Kettle

[GAM]

I'm with Mark M. The lag of heating up the steel alone would make some difference, not to mention the surface of the steel dissipating the heat.

S

[GuingesRock]

I'm with Mark M. The lag of heating up the steel alone would make some difference, not to mention the surface of the steel dissipating the heat.

S

Grrr

I'll prepare my argument later Mark.

We're going to need someone to do the study when the theoretic preamble is done.

[GuingesRock]

Here’s my argument for consideration.

The gas burner will heat the pot by a process of radiation, conduction and convection. Those are the three forms of “heat energy”.

The bottom of a shiny stainless steel pot will deflect radiant heat (think foil hypothermia blanket). A sooted up base will absorb more radiant heat, but will insulate against convection and conduction. A cast iron pot will be more efficient than stainless steel because it will soak up radiant heat and also is a great conductor so will utilize more of the other two forms of heat. A shiny Aluminium pot will do very well with convection and conduction and not do very well with radiant heat.

Aluminum, copper and cast iron are all excellent conductors of heat. That’s why chefs prefer cooking vessels made from those metals. They are efficient, heat up (and cool down) quickly, and on demand, and don’t form hot spots that burn the food. Stainless steel is a very poor conductor of heat and does poorly with radiant heat also. Having a layer of aluminum inside the base does nothing to help this situation with regard to efficiency. A tri-clad bottom is simply there to stop what is essentially a fairly useless cooking vessel, from burning food, by distributing the heat more evenly across the base and reducing hot spots which occur in areas where the heat applied is at its most intense. I don’t see why a tri-clad SS pot should be less efficient than a SS pot with plain SS base. Where did you get that information Mark? Both stainless steel pots would be much less efficient than copper, iron, or aluminum.

A steel plate on top of the burner would efficiently absorb all three forms of heat energy, and because of its good conductivity, it would both spread out the heat to a large area (the entire bottom of the pot) and conduct the heat readily to the pot, thus distributing the heat evenly to the entire bottom surface of the pot. The gas flame on the bottom of a stainless steel pot will not be efficient because a) radiant heat is deflected away and wasted and b) because of the poor (slow) conductivity of the stainless, not much convection and conduction energy will be absorbed by the pot. A lot of it will convect away around the pot and heat up the surrounding air instead.

The cheapest way around poor efficiency and hot spot formation is an aluminum pot. That’s by far the cheapest option any way.

Stainless might be the vessel of choice for a kettle with an element though. There would be much less loss of all three forms of heat and thus would increase efficiency. Stainless would also be better at holding mash temperatures in a mash tun. Imagine you are trying to heat a pot that has an asbestos coating on the outside. It would take endless bottles of propane to heat the damn thing. Then use that pot as a mash tun, or a kettle with an element inside. The second scenario is as perfect as the first scenario is imperfect.

I think the steel plate would efficiently absorb conduction, convection and radiant heat from the gas flame, spread it to a greater area of the bottom of the stainless steel pot, thus facilitating heating of the pot, improving efficiency, and providing a more even distribution of heat to your precious wort.

[Buccaneer]

I'm pretty sure this puts the whole argument to rest. http://www.madsci.org/posts/archives/20 ... .Ph.r.html" onclick="window.open(this.href);return false;

[MitchK]

Just a note: Cast iron is actually a terrible conductor of heat and cast iron pans get hot spots all the time if your pan isn't perfectly sized to your burner. The cast iron fetishism online doesn't make a lot of sense - its only real advantage IMO for cooking is that they're usually HEAVY AS HELL which means they store a ton of heat energy (so your pan doesn't cool way down as soon as your food hits it - a big deal when dealing with shitty residential stoves that would take too long to heat the pan back up). You'll find for 99% of good cookware aluminum or cooper is involved for even heat - either triclad, disc bottom, or pure aluminum being the only real common commercial options.

Basically the problem is that triclad is definitely a better pot than plain stainless for almost anything - but does it matter for wort? Wort itself is a liquid that will itself undergo convection in the pot, with the hottest wort rapidly coming up to the surface and being replaced with cooler wort. I wouldn't bother with a triclad base if I was boiling anything in water - the water itself perfectly spreads the heat around just as well as slapping a disc of aluminum on the bottom would (or better).

