Thermal layers in keggle?

Ran a test on my electric keggle (HLT) last night. 25 degree gradient from bottom of keggle to the area above the element.

Element is about 3" or 4" off bottom. Temp sensor is near bottom. Turning a recirc pump on fixed this, but I was hoping to not have to do this.

Is this normal? Any scathingly brilliant ideas here? TIA.

Recirculation or moving the temperature sensor are your only choices. Hot water rises.

No cure, except agitation.

JKoravos said:

No cure, except agitation.

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I was agitated. Didn't help.

When I was brewing last night I noticed something peculiar about my keggle. Temp rise was pretty constant till it hit 206/207F ish. Then it would just kind of hover there and then would shoot up 3 degrees very rapidly then drop back down to 206/207. It will do this for a while (larger the volume the more it cycles) and it gradually works its way up to 212 while doing this. So there is a fair amount of stratification and convection going on as it approaches boil. Running the recirc pumps evens it out some but they don't seem to perform as well once it hits a good boil.

This is an e-keggle with the element about 3 inches off the bottom. I wonder if conventional keggles perform the same way.

CodeRage said:

I wonder if conventional keggles perform the same way.

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Dunno: my keggles have never seen a flame. I assume that if the heat is applied to the bottom, and it rises, the heat dissipates better through the column. But then it is amazing how wrong some of my assumptions are.

passedpawn said:

I was agitated. Didn't help.

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LOL.

....

passedpawn said:

Dunno: my keggles have never seen a flame. I assume that if the heat is applied to the bottom, and it rises, the heat dissipates better through the column. But then it is amazing how wrong some of my assumptions are.

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This is a problem I see at work fairly often (I'm a process engineer at a chemical company. I work with 2000 gallon vessels on a regular basis). You're going to see some temperature gradient unless you take steps (as noted above) to minimize it. If you keep your heat source low in the keggle, then the heated water will have a chance to rise to the top and displace the cooler water there (where it's lost some heat due to evaporation and radiation), providing decent mixing current.

This is all theoretical, of course. In practice this doesn't work nearly as well until you get a full, vigorous boil going. In the plant we have agitators in the vessels, you're using a recirc pump. Either way works (though for us a pump that can handle liquids with viscosities in the tens of thousands of centipoise is just not as feasible as a multi-blade agitator!). You just have to give all the material a chance to come in contact (or at least close proximity) to the heat source, and to keep the batch well mixed. That's just how it is with larger vessels, unfortunately. Convection currents just don't give you enough agitation unless you're at full boil, and even then it might not give you complete mixing. Sorry for the non-scientific description, my fluid mechanics is a little rusty!