Can Heat Intensify

[roker]

Hypothetical question for heating engineers on a hot water tank.
without going into fine mathematical details.
If I have a hot water tank that is 60 deg in the top half and 20 deg in the bottom half and I stir it up it will be roughly 40 deg throughout.
is it reasonable to assume that this would settle back to 60deg and 20deg or even 70deg top and 10deg bottom?
thereby acting as a heat intensifier

 

[newirishman]

Not sure if I understand correctly what you mean.
anyways, it won’t be a 60in upper half and 20 in lower, it’ll be rather continuous. Heating the water in the upper half creates a flow, therefore mixing the water up over time.
In your example, after stirring, if all the water is on 40 degrees uniform, it will just cool out slowly, unless you keep heating it.
It won’t “settle back”.

 

[Branz]

roker: no, from basic thermodynamics: heat moves from hot to cold, thereby reducing the amount of energy which is available to do work..
\newirishman: did you mean to heat the bottom, which will rise up as is less dense? otherwise it wont mix

 

[roker]

Not sure if I understand correctly what you mean.
anyways, it won’t be a 60in upper half and 20 in lower, it’ll be rather continuous. Heating the water in the upper half creates a flow, therefore mixing the water up over time.
In your example, after stirring, if all the water is on 40 degrees uniform, it will just cool out slowly, unless you keep heating it.
It won’t “settle back”.

but the hot water will rise to the top again

 

[Micks'r]

but the hot water will rise to the top again

No.
What "hot water"? If the water is all the same temperature after it's mixed up, there is nothing to drive the stratification you're talking about.

 

[roker]

good point Mick'sr. it will need more heat to to rise to the top.

 

[Leo]

The temperature of any quantity of the water can not rise unless external energy is applied.

Over time, unless the tank is insulated against all loss (practically impossible), the temperature of the water will drop. This drop will not be uniform across the entire contents of the tank, and as water around the edges or connectors cools, it will sink to the bottom. You'll end up with a slow circulation of water within the tank with warmer water at the top, cooler at the bottom until the point it reaches equilibrium with the external environment.

 

[Micks'r]

Good point |Leo, you're correct of course. I would expect less than 5 degC differential top to bottom during the cooling process.