensive PV systems coupled to expensive Li-ion batteries for energy storage.  Very simple solar thermodynamic systems can provide round the clock power with an acceptable energy return on Mars.  This sort of thing works on Mars because it has a CO2 atmosphere at a temperature close to CO2 triple point and large temperature extremes across the day, providing the temperature difference needed for thermodynamic cycles.  Liquid CO2 can be stored in polyethylene lined pits at ambient average temperatures at a pressure of 5.1bar.

To raise mechanical power for individual applications we do not even need to generate electricity.  Simply heat the CO2 above its saturation point in a closed container and use the high pressure gas to drive compressed air tools.  These are less energy efficient than electric tools, but much easier to make and are therefore more suitable for manufacture on Mars.

My previous analysis indicates that a solar thermal electric plant could be built using liquid CO2 as the heat sink and working fluid and brine as the hot thermal store.

The solar collector would gather heat during the day at about zero Celsius and would radiate heat at night at about -70 Celsius.   The whole system appears to have an EROI of ~20, which is quite respectable for a power plant capable of providing a constant base load power supply.  The good EROI stems from the fact that the collectors are simple unglazed clay panels, containing mild steel heat transfer pipes.  Energy is stored in Polyethylene lined pits containing liquid CO2 and brine, which have very low energy cost.  Again, this is possible on Mars because of its unique surface conditions.  On Earth, nothing like this would work.

Last edited by Antius (2017-11-03 09:42:44)


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