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#51 2019-11-18 19:15:46

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 230

Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

Carbon dioxide will boil at about 0 degrees Celsius at 30bar.  And it will condense at -40C at a pressure of 10bar.

http://www.chemistry-blog.com/2009/02/0 … xtraction/

Solar heating panels can provide a hot source at about zero Celsius.  The tower would be useful for drying the saturated vapour.  Liquid CO2 droplets will drop back into the boiler by gravity, and the vapour will be much dryer at the top of the tower, whereupon the vapour will enter the turbine.


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#52 2019-11-18 20:52:42

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,390

Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

1. Mars atmospheric pressure is the issue for how to make use of the co2 that it has 610 Pa (0.088 psi) or not even 0.1 bar as the chart of the triple point shows.
2. The average temperature is about minus 80 degrees Fahrenheit (minus 60 degrees Celsius), although it can vary from minus 195 F (minus 125 C) near the poles during the winter to as much as a comfortable 70 F (20 C) at midday near the equator.

So to do anything we need to collect many cubic volumes of mars air and condense it without expending a ton of energy to do so and thats the first hurdle for mars.

We have talked about using the natural temperature swing with obsorbants to bring the co2 levels to a chamber for heating. The releasal would pressurize the co2 in the chamber of which its a simple repeat to build up the volume that we need.

That means timing control, monitoring and a power source that acheives the goal.

Evaluation of Mars CO2 Capture and Gas Separation Technologies
https://ntrs.nasa.gov/archive/nasa/casi … 015862.pdf

Nasa evaluation for The Mars Oxygen ISRU Experiment (MOXIE)
https://ssed.gsfc.nasa.gov/IPM/PDF/1134.pdf

3D modelling of the early martian climate under a denser CO2 ...
http://people.seas.harvard.edu/~rwordsw … et2013.pdf

https://www.kiss.caltech.edu/final_repo … report.pdf

https://www.kiss.caltech.edu/workshops/ … cht_sc.pdf

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#53 2019-11-26 06:40:01

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 230

Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

SpaceNut wrote:

1. Mars atmospheric pressure is the issue for how to make use of the co2 that it has 610 Pa (0.088 psi) or not even 0.1 bar as the chart of the triple point shows.

I think this would have to function as a closed system.  The solar collector and boiler would be at the bottom of a tall hill on the south facing side and would generate vapour at a pressure of 30bar.  The CO2 vapour would rise up an upcommer pipe, several hundred metres high and would enter the turbine at the top.  The condenser would be another set of radiator panels on the north side that would condense the CO2 into liquid that would then reenter the boiler at the bottom.  The weight of liquid CO2 in the condenser side would be such that a pump would not be needed.  In fact, the only strictly necessary moving part would be the turbine, as all other components could work on natural circulation, with vapour pressure in the upcommer, balancing the static pressure in the downcommer.

Both the upcommer and downcommer could be shafts drilled into the solid rock, as would the boiler.  The heater panels could be coiled hose beneath a thin layer of regolith.  The condenser would be much the same at the top of the hill.  All components aside from the turbine would be very low tech with low embodied energy.

This is another concept that would work on Mars but not on Earth.  On Mars, the very thin atmosphere allows very large temperature variations between areas in sunlight and shadow.  There could be very significant temperature variations between the south side and north side of a hill.  The system would continue to function at night, thanks to the heat stored in the rock surrounding the boiler.

Last edited by Calliban (2019-11-26 06:51:37)


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#54 2019-11-26 10:46:18

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,390

Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

I agree that a closed chamber that rises from a valley to the top of a small mountain can and could be used with the natural solar and night temperatures to make an energy source for man once built. Like you indicate we have a number of working fluids that man could use to make the system work...
In particular the liquid to vapor change and back is how such a system would work for water, Co2 and Freon or refridgerant class gasses  as well.

