7 ms·

How would this work? Surely sunlight can't create enough heat to ionize a gas (creating plasma?). Why don't the whole hydrogen atoms go through the membrane t

How would this work? Surely sunlight can't create enough heat to ionize a gas (creating plasma?). Why don't the whole hydrogen atoms go through the membrane to the lower pressure area? How does he alternate which side is heated? How does he cool the other side?

Groxx 16y ago
any source of energy will have a chance of causing far more energetic particles, if not directly then through particle interactions. For the same reason, water far below boiling will steam. As to the rest, can't help you there. IANAPP :)
MaysonL 16y ago
The maximum heat you can get from sunlight is the temperature of the sun: definitely hot enough to ionize most gases.
- shasta 16y ago
  Right. Cuz the photons are the same temperature as the sun. That's why sun photons feel warm.
  - aphyr 16y ago
    It's more true than you might think. http://en.wikipedia.org/wiki/Plancks_law http://en.wikipedia.org/wiki/Plancks_law
  - MaysonL 16y ago
    see: http://www.physicsforums.com/showthread.php?t=349697 http://www.physicsforums.com/showthread.php?t=349697
    - shasta 16y ago
      Interesting, thanks. It seems plausible that it isn't possible to redirect light from a uniform temperature black body to produce a higher temperature somewhere else. I'll have to think about it more, though. The thermodynamical argument made in that thread seems flawed to me.
anthonyb 16y ago
Sure it can - you just have to focus the sun's rays into a smaller area. The sun delivers on the order of 1000W per sqm during the day, so (eg.) focusing 100 sqm into 1 sqm == 100,000W. 12 hours of daylight will then give you a theoretical production of 1.2MWh per day, but it's usually a lot less, due to the angle of the sun in the morning/evening and inefficiencies in your energy capture.
- kjuhygtfrde 16y ago
  On HN we obey the 2nd law of thermodynamics
  - anthonyb 16y ago
    That entropy always increases? How exactly does that apply in the case of focusing photons?
    - kjuhygtfrde 16y ago
      Another way of stating it is that heat flows from hot->cold. You can't concentrate the light/heat from a blackbody source to more than the temperature of the source. So you can't focus sunlight to more than 6000k however many mirrors you use.
      - btilly 16y ago
        The laws of thermodynamics do not prevent energy from flowing from cold to hot. They just say that for that to happen, entropy elsewhere must increase more. As a trivial example disproving your claim, energy from the Sun can be collected in solar panels that can be used to run devices that can hit any temperature you want. For an extreme example, for fusion experiments they produce temperatures of over 11,000,000 degrees C. For another trivial example, most of us have refrigerators that can transport heat energy from a colder place (the inside of the fridge) to a warmer place (your kitchen).
    - ramchip 16y ago
      Disclaimer: not a physicist. My intuitive understanding is that, as you heat the absorber, it becomes hotter and hotter, until it reaches the same temperature as the sun's surface. At this point, the absorber (also a blackbody) radiates just as much energy as it receives from the sun; thus there is no more heat exchange. Otherwise, you would be taking two objects at the same temperature and making one hotter and the other one colder with no work from outside the system, violating thermodynamics. There is a more formal study in solar energy books like (http://books.google.com/books?id=81WI2LwrpkcC&lpg=PA25&ots=PZpR4ybY16&dq=limit%20temperature%20blackbody&pg=PA25#v=onepage&q&f=false http://books.google.com/books?id=81WI2LwrpkcC&lpg=PA25&#...) or (http://www.physics.drexel.edu/~jenks/Solar%20Energy.pdf http://www.physics.drexel.edu/~jenks/Solar%20Energy.pdf) (PDF, page 21 onwards is quite relevant).
ursablanco 16y ago
At a guess, it doesn't need to create a full-on plasma, just needs a lot Hydrogen ions hitting the membrane. A small amount of ionization will suffice - sort of like 'micropayments' or a long tail phenomenon. Because that's what the membrane filters do. See: http://en.wikipedia.org/wiki/Proton_exchange_membrane http://en.wikipedia.org/wiki/Proton_exchange_membrane http://en.wikipedia.org/wiki/Proton_conductor http://en.wikipedia.org/wiki/Proton_conductor Mainly they work on size - small versus really small. Again, at a guess, it doesn't need to cool the other side - it's not a temperature gradient, it's a concentration gradient. And since the ions are being reacted back to H2 at a brisk rate, it's not a big problem. The more thermal energy you could maintain in the ions the better, because they wouldn't need as much heating once they'd been recycled. It has a whiff of perpetual motion machine to it. Maxwell's Demon, I think.
gvb 16y ago
> How would this work? Surely sunlight can't create enough heat to ionize a gas (creating plasma?). He isn't ionizing the gas, he is increasing the gas pressure by heating it. "Only instead of using those pressure gradients to move an axle or a wheel, he’s forcing ions through a membrane." See next for why that is important. > Why don't the whole hydrogen atoms go through the membrane to the lower pressure area? He uses a semi-permeable membrane http://en.wikipedia.org/wiki/Semipermeable_membrane http://en.wikipedia.org/wiki/Semipermeable_membrane. They also have use in chemical applications such as batteries and fuel cells. The membrane blocks the atoms, but allows the ions (protons) through. It does require a substantial amount of pressure for it to work. That is where the heat -> pressure comes into effect, and why the reconstituted hydrogen on the "cold" size has to be compressed and pumped back into the "hot" side. While this sounds a little like a perpetual motion machine, it isn't because the sun's heat is adding the energy that is being extracted via the electrons. > How does he alternate which side is heated? How does he cool the other side? He heats one side and cools one side, no alternating. The heating (and cooling) cause a pressure differential, which drives the reaction via the semi-permeable membrane. --- I suspect there are some pretty substantial challenges remaining before this becomes a sizable / viable energy source. It sounds like it is related to proton exchange fuel cells, except instead of using the catalyst + oxidant to drive the reaction, it is using pressure. Refs: http://en.wikipedia.org/wiki/Fuel_cell#Proton_exchange_fuel_cells http://en.wikipedia.org/wiki/Fuel_cell#Proton_exchange_fuel_... http://auto.howstuffworks.com/fuel-efficiency/alternative-fuels/fuel-cell2.htm http://auto.howstuffworks.com/fuel-efficiency/alternative-fu...
- tocomment 16y ago
  So if the sunlit side is under higher pressure, how do the hydrogen atoms return to that side? I must still be missing something. Also, is there really enough hydrogen ionizing at 400C?
  - gvb 16y ago
    > So if the sunlit side is under higher pressure, how do the hydrogen atoms return to that side? I must still be missing something. The article says it is compressed in order to move it back to the high pressure side. > Also, is there really enough hydrogen ionizing at 400C? I don't believe (traditional) ionization is occurring. My guess is that it works at the molecular level like reverse osmosis works with salt water to form fresh water. http://en.wikipedia.org/wiki/Reverse_osmosis http://en.wikipedia.org/wiki/Reverse_osmosis The dissociation of the hydrogen atoms into protons and electrons is through heat and pressure, facilitated by the semi-permeable membrane. Note that the membrane is key and is very unique. Johnson [...] proved he could make a ceramic membrane capable of withstanding temperatures above 400 degrees Celsius. A semi-permeable plastic membrane is non-trivial. A semi-permeable ceramic membrane that passes protons, strips electrons, and blocks hydrogen atoms while running at 400^C has to be really, really tough to do.
tlb 16y ago
The effect is pretty straightforward and not hard to make work in a lab. The problem is that it works at very high temperatures, and ion-permeable membranes degrade quickly at those temperatures. Anything sufficiently hot will randomly eject atoms and evaporate, even ceramic. It sounds like his work is an improved ceramic membrane, but it's not useful unless it lasts thousands of hours at full temperature, with temperature cycling every day.

