Electrolysis under pressure

Discussion in 'Physics & Math' started by Harro, Oct 29, 2008.

  1. Harro Registered Senior Member

    Messages:
    113
    I have an Idea about making hydrogen underwater, and want to do a feasibility study but don’t know where to start. It could be deep out at sea or the bubbles could feed though a tube full of water and travel up the tube at surface level.

    If I then captured the hydrogen and oxygen in a container and mechanically captured the energy as it ascends to the surface how deep would I need to go so it could perpetually power the electrolysis to produce more Hydrogen Oxygen gas? As a continuous cycle.

    I was thinking of attaching aerodynamic down turned cups attached to a belt, the bubbles feed into the cups. The captured bubbles drive the belt that powers a generator. As the cups ascend, the cups on the other side of the belt face up to reduce drag on the way down. When they reach the top they flip over releasing the gas into a container.

    Numbers I think I need to know

    How much energy is required for electrolysis under how much pressure?

    Do the bubbles accelerate as they near the surface having less atmospheres of pressure forcing down on them?

    How much resistance is the water having an effect on the aerodynamic cups on the way up and on the way down?

    What depth would I need to go, how long would the pulley system need to be?

    What’s the potential energy of x volume of Hydrogen and Oxygen gas under y amount of meters under water?

    What’s the efficiency of the generator?

    Am I asking the right questions, have I forgotten something?

    My intuition tells me I’d be breaking thermal dynamics laws as Id be able to get free energy from burning Hydrogen and Oxygen. What do you think?

    Even if it was to add some solar energy to the generator would this be a more efficient way of making Hydrogen?

    Would I be better of drilling deep into the earth and capturing the energy as the gas bubbles up, so I only have air resistance on the cups?
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. kevinalm Registered Senior Member

    Messages:
    993
    Won't work. Conservation of energy. What you aren't aware of is that the energy required for electrolysis is pressure dependent. Guess how much more energy is required at depth.

    Please Register or Log in to view the hidden image!

     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. MacGyver1968 Fixin' Shit that Ain't Broke Valued Senior Member

    Messages:
    7,028
    One question I had...if you released a gas at the bottom of the ocean, would the bubbles float to the surface at the same rate the whole way up or would pressure change the speed any?
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. Harro Registered Senior Member

    Messages:
    113
    lol..conservation of energy is the word I was looking for.

    cant you teach me how pressure has an effect on electolysis?
     
  8. kevinalm Registered Senior Member

    Messages:
    993
    Chem class was a long time ago, but iirc the equation governing electrolysis is concentration dependent. Now when a gas is involved in the reaction, the concentration is determined by the volume density of the molecules of the gas, so the pressure directly affects the concentration.

    Basically, the voltage a electrolytic reaction runs at is defined at STP, but varies depending on many factors, including pressure, temp, concentration etc.
     
  9. spidergoat pubic diorama Valued Senior Member

    Messages:
    54,036
    I think you would be better off trying to capture the geothermal heat of a black smoker, or maybe a sterling engine.
     
  10. Read-Only Valued Senior Member

    Messages:
    10,296
    And that's not all.

    Please Register or Log in to view the hidden image!



    Since the ocean contains sodium chloride (and other salts), you couldn't produce any hydrogen - you'd only get sodium hydroxide along with other hydroxides.
     
  11. kevinalm Registered Senior Member

    Messages:
    993
    It would definately be a complex relltionship. Pressure, temp, bubble size. In fact, iirc an air bubble deep enough will sink. I know some deep sea submersibles use gasoline in the ballast tanks instead of air because gasoline won't compress much (compared to air) and will always float.
     
  12. Harro Registered Senior Member

    Messages:
    113
    Ok thanks guys and gals, looks like i'll have to come up with a new idea.
    Would hydrogen electrolysis efficiency improve at altitude?
    Maybe a hydrogen production plant in the Himalayas.
     
  13. Brm123 Registered Member

    Messages:
    1
    I thought of this years ago. Still trying to work the math. Very complex issue. Mechanical conversion is very inefficient. Also have to consider the ability to create a sufficient volume of gas at a given depth and temperature to achieve buoyancy. At 1000 meters average temp is 6 degrees (C). Pressure is about 1000 decibars.
     
  14. Read-Only Valued Senior Member

    Messages:
    10,296
    Sorry, but there's really no point in beating yourself to death with the math. The greatest problem with the idea lies in the fact of energy losses in conversion and friction. For example, it's generally accepted that the efficiency of electrolysis is something less than 50%. Couple that with the other losses and it simply isn't worth the effort.
     

Share This Page