High temperature.

[Naplumb]

Hello all. Hypothetical scenario.
I have a cylinder 6 feet tall. 2 feet dia.
An electrical immersion heater is fitted in the top of a cylinder with the fail safe disabled. This is placed 2 feet from the top of the cylinder.
The cylinder has a manual vent at the top to aid venting the air after filling with water and is then shut tight.
Their is a cold feed at the bottom of the upright cylinder feeding water from a cold cistern 10 feet above.
The immersion is energised indefinately with the fail safe disabled.

What happens next ??.
Many Thanks.

 

[metengr]

A hot water heater that EXPLODES.

 

[JStephen]

"It depends".

If there is no backflow prevention, then as the water heats up and possibly boils, you'll just back water up into the cistern.

If there is some sort of backflow preventer, then some sort of rupture would be likely. It could be an explosion, or more gradual.

If the heater is not too high a wattage, you could also just reach an equilibrium where heat loss in the rest of the tank equals heat input at the heater. The contents would have to warm up some for this to happen, which raise pressure or move water somewhere.

 

[Naplumb]

Thanks for the reply.
If a vent is fitted to this set up will any hot water go back up the cold feed ??.

 

[jte]

Ok, since this is posed as a hypothetical, and with the understanding that there is no intent to actually implement such a system (though who'd have thunk this one up without some "experience"?)... With 10' head, you'd have on the order of 20 psig at the bottom of the system. So you could potentially boil the water to 20 psi steam at roughly 250°F. Since the immersion heater loses its heat transfer ability as it transitions from heating water to heating steam, the heating element will start to get hotter than it usually runs while the rest of the system finds some equilibrium as stated above. I'd guess an upper limit system temperature (excluding heating element) of 275°F. Just a WAG, not even a SWAG...

With an open vent with its opening at least as high as the high liquid level in the cistern, I'd guess that the steam will burp out the vent rather than backfeed into the cistern.

jt