Explosion of Hydrogen and the Force createrd !

[Vasanth M S]

Hello readers,

 

I was just wondering that Hydrogen in di-atomic state has its capability to explode when lighted with a spark. So in that case what is the amount of Force that is exerted by the explosion of Hydrogen? Does explosion of Hydrogen produce smoke? In that case what if the explosion is to take place with a lot of Oxygen supplied?

 

Please help me answer this and clear my doubts.

 

Thanks in advance.

[swansont]

(I recall reading somewhere that hydrogen technically does not explode, but undergoes a fast burn, though this may just be semantics.) You have to look at the energy of the H2 and O2 bonds, vs the bonds of the H2O that is formed, to see the energy that's released. You go from 1.5 moles of gas to 1 of water vapor, so there is actually a reduction in volume of the product, if it were to remain at the same temperature and pressure.

 

There's no smoke, since there's nothing to form smoke involved if it's just the H2 and O2

[Enthalpy]

For this activity, "explosion" is any combustion including a candle flame, a "deflagration" propagates by the heat or burnt material that ignites still unburnt material at the front, and a "detonation" propagates by the pressure wave. Typically a solid or liquid high explosive detonates.

 

Most gases can either deflagrate or detonate depending on the conditions: mix ratio, initial temperature, also initial pressure, impurities... So do some solids by the way: TNT can burn slowly and badly and needs a blast cap to detonate. In most cases, exploding materials can switch from deflagration to detonation, and without a clearly identified cause, especially if the amount suffices.

 

While methane and natural gas rather easily stay in the deflagration mode, acetylene and more so hydrogen are prone to switch to detonation, so measuring the deflagration speed (only 3m/s for hydrogen in air, 14m/s in oxygen) is dfficult.

 

You can observe a full-size hydrogen boom at the video of reactor #1 at Fukushima dai-ichi (not at #3 which I consider is a vapour expansion). Quite efficient, from a limited amount of hydrogen.

To estimate the explosion pressure, a naive approach would consider 300K and 1atm before, roughly 3000K and (in air) as many moles after, to deduce 10atm. Though, it's known to be an underestimation. A first reason is that the gas mix is already compressed by the wave when it ignites; from 300K to 850K, this supposes 38atm at ignition and then T and P *3.5 would result in 135atm - but this one estimate is too high. A further reason is that detonation wavefronts are not plane waves in real situations - only in experimental setups.

[Strange]

You go from 1.5 moles of gas to 1 of water vapor, so there is actually a reduction in volume of the product, if it were to remain at the same temperature and pressure.

 

Maybe that is why it is not classified as an explosion. Most explosives are liquids or gases which release large volumes of gas (often nitrogen based).

[swansont]

 

Maybe that is why it is not classified as an explosion. Most explosives are liquids or gases which release large volumes of gas (often nitrogen based).

 

That was my guess. Some phase change that leverages the volume that a gas must take up, in addition to being exothermic.

[StringJunky]

Quote

 

Violence of combustion

 

Combustion can vary in degree of violence. A deflagration is a propagation of a combustion zone at a velocity less than the speed of sound in the unreacted medium. A detonation is a propagation of a combustion zone at a velocity greater than the speed of sound in the unreacted medium. An explosion is the bursting or rupture of an enclosure or container due to the development of internal pressure from a deflagration or detonation as defined in NFPA 69.

 

http://en.wikipedia.org/wiki/Flammability_limit

Edited October 29, 2014 by StringJunky

[Strange]

Well, if we are talking explosives, time to link to one of my favourite blogs: the "things I won't work with category" of In the Pipeline.

http://pipeline.corante.com/archives/things_i_wont_work_with/

[Vasanth M S]

Well Thanks guys,

 

I appretiate your answers. But still there are scopes for developing hydrogen fuel. Thats why I got the interest. Anyway I came to know that explosion of hydrogen produces about 25 Joules per liter. I wonder how that can become an alternative to CNG and other hydrocarbons because CNG produces about 2500 Joules per liter. Gosh! We are running out of alternatives.

[swansont]

Well Thanks guys,

 

I appretiate your answers. But still there are scopes for developing hydrogen fuel. Thats why I got the interest. Anyway I came to know that explosion of hydrogen produces about 25 Joules per liter. I wonder how that can become an alternative to CNG and other hydrocarbons because CNG produces about 2500 Joules per liter. Gosh! We are running out of alternatives.

 

Metal hydrides have been around for a while as a storage medium; they limit the amount of hydrogen available in case of a catastrophic incident. I'm not sure what advances might have been made over the years.

 

One thing, though, about the comparison with CNG — hydrogen is not a fuel source, as natural gas is. There is a net gain in available energy when you get natural gas, which is not the case with hydrogen. Hydrogen is a storage/transport medium, more like a battery.

[Enthalpy]

[...]hydrogen produces about 25 Joules per liter. [...] CNG produces about 2500 Joules per liter.

 

Are these bizarre tiny figures for liters of air? Even then, 0.044mol of air, or 0.0093mol of O₂, making 0.019mol of H₂O, would release 4500J. Anyway, hydrogen cars operate already even if not quite satisfactory, so energy density doesn't rule them out. In fact, if hydrogen is stored as a liquid and used in a fuel cell, it's better than hydrocarbons, both at identical mass and at identical volume.

[Vasanth M S]

Using Hydrogen as a liquid releases more energy on combustion then when it is at gaseous state. But then you would need containers to hold fuel with 20 Kelvin range for Hydrogen to be in liquid state. Now making a fuel tank that can remain at 20 K is cost consuming.

[Enthalpy]

That's a bit of metal, some polymer straps, and a stack of plastic films.