OTU Only: Refined verses Unrefined Fuel

[mike wightman]

So you finally accept that CT 77 ship tons are metric tons and not 14 cubic metre cubes? :devil:

Either mass is an issue due to one ship ton being one metric ton, or one ship ton is a displacement ton in which case the mass of the ship doesn't make any difference. :CoW:

 

[Ulsyus]

Only by volume, not by mass. Water is 9x the mass for the same amount of hydrogen. Sure, 1/14th the volume, but a LOT more mass.

So if a dton of water is carried, can it be run through the refining machinery as we go and have it converted to D₂ and O₂ for use later on??

 

[Timerover51]

Let us look at some energy data. The DA Pamphlet, Effects of Nuclear Weapons, gives the following energy yield for the fission of 57 grammes of U-235 or Pu-239.

The complete fission of 0.057 kg. (57 grams or 2 ounces of fissionable material is equivalent to 1 kiloton of TNT. Equivalents to this are:

10 to the 12th Calories
2.6 X 10 to the 25th Million Electron Volts
4.18 X 10 to the 19th Ergs
4.18 X 10 to the 12th Joules
1.16 X 10 to the 6th Kilowatt-hours
3.97 X 10 to the 9th British Thermal Units

Now, the fusion of an equivalent mass of Deuterium, 57 grammes, will yield 2.914 times the energy of the U-235 fission, or the equivalent of 3.38 X 10 to the sixth kilowatt-watts. I believe that the energy from Hydrogen will be very similar. So, 57 grammes of Deuterium will produce 3.38 X 10 to the third power Megawatt-hours of electricity.

Therefore, 57 kilograms of Deuterium, and presumably, Hydrogen, will yield 3.38 X 10 to the third power Gigawatt-hours of electricity. Looking at it another way, 57 kilograms of Deuterium, if completely fused, will equal 2.9 Megatons of TNT. Now, you are running not kilograms, but metric tons of fuel through the power plant in a very short period of time. Either your power plant is incredibly inefficient, or it is handling enormous amounts of power without frying. I find either alternative hard to believe.

 

[Enoki]

So if a dton of water is carried, can it be run through the refining machinery as we go and have it converted to D₂ and O₂ for use later on??

The problem with carrying water, or to a lessor degree methane or ammonia as your fuel base is you end up with a considerable amount of waste material when you refine it. You also risk contamination of your fuel tanks if you are putting the refined fuel back in a tank that contained something else. There's little chance you can get all the non-hydrogen out of a tank once you put it in. Even small amounts of water, methane, or whatever, mixed in with the refined hydrogen would be a contamination issue.

I'd think the ship's fuel tanks are something along the lines of advance dewars (eg., thermos bottles) that can recover the hydrogen as it off-gasses and recompress it into liquid. This would eliminate more or all gas loss.

So, I can't see a ship loading up with raw material like water or gas off a gas giant and putting in tanks to be refined unless it had separate tanks specifically for that purpose. That would take up considerable volume in the ship. Instead, I'd expect the ship to have a refining plant big enough to convert the intake of raw material directly to liquid hydrogen and dump the waste as it did.

That would then mean that the ship has to sit (more or less) where it can collect and process fuel for the time it takes to do this conversion. That could be anything from hours to days depending on the size of the processing plant aboard. The less refinable, or more contaminated the raw material is the longer this would take. So, a processing plant at say a class C starport using the local contaminated liquid hydrogen could pretty quickly clean out the contaminants. On the other hand, pulling raw material from say a gas giant that is mixed methane and ammonia with dust in it would take far longer. Salt water might take longer than freshwater. That sort of thing.

 

[Straybow]

Let us look at some energy data...

Therefore, 57 kilograms of Deuterium, and presumably, Hydrogen, will yield 3.38 X 10 to the third power Gigawatt-hours of electricity. Looking at it another way, 57 kilograms of Deuterium, if completely fused, will equal 2.9 Megatons of TNT. Now, you are running not kilograms, but metric tons of fuel through the power plant in a very short period of time. Either your power plant is incredibly inefficient, or it is handling enormous amounts of power without frying. I find either alternative hard to believe.

In this post [Going Pirate #39] I show that if fuel is ordinary hydrogen with 0.015% deuterium, D-D fusion of the 321g in each ton is sufficient to explain the listed power output (250 MW per EP).

 

[Straybow]

So if a dton of water is carried, can it be run through the refining machinery as we go and have it converted to D₂ and O₂ for use later on??

It can only be electrolyzed to D2 if it is heavy water.

The problem with carrying water, or to a lessor degree methane or ammonia as your fuel base is you end up with a considerable amount of waste material when you refine it.

Just liquifying H2 requires 14 GJ/ton and lots of time. Electrolyzing water takes a whopping 142 GJ/ton, or about 71 GJ/ton if half the energy can be provided by waste heat. Dissociation of CH4 takes 414GJ/ton of H2. I'm less familiar with the process, but I imagine about half of that energy can be provided through heat. Nothing is cheap, energy-wise.

 

[whartung]

It can only be electrolyzed to D2 if it is heavy water.

Just liquifying H2 requires 14 GJ/ton and lots of time. Electrolyzing water takes a whopping 142 GJ/ton, or about 71 GJ/ton if half the energy can be provided by waste heat. Dissociation of CH4 takes 414GJ/ton of H2. I'm less familiar with the process, but I imagine about half of that energy can be provided through heat. Nothing is cheap, energy-wise.

But it's demonstrably cheap Traveller-wise, since most any Tom, Dick, or Free Trader can seem to belly up to an ocean to fill their tanks and jet off to some other corner of the galaxy.