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#1 2017-10-18 06:54:18

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 948

Mars Atmospheric Kinetic Engine

A recent post on Martian compressed air energy storage got me thinking about a possible Martian renewable energy source that has thus far been overlooked.  I have not yet performed any sort of detailed analysis of this yet.
https://commons.wikimedia.org/wiki/File … iagram.svg

The idea works like this:

1.    Build a compressor station at the top of a mountain.  Average Martian temperatures are very close to the triple point of CO2 (217K).  This means that with intercooling, very little mechanical work would be needed to compress CO2 into a saturated liquid at typical Martian temperatures.
2.    Run the liquid CO2 down the side of the mountain through a steel pipe.
3.    At the bottom of the mountain, build a two stage turbine – the first would extract kinetic energy from the falling liquid CO2 much like a hydropower plant here on Earth; the second would boil the CO2 using either ambient heat or stored solar heat and extract thermodynamic work.

Provided the thermodynamic expansion stage provides sufficient energy to cover the energy of compression, kinetic energy of the falling CO2 would result in net energy generation.  The idea is sort of like hydropower, but using liquefied CO2 as the working fluid rather than water.

Last edited by Antius (2017-10-18 06:54:45)

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#2 2017-10-18 07:09:30

louis
Member
From: UK
Registered: 2008-03-24
Posts: 2,599

Re: Mars Atmospheric Kinetic Engine

That's a clever idea. You should patent it - quick! lol

Sounds feasible...as long as carbon dioxide is close to the liquid point...what is an efficient "drop"? I'm guessing it has to be something like 400 feet to work well. 

Does moving downhill impart heat to the CO2 - would that be a problem?


Antius wrote:

A recent post on Martian compressed air energy storage got me thinking about a possible Martian renewable energy source that has thus far been overlooked.  I have not yet performed any sort of detailed analysis of this yet.
https://commons.wikimedia.org/wiki/File … iagram.svg

The idea works like this:

1.    Build a compressor station at the top of a mountain.  Average Martian temperatures are very close to the triple point of CO2 (217K).  This means that with intercooling, very little mechanical work would be needed to compress CO2 into a saturated liquid at typical Martian temperatures.
2.    Run the liquid CO2 down the side of the mountain through a steel pipe.
3.    At the bottom of the mountain, build a two stage turbine – the first would extract kinetic energy from the falling liquid CO2 much like a hydropower plant here on Earth; the second would boil the CO2 using either ambient heat or stored solar heat and extract thermodynamic work.

Provided the thermodynamic expansion stage provides sufficient energy to cover the energy of compression, kinetic energy of the falling CO2 would result in net energy generation.  The idea is sort of like hydropower, but using liquefied CO2 as the working fluid rather than water.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#3 2017-10-18 09:18:27

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 948

Re: Mars Atmospheric Kinetic Engine

I am not sure about minimum feasible drop.  I don't think heat addition will be a problem, in fact looking at the CO2 phase diagram I would say that for drop heights greater than about 1km, some heating is necessary to prevent the formation of dry ice under static or dynamic pressure.  The pipes could conceivably clog up with dry ice if the system is left static for too long.

I know that such a system is unlikely to work on Earth.  To liquefy air, one must extract approximately 300KJ/Kg of heat at a coefficient of performance of about 0.33 at 90K.  So one must invest nearly 1MJ/kg to liquefy the air, whereas the gravitational potential energy for a drop of 2km, say, would be 20KJ/kg.  Even if the device produces net energy, the EROI would be terrible, which means the economics would be terrible.

The unique properties of the Martian atmosphere, i.e. a gas close to its triple point temperature, means that this might be possible on Mars with a much lower embodied energy.

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#4 2017-10-18 09:48:04

Terraformer
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From: Lancashire
Registered: 2007-08-27
Posts: 2,479
Website

Re: Mars Atmospheric Kinetic Engine

Maybe not for air, but if the air regularly gets close to it's dew point...


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#5 2017-10-18 10:54:06

elderflower
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Registered: 2016-06-19
Posts: 521

Re: Mars Atmospheric Kinetic Engine

Condensing water vapour at high altitude is called a cloud. Clouds can be caught, as is done by the vegetation on the peak of Ascension Island. This is the source of virtually all the Island's moisture and sustains its (limited) agriculture. I don't think they have tried to get power from it as there would be more reliable sources.
On bigger mountains hydro power becomes practical, but generally one waits for the clouds to become rain to supply water in large quantities.

