Water heater design

[Restrell]

Hi there,
Im working in a water heater design and have a question that i think has to do with heat transfer theory.
I have a 0.5 gal tank and a 10 gal tank both with same volumetric flow lets say 2 gpm, both with 12 kw of power( 2 heating elements of 6 kw each). How does the water tank size will affect delta T and why?
Thanks

 

[IRstuff]

I'm not sure what you're getting at. If heat loss is also identical, then delta T would be the same, since the heat loss, by the joule mass flow, is the same

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[gruntguru]

Yes, no difference except from a cold startup. The larger tank outlet will take longer to reach the equilibrium delta T (of about 23*C).

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[MintJulep]

Unless shell losses are non-negligible.

 

[Restrell]

Thanks, thats what I thought but it is a bit counter intuitive and I needed to check it, the key part is the cold startup until thermal equilibrium is reached but delta T has to be the same.

 

[LittleInch]

Grunt guru is correct. The practical issues will be where the heating elements are to establish an even temperature in the big tank, the degree of heat loss difference from the external shell and the probably more than 20 times longer it takes to achieve steady state with your bigger tank from the same initial start point. This is where the intuitive part comes in. On the other hand if your bigger tank then looses heat input it has a much bigger heat store than the smaller one and will tend to smooth out change sin temperature vs flow compared to the bigger unit. All depends on what you want it to do.

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