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High temperature.

High temperature.

High temperature.

(OP)
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.

RE: High temperature.

A hot water heater that EXPLODES.

RE: High temperature.

"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.

RE: High temperature.

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

RE: High temperature.

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

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