What boils faster?

[joejaz]

What boils faster aluminum or stainless steel?

 

[evanmars]

Aluminum, it boils at 2467*C. Steel boils at around 3000*C


Aluminum is also a better conductor of heat than stainless steel.

 

[SenorWanderer]

Aluminum, it boils at 2467*C. Steel boils at around 3000*C


Aluminum is also a better conductor of heat than stainless steel.

yes! you rule!

 

[Llarian]

Aluminum, it boils at 2467*C. Steel boils at around 3000*C.

Hah. I was going to make the same comment, but I figured somebody would beat me to being a smartass.

-D

 

[Funkenjaeger]

Just to put some numbers on it, according to wikipedia the thermal conductivity of stainless steel is 15 W/(m*K), and that of aluminum is 237. Even without knowing much about thermodynamics, seeing that aluminum has a 15x higher thermal conductivity than stainless steel has got to mean something.

 

[McKBrew]

If you look at alot of the stainless steel pots, they all have a layer of aluminum sandwiched in the bottom to make for a faster boil. Look at the description of the Megapot here.

http://www.northernbrewer.com/kettles.html

 

[rohanski]

Swmbo.......

 

[Vagrant]

Aluminum, it boils at 2467*C. Steel boils at around 3000*C


Aluminum is also a better conductor of heat than stainless steel.

haha, that's classic. Goes well with your avatar too =)

 

[david_42]

The layer of aluminum in high-end SS pots isn't to speed the heat transfer, it is intended to spread the heat out and prevent hot spots. This allows higher flames and faster cooking.

Given the thickness of our pots, the differences in conductivity are meaningless. I get the same scorch pattern for the stand, aluminum or SS, which is why I use a heat diffuser.

 

[homebrewer_99]

WATER!!!!

Well, at least all the smart asses have checked in.

I'm in good company!!

 

[z987k]

copper, or silver for that matter!

 

[shafferpilot]

aluminum = cheaper cost
stainless = easier to clean/doesn't corrode

Other than that, you won't notice ANY differences.

 

[z987k]

And the time difference on the boil, I guarantee Aluminum boils water faster than SS. I have 2 small copper pots that we boil water in for tea because it takes considerably less time than any SS pot we own.

 

[mr x]

It's all relative. Mass of metal involved, surface area, etc...

All things being equal one is most likely going to be faster, but that's the catch - all things rarely are equal. And faster may only be by seconds, which is practically equal in the non tech lab world.

 

[z987k]

q = k A dT / s or amount of energy transfered, lookup Fourier's Law.

My aluminum pot: 136BTU/hr-ft-F * (3.14*.5ft^2) * (212F-70F) / 0.010416667ft ~ 1455KW
Same pot in 430SS: 8.11*.785*142/0.010416667ft ~ 88KW

Now do the SS with more surface area, say instead of a 1ft circle, 2 foot circle(keggle?), and 1/16" thickness.

8.11*(3.14*1ft^2)*142/0.005208333ft ~ 694KW

So even given more surface area and less material in between the Al still transfers much more heat, more than twice.

Further, in time to boil 1 gallon of water:

3628.672g * (100C-21C)= 286665cal
1 KWh = 860424cal
So we need .333KWh to boil our water.
.333KWh/694KW=.000479827h
.333/88=.003784091h
.333/1455=.000228866h
twice as long with the equal SS

Now this is assuming some things, but I think it's safe to say that Aluminum will boil water much faster than Stainless.
BTW, I think the math is right, I referenced the formulas and used a calculator

 

[mr x]

Convert that time to minutes and seconds.

 

[FlyGuy]

Now this is assuming some things, but I think it's safe to say that Aluminum will boil water much faster than Stainless.
BTW, I think the math is right, I referenced the formulas and used a calculator

Nicely proven, assuming the math is correct -- I did not check because it seems to affirm what those of us who have used both know: aluminum pots just plain transfer heat better than SS pots. (They also cool more quickly if you are using an ice bath for chilling!)

 

[mrfocus]

Convert that time to minutes and seconds.

0.000479827h * 3600 s/h = 1.7273772s

0.000228866h * 3600s/h = 0.8239176s

Hum, even if the burner is completely heated up... that seems incredibly low.

 

[mr x]

The mathematical formulas are a good starting point for a proposed thesis. The problem is, does your mathematical model fit the application. My experience having done things like this before and looking at the post above is that the model seems to simple. Real world applications can take pages of complex calculations for a correct analysis.

Will it make much difference? Who knows. The greater the volume boiled the greater the difference in time most likely. So that's another consideration when someone says 'much faster'.

I applaud the application of science by z987k. Very good (aside from what appears to be a math error). I would like to try a real replication and see what happens. I'll have to look around the lab and see if I can find something to make an accurate comparison. I've got tons of glass and stainless, aluminum may be hard to find...anyway just my 2c.

 

[z987k]

I did that pretty late last night I was guessing there would be an error somewhere thats why I put thing thing at the bottom, I'll have more time at 5 to re-look it and post sources so you can look at everything. The amount of energy transfered isn't dependent on the volume of water. If you look at Fourier's Law, in english it says energy = specific heat of material * surface area * temperature difference / thickness of the material.
Just looking at the time part, it may be that my gallons into grams is off, therefore making those times a bit to small.
Also in reality it's going to be much more complicated due to a number of things one of the top of my head is the heat loss in the sides of the pot, but I think overall it's a safe bet that Aluminum being ~17 times as conductive as SS, Aluminum will boil something faster.