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#7 2017-10-18 20:47:23

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 10,527

Re: Mars Atmospheric Kinetic Engine

http://www.scielo.org.co/pdf/dyna/v81n1 … 185a21.pdf

Over the last decade, organic Rankine cycles (ORCs) have widely been studied to harness low-grade heat sources that provide temperatures ranging between 80 and 400°C.

An ORC includes the same components as a traditional Rankine cycle, namely a pump, an evaporator, a turbine (or expander) and a condenser. The major difference comes from the choice of working fluid: water is replaced by an organic component.

Different technologies of concentrating collectors can be used for ORC solar power plants, such as solar towers, parabolic troughs, Fresnel linear collectors and solar dishes.

The liquid fluid is pressurized by a pump and vaporized to a superheated state by means of a heat input. The vapor is then expanded in a turbine connected to a generator. Finally, the vapor is condensed and heat is released into the environment. A regenerator is included to use the residual high-temperature vapor refrigerant exiting the expander to preheat the liquid refrigerant after the pump.

http://www.agir.ro/buletine/1733.pdf

https://en.wikipedia.org/wiki/Solar_Turbine_Plants

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#8 2017-10-19 10:04:58

elderflower
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Registered: 2016-06-19
Posts: 521

Re: Mars Atmospheric Kinetic Engine

Working fluid doesn't have to be organic. For low temperature heat sources ammonia can be used. For very high temperature heat sources mercury. In the latter the mercury is condensed in a water boiler which is used as a second stage.

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#9 2017-10-19 10:14:08

louis
Member
From: UK
Registered: 2008-03-24
Posts: 2,599

Re: Mars Atmospheric Kinetic Engine

I've wondered before now about regolith:  if you had enough loose regolith on a  suitable very high mountain could you use it to drive a turbine (simply pushed into a feeder hopper, using a bulldozer).  Of course, eventually you run out of loose regolith, but then you can just move to the next mountain...land is not really an issue on Mars. smile Would probably be more like a traditional waterwheel than a modern hydro turbine I imagine.

However, I think the liquid CO2 powered turbine sounds good and definitely worth investigating.

elderflower wrote:

Working fluid doesn't have to be organic. For low temperature heat sources ammonia can be used. For very high temperature heat sources mercury. In the latter the mercury is condensed in a water boiler which is used as a second stage.

Last edited by louis (2017-10-19 10:16:19)


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#10 2017-10-19 20:33:00

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 10,527

Re: Mars Atmospheric Kinetic Engine

Power Cycles for Electricity Generation

Most of our development to this point has been oriented toward obtaining heated fluid from a solar collector. Often, the industrial demand to be satisfied by a solar energy system is for this heat. However, a more valuable form of energymechanical or electrical energy (both are equivalent in the thermodynamic sense)is sometimes desired either exclusively or in combination with thermal energy. The device used to produce mechanical work or electricity from solar generated heat is a power conversion cycle, or heat engine.

Several considerations peculiar to solar energy systems affect the choice of the power conversion cycle and how the solar energy system is designed to incorporate it. These considerations are discussed in this chapter along with a detailed discussion of the three power cycles usually considered for solar applications: the Rankine, Stirling, and Brayton cycles.

This development will follow the outline below:

image001.jpg


image002.jpg


image012.jpg

Experimental Study and Modeling of a Low Temperature Rankine Cycle for Small Scale Cogeneration

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#11 2017-10-20 08:39:58

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 948

Re: Mars Atmospheric Kinetic Engine

I ran a few quick and rough EROI calculations on a Mars built solar dynamic system and was pleasantly surprised by the results.

Anhydrous liquid ammonia has good compatibility with carbon steel:
https://www.calpaclab.com/carbon-steel- … ity-chart/

It is also liquid across a temperature range of -75 to 25°C, the latter requiring a vapour pressure of 1MPa (10bar).
https://en.wikipedia.org/wiki/Ammonia_(data_page)

On this basis, I would propose that anhydrous ammonia would be an excellent working fluid for a solar or geothermal power system on Mars.

A solar thermal collector could be a flat clay plate (no cover glass needed in the vacuum of Mars) with low carbon steel tubes embedded in it, containing liquid anhydrous ammonia.  During the day, the collector would collect heat at say 0°C.  The cold store would be a tank of saline solution that will melt at -20°C, serving as a heat sink.  At night, the cycle can be reversed.  The heat sink becomes a heat source at -20°C and the panel will dump heat into space at a temperature of -70°C.  At zero Celsius, ammonia boils at 4.3bar.  At -20C, it boils at 1.9bar.  Could we use a single stage LP turbine? It would have a feed pressure of 4.3bar during the day and back pressure of 1.9bar; and a feed pressure of 1.9bar at night and back pressure of 0.1bar.  I don't honestly know.  Assuming the device works at 2/3rd Carnot efficiency, the average efficiency of the device would be 9.5%.

