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#1 2005-10-31 11:33:38

MarsDog
Member
From: vancouver canada
Registered: 2004-03-24
Posts: 852

Re: Hydrogen Car Powered by Expansion of Liquid H2

Hydrogen has large heat capacity.
Needing only heat exchanger to expand and then power a pneumatic motor.
Simple and lightweight.

http://www.uigi.com/physical_prop_m.html

In the experimental vehicle, instead of liquid Nitrogen use liquid Hydrogen.

http://www.aa.washington.edu/AERP/CRYOC … /Index.htm

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#2 2005-10-31 11:51:45

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 25,731

Re: Hydrogen Car Powered by Expansion of Liquid H2

But the problem with using Hydrogen here on Earth is that the smallest of sparks will cause it to ignite.
But you are correct in that we can save energy in the form of compressed gasses or at least in liquid form to allow for a vehicle to move by its use.

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#3 2005-10-31 14:03:20

MarsDog
Member
From: vancouver canada
Registered: 2004-03-24
Posts: 852

Re: Hydrogen Car Powered by Expansion of Liquid H2

At 4 miles per KWH
I calculated to more than 100 miles per cubic meter of liquid H2.

But at Earth temperatures liquefying H2 is very inefficient.
The pneumatic engine may only get 10% of the energy used to make the liquid H2.

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#4 2005-10-31 20:16:26

John Creighton
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From: Nova Scotia, Canada
Registered: 2001-09-04
Posts: 2,401
Website

Re: Hydrogen Car Powered by Expansion of Liquid H2

At 4 miles per KWH
I calculated to more than 100 miles per cubic meter of liquid H2.

But at Earth temperatures liquefying H2 is very inefficient.
The pneumatic engine may only get 10% of the energy used to make the liquid H2.

That is not that good. My parents ford focus can go over 200 km on little more then half a tank of gas.

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#5 2005-11-01 14:34:30

C M Edwards
Member
From: Lake Charles LA USA
Registered: 2002-04-29
Posts: 1,012

Re: Hydrogen Car Powered by Expansion of Liquid H2

Cindy started this topic at about this time last year. 

Compressed gas & liquified gas pneumatic motors are a good idea for vehicle power.  I'm not sure about the wisdom of holding out for exotic liquid hydrogen when you can just use the ambient air as your working fluid, though.


"We go big, or we don't go."  - GCNRevenger

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#6 2006-09-15 20:50:52

dixoy
Banned
Registered: 2006-09-15
Posts: 1

Re: Hydrogen Car Powered by Expansion of Liquid H2

very informative post mate! thanks!

Enkei Wheels

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#7 2006-11-14 18:42:16

MarsDog
Member
From: vancouver canada
Registered: 2004-03-24
Posts: 852

Re: Hydrogen Car Powered by Expansion of Liquid H2

Compressed gas & liquified gas pneumatic motors are a good idea for vehicle power.  I'm not sure about the wisdom of holding out for exotic liquid hydrogen when you can just use the ambient air as your working fluid, though.

Choices are Hydrogen and Oxygen from the water. CO2 freezes out.
We might see the Hydrogen economy on Mars before Earth.
A few extra kilometers from expansion before the gasses are used in a fuel cell ?

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#8 2006-11-16 09:24:50

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Hydrogen Car Powered by Expansion of Liquid H2

You really can't use cryogenics for simple vehicle power: where does the energy come from when you put the stuff in your tank? It comes from ambient heat around the vehicle. The trouble is that there isn't much heat available on Mars, its pretty cold and the atmosphere is quite thin, so the rate at which heat would enter the tank will be small. This is the energy you will use to push the vehicle, and because it is slow, your vehicle won't get anywhere. Furthermore, if you are using supercold H2 you will either be dumping a highly flammable gas into your dome or else dumping the super valuable gas into the open air. Or you would have to lug huge tanks to catch the gas as it boils.

Liquid CO2 is a bit better, but you will have to bother with scrubbing it out of the air inside your dome too, and both it and LH2 will form a nice coating of water ice when used indoors, which will prevent heat from getting into the tank and stopping your gas car dead. Not to mention increasing its weight and draining precious humidity out of the air. Even outside, I would be concerned for solid CO2 building up on the outside of an Hydrogen tank.

This is not a very good idea... it would be a better idea just to compress ambient air in the dome into composite tanks with no liquification.

As far as using Hydrogen in a fuel cell, you would have to carry oxygen with you if you use it outside the dome.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#9 2006-11-20 06:58:42

MarsDog
Member
From: vancouver canada
Registered: 2004-03-24
Posts: 852

Re: Hydrogen Car Powered by Expansion of Liquid H2

where does the energy come from when you put the stuff in your tank? It comes from ambient heat around the vehicle

Car.gifPlumbLine.gif

Similar to above diagram, the heat exchanger would be a CO2 snow maker.
Maybe, coat the heat exchanger with teflon to prevent sticking.

Latent heat of vaporization of one cubic meter of liquid H2 ;
http://www.uigi.com/hydrogen.html
71*446/3600 =  8.8 Kilowatt hours.
In addition, there is the gas phase Specific Heat (Cp) = 14.34  kJ/kg °C
(71*14.34/3600 = 0.28 KWH / m^3 °C)
which also contributes, at lower fficiency.
 

