Does a larger pot come to a boil faster?

[dallasdb]

Okay so now let me explain the title.

I'm wondering if a wider diameter (squattier?) pot will bring water to a boil faster due to more contact area for the flame to hit on the bottom?

In particular, I'm wondering if I brew a 5 gal batch in a 20 gal kettle (squattier by design) would get to a boil faster than say a 9 gal kettle which naturally would have a smaller diameter aka less direct contact area with the flame.

Hopefully I explained it well enough. What do you think?

Anyone actually have experience with this before?

 

[unionrdr]

On my electric stove,the slightly skinnier 4G kettle will boil with no lid & 3 gallons of water. The 5G with 3 gallons of water needs the lid on to boil. So I think the slightly skinnier lower total volume kettle boils faster.

 

[dallasdb]

On my electric stove,the slightly skinnier 4G kettle will boil with no lid & 3 gallons of water. The 5G with 3 gallons of water needs the lid on to boil. So I think the slightly skinnier lower total volume kettle boils faster.

Hmmm... interesting.

I didn't mention in the OP I was thinking in particular of an open flame.

I wonder in your instance if the electric stove boils the slightly skinnier kettle because the diameter of the kettle matches the electric element better aka no excess pot hanging on the outside of the element not getting heat.

In my application, the propane burner flame would natural spread out across the bottom of the pot. I can get the flame screaming and it will even come up the sides of the pot.

Anyone have experience with this on a burner?

 

[MisterTipsy]

This was copied from a physics forum:

Water will boil (roughly) equally fast in two different shaped vessels given the same heat input.

Water will evaporate faster from a vessel with more surface area exposed to the atmosphere than from one with less surface area exposed to the atmosphere.

This also means that if you heat the water up to slightly less than the boiling point, the one with more surface area will evaporate faster and as a result, keeping the temperature steady will require more heat input.

http://www.physicsforums.com/showthread.php?t=257601

 

[sonex]

I believe it depends on the surface area of the heating sourse and the material of the bottom of the pot. a tri layered pot bottom transfers heat faster and more even than a single layer pot. once the bottom of the pot exceeds the size of the heating area there is no more gain on heating effectiveness.

 

[dallasdb]

This was copied from a physics forum:



http://www.physicsforums.com/showthread.php?t=257601

That's really interesting... I understand the increased evaporation aka increased surface area exposed to the atmosphere.

But wouldn't that be the same for increased area exposed to flame (larger bottom diameter of the pot directly exposed to the heat source).

Oh and BTW, the guy that posted the answer you quoted only has 7 posts on that forum! I'm not sure if I trust a newbie.

I'm going to continue my search.

 

[dallasdb]

This link on Yahoo Answers contradicts the other forum. (ya ya I know it's Yahoo Answers but the first answer is logical and makes sense)

However, a few responses down in the link I provided, one responder poses some great points.

Copied from the Yahoo Answers link

" wonder if the size of the pot doesn't matter. If the same amount of thermal energy is applied into the system, then the change in temperature of the water should be the same. The only thing I can think that would cause a larger pot to permit water to boil faster would be if the larger pot prevented more energy from leaving the system. That is, the smaller pot allows thermal energy (heat) to "escape" because a flame would warm the air around it instead of just the pot.

The problem I see with "larger surface area so faster heating" is that one must then assume that the surface area will heat to the same exact temperature in the same amount of time despite its size. If there is larger surface area then it is true that it will heat faster, but it is also true that it will require more energy to heat a larger surface area."

 

[MisterTipsy]

That's really interesting... I understand the increased evaporation aka increased surface area exposed to the atmosphere.

But wouldn't that be the same for increased area exposed to flame (larger bottom diameter of the pot directly exposed to the heat source).

Oh and BTW, the guy that posted the answer you quoted only has 7 posts on that forum! I'm not sure if I trust a newbie.

I'm going to continue my search.

The person who answered the question has 19,000+ posts and has the title Physics Forum Mentor.

 

[dallasdb]

I think this is the best answer I've found so far. Another reliable source... Wiki Answers!
"The answer depends on the heat source. If none of the heat is wasted then it takes exactly the same length of time.
For the pot to be larger one would assume that the base takes up a greater area than a small pot. The small pot on a large gas burner would waste energy because heat would rise up the sides of the pot and be wasted whereas the larger pot would absorb more of the heat."

Anyone disagree or have other comments?

