Half a croissant, on a plate, with a sign in front of it saying '50c'
h a l f b a k e r y
Ask your doctor if the Halfbakery is right for you.

idea: add, search, annotate, link, view, overview, recent, by name, random

meta: news, help, about, links, report a problem

account: browse anonymously, or get an account and write.




Compressed gas used to generate electrical power
  [vote for,

Batteries suffer from a number of problems: They contain hazardous materials. If you don't use them soon enough, they die, and sometimes corrode the device you intended for them to power.

Rechargeable batteries are somewhat better, in that they corrode less often, and can be recharged if they die. Unfortunately, early nickel-cadmium batteries gave rechargeable batteries a crippling bad rap by marketing 1 volt rechargeable batteries for use in 1.5 volt non-rechargeable battery receptacles. The resulting underpowered performance has been assumed to remain with any kind of standard rechargeable battery.

Frankly, I'm not sure that a battery is really the be-all-end-all in power storage anyway. Losses are pretty significant, both with the initial storage, and over time. This makes them far less than ideal in emergency situations.

Thus, I bring you GASPERIES, which instead of storing power electrically, will store it in the form of a compressed gas.

Typical gasperies will include a gas cylinder, "air-powered" engine, electrical generator, a capacitor, A solenoid, and a timer.

Initial electrical power will be stored in the capacitor. When you turn on your gaspery powered electrical device, the capacitor will discharge, powering the solenoid to open the gas cylinder, and reconnect the timer circuitry for use later on. With the cylinder open, the air powered engine will kick in, and cause the generator to produce electrical power.

When you turn off the electrical device, the circuit will be broken, and the solenoid, devoid of power, will switch closed once more. As this occurs, the air powered engine, and generator will begin to die at a predicted rate which is sufficient to recharge the capacitor.

I've been looking around for figures and such, but can't seem to get anything really definite. What is clear is that if no other gas suffices, CO2 cartridges would likely contain sufficient power to operate a device of this nature. Larger batteries might allow for a simple compressed gas cylinder capable of recharging via a home compressor, or gas station air pump.

Assuming a proper seal on the device, losses over time will be negligible, something I cannot say for traditional batteries that may die after a few days inside a hot car.

Gasperies might also have a number of other benefits over traditional batteries: Possibilties for recharging exist, if not, CO2 cartridges are becoming ubiquitous thanks to paintball and airsoft enthusiasts.

As the compressed gas is released, it will produce a cooling effect, quite desirable since electronics operate more efficiently at lower temperatures.

Also, as compressed gas is used in "extreme" activities, such as the use of pneumatic hand tools, scuba diving, and air gun activities, these will not suffer the stigma attached to "Weak rechargeable" batteries caused by the NiCad fiasco.

Certain battery sizes will likely not be replacable by gasperies, and certain uses may be inappropriate for some gasperies, but I suspect there would be a viable market somewhere.

ye_river_xiv, Aug 08 2008

Energy Density http://en.wikipedia...wiki/Energy_density
[MisterQED, Aug 08 2008]

Pnu-power http://www.pnu-power.com
compressed air battery [pashute, Sep 12 2011]


       The power loss from the energy conversion would be too great to make this feasible. It's better to store the energy in its intended form or have a very efficient converter.
Cedar Park, Aug 08 2008

       Which scale ?
wjt, Aug 08 2008

       There's the hydrogen fuel-cell, which is a different take on the idea (the energy is converted by combustion, rather than here by (de)compression)
zen_tom, Aug 08 2008

       For some reason I read this whole thing looking for a punchline. Maybe it’s the name, maybe I need more sleep...   

       The problem is energy density and the need for heat. I was hoping to find a good link, but I have failed so far because it is a little complicated by the need for heat.   

       As you know compressed CO2 stores as a liquid, which boils to create the gas you use to run whatever. The pressure you get depends on the temperature of the CO2 so if you take off too much gas, it gets cold and the pressure and power available drops.   

       Even in airguns CO2 is being replaced by N2 because it packs more punch as long as you container can hold the pressure, but even then you only have about a third of the energy density of rechargables per Wikipedia’s “Energy Density” page. (link)
MisterQED, Aug 08 2008

       //but even then you only have about a third of the energy density of rechargables per Wikipedia’s “Energy Density” page.//   

       Wait... What?   

       According to that page, a NiCad battery has energy density by mass (Mj/kg) of 0.14-0.22 A lead acid battery (Like those in cars, and jump starters) has energy density by mass of 0.09-0.11, and an energy density by volume (Mj/L) of 0.14-0.17, and a practical recovery of 75-85%.   

