For starters - Yes, I am aware of the Hindenburg disaster hydrogen (H2) is flammable and if not kept separate from oxygen (including the depleted oxygen level of normal atmosphere) can burn. It does however take a very hot spark (over a 1,000 degrees F) to ignite and only when it has been mixed with oxygen or air in correct ratio. So long as you keep it separate from air and don't build your air-ship out of flammable canvas doped skin that ignites at much lower temperature and burns hot enough to then open up the H2 gas envelopes and mix it with the air and then ignite it - not a problem, especially on an unmanned vehicle.
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Okay, that stated, neutral buoyancy air-ships unlike any other aircraft do not require power even outside power such at thermals or up-drafts to stay aloft and only require power to move. This combined with their large surface are allows for potentially the perfect purely solar powered aircraft.
It is also true that there is always some very low but constant gas seepage (not enough to provide sufficient % fuel mix to be flammable) through the membrane walls of the gas cell(s) that means that buoyancy is constantly lost slowly over time and gas replenishment is necessary, this is especially true with pressurized gas envelopes on air-ships with non-rigid frames (blimps). Short term this issue is often addressed with ballast which is dropped to reduce the payload carried, among the most common and safest ballast used is water. Long term the only solution is lifting gas replenishment. For a hydrogen lifting gas airship, especially a solar powered one, this offers a unique potential of being able to replenish lifting gas in-flight from the water ballast through low voltage safe electrolysis of the water ballast splitting the H2O molecule and replenishing the lifting gas with the H2 produced and off-venting the oxygen to the atmosphere in an unmanned craft, or providing enriched oxygen to the crew of a manned craft (although care must be taken to ensure oxygen enrichment is not high enough to create a combustion hazard).
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I have a small RC blimp that I am experimenting with hydrogen lifting gas filling instead of helium fill which it was designed to use (ready made kit aircraft). At this point I have been producing the hydrogen through electrolysis of water using stainless steel electrodes in a solution of water with NaOH electrolyte. Hydrogen production has been incredibly slow with my present apparatus which is of the "Hofmann voltameter" type, homebuilt with PVC pipe and stainless steel tubing to form the electrodes (entire inner surface of the tubes are electrodes upon which the electro-chemical reaction takes place) with the PVC plastic being used as an insulating connecting joint in-between to provide the ionic bridge and it can take hours to fill the little blimp to sufficient pressure to hold its shape.
I've got to build a better apparatus capable of converting more electricity into larger amounts of hydrogen quicker and preferably in a smaller, lighter, and more compact system especially if in a larger scale home-build I am planning to do on-board lifting gas replenishment through electrolysis from the water ballast.
I've looked at HHO gas generators which are used in some internal combustion automotive applications to provide an injection of pure hydrogen and oxygen gas at the atmospheric intake for a short burst in power on demand (similar results to nitros injection systems) that run off the vehicles 12VDC electric system and store up pure hydrogen and oxygen gas at pressure until needed. Those systems use a stack of very thin stainless steel plates seperated from each other by mere millimeters to form a reasonably small cell capable of reasonably high gas production but they make no attempt to keep the hydrogen and oxygen gas produced separated but rather collect and store them as a mix under pressure something that not only will not work for my application but I consider rather dangerous to say the least. Mixing pure hydrogen gas with pure oxygen gas especially in a pressurized container where pressure reduces the necessary ignition temperature is like building a bomb. Hydrogen is safe and can't burn or explode so long as you keep it separate, its when it mixes with air that things can go wrong, mixing it with pure oxygen is really asking for it especially in a pressurized mix that lowers the ignition temperature.
I can use the same basic design though of thin plates stacked very close together and I've already sourced some nice think stainless steel rolled stock that should maximize surface area of the electrodes while minimizes size and weight.
The question is how to get the plates as close together as possible (closer together make more gas faster due to allowing higher current passage and also reduces the physical size and weight of the water/electrolyte mix the cell is filled with) while still keeping the hydrogen gas bubbles generated at the negatively charged plates separated from the oxygen gas bubbles generated at the positively charged plates.