[Timelord_]

Just a quick update. Scored a sweet 15 gallons from Dave on Saturday. Hopefully I can put it to use next weekend.

[RossBee]

Just a quick update. Scored a sweet 15 gallons from Dave on Saturday. Hopefully I can put it to use next weekend.

[LeafMan66_67]

Just a quick update. Scored a sweet 15 gallons from Dave on Saturday. Hopefully I can put it to use next weekend.

Excellent choice! Good luck with your new setup!

[mcgster]

I'm pretty sure this puts the whole argument to rest. http://www.madsci.org/posts/archives/20 ... .Ph.r.html" onclick="window.open(this.href);return false;

Nice find, stacking layers on anything inherently lowers your efficiency in any system, particularly heat transfer. That lays it out nicely.


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[GuingesRock]

Stacking layers on anything inherently lowers your efficiency in any system, particularly heat transfer.

Wouldn't that be a function of the thermal conductivity of the metal each layer is made of, and the thickness of each layer, rather than simply the number of layers? ...assuming good contact between the layers that is. Air between layers would insulate.

[mcgster]

Stacking layers on anything inherently lowers your efficiency in any system, particularly heat transfer.

Wouldn't that be a function of the thermal conductivity of the metal each layer is made of, and the thickness of each layer, rather than simply the number of layers? ...assuming good contact between the layers that is. Air between layers would insulate.

No not at all, adding more layers ALWAYS reduces efficiency, you can't add efficiency to a system in heat transfer by adding more layers, even if one is SUPER conductive on top of one that is very poorly conductive. It defies the basic principles of thermodynamics.

[GuingesRock]

Basically the problem is that triclad is definitely a better pot than plain stainless for almost anything - but does it matter for wort? Wort itself is a liquid that will itself undergo convection in the pot, with the hottest wort rapidly coming up to the surface and being replaced with cooler wort. I wouldn't bother with a triclad base if I was boiling anything in water - the water itself perfectly spreads the heat around just as well as slapping a disc of aluminum on the bottom would (or better).

This is the unknown. Thanks for the info on cast iron. The debate moved on there for a bit about efficiency. Randy Mosher gives some good arguments I thought.

I wondered, you sound like you might know about this stuff ... wort isn't water though, or things being boiled in water, it's verging on soup, and is definitely a high sugar solution. I think I managed to burn soup before, not sure, but definitely burnt thin stew so it was visibly burnt and stuck to the bottom. What about just below actually visibly burnt and stuck on, but instead wort solids being overheated and then carried away by the convection currents. You say triclad is better than plain SS, but is aluminum better still? Do they use a lot of aluminum in catering? Do they use SS much?

[GuingesRock]

Stacking layers on anything inherently lowers your efficiency in any system, particularly heat transfer.

Wouldn't that be a function of the thermal conductivity of the metal each layer is made of, and the thickness of each layer, rather than simply the number of layers? ...assuming good contact between the layers that is. Air between layers would insulate.

No not at all, adding more layers ALWAYS reduces efficiency, you can't add efficiency to a system in heat transfer by adding more layers, even if one is SUPER conductive on top of one that is very poorly conductive. It defies the basic principles of thermodynamics.

It's more complicated though. What if the extra layer was of a material that would absorb radiant heat rather than reflecting it away? You also need to take into account you are using a gas flame open to the air with high heat loss from convection to the air around the pot. The quicker and more efficiently the layer next to that open flame can absorb the heat, the less will be lost to the air, with a potential to improve efficiency.

Placing a pot on a flat uniform heat source is a simpler scenario to consider.

[mcgster]

Its not really more complicated than that, the difference in radiant heat absorbed is negligible, look at the heat transfer formulas for calculating heat transfer on a gas stove, the radiant heat transferred even in the best case is minuscule, it doesn't even come close to the loss you get from the different materials used. Sorry Mark i think you are off base on this one. You are misunderstanding how heat transfer takes place driven by the delta T between materials, the more steps you add in that process, aside from adding insulation to retain transferred heat, will lessen that. There is just no way adding a piece of scrap metal, copper, gold, anything, in between the pot will improve this.

