In addressing the problems of "winter", aggressive arguments are being made from what seems half-remembered science classes.
It is VERY true that many people would be intimidated by this sort of push-back, and never try to post to Bee-L again if so treated, something to think about. I will "keep up the good work", and pull the discussion back to "winter" and bees...
First, it should be clear that water vapor that *stays* vapor is not a problem in winter. It is the **condensation** that is the start of the problem, and the gas laws don't apply at all to condensation, which is... water. So, I think that special attention must be paid to condensation.
> But rest assured that water vapor in air does follow the ideal gas laws with more than enough accuracy to serve any practical bee keeping question.
I think that the question itself has been misconstrued in the above - in winter, don't need to care much about the water vapor that stays vapor, as it will harmlessly exit the hive.
The only "practical beekeeping question" at hand seems to concern the water vapor when it CANNOT be described by the "ideal gas law", as it transitions from water vapor to liquid, and then liquid to ice, and then back again. The key here is that we use the word "vapor", as a vapor includes both the liquid and the gas phases coexisting (at temps well above the condensation point), while "a gas" has no liquid state molecules existing at the stated temperature range.
Here's why this is a significant issue - a bad scenario for a hive would include water as simultaneous liquid water, water vapor, and solid ice. The ice forms on a cold surface, that ice melts, it drips cold water on the bees, which tends to kill the clustered bees, as wet bees don't survive cold like dry ones do. Meanwhile, the bees produce more water vapor via respiration.
On the other hand, if one avoids all condensation, one avoids then potential for ice, but the bees then lack water, as the condensation is a good source of water when the bees are less-tightly clustered.
So, we are working with more than just "a gas" here, and the "ideal gas laws" don’t help, as we have different temperatures all over the hive. Thermographs show just the temperature of the woodenware, but they are instructive, as it is clear that the cluster is warmest, there is a rapid drop-off in temp as one gets away from the cluster. So we have air (and water vapor) at one temperature within the cluster, at another within an inch of the cluster, and then far colder away from the cluster. The surfaces of the hive are colder still. The multiple temperatures mean that we have distinct conditions at different points, and that the problem cannot be described with one equation, even if "PV = nRT" was useful to describe water vapor. Not the "T" - it allows only one temperature value, and what is clearly varying in different spots around the hive is temperature.
So, applying the actual problem at hand to a few of the statements offered:
> All gasses condense...
But isn't water vapor **more** than "a gas"? A "vapor" includes both the liquid and the gas phases coexisting at the stated temperature range.
The ideal gas laws only apply to "ideal gasses", not liquids, and with a vapor you have both coexisting, all the time.
And what gasses do condense at temperature ranges and pressures found in a beehive?
Hydrogen does so at -252 °C, nitrogen at −196 °C, helium at -269°C... please explain, as I can only think of water.
Can anything else be in solid, liquid, and gaseous states all at the same time in a beehive occupied by living bees?
I can’t think of any other substance that can - water.
> There are no gasses that are truly ideal.
I'm not clear on this argument - is there some problem in applying the gas laws to the "less ideal" ideal gasses?
Don't all the actual "ideal gasses" at least remain gasses in the range of temperatures one finds in a beehive?
What problems do the slightly less ideal gasses pose? (I'm not talking about the bogus "zero volume" that the ideal gas laws can produce - clearly that can't happen, as the gas becomes a liquid or solid rather than magically achieving "zero volume" as a gas.)
> But the ideal gas law is still a reasonable approximation at low pressures and ambient temps such as we find in air at ambient conditions.
But the ideal gas law misleads one into viewing water vapor as an ideal gas, and ignoring the phase changes that are the crux of the problem. Might the subjective assumption that "the approximation is reasonable" be part of the reason why a useful solution to the stated problem remains so elusive?
> It is easy enough to directly measure relative humidity. You simply determine the amount of water in some volume of air then go to a phase diagram and calculate relative humidity based on the determined amount versus the amount that would be present at that temperature due to the vapor pressure of water at that temperature.
But that is measuring something else, with extra steps. How is that "directly measuring relative humidity"?
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