Comments on: US Army creates powder that recharges equipment in the field

By: Scipio Americanus

Scipio Americanus — Sat, 09 Sep 2017 14:29:46 +0000

Something the powdered aluminum power system is very useful for is powering long-duration unmanned underwater vehicles.

By: Alrenous

Alrenous — Sat, 09 Sep 2017 13:43:21 +0000

0.1 * 140 MJ = 14 MJ, 14,000 kJ. 40 kW-h is still far lower than 220.* Yes, that kW number makes no sense. It's not supposed to be kilowatt-hours. It's not 220 kW for three minutes; that's 40,000 kJ. Either the researcher was black-out drunk or the journalist was. Also, what the hell is a 'nanogalvanic.' Sounds like they've nano-mixed the catalyst, essentially, as something is preventing the aluminum from oxidizing directly with the air. (Instead it needs to be stored in airtight containers or it will oxidize with ambient humidity. I wonder what happens if you touch it with a sweaty hand.) New Scientist confirms it's an alloy. Notably, an alloy won't release the full 0.11 kg of hydrogen per kilogram. While they're at it, NS dives head-first into perpetual motion. Essentially this powder lets you store and release aluminum smelter energy. This is not useful for powering cars. It's good for survivalist gear, including backup generators. Though recharging your phone by pouring water into it sounds...interesting. *(Incidentally, too much rounding. It's 16 MJ to two sig figs. I mention it in case anyone else has numbers like these stick in their head forever. Or 13 MJ if you use the lower 120 MJ/kg number.)

By: Ross

Ross — Fri, 01 Sep 2017 17:24:47 +0000

Damn it you’re all making me want to look up the exothermic reactants and energy balance for cement now. Thanks a lot.

By: Isegoria

Isegoria — Thu, 31 Aug 2017 23:40:43 +0000

A New Scientist piece suggests that the powder yields aluminum oxide and hydrogen, with near 100-percent efficiency, so, if my rusty chemistry skills haven't failed me, each kilogram of aluminum should release 0.1 kilograms of hydrogen, for 4 kilowatt-hours of energy, or 1,400 kilojoules.

By: Scipio Americanus

Scipio Americanus — Thu, 31 Aug 2017 17:18:50 +0000

Assuming they actually meant 220 kilojoules of energy being released over 3 minutes, and that we use the figure Candide gives for the energy density of hydrogen, I come up with a maximum of 0.93 grams (10.4 liters)per second of hydrogen being produced by the kilo of aluminum catalyst. Presumably it's not 100% efficient and we also get some heat, but as a max figure that at least looks more physically plausible.

By: Candide III

Candide III — Thu, 31 Aug 2017 15:10:59 +0000

Burning aluminum in air yields 31 MJ/kg, that is 8.6 kWh/kg. There is just no way reacting it with water yields 220 kWh/kg. No chemical fuel yields that much. Hydrogen is the most energy-dense fuel per unit weight and it’s only 140 MJ/kg, that is 39 kWh/kg.

By: Isegoria

Isegoria — Thu, 31 Aug 2017 13:08:18 +0000

Another point of comparison is the energy density of most chemical batteries, which is on the order of one-tenth of one kilowatt-hour per kilogram.

By: Isegoria

Isegoria — Thu, 31 Aug 2017 12:55:35 +0000

By comparison, a kilogram of gasoline stores 46 megajoules of energy, or 13 kilowatt-hours, and a kilogram of hydrogen stores three times that, or 39 kilowatt-hours. So, if one kilogram of this aluminum powder produces 220 kilowatt-hours of energy, that suggests that it frees 5.6 kilograms of hydrogen, in three minutes. Have a big balloon ready. (And have a ready supply of water.)

By: Wang Weilin

Wang Weilin — Thu, 31 Aug 2017 01:04:35 +0000

220KW in 3 minutes! Sounds more like a slow motion explosion.

By: Slovenian Guest

Slovenian Guest — Wed, 30 Aug 2017 20:00:18 +0000

EEVblog - Voltage vs Power vs Energy