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#10 2006-11-21 08:00:25

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Hydrogen Car Powered by Expansion of Liquid H2

You aren't following me MarsDog,

The idea will never work because you need a lot of power (energy per time) to make a rover move, particularly uphill or against rough terrain.

A tank of cryogenic fluid is not a source of energy, it is simply a way to capture ambient heat in the air around the vehicle and convert it into mechanical motion (by expansion into a gas).

Since the Martian air is so thin and cold, there really isn't any energy for the cryogenic fluid to absorb, and so there won't be enough power to get your rover to move with any reasonably compact system.

It really doesn't matter what its heat capacity is, there isn't hardly any heat to feed it in the first place, which is the real problem. Yes it will eventually absorb a great deal of heat, but that isn't the measure of performance, you need all that heat energy in a short time to give your rover enough push.

You wouldn't want to use such a thing inside either, since the gas released would asphyxiate your citizens, and besides why bother batteries would work better for short-range indoor travel anyway.

And CO2 snow maker coated with teflon? No, even if it did work (which it wouldn't) then you would need some sort of mechanical CO2 remover. You underestimate how tight a hold that condensed solids have on the substrates.

And, have you given any thought to how valuable all this Hydrogen you would dumping overboard is? Since no tank of reasonable size could capture all the gas, and even if it could the high storage pressure would greatly reduce performance even more (less expansion, less push).


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#11 2007-02-10 21:59:34

dicktice
Member
From: Nova Scotia, Canada
Registered: 2002-11-01
Posts: 1,764

Re: Hydrogen Car Powered by Expansion of Liquid H2

Yep, GCNR, you got it right. Incidently, the thought of a safe hydrogen filled airship keeps coming to mind, however powered.

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#12 2007-02-12 17:12:42

dreammaker
Member
From: poughkeepsie, ny
Registered: 2007-01-01
Posts: 26

Re: Hydrogen Car Powered by Expansion of Liquid H2

using CO2 for a solar heat power plant might not be such a bad idea... take the CO2 from the poles and put it through the furnace and the resulting gas which expands many many times would be great  to turn a turbine.. you'd be taking CO2 from the poles adding heat to them and releasing in the air... its a win win situation.

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#13 2007-06-18 06:14:23

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

Re: Hydrogen Car Powered by Expansion of Liquid H2

Cryogenic heat engines have been proposed as alternative transportation power sources here on Earth.  There are a number of problems:

1) Low power density ~ LN2, the most common assumed propellant, has energy density 1-2% that of gasolene;
2) low thermodynamic efficiency of the heat engine (<10% for the entire cycle)
3) the power of the vehicle is limited by the rate of heat transfer from the surroundings.

Electric power is generally used to compress (and in the case of H2, manufacture) the working fluid.  Which raises the question, why not simply use a battery electric vehicle, which is far more efficient and has a similar power to weight ratio?

Generally speaking, H2 is a very poor fuel in any situation, due to its low boiling point, low density, its ability to soak through most metals and its very low ignition activation energy.

Zubrin's methane/oxygen rover concept is about the most practical suggestion for an extraplanetary rover that I have seen so far.  You generally have to go a long way to beat a bog standard IC engine in terms of energy density and performance.  It would be even better if the methane could be replaced by something denser or with a higher boiling point, like ethylene, (m)ethanol, acetylene or even synthetic gasolene.  All can be manufactured on Mars from air and water.

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#14 2022-02-05 19:11:33

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 25,731

Re: Hydrogen Car Powered by Expansion of Liquid H2

bump hydrogen use

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#15 2022-02-11 19:21:58

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 1,922

Re: Hydrogen Car Powered by Expansion of Liquid H2

I like the idea of a CO2 expansion engine on Mars.  A vehicle could carry an RTG coupled with a Stirling engine, which would compress Martian CO2 into liquid at night, when temperatures will be only around 200K.  The CO2 could be stored within a pressure vessel.  Very little compressor work needed so far beneath the CO2 critical point.  During the day, the same RTG would heat the CO2 and convert it into high pressure gas needed to drive an engine.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#16 2022-02-11 20:09:40

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 25,731

Re: Hydrogen Car Powered by Expansion of Liquid H2

The liquid co2 for mars is as safe use as we are not exposed to it unlike an earth use of similar products but its not Hydrogen either..

Not all RTG units are equal to the application of heat producing to make this viable but they can be made to do so.

https://www.energy.gov/sites/prod/files … eurial.pdf
2012 THERMOELECTRICS APPLICATIONS WORKSHOP

https://www.osti.gov/servlets/purl/1033364
EFFECT OF FUEL AND DESIGN OPTIONS ON RTG PERFORMANCE VERSUS PFF POWER DEMAND

https://ntrs.nasa.gov/api/citations/200 … 003866.pdf
Realistic Specific Power Expectations for Advanced Radioisotope Power Systems

https://www.energy.gov/ne/articles/powe … generators
Powering Curiosity: Multi-Mission Radioisotope Thermoelectric Generators

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