 

[dallasdb]

The person who answered the question has 19,000+ posts and has the title Physics Forum Mentor.

I guess I should've looked at the responses! I thought you were referring to the OP's post "I know it will take exactly the same amount of energy to bring each vessel to the boil."

My bad!

Here is my issue, "Water will boil (roughly) equally fast in two different shaped vessels given the same heat input."

The "same heat input" can be controlled if you are electric brewing.

BUT if you have a propane burner this doesn't apply IMO. It is the same heat source but I don't believe they will both boil at the same rate due to differences in wasted energy.

So my hypothesis is a larger pot on a propane burner will have less wasted energy.

What do you think?

 

[passedpawn]

Over a flame:
A wider pot will come to boil faster. Much of a heat energy from a flame is lost to the air. Wider pots capture more of this energy. The ideal pot would also have a tube up the middle, like a bundt pan, to increase the surface area even more.

Over an electrical stove:
Wider is better until the pot is as wide as the element; then no difference

Electrical element inside the pot (i.e., electric brewpots):
Doesn't matter

Yes, there is faster evaporation with a wider pot, but that is irrelevant to the question of how fast you will get to a boil.

Surface area to volume ratio has some effect because of the heat loss of the system. Ideally, to reduce heat loss, your pot would be a perfect sphere. But that's not practical!

 

[MisterTipsy]

I guess I should've looked at the responses! I thought you were referring to the OP's post "I know it will take exactly the same amount of energy to bring each vessel to the boil."

My bad!

Here is my issue, "Water will boil (roughly) equally fast in two different shaped vessels given the same heat input."

The "same heat input" can be controlled if you are electric brewing.

BUT if you have a propane burner this doesn't apply IMO. It is the same heat source but I don't believe they will both boil at the same rate due to differences in wasted energy.

So my hypothesis is a larger pot on a propane burner will have less wasted energy.

What do you think?

I think that the difference will be negligible.

Are you going to choose one kettle over the other because it gets to a boil 2 minutes faster than another kettle with the same input?

 

[MisterTipsy]

It's a test you can perform at home to see for yourself. Boil a gallon of water in two different sized pots with the same heat source and time them.

 

[unionrdr]

In my case on an electric stove,the smaller pot will boil without a lid. The larger one won't without a lid. but the larger one is a hair larger than the burner coil.

 

[betarhoalphadelta]

The larger pot [likely] also has a larger thermal mass. It also likely has more surface area for heat to be conducted away from the liquid and lost to the air. So there are other factors counteracting the "less wasted heat" theory. I would suspect that these reasons may be why the poster above me has trouble boiling in his larger pot compared to his smaller pot.

But overall I think it will be negligible.

 

[MisterTipsy]

In my case on an electric stove,the smaller pot will boil without a lid. The larger one won't without a lid. but the larger one is a hair larger than the burner coil.

I think in your case the larger pot won't boil because of the increased rate of evaporation due to having a larger water surface area and the energy your stove top produces isn't sufficient to overcome the effect of evaporation.

Lets say your stove top puts out 10,000btu. If it produced 40,000btu, then I think both of your pots would achieve a boil at similar rates without a lid.

 

[unionrdr]

I think your theory is the most likely MrT. Now that I think about (with coffee!) it did get more evaporative loss on the same burner at the same setting than the 1G smaller pot (4G total). Both are SS from the same set too.

 

[MisterTipsy]

Sometimes things that seem logical based on interpretations of common knowledge aren't correct in the world of science.

For example, did you know that you can freeze hot water faster than cold water? This seems very counter intuitive, but it is true. If you are able to prove why this happens, you can earn $2,000. http://en.wikipedia.org/wiki/Mpemba_effect

Another one is lower temperature boilers can sometimes vaporize water faster than higher temperature boilers. It sounds wrong, but it isn't. http://en.wikipedia.org/wiki/Leidenfrost_effect

 

[unionrdr]

Well,as was stated I used the same burner at the same temp for both pots with the same volume of water. It seems that the smaller diameter pot that fit the diameter of the burner more closely was more thermally efficient than the larger one that overhung the burner a bit.

 

[MisterTipsy]

Well,as was stated I used the same burner at the same temp for both pots with the same volume of water. It seems that the smaller diameter pot that fit the diameter of the burner more closely was more thermally efficient than the larger one that overhung the burner a bit.

My last post wasn't directed at you specifically. I believe what you observed.