If the steel tubes are 1cm in diameter and the steel has a yield strength of 250MPa, then a design factor of 5 would give a tube wall thickness of 0.1mm.  If the tubes are spaced 5cm apart, then a total of 20m of tubing would be needed for 1m2 of panel.  That would weigh in at 0.5kg steel per m2 of panel, not including manifolds or other pipework.  If we roughly double steel mass to include those items and valves, we would need on average about 1kg of steel per m2 of solar plant.  Let us assume an embodied energy of 30MJ/kg of new steel.  The clay panels would have relatively low embodied energy.  The thermal storage tank could simply be a pit, lined with polyethylene and filled with brine.  The heat exchanger within the brine would probably consist of polyethylene tubes as these have a relatively low glass transition temperature, will not be corroded by the brine and can be manufactured from Mars-made ethylene gas.

Martian insolation is about 400W/m2 year-round average, close to the equator.  If the system runs for 20 years at 9.5% efficiency, then each m2 of solar collector would produce some 8GJ of mechanical / electrical power over the course of its lifetime.

Based upon an energy investment of 30MJ/m2, the EROI of the panels would appear to be ~266.  Of course, I have made a lot of simplifications here.  I haven't included the energy required to build the thermodynamic plant, the salt water storage pit, or to mould and bake the clay panels with the tubes embedded in them.  I have also assumed that the collectors are 100% efficient, whereas in reality, they will probably make half that.  But even if EROI is an order of magnitude lower than I have estimated, an EROI of 26 is not bad for a round the clock power supply.  As ammonia has good or excellent compatibility with mild and low carbon steels, it should be possible to cast, machine or 3D print most of the components on Mars. 

As an aside, this sort of simple thermodynamic system would never be possible on Earth because:
1.    Earth has insufficient diurnal temperature ranges for it to be an efficient option and simple brine-based phase change materials would not be useful;
2.    Due to the thick atmosphere, Earth-based panels require evacuated glass tubes to build up decent temperatures, which ramps up the required energy investment dramatically;
3.    Aside from deserts, Earth based northern locations where most people live do not benefit from persistent periods of direct sunlight.  With little cloud cover, Mars would have clear sky most of the time;
4.    Earth based panels must be insulated to prevent heat losses to the surrounding air and surroundings due to radiation.  Mars based panels will lose no heat to surrounding air and only half as much to radiation; because their operating temperature in full sun will be close to 0°C rather than 50°C.

This is why on Earth; solar power tends to rely on PV.  This has high embodied energy and poor EROI, especially when storage is factored in.  All in all solar thermal power looks a lot more doable on Mars than it is on Earth.  The system works well with low grade easily manufactured materials: baked clay, polyethylene sheeting and pipes and carbon steels.  Energy storage is achieved prior to generation in the phase change of brines.  These should be cheap on Mars, as water is available as ice and the soils are saturated with salts and chlorates.

Of course, one downside of an extended solar based power system is the large amount of EVA time needed to assemble and maintain the system on the surface of Mars.  A 10MWe system would need to cover an area of about 1km2.  But it would only need to be built once.

Last edited by Antius (2017-10-20 08:48:48)

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#12 2017-10-20 09:14:58

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 948

Re: Mars Atmospheric Kinetic Engine

Darn!  Silly me!  At a temperature of -70C (200K) the system will only radiate 90W/m2 into the Martian night.

Earthenware clay is fired at a temperature of 760C.
https://www.goshen.edu/art/DeptPgs/rework.html

Assuming a clay density of 2000kg/m3, a 1m2 x 0.02m thick clay panel would weigh 40kg.  If specific heat is 1KJ/KgK, then some 30.4MJ of heat would be needed to heat the clay to sinter temperature.  So the embodied energy of the panel is 60.4MJ/m2.  That reduces the panel EROI to about 33.  Not as good as I originally thought, but still better than PV when storage losses are accounted for and much easier to make on Mars.

