Why doesn't the water boil?

[Swamp Fox]

I have a cast iron "steamer" on top of my stove. At times, I have seen the thermometer on top of the stove get to 650-700 degrees and the water in the kettle doesn't boil. It does totally evaporate over a 24 hour period, however, I have never seen it boil. If water boils at 212 degrees F, why doesn't it boil when the stove top gets over 600 degrees? Probably has something to do with physics and a law relating to resistance and transferrence of heat? (I must have a lot of time on my hands to wonder about stuff like this).

 

[cmonSTART]

I often wonder the same thing and I really hope someone can shed some light on this.

 

[webbie]

I think you have it right - the shape of the steamer allows for max. heat dissipation - whereas a tea kettle (for the kitchen range) has a very large bottom and very small top.

 

[jtp10181]

Put a meat thermometer in the water if you wanna know. It will probably read slightly less than 99C (211F).

http://www.newton.dep.anl.gov/askasci/chem03/chem03444.htm

Found that on Google if you can make sense of it. Basically it says water will evaporate at at temp between the melting point and the boiling point. It will happen more as temp increases. It also states the water will actually get cooler when some of the molecules evaporate. My guess is the temp of the top of you stove is just enough to maintain that ALMOST boiling temp but not hot enough to push it over the edge into a boiling state. FYI liquid water will never get over 99-100C at atmospheric pressure. Once its hits 100C its vapor, so anything still liquid has to be less than that.

 

[Swamp Fox]

Thanks, That makes sense and answers my question.

 

[tw40x81]

My guess is that if you put a tight fitting lid on the pot, it will boil. I heated some some turkey soup made dumplings on the Englander 13 stove yesterday, and the soup was at a rolling boil using a lid. Just giving the nuke plant in Berwick a little rest, as my other stove is electric.

 

[steam man]

To raise the temperature of 1lb of water 1 deg you need to add one BTU. To change state from liquid to a gas (without changing temperature) you need to add 970 btu/lb which is the latent heat of evaporation. You just are not adding enough heat to overcome the heat loss at this point. Adding a tight cover would increase the pressure and also the temperature at which water boils. This is how a pressure cooker operates. Think why water boils at a higher temperature at sea level 212 deg than on a mountain. Anyone in Denver know what temp water boils at there?

 

[mtarbert]

It takes alot of energy to boil water. Takes 1 caloire to rase the temp of 1 cc 1 degree but, after the water reaches the boiling temp 540 calories must be added to actually boil the water. Just think about the boiling pot on the stove....when you remove it from the heat it stops boiling almost immediatly.
Mike

 

[mayhem]

Its the shape of the steamer and the size of the outlet at the top compared to the surface area of the inside. I have both a steamer and a cast iron kettle for the stovetop...the kettle will boil the water, but the steamer just steams it away gently.

 

[backpack09]

I use a small Japanese tea kettle, and it definitely boils.

 

[jbrown56]

Hi, We use a 1/2 gal. soapstone steamer on a trivet. With the steamer full and the stovetop at 500* it was boiling away. If the temp drops to 475* it will stop boiling.

Jim

 

[swestall]

Two things: where'd you get that soapstone steamer?

And, if the water isn't boiling, it's not hot enough? I find that my water boils when the stovetop gets upwards of 550 for a long time. In a tea kettle, with the top on.
I used to boil a larger kettle with no lid on a cast stove at 650 for a long time.

 

[Highbeam]

Chineysweeponline.com sells the stone kettles. Mine came from Hearthstone. It only kind of makes a little more noise when the stove top is at 500 but no actual visible boil.

Here's another tidbit for discussion. As the water boils away we add more fresh water over and over. Well what we are doing is concentrating the dissolved gunk in the water since only the pure water evaporates. The concentrated minerals act do raise the boiling temperature and lower the freeze point just like adding salt to the roads.

I notice that I get more evaporation when I have recently cleaned the kettle and filled with new water.

 

[Backwoods Savage]

An old trick for those who have lime is to put a piece of cheesecloth in the water. Then you don't have to clean nearly as often.

As for why the water doesn't boil. The entire pot is not making contact with the top of the stove. Everything above the stovetop is just sitting there in the air allowing it to stay cooler. Yes, cast will work much better in most instances for making stuff boil.

 

[Jimbob]

If you want to prevent lime buildup in the steam kettle, just use melted snow in there, it contains NO minerals, just don't gather the snow from around the base of a fire hydrant.:coolsmile:
Also, Chesley, check the bottom of that cast iron kettle. If it has little "tits" on the bottom of it, they will prevent the bottom of the kettle from making direct contact with the stove. Simply grind off anything that prevents the bottom of the kettle from touching the stove top.

Hope this helps.

 

[kgrant]

Just for the heck of it, put that pot that won't boil on your cooking stove and see if you can get it to boil. I'm just curious.

When I'm at the cabin and heating dish water, I use two different pots. They both hold about the same amount of water. One is skinny and tall, the other is wide and short, both same thickness of material. The tall one will be almost boiling and the other short one I can still stick my finger in.

 

[micah]

Because your watching it?

"A watched pot never boils" not sure who said that but my mom used to tell me that all the time as a kid.

 

[Henz]

very interesting, at our hunting camp we use an old cast iron wood fired kitchen stove..we can get water to poil in a saucepan with the same dia bottom as the top

 

[Cazimere]

Same here. The kettle boils and the pot steams : )

 

[swestall]

One is covered, the other is not...holds heat in a bit, enough to make the difference.

 

[tnunemac]

Anyone in Denver know what temp water boils at there?

It's about ~202 F in Denver, and ~196 F at 8200 ft in the foothills west of Boulder, where we're building. We'll be moving in a few weeks, and I'm already breaking in our new Hearthstone Mansfield.