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#55 2019-11-26 13:02:26

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 230

Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

The atmospheric steam engine.

https://eprints.soton.ac.uk/348565/1/Mu … 202013.pdf

An interesting idea for converting low quality heat into mechanical power.  The low pressures and temperatures lead to relatively low efficiency - around 10% for a 69C boiler temperature.  However, the advantage of low pressures and low temperatures are simplicity.  The system is very easy to build using common materials.  There is no danger of explosion, as pressures are <1bar.  The system does not need a pump, as the vapour pressure of water is 20KPa at 60C.  A condensed water column just 2m tall would be sufficient to force return coolant into the boiler.

On Mars, we would probably use something other than water in low temperature heat engines.  CO2 is the most likely choice, though it would mean operating at higher pressures.


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#56 2019-11-26 14:01:59

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,390

Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

Thanks for the link here is some more stuff as it relates
https://www.clarke-energy.com/gas-engin … eneration/
schematic-trigen.gif

Waste heat recovery technologies and applications

Revealing the Secrets – How to design a Heat Driven Refrigeration System

Combined Refrigeration Cycle for Thermal Power Plant Using Low Grade Waste Steam


https://ww2.energy.ca.gov/2018publicati … 18-026.pdf
Building Energy Efficient Cooling and Heating

another working fluid
https://www.goodway.com/hvac-blog/2012/ … lar-power/

https://goldman.com.au/energy/company-n … ller-work/

https://res.mdpi.com/d_attachment/energ … -00234.pdf

  • TABLE 4-2
    Efficiencies of common energy conversion devices
    Energy Conversion Device Energy Conversion Typical
    Efficiency, %
    Electric heater Electricity/Thermal 100
    Hair drier Electricity/Thermal 100
    Electric generator Mechanical/Electricity 95
    Electric motor (large) Electricity/Mechanical 90
    Battery Chemical/Electricity 90
    Steam boiler (power plant) Chemical/Thermal 85
    Home gas furnace Chemical/Thermal 85
    Home oil furnace Chemical/Thermal 65
    Electric motor (small) Electricity/Mechanical 65
    Home coal furnace Chemical/Thermal 55
    Steam turbine Thermal/Mechanical 45
    Gas turbine (aircraft) Chemical/Mechanical 35
    Gas turbine (industrial) Chemical/Mechanical 30
    Automobile engine Chemical/Mechanical 25
    Fluorescent lamp Electricity/Light 20
    Silicon solar cell Solar/Electricity 15
    Steam locomotive Chemical/Mechanical 10
    Incandescent lamp Electricity/Light 5

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#57 2019-11-27 04:08:44

Terraformer
Member
From: Lancashire
Registered: 2007-08-27
Posts: 3,163
Website

Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

Calliban wrote:

The atmospheric steam engine.

https://eprints.soton.ac.uk/348565/1/Mu … 202013.pdf

An interesting idea for converting low quality heat into mechanical power.  The low pressures and temperatures lead to relatively low efficiency - around 10% for a 69C boiler temperature.  However, the advantage of low pressures and low temperatures are simplicity.  The system is very easy to build using common materials.  There is no danger of explosion, as pressures are <1bar.  The system does not need a pump, as the vapour pressure of water is 20KPa at 60C.  A condensed water column just 2m tall would be sufficient to force return coolant into the boiler.

On Mars, we would probably use something other than water in low temperature heat engines.  CO2 is the most likely choice, though it would mean operating at higher pressures.

That's still about half the efficiency of solar panels, for a temperature which can be achieved using solar thermal collectors. Hmm.


"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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#58 2019-11-27 07:21:21

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 230

Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

Terraformer wrote:

That's still about half the efficiency of solar panels, for a temperature which can be achieved using solar thermal collectors. Hmm.

As I noted on the 'Gravity Storage' thread, solar thermal panels are easier to make, have lower embodied energy and heat can be stored for later use.  That being said, I still think a nuclear reactor is a much better approach.  You get the same amount of power from a device containing a tiny fraction of the materials and embodied energy of any practical solar plant.  And it covers a much smaller area.  Here on Earth, this sensible solution has been regulated to death.  So we are left trying to gather nature's scraps, in the form of ambient solar energy.


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