Author Topic: Stainless steel vs aluminum kettle?  (Read 5604 times)

Offline richardt

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Re: Stainless steel vs aluminum kettle?
« Reply #15 on: March 06, 2012, 12:09:40 PM »
Isn't there a better way to conserve the energy, i.e. use a cooler (pro: it is already insulated) and use a smaller RIMS-type module to heat the liquor or the wort?  That way one wouldn't have to worry about heat loss through metal vessels.

I had an HLT using a 10 gal igloo cooler (round) with an element mounted in the side.  Worked fine.  I also have a RIMS setup for my mash tun, and use the RIMS to heat the strike water.  I think Martin was addressing the boil kettle design.  I have a couple of layers of reflectix around my keggle mash tun and that provides sufficient insulation as well as being removable for cleaning.

Yeah, that's what I was wondering about:  Is there a good SS vessel (that's already insulated like a cooler) that could be re-purposed into a BK?

Offline weithman5

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Re: Stainless steel vs aluminum kettle?
« Reply #16 on: March 06, 2012, 12:28:49 PM »
on byo there is a countertop brewing system, (under projects about 7-8 down the list) electric that addresses some of these. note the cooler mash tun and insulated boil kettle.
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Offline hopfenundmalz

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Re: Stainless steel vs aluminum kettle?
« Reply #17 on: March 06, 2012, 01:36:08 PM »
There is another important factor in the selection of material type for kettles and that is heat transfer coefficient. 

Depending on how you are heating your wort and kettle, that should be an important factor.  I formerly heated my kettle on a gas burner.  An aluminum kettle has a far better coefficient of heat transfer than stainless steel.  That means that you will heat your wort quicker in a aluminum kettle. 

Martin, I don't agree with this.  If you look at the Overall Heat Transfer Coefficient the conductivity of the metal is the lowest resistance in the circuit.  If you heat with fire, the gas to metal has the highest resistance, the liquid is the next highest.  If you run the numbers, there is negligable time difference.  I actualy ran a test for 2 pats I had that were the same size and geometry. One was SS and the other was AL.  The SS kettle got to a boil faster!  I expected the AL to be a little faster.  I think it was due to more bubbles in the AL acting as insulators (rougher finish) and more loss of heat through the side walls in the AL.

Aluminum will spread the heat better so you avoid hot spots. 

This explains what I am talking about.  The example is very good.
http://www.engineeringtoolbox.com/overall-heat-transfer-coefficient-d_434.html

Heat transfer is also a function of wall thickness.  Aluminum pots are necessarily thicker.  What is gained in the k value is given back in dx sub w.

This is true. AL has about 1/3 the Young's modulus and 1/3 the shear modulus, so they need to be thicker to be as strong.  Of course not exactly 3 times as thick, as if it were a simple beam for example, h^3 would work in AL favor after some thickness increase.

Having worked on car designs, you learn quickly that making a part out of AL does not result in an automatic weight reduction to 1/3 that of steel.
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Offline mabrungard

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Re: Stainless steel vs aluminum kettle?
« Reply #18 on: March 07, 2012, 08:28:36 AM »

Martin, I don't agree with this.  If you look at the Overall Heat Transfer Coefficient the conductivity of the metal is the lowest resistance in the circuit.  If you heat with fire, the gas to metal has the highest resistance, the liquid is the next highest.  If you run the numbers, there is negligable time difference.  I actualy ran a test for 2 pats I had that were the same size and geometry. One was SS and the other was AL.  The SS kettle got to a boil faster!  I expected the AL to be a little faster.  I think it was due to more bubbles in the AL acting as insulators (rougher finish) and more loss of heat through the side walls in the AL.

Aluminum will spread the heat better so you avoid hot spots. 


Thanks for the info, Jeff.  I'm always interested in learning more from someone that knows better!

I'm assuming that I should still be quite concerned with heat loss through the Al kettle walls.  Last night during testing, I had water boiling at the normal 212F and did a surface temp check with an IR thermometer and it read about 110 to 120 F.  I'd say that insulation will be a desirable thing for that electrically heated kettle.  Does anyone know if the aluminum-foil backed plastic bubble sheet insulation is heat resistant enough to handle 200F+  ??  I don't have the manufacturer's information on the remnant of the insulation roll that I have to check for this info.   I was thinking that a couple of wraps of that bubble sheet with a velcrow seam would make it easy to install and remove as needed for use and cleaning.
 
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Offline punatic

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Re: Stainless steel vs aluminum kettle?
« Reply #19 on: March 07, 2012, 09:34:13 AM »
I have a sanke keg wrapped in Reflectix that is unaffected by the heat at 172.6 degrees F.  I believe 212 degrees would not be a problem either.
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Re: Stainless steel vs aluminum kettle?
« Reply #20 on: March 07, 2012, 09:37:56 AM »
Not really scientific but, I've never seen aluminum in a commercial brewery.

Fortunately, I don't brew in a commercial brewery.
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Offline weithman5

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Re: Stainless steel vs aluminum kettle?
« Reply #21 on: March 07, 2012, 09:43:30 AM »
the electric countertop brewery i referenced on byo website, he does have the kettle wrapped in that bubble wrap type insulation.
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