Question

I'm editing an article on BLEVE explosions and want to explain the amount of energy released when a 40 gallon water heater at 100 C bursts, flashing hot water to steam.

Are these calcs right?

http://inspectapedia.com/plumbing/BLEVE_Explosions.php has the details:

The chat window doesn't let me post the math (see the web article) but I calculate that flashing 40 gal hot water to steam at 100 C releases energy of about 184 pounds of TNT

Answer 1

I've briefly scanned the link. Here's my back of the envelope guess.
Interesting looking question, albeit in gallons and pounds of expl TNT.
Lots of mixed units here.
water density = 1000 kg/m3. water latent heat of vaporisation = 2.3 10^6 J/kg
1 gallon = 4.5 ^-3 m3.
40 gal ~ 0.16m3
1m3 = 1000 kg
0.16m3 = 160kg
160kg x 2.3 x 10^6 J/kg = 368,000,000 J = 368 MJoules ???
Could be some "pop" that.
Equiv to 184 pounds of TNT ?
Either way, I'm not sure I'd like to be hanging around there.
Hope this helps a little
http://perendis.webs.com

Answer 2

Thank you, this reply was very helpful. I'll add your calculations to the article I cited.
If you want to be cited as a technical reviewer/contributor to our BLEVE article contact me at editor@InspectApedia.com
Kudos.

Answer 3

I've just had a quick look at the "chemistry definition" of TNT expls. It's from small numbers of moles to about a factor of 10 more moles of something or other in a very short space of time. Nitro is pretty scary too !

Answer 4

@Daniel_Friedman I hope that I've sent you an email (and that you've received it)
osprey2015hotmail.com