Airship Hydrogen resupply
September 5, 2016 at 5:10 pm
(This post was last modified: September 6, 2016 at 3:41 am by Alex K.)
So, in my just-for-fun hard steampunk novel, an Airship gets stranded far from civilization because they have a Helium or Hydrogen leak. They want to replace the lost buoyant gas by newly made Hydrogen, and I was wondering whether that's feasible. So I'll take all of you brave folks through the numbers.
My template for the airship is the LZ104 "Afrika-Schiff", because it isn't too big, yet has a sufficient range for the story and with 50 tons a lot of payload capability to carry all kinds of nonsense relevant for the story.
![[Image: 300px-LZ_104.jpg]](https://upload.wikimedia.org/wikipedia/commons/thumb/1/10/LZ_104.jpg/300px-LZ_104.jpg)
It has 70 000 m^3 of Hydrogen. I assume that 10% of that are lost in an accident, so 7000 m^3, which is still a lot. The LZ104 would carry 1622 tons of fuel on its mission and was equipped with 5 motors with a whopping 240 horsepower each, corresponding to 180 kilowatts.
Now, my question was, assuming that the crew runs 1 ton of the fuel through one of the motors to generate electricity, how much energy would that be? Assuming perfect efficiency, a ton of petroleum gives you 4100 kWh. A 240 horsepower motor needs to run roughly 24 hours to do convert this amount of oil into energy, so that's realistic.
The question is now, how much Hydrogen do you get from those 4100 kWh of energy? Now, I assume that the crew finds some sort of alcaline material like KOH to pour into the water to do efficient electrolysis, splitting the water into O2 and H2. It turns out that under ideal conditions, one can generate 12 m^3 of H2 from one 1kW. That's good news, because the 4100 kWh would then be enough to make 50000 m^3, i.e. to refill almost the entire airship. This means that if we assume an overall efficiency of like 14% of the overall process of running the motor, making electricity and doing the electrolysis, the ton of oil is enough to replenish the missing 7000 m^3 of Hydrogen. That's not too far off the mark to make it realistic.
My template for the airship is the LZ104 "Afrika-Schiff", because it isn't too big, yet has a sufficient range for the story and with 50 tons a lot of payload capability to carry all kinds of nonsense relevant for the story.
It has 70 000 m^3 of Hydrogen. I assume that 10% of that are lost in an accident, so 7000 m^3, which is still a lot. The LZ104 would carry 1622 tons of fuel on its mission and was equipped with 5 motors with a whopping 240 horsepower each, corresponding to 180 kilowatts.
Now, my question was, assuming that the crew runs 1 ton of the fuel through one of the motors to generate electricity, how much energy would that be? Assuming perfect efficiency, a ton of petroleum gives you 4100 kWh. A 240 horsepower motor needs to run roughly 24 hours to do convert this amount of oil into energy, so that's realistic.
The question is now, how much Hydrogen do you get from those 4100 kWh of energy? Now, I assume that the crew finds some sort of alcaline material like KOH to pour into the water to do efficient electrolysis, splitting the water into O2 and H2. It turns out that under ideal conditions, one can generate 12 m^3 of H2 from one 1kW. That's good news, because the 4100 kWh would then be enough to make 50000 m^3, i.e. to refill almost the entire airship. This means that if we assume an overall efficiency of like 14% of the overall process of running the motor, making electricity and doing the electrolysis, the ton of oil is enough to replenish the missing 7000 m^3 of Hydrogen. That's not too far off the mark to make it realistic.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