Groxx 16y ago

any source of energy will have a chance of causing far more energetic particles, if not directly then through particle interactions. For the same reason, water far below boiling will steam. As to the rest, can't help you there. IANAPP :)

MaysonL 16y ago

The maximum heat you can get from sunlight is the temperature of the sun: definitely hot enough to ionize most gases.

shasta 16y ago
Right. Cuz the photons are the same temperature as the sun. That's why sun photons feel warm.
- aphyr 16y ago
  It's more true than you might think. http://en.wikipedia.org/wiki/Plancks_law http://en.wikipedia.org/wiki/Plancks_law
- MaysonL 16y ago
  see: http://www.physicsforums.com/showthread.php?t=349697 http://www.physicsforums.com/showthread.php?t=349697
  - shasta 16y ago
    Interesting, thanks. It seems plausible that it isn't possible to redirect light from a uniform temperature black body to produce a higher temperature somewhere else. I'll have to think about it more, though. The thermodynamical argument made in that thread seems flawed to me.

anthonyb 16y ago

Sure it can - you just have to focus the sun's rays into a smaller area. The sun delivers on the order of 1000W per sqm during the day, so (eg.) focusing 100 sqm into 1 sqm == 100,000W. 12 hours of daylight will then give you a theoretical production of 1.2MWh per day, but it's usually a lot less, due to the angle of the sun in the morning/evening and inefficiencies in your energy capture.

kjuhygtfrde 16y ago
On HN we obey the 2nd law of thermodynamics
- anthonyb 16y ago
  That entropy always increases? How exactly does that apply in the case of focusing photons?
  - kjuhygtfrde 16y ago
    Another way of stating it is that heat flows from hot->cold. You can't concentrate the light/heat from a blackbody source to more than the temperature of the source. So you can't focus sunlight to more than 6000k however many mirrors you use.
    - btilly 16y ago
      The laws of thermodynamics do not prevent energy from flowing from cold to hot. They just say that for that to happen, entropy elsewhere must increase more. As a trivial example disproving your claim, energy from the Sun can be collected in solar panels that can be used to run devices that can hit any temperature you want. For an extreme example, for fusion experiments they produce temperatures of over 11,000,000 degrees C. For another trivial example, most of us have refrigerators that can transport heat energy from a colder place (the inside of the fridge) to a warmer place (your kitchen).
  - ramchip 16y ago
    Disclaimer: not a physicist. My intuitive understanding is that, as you heat the absorber, it becomes hotter and hotter, until it reaches the same temperature as the sun's surface. At this point, the absorber (also a blackbody) radiates just as much energy as it receives from the sun; thus there is no more heat exchange. Otherwise, you would be taking two objects at the same temperature and making one hotter and the other one colder with no work from outside the system, violating thermodynamics. There is a more formal study in solar energy books like (http://books.google.com/books?id=81WI2LwrpkcC&lpg=PA25&ots=PZpR4ybY16&dq=limit%20temperature%20blackbody&pg=PA25#v=onepage&q&f=false http://books.google.com/books?id=81WI2LwrpkcC&lpg=PA25&#...) or (http://www.physics.drexel.edu/~jenks/Solar%20Energy.pdf http://www.physics.drexel.edu/~jenks/Solar%20Energy.pdf) (PDF, page 21 onwards is quite relevant).

