OK, how about this:
Boiling is the visible product of a phase change from a liquid to a gas. Boiling occurs when a fluid is at its
http://en.wikipedia.org/wiki/Boiling_point and can therefore exist in both the liquid and gas phases. A mass existing entirely in the liquid phase at its saturation temperature is called a saturated liquid and has a quality of 0. For this same
Control Mass existing entirely as a vapor at the saturation temperature, It is called a saturated vapor(or saturated steam) and has a quality of 1.
-Quality is a term used to express the fraction of a mass in the vapor phase and is found by the M[/SIZE]
vapor/M
total. Quality is only used to describe a fluid at the saturation temperature
-lbm: pound mass, the amount of mass that exerts 1 pound of force on earth
Back to Boiling.
For water, The amount of energy need to convert 1lbm saturated liquid to 1 lbm saturated steam is 970 BTU/lbm at 14.7psia. this quantity is known as laten Heat of Vaporization
to approximate our brew pot, we will assume it is a control mass and that there is no heat transfer into or out of the system. to keep it simple, we will assume the pot contains 1lbm of water.
The
specific heat of water is 1BTU*(ºF*lbm)^-1.
So, in an engineering problem, the units always cancel out leaving the desired quantity.
Say we want to heat the water to 212ºF from 62ºF, so ΔT is 150º
150ºF*1lbm*1BTU*(ºF*lbm)^-1=150BTU ºF and lbm cancel so the answer is in BTU
Since we are now at our saturation temperature, say we want to boil 10% of our water off, what we are saying from a thermodynamic perspective is that we want to convert 10% of our water into steam, or change the quality from 0 to .1
Since the water is at its saturation temperature, any additional energy transferred into it will cause a phase change, but no temperature increase until it is at a quality of 1.
So, back again to the example. We now want to boil off .1 lbm of water, we use the previously stated so
.1lbm*970BTU/lbm=97BTU where lbm cancels.
So thats easy enough. we just "boiled" .1lbm of water. Now, this process could have happened quickly over the period of a couple seconds or very slowly over an hour or something, but it still could be considered boiling. If we were to take the steam that was created during this process and condense it back into a liquid, that 97 BTU's would be released into the condenser, similar to Monti's calendria.
Some other things to keep in mind:
The properties of water are not constant, You need a certain number of properties to define the state of a fluid at any state, If the pressure was changed, all the values in the problem would change.
A BTU is a unit of energy, A Watt is a unit of energy flow, not a unit of energy. So saying a burner is 100,000 BTU is technically incorrect, a better statement would be 100,000 BTU/hr. Granted, it can usually be assumed that burner measurements are on a per hour basis, when talking about a quantified heat transfer, it would generally be better to state terms properly.
So back to the original question:
Boiling is a process, Not a state point, so saying something is boiling doesn't mean much at all actually other than its undergoing a phase change.