[GuingesRock]

look at the heat transfer formulas for calculating heat transfer on a gas stove

Sounds like you may have something of relevance. Would you post them up so we can throw into the mix.

I haven't looked up anything. Just trying to think around the issue. Would love to have something like that to look at. It sounds like radiant heat to a pot on a gas flame is negligible, but what kind of pot is that? Grilling food under a grill is nearly all radiant heat. Radiant heat is what you feel when you hold your hands out to be warmed from a gas fire, or stand by a bonfire. It's there.

[Buccaneer]

If you could add a layer of some highly conductive metal to something and increase heat reaching that something, people would have stacks several inches/feet/miles thick and a candle would heat an entire neighbourhood.

[mcgster]

If you could add a layer of some highly conductive metal to something and increase heat reaching that something, people would have stacks several inches/feet/miles thick and a candle would heat an entire neighbourhood.

Hahahaha

[GuingesRock]

If you could add a layer of some highly conductive metal to something and increase heat reaching that something, people would have stacks several inches/feet/miles thick and a candle would heat an entire neighbourhood.

Talking about whether it might be possible to collect more of the heat that is actually being produced by the flame, with less escaping to the air.

[GuingesRock]

TTYL

[Jimmy]

If you could add a layer of some highly conductive metal to something and increase heat reaching that something, people would have stacks several inches/feet/miles thick and a candle would heat an entire neighbourhood.

Talking about whether it might be possible to collect more of the heat that is actually being produced by the flame, with less escaping to the air.

That's what a heat shield is for.

[Buccaneer]

Can you collect it? Sure, there's some substance that will absorb more. It's still got to cross some interface, though, so you're still losing heat. And you need to remember that the material itself isn't going to transfer 100% of the heat it receives, so as the article said, you're heating the material, the container, and the contents. Like everything, there's probably a way to throw money at the problem and eke out a few more calories, but it's still a lossy system.

[mcgster]

If you could add a layer of some highly conductive metal to something and increase heat reaching that something, people would have stacks several inches/feet/miles thick and a candle would heat an entire neighbourhood.

Talking about whether it might be possible to collect more of the heat that is actually being produced by the flame, with less escaping to the air.

You can certainly capture more heat energy into that plate and prevent it from escaping to the environment but more won't transfer to the pot.

If the diameter of your pot is 14", this gives you a surface area of about 1 square foot, the only heat you transfer to your pot will occur in that 1 square foot of surface area, even if your plate was a box to truly capture more of the heat, the heat is going to transfer to your wort based on the delta T in that 1 square foot, the difference in delta T drives your rate of transfer, the plate inherently lowers that delta even if it does pick up some extra heat, you are dissipating the heat over an extra surface, adding an extra delta T into the equation.

[CorneliusAlphonse]

Want me to whip together a FEA model of this situation? Could model thin stainless, thin stainless with plate, and thin aluminum. But I could also just tell you what the difference is going to be: the thin stainless is going to have more extreme hot spots on the inside surface, while the other two should pretty comparable with more even temperatures. The inside surface will be notably hotter in the aluminum pot I think. The aluminum pot will lose more heat through the sides, while the stainless with plate will take more heat to heat up the plate/lost through imperfect contact between plate and pot, leaving the thin stainless as (probably) the most energy efficient, or maybe thin aluminum.

PS I'm not actually gonna do a model, but I could sketch a temperature distribution thing probably

PPS I'm glad you got a pot from Dave, timelord, despite the derailing of your thread!

[GuingesRock]

We need a pot and a plate and a burner. Keep the burner running at the same heat. Boil 2 gallons in the pot and measure how long it takes to boil and then put plate under pot and repeat.

[gm-]

You can easily try this at home on your stove, put a small pot inside of a bigger pot and boil some water, then try it again without the bigger pot. I can guarantee the small pot alone will be quicker.