ursablanco 16y ago

At a guess, it doesn't need to create a full-on plasma, just needs a lot Hydrogen ions hitting the membrane. A small amount of ionization will suffice - sort of like 'micropayments' or a long tail phenomenon. Because that's what the membrane filters do. See: http://en.wikipedia.org/wiki/Proton_exchange_membrane http://en.wikipedia.org/wiki/Proton_exchange_membrane http://en.wikipedia.org/wiki/Proton_conductor http://en.wikipedia.org/wiki/Proton_conductor Mainly they work on size - small versus really small. Again, at a guess, it doesn't need to cool the other side - it's not a temperature gradient, it's a concentration gradient. And since the ions are being reacted back to H2 at a brisk rate, it's not a big problem. The more thermal energy you could maintain in the ions the better, because they wouldn't need as much heating once they'd been recycled. It has a whiff of perpetual motion machine to it. Maxwell's Demon, I think.

gvb 16y ago

> How would this work? Surely sunlight can't create enough heat to ionize a gas (creating plasma?). He isn't ionizing the gas, he is increasing the gas pressure by heating it. "Only instead of using those pressure gradients to move an axle or a wheel, he’s forcing ions through a membrane." See next for why that is important. > Why don't the whole hydrogen atoms go through the membrane to the lower pressure area? He uses a semi-permeable membrane http://en.wikipedia.org/wiki/Semipermeable_membrane http://en.wikipedia.org/wiki/Semipermeable_membrane. They also have use in chemical applications such as batteries and fuel cells. The membrane blocks the atoms, but allows the ions (protons) through. It does require a substantial amount of pressure for it to work. That is where the heat -> pressure comes into effect, and why the reconstituted hydrogen on the "cold" size has to be compressed and pumped back into the "hot" side. While this sounds a little like a perpetual motion machine, it isn't because the sun's heat is adding the energy that is being extracted via the electrons. > How does he alternate which side is heated? How does he cool the other side? He heats one side and cools one side, no alternating. The heating (and cooling) cause a pressure differential, which drives the reaction via the semi-permeable membrane. --- I suspect there are some pretty substantial challenges remaining before this becomes a sizable / viable energy source. It sounds like it is related to proton exchange fuel cells, except instead of using the catalyst + oxidant to drive the reaction, it is using pressure. Refs: http://en.wikipedia.org/wiki/Fuel_cell#Proton_exchange_fuel_cells http://en.wikipedia.org/wiki/Fuel_cell#Proton_exchange_fuel_... http://auto.howstuffworks.com/fuel-efficiency/alternative-fuels/fuel-cell2.htm http://auto.howstuffworks.com/fuel-efficiency/alternative-fu...

tocomment 16y ago
So if the sunlit side is under higher pressure, how do the hydrogen atoms return to that side? I must still be missing something. Also, is there really enough hydrogen ionizing at 400C?
- gvb 16y ago
  > So if the sunlit side is under higher pressure, how do the hydrogen atoms return to that side? I must still be missing something. The article says it is compressed in order to move it back to the high pressure side. > Also, is there really enough hydrogen ionizing at 400C? I don't believe (traditional) ionization is occurring. My guess is that it works at the molecular level like reverse osmosis works with salt water to form fresh water. http://en.wikipedia.org/wiki/Reverse_osmosis http://en.wikipedia.org/wiki/Reverse_osmosis The dissociation of the hydrogen atoms into protons and electrons is through heat and pressure, facilitated by the semi-permeable membrane. Note that the membrane is key and is very unique. Johnson [...] proved he could make a ceramic membrane capable of withstanding temperatures above 400 degrees Celsius. A semi-permeable plastic membrane is non-trivial. A semi-permeable ceramic membrane that passes protons, strips electrons, and blocks hydrogen atoms while running at 400^C has to be really, really tough to do.

tlb 16y ago

The effect is pretty straightforward and not hard to make work in a lab. The problem is that it works at very high temperatures, and ion-permeable membranes degrade quickly at those temperatures. Anything sufficiently hot will randomly eject atoms and evaporate, even ceramic. It sounds like his work is an improved ceramic membrane, but it's not useful unless it lasts thousands of hours at full temperature, with temperature cycling every day.