I need some kind of non-electrically involved middle membranes between the plates that allow the free flow of ions in the liquid while preventing gas bubbles from crossing over to the other side and the gases mixing. It must also be non-degraded by the caustic water NaOH electrolyte mixture in the cell.
Anyone ever worked with water electrolysis cells before? Anyone know what I could use for that middle membrane?
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Okay, that stated, neutral buoyancy air-ships unlike any other aircraft do not require power even outside power such at thermals or up-drafts to stay aloft and only require power to move. This combined with their large surface are allows for potentially the perfect purely solar powered aircraft.
It is also true that there is always some very low but constant gas seepage (not enough to provide sufficient % fuel mix to be flammable) through the membrane walls of the gas cell(s) that means that buoyancy is constantly lost slowly over time and gas replenishment is necessary, this is especially true with pressurized gas envelopes on air-ships with non-rigid frames (blimps). Short term this issue is often addressed with ballast which is dropped to reduce the payload carried, among the most common and safest ballast used is water. Long term the only solution is lifting gas replenishment. For a hydrogen lifting gas airship, especially a solar powered one, this offers a unique potential of being able to replenish lifting gas in-flight from the water ballast through low voltage safe electrolysis of the water ballast splitting the H2O molecule and replenishing the lifting gas with the H2 produced and off-venting the oxygen to the atmosphere in an unmanned craft, or providing enriched oxygen to the crew of a manned craft (although care must be taken to ensure oxygen enrichment is not high enough to create a combustion hazard).
------------------------------------------------
I have a small RC blimp that I am experimenting with hydrogen lifting gas filling instead of helium fill which it was designed to use (ready made kit aircraft). At this point I have been producing the hydrogen through electrolysis of water using stainless steel electrodes in a solution of water with NaOH electrolyte. Hydrogen production has been incredibly slow with my present apparatus which is of the "Hofmann voltameter" type, homebuilt with PVC pipe and stainless steel tubing to form the electrodes (entire inner surface of the tubes are electrodes upon which the electro-chemical reaction takes place) with the PVC plastic being used as an insulating connecting joint in-between to provide the ionic bridge and it can take hours to fill the little blimp to sufficient pressure to hold its shape.
I've got to build a better apparatus capable of converting more electricity into larger amounts of hydrogen quicker and preferably in a smaller, lighter, and more compact system especially if in a larger scale home-build I am planning to do on-board lifting gas replenishment through electrolysis from the water ballast.
I've looked at HHO gas generators which are used in some internal combustion automotive applications to provide an injection of pure hydrogen and oxygen gas at the atmospheric intake for a short burst in power on demand (similar results to nitros injection systems) that run off the vehicles 12VDC electric system and store up pure hydrogen and oxygen gas at pressure until needed. Those systems use a stack of very thin stainless steel plates seperated from each other by mere millimeters to form a reasonably small cell capable of reasonably high gas production but they make no attempt to keep the hydrogen and oxygen gas produced separated but rather collect and store them as a mix under pressure something that not only will not work for my application but I consider rather dangerous to say the least. Mixing pure hydrogen gas with pure oxygen gas especially in a pressurized container where pressure reduces the necessary ignition temperature is like building a bomb. Hydrogen is safe and can't burn or explode so long as you keep it separate, its when it mixes with air that things can go wrong, mixing it with pure oxygen is really asking for it especially in a pressurized mix that lowers the ignition temperature.
I can use the same basic design though of thin plates stacked very close together and I've already sourced some nice think stainless steel rolled stock that should maximize surface area of the electrodes while minimizes size and weight.
The question is how to get the plates as close together as possible (closer together make more gas faster due to allowing higher current passage and also reduces the physical size and weight of the water/electrolyte mix the cell is filled with) while still keeping the hydrogen gas bubbles generated at the negatively charged plates separated from the oxygen gas bubbles generated at the positively charged plates.
I need some kind of non-electrically involved middle membranes between the plates that allow the free flow of ions in the liquid while preventing gas bubbles from crossing over to the other side and the gases mixing. It must also be non-degraded by the caustic water NaOH electrolyte mixture in the cell.
Anyone ever worked with water electrolysis cells before? Anyone know what I could use for that middle membrane?