Originally Posted by hellosailor
Well, there is also the rather blunt implication that all my physics teachers lied.
I was always taught that water took at least 4 minutes to boil, no matter how may calories you threw at it. Heck, in the 70's the folks at Mountain Safety Research did quite a lot of work making the first winter camping stoves that could melt snow in order to provide water in the shortest possible time (fuel is heavy) and they couldn't beat 4 minutes either.
Intriguing. Had to check out this kettle...a nickel under 200 bucks at Williams Sonoma for the two quart model.
Two quarts. Four pounds of water.
Takes a BTU to raise the temp of a pound of water by a degree F. So four BTUs from the flame to raise the temp of the water in that kettle a degree if the flame-water interface is a hundred percent efficient.
on my boat is about 82F in the summer, so the water I put in the kettle has to be raised 130F to 212F to make the kettle whistle blow. That takes 130 BTU for every pound, or 520 BTU for the four pounds of water in the kettle.
My burner puts out an advertised 7000 BTU/hr. That's a bit less than 120 BTU/min.
So it takes, at a minimum, 4.3 minutes to transfer that 520 BTU from my burner to my water and make the whistle blow.
I think your physics teachers didn't lie to you.
Even a high powered propane
burner at 9K BTU/hr would require almost three and half minutes, minimum, to boil that kettle full of water.
Reduce the water in the kettle to a quart, and the time to boil is reduced by half, and if you're only boiling a pint for a single
mug of coffee, the boiling time could theoretically be reduced to less than a minute.
A Butterfly kerosene burner (7K BTU/hr) boils a quart of water in my kettle in about eight minutes.
That snow to water problem is a bit harder...got to transfer the latent heat of fusion from the energy source to the snow...a lot more than 1 BTU/lbm...
(Of course, the actual heat transfer is a more complex problem than this, requiring knowledge of things such as heat transfer coefficients of materials, surface areas, flame temperature, flame distribution across the heat transfer surface, ambient temperature, initial temperature of the water.)