What Would Happen if a Supercap with 318 Wh-kg Energy Explodes?

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Discussion Overview

The discussion revolves around the potential consequences of an explosion from supercapacitors (supercaps) with a specific energy of 318 Wh-kg, particularly in the context of their use in hybrid vehicles. Participants explore the mechanisms of failure, comparisons to traditional explosives, and the implications of such energy densities in various applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express curiosity about the explosion power of supercaps with high energy density, comparing it to traditional explosives and questioning their safety in hybrid vehicles.
  • There is a discussion on the difference between overheating and electric field explosions, with one participant suggesting that the explosion of a capacitor is more likely due to overheating rather than energy release from the electric field.
  • Another participant highlights that explosiveness is defined by power density rather than energy density, noting that while supercaps have lower energy density than gasoline, their explosiveness is a separate consideration.
  • Concerns are raised about the potential for supercaps to explode if physically damaged, particularly in crash scenarios, and whether certain types of supercaps (e.g., pseudocapacitance-based) are inherently less dangerous.
  • Calculations are presented regarding the pressures involved in supercap operation, with one participant questioning how an explosion could occur given the attractive forces between capacitor plates.
  • There is speculation that if a supercap were to short circuit, it could lead to an explosion due to thermal expansion, suggesting that protective measures would be necessary for their use in vehicles.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the safety and explosiveness of supercaps, with multiple competing views on the mechanisms of failure and the implications of their energy densities. The discussion remains unresolved regarding the conditions under which a supercap might explode.

Contextual Notes

Limitations include assumptions about the conditions leading to explosions, the definitions of energy and power density, and the specific characteristics of different supercap technologies. The discussion does not resolve the uncertainties surrounding these factors.

Stanley514
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There is a claims that some scientists have developed supercaps with specific energy as high as
318 Wh-kg.Some ot them are using pseudocapacitance principle http://www.springerlink.com/content/w542251jg6034207/"
Im really wondering what would be the power of explosion of such type supercap if it will be installed, let's say, in a hybrid auto?I remember some wrighter wrote that he was terribly scarried by exposion of capacitor with millifarad capacitance in an old-type TV.
So what will happen if supercap with million times greater energy will explode?And also why military is still using traditional explosives?Would not 318 W-kg supercaps be a new word?
Also what about terrorists who will be able to make or purchase such a supercaps?
I whish to know what type of supercap is less dangerous: these based on pseudocapacitance,double electrolitic or graphene based type?
 
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Stanley514 said:
...supercaps with specific energy as high as
318 Wh-kg... what would be the power of explosion of such type supercap if it will be installed, let's say, in a hybrid auto?...
318 watt-hr/kg ~1.1 106 J/kg.
Energy density of ordinary gasoline is roughly 3 107 J/kg.
So they have a way to go to even match the energy density of good old fashion gasoline.
The exploding capacitor you mentioned most likely had burst from excess fluid pressure caused by overheating--not from electric field energy.
 
So they have a way to go to even match the energy density of good old fashion gasoline.
That`s exactly true,but explosiveness of any explosive material is defined by power density rather than energy density.This is why TNT is used instead of gasoline or natural gas.Because it could explode much faster than a gas.
The exploding capacitor you mentioned most likely had burst from excess fluid pressure caused by overheating--not from electric field energy.
What is difference between overheating and electric field explosion?For example if hybrid auto on supercaps will get into a crash and supercap will be physically distructed what power of explosion could be?
Those supercaps which use effect of pseudocapacitance are less dangerous or not?
 
Stanley514 said:
...What is difference between overheating and electric field explosion?
For fun we can calculate some pressures. For the capacitor in the TV, assume 1 millifard at 300Volts. Guess a can size of 2" diameter by 3" long. then the pressure calculates to
(1/2).001 F (300 Volt)2 /(pi (1 in)2 3in)~3 atm.
For the super Cap mentioned assuming a mass density of 2 gm/cc we get
(2 gm/cc)*318 watt hr/kg~2.2 104 atm.
Which is certainly impressive, but these are all negative pressures. The force between capacitor plate is attractive. How do you get an explosion out of that?

Regarding the exploding TV capacitor: Those capacitors were sealed into a metal can filled with liquid electrolyte. A short circuit could heat the contents and cause it to burst. But that is not what I would call an electric field explosion. It's like leaving an aerosol can in a car with the windows rolled up on a very hot day.
 
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The force between capacitor plate is attractive. How do you get an explosion out of that?
A short circuit could heat the contents and cause it to burst.
You answered yourself to you question.Also I suggest that when supercap is physically distructed it will probably short circuited and explode because short circuit will cause a thermal expansion of very high power and hence explosion.I think that large supercups may never by used in hybrid vehicles unless they will not provide huge cevlar casing for protection.But they still may be used in wind or solar power apps...
 

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