According to this link, a SKODA 660MW supercritical steam turbine has a weight of 1000te and an efficiency of 51%.
http://e2010.drustvo-termicara.com/reso … /fiala.pdf

That's 660W/kg.  If the ammonia turbine has efficiency of 9.5%, then power density would be 123W/kg - if working fluid energy density and flow rates were the same, which of course they aren't.  Since supercritical steam enters the turbine at a pressure of at least 22MPa, it would have roughly 50 times the energy density of ammonia vapour in our system.  So the ammonia turbine would have at least an order of magnitude lower power density, although the lower pressure differential may allow thinner blades.  If power density is ~10W/kg, then the turbine embodied energy (steel alone) would be about 16% that of the panels.  All in all, a whole system EROI of 20 still looks achievable.

Last edited by Antius (2017-10-20 09:31:40)

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#13 2017-10-20 12:04:06

JoshNH4H
Mod and Martian
From: New York, NY, USA, Earth, Sol
Registered: 2007-07-15
Posts: 2,134
Website

Re: Mars Atmospheric Kinetic Engine

Referencing my earlier posts on EROI, I don't think it's reasonable to say that speculative EROI calculations are anywhere near right or that they should carry much weight in our analyses.


-Josh

If you try to talk to me about cold fusion or propellantless drives I will ignore you.
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#14 2017-10-20 12:24:21

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 948

Re: Mars Atmospheric Kinetic Engine

JoshNH4H wrote:

Referencing my earlier posts on EROI, I don't think it's reasonable to say that speculative EROI calculations are anywhere near right or that they should carry much weight in our analyses.

I don't agree.  My own efforts are not very robust.  But a comprehensive analysis is a good proxy for telling us how the economics of a concept will pan out, if we exploit things like scale economies and if regulatory issues do not exist.  EROI tells us how good something might be.

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#15 2017-10-20 12:57:40

JoshNH4H
Mod and Martian
From: New York, NY, USA, Earth, Sol
Registered: 2007-07-15
Posts: 2,134
Website

Re: Mars Atmospheric Kinetic Engine

Well my point in the other thread was not so much that comprehensive EROIs are hard but that they are impossible, because there can be no consistent definition of EROI.  At best, including labor, you will end up with a number that's almost precisely equal to a cost-benefit analysis


-Josh

If you try to talk to me about cold fusion or propellantless drives I will ignore you.
Mod actions in red

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#16 2017-10-20 19:55:48

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 10,527

Re: Mars Atmospheric Kinetic Engine

Back to the other parts of Antius post # 11 & 12, I take it that you are planning to create the flat clay plate (no cover glass needed in the vacuum of Mars) with low carbon steel tubes embedded in it, containing liquid anhydrous ammonia all from insitu materials and thats not bad of course less pumps. The flat plate clay collector could be covered by thermo blankets like those used in survival kits just place them on a roller system to cover the collector at night and wait until the sun hits it in the morning to uncover it.

Continuing with the rest of the system plan of a thermal storage tank could simply be a pit, lined with polyethylene and filled with brine will need an insulator to keep the ground from wicking away the hard earned heat and this holds true for the clay flat plate collector as it would have the same issue if making contact with the ground.

The heat exchanger filled with brine making use of polyethylene tubes makes for easy coiling of it within the pit will give plenty of hot water if we put it into another tank for the crew to shower with.

Adding a heat loop from the RTG to the pit is a plus for making it a continous output system.

Now back to the post #1 which when I reread it is describing an upside down, down draft chimney system where the opening at the top is greatly larger than the one at the bottom and with the help of an active cooling system gridding inside the unit we can liquify the CO2 from the power we are generating from the other system.

If fact this could be just a spiraling mining project to create the chimney from any hill or mountain creating that funnel effect for the condensing and force to aid in liquifing the co2 for later use.

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#18 2017-10-22 17:15:54

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 10,527

Re: Mars Atmospheric Kinetic Engine

I have been looking at the types of pumps, compressors and turbines to make use of in the design; and common used parts that can do both as applied in the schematics of the system.
https://en.wikipedia.org/wiki/Axial_compressor

350px-Axial_compressor.gif

Of course the ends are capped and would have flow check valves to cause the correct rotation to happen and one would connect the shafts to a generator or alternator design to allow power to be created by the motion of the axial unit.

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#19 2017-10-29 06:58:33

elderflower
Member
Registered: 2016-06-19
Posts: 521

Re: Mars Atmospheric Kinetic Engine

CO2 has been used as a refrigerant in the past- quite extensively. It has the drawbacks that pressures are very high and its critical point has quite a low temperature. When the heat sink gets a bit warm it can't be used in a regular reversed Rankine cycle refrigeration system. Apart from being flammable, propane is much more convenient.

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