 

[mr x]

The amount of energy required to be transferred is somewhat dependent on water volume. A large volume will require more energy to get to the same temperature, that's why 5 gallons takes longer to boil than 1 gallon.

 

[Whiskey]

Something else to keep in mind is the quality or thickness of the pot. I thin walled aluminum turkey fryer may get the liquid boiling faster due to the aluminums high heat transfer you will also loose more heat long the side then say a thicker stainless steel pot of the same size, so while the aluminum pot is heating up the bottom much quicker it stands to reason that the entire volume of wort may hot heat as quickly. This may not have much effect on a short squat 5 gallon pot but will have an effect on a taller pot like a 10 gallon one.

 

[shafferpilot]

sounds like we need a "scientific" side by side test if we're ever gonna answer a question like this one

 

[mrfocus]

AHA, I have found the error.

Ok, so Fourier's Law tells us how much heat can be transfered per second!!! (dQ/dt = Watts / second)

surface area with 8 inches (typical diameter of a stove top and close enough for a propane burner used with a turkey fryer) = 0.2032 meters

surface area of a circle = Pi * (radius ^2)
3.1416 * (0,1016 ^2)
3.1416 * 0.010322 = 0.0324m^2

For stainless steel:
dQ/dt= k * A * (dT/dx) (thermal conductivity times surface area times temperature difference divided by distance between objects)
dQ/dt= 15 * 0.0324m^2 * (80C / 0.05m) (0.05m = 2 inches, I'm including some leeway for wether it's a propane burner or a stove top).

dQ/dt= 777.6W/s

Basically, a stainless steel pot of 8 inches in diameter placed on a stove top 5cm from it can transfer a maximum of 777W/s.

Aluminium:
replace k (15) by 237
12286W/s

So, what does this mean? It basically tells us how many watts the material can transfer in a second...

Well, everybody using a turkey fryer and a stainless steel pot are waisting a bunch of energy, although probably protecting their wort from burning, since the average stove element is about 2000Watts, I have no clue how many Watts a turkey fryer is...

Also, that means that people using stove tops are better off with aluminium as well, seeing how they will get the most from their burner.

The big problem now is how not to burn the wort, yet use the energy efficiently.

BTW: The amount of Joules needed to heat up water is: 4.184 J / (g * K)

So, let's say for 7 gallons of pure water:

4.184 J * (7gallons *3.78 l/g * 1000g/l) * (373 - 293K)

4.184J * 26460g * 80K = 8856691,2Joules...

1 Watt = 1 Joule per second...

Let's say the stove top has a 2000W element, someone using Stainless steel would be limited by the pot, thus the maximum amount of wattage would be 777W.

8856691,2 Joules / (777 joules / second) = 11398s = 3.16 hours!!

Now, that same person, trying to boil with an aluminium pot on the same stove top would reach the limit of the element, thus 2000W would be transfered!

8856691,2 Joules / (2000 joules / second) = 4428s = 1.23 hours!

Now, for those of you doing things like extract brewing with only 3.5 gallons to boil, the numbers would be:

4.184J * (3.5g * 3,78l/g * 1000g/l) * 80degrees K

4428345.6Joules

Stainless steel: 5699s = 1.58hours

Aluminium: 2214s = 0.61hours

Soooooo, what can we conclude?

Aluminium does transfer heat in a greater quantity per second. For someone using a stove top, the difference is about 2.57 times faster, and this is limited by the wattage of the element.

I still don't have absolute faith in my calculations, and I would like some people to tell us their setup (aluminium or stainless steel), what kind of burner they use, how much water they are boiling and how long it takes to boil.

BTW: Sorry if this is such a long post...

 

[Fingers]

Yeah, but that's all just a little vague, mrfocus. Could you come up with a little more detail?

 

[mr x]

Here's the problem with that post. Those numbers don't look right.

I just don't believe it takes 1 hour longer to boil 3.5 gallons of water.

 

[mrfocus]

Here's the problem with that post. Those numbers don't look right.

I just don't believe it takes 1 hour longer to boil 3.5 gallons of water.

Well, one of the problems is that I sort of averaged between a turker fryer and a stove element.

For a stove element, dx would most likely be something like 0.02m (2cm) if you count the thickness of the stainless steel/aluminium and the uneveness between the stock pot and the element.

Thus, dQ/dt = 15 * 0.0324 * (80 / 0.02) = 1944W/s

Which is basically the same amount as the maximum of your element, so about 2278s = 38 minutes = 0.63hours.

I just did some testing.

4L of water at 23C to 100C.

dQ/dt = 15 * 0.0324 * (77 / 0.02) = 1871.1W/s

4.184J/(g * K) * 4000g * 77K = 1288672Joules

1288672 / 1871.1 = 688s = 11.5 minutes, in a perfect world (without any heat loss, etc.)

Actual time was 15.5 minutes... Considering the heat lost on the under side of the element, the heat lost through vapor, etc. it's actually quite close...

 

[mr x]

Just brewing this morning. I put 3 gallons cold water ( probably less than 16 C - I'll check later) in a 3 gallon ss pot (thin stock pot) on a large burner on high (from cold). Time to boil was 35-37 min.

 

[z987k]

Mrfocus, I'm really glad you went through and re-did the calculations, I was about to one night and then I was like, aw f-this to much time.

BTW the turkey fryers range from ~65,000BTU to 250,000BTU so roughly 20KW to 73KW. (BTU/hr * .293 = W) I know mine is toward the bottom of that range.

I think this should be the end all thread Steel vs Aluminum.

 

[Orfy]

Nah.....

There'll be another 2 next week.