       Compressed air at 20 bar and 12 Celcius, on the other hand has an energy density by mass of 0.27, and by volume of 0.01. Granted, by volume, the energy density of this compressed air sucks, but by mass, it's much better than lead/acid.   

       Liquid nitrogen, according to this page has an energy density of 0.77 by mass, and 0.62 by volume, about three to six times better by volume, and better by almost a factor of ten by weight.   

       As I stated, certain uses may be inappropriate... possibly most uses...   

       But if liquid nitrogen can outperform lead-acid in energy density by volume and weight, (as it apparently does unless I cannot read a chart) then there is definitely one very obvious use: Jump starters.   

       With liquid nitrogen besting lead acid 3-6 times in energy storage by volume, and almost ten times in energy storage by weight, it probably wouldn't take all that much work to make a nitrogen storage tank, and energy generator as described that, even after losses due to inefficiency, was at least comparable to existing lead-acid battery jump starters. As these lose their charge within a few months, all you would need is a good seal to have a very marketable product.   

       FYI, a google search for liquid nitrogen air guns brought me up essentially nothing. the top link was NASA's web page, followed by the wikipedia entry on air guns, where CO2 cartridges were the most highly praised device. I'd like to see some actual links regarding energy density of liquid nitrogen versus CO2 cartridges... if they exist.   

       Regarding the CO2's supposed loss of energy due to cooling, there are plenty of places to find info. BB guns fired at a rate of less than a bullet each five seconds apparently do not suffer from this problem. As each of those pellets is imparted with a significant amount of energy, I suspect we can devise a slow leak with a sufficiently efficient air engine/generator to prevent the cooling from being a serious problem. Indeed, if we want gasperies to last anywhere near as long as regular batteries, a very slow leak indeed will be necessary.
ye_river_xiv, Aug 09 2008

       //all you would need is a good seal//
The storage dutration is an advantage of compressed gas. The standard little CO2 cylinder may last hundreds of years. But it's not recommended in a "hot car".
Amos Kito, Aug 09 2008

       It seems like you could store a lot of energy in compressed gas but nature is two steps ahead with that "phase change" thingy.
WcW, Aug 09 2008

       //I have to admit I thought the air car was a joke, but after ye_river_xiv's research its not that barking mad - see link.//   

       Oh, don't thank me. My research came up with essentially nothing. Thank Mr. QED, who found the energy density link. All I did was read the chart... and ignore the fact that Lithium ion batteries are absolutely spectacular in terms of energy density, whereas the NiCad and Lead acid batteries are crap...   

       Well, I also considered the fact that a toy car with two AA batteries can barely go uphill, whereas a toy car with one CO2 cartridge can go uphill and across a room. One might also consider energy density in vermin-killing ability, where the CO2 cartridge seems to have a clear advantage over the 12 volt battery, but I'd rather keep that as a thought experiment, and not test it empirically.
ye_river_xiv, Aug 10 2008

       Okay, I hate writing a long anno, then realizing the discussion is years old, so I'm going to post it anyway.   

       //I also considered the fact that a toy car with two AA batteries can barely go uphill, whereas a toy car with one CO2 cartridge can go uphill and across a room.//   

       But the electric will continue to barely go uphill all day, while the C02 cartridge will make it once.   

       For liquid nitrogen (or any liquified air component) you need to take into account the bleed off required to keep the rest of the system at cryogenic temperatures until use. This will eat up a significant portion of your fuel during idle periods. The alternative, of course, is to keep it in an extremely heavy tank. How heavy?   

       A 12g CO2 cartridge (weight of gas) weighs 40.9g total. The tank weighs two and a half times as much as the gas inside. There is, of course the chance for some savings in larger spherical tanks, and you can go to lighter weight composites, but the tank is still a significant weight adder.   

       Once you count in the weight of the bottle/tank to store the compressed air, it is roughly comparable with lead acid batteries. At that point in place of recovery from the battery, you have a relatively inefficient air motor and an electrical generator. (You also technically need to consider these weights in your energy/unit weight calculations).   

       This ignores the fact that almost all batteries on any scale smaller than automotive are NiCad or Li+ with considerably better energy density than your compressed air at the start.
MechE, Sep 12 2011

       Some forms of berries give me gas, but that depends usually on how many I eat.
RayfordSteele, Sep 12 2011


back: main index

business  computer  culture  fashion  food  halfbakery  home  other  product  public  science  sport  vehicle