There are various ways to electronically determine boiling point of water. Also there are various things that influence the boiling point of water like altitude, pressure variations, purity of water and water and other chemical (or binary) mixtures. Most of these are in general well understood.
There are many ways like acoustical detection, detecting steam, and so on. I am interisted in detecting it in the simplest possible way, (preferre by single parameter like temp) accurately and without measuring many factors like pressure etc. This is for a hobby project and because I find it stimulating as a first principle challenge.
I am not concerned by what the temp is at boiling, merely that it has started boiling. So all those other factors are not important to me and the fact that the liquid is boiling is the only parameter that is important.
As part of this, I am thinking that if we could detect boiling, we can also detect when it is about to start boiling. This may be important if we should want to prevent the onset of boiling. Absolute temp cannot be used as all those other factors will influence the boiling point temp.
My thinking is as follows:
Water or a chemical mixture with water will raise its temp at a constant rate with a constant energy input. Pure water or water and sugar (or coolant antifreeze) mix (binary mix) will raise its temp at the same rate for the same heat energy input. After it has been heating for a while it will get close to boiling point and then the rate of change of temp will have to slow down more and more as the liquid gets closer to boiling point. At boiling point the temp change will stall until the water has evaporated and only the antifreeze remains. With binary mixtures in general, evaporation of the lowest boiling point chemical in the mixture causes a change in boiling point and a slow rise in boiling point temp.
Stating as follows: Detecting pre boiling, onset of boiling and the subsequent slow change in temp as the mixture changes should be possible by measuring only temperature, or rather the rate of change of temperature.
Pre boiling is a constant rate of change when the liquid starts heating with a constant input of heat.
Slowing down of rate of change indicates a region close to boiling. Finding what this slow down rate of change is close to boiling can be determined I guess, ie. change over time.
When the rate of change for
pure water stops or get very small we know water is boiling. We should now be able to keep it just at the point of boiling or at the onset by varying the heat input. We can also control the rate of boiling by increasing the heat input energy.
As water evaporates into steam from our mix with Ethylene glycol (antifreeze) the temp would change by increasing, also the rate of change of temp will now be increasing from zero or from a very small number.
Does this make any sense or is my logic flawed? (No sacred cows here
)
I want to be able to program a PLC with 4-20mA SCR to let me know at the onset of pre boiling (just before it boils) with an alarm and then keep the liquid at that temp for a amount of time allowing me to add other chemicals to the mix. After the addition the boiling point is now changed and the temp will again rise, when the rate of change slows down because we approach boiling again it must allow the liquid to just start boiling.