| View previous topic :: View next topic |
Mick Harper
Site Admin
In: London
|
|
 |
|
Although born in a test tube I am not by nature very scientific. So I will be needing help with some basic scientific problems from those of you who are. The first one concerns evaporation. As I understand it, as I dimly remember it, water must evaporate when exposed to air unless and until that air is saturated with evaporated water aka water vapour.
First off: is this correct?
|
|
 |
|
 |
|
Chad
In: Ramsbottom
|
|
|
|
Sort of.
Evaporation still takes place even into saturated air, but the number of molecules leaving the water is balanced by the number of molecules returning to it.
And water molecules will also pass from air to water... even when the air is not full saturated.
It's all a matter of ratio.
|
|
| |
|
|
|
Mick Harper
Site Admin
In: London
|
|
|
|
|
So let me get this straight. If liquid water is put in conjunction with non-saturated air then, even though the molecules are going both ways, the balance will always be water-to-air until saturation is reached (assuming the water was not all used up). In what circumstances would, over the long term, saturation not be reached?
|
|
| |
|
|
|
Chad
In: Ramsbottom
|
|
|
|
|
In a closed system, eventual saturation is inevitable.
|
|
| |
|
|
|
Mick Harper
Site Admin
In: London
|
|
|
|
|
Are you sticking to this position? Obviously I am about to explode it.
|
|
| |
|
|
|
|
|
Mick Harper
Site Admin
In: London
|
|
|
|
|
Very well, but I'll wait a few hours to see if anybody disagrees.
|
|
| |
|
|
|
Chad
In: Ramsbottom
|
|
|
|
|
We must of course assume constant temperature, pressure and other environmental variables.
|
|
| |
|
|
|
Grant
|
|
|
|
|
What about surface tension? Doesn't that have something to say about evaporation rates?
|
|
| |
|
|
|
Mick Harper
Site Admin
In: London
|
|
|
|
| Evaporation still takes place even into saturated air, but the number of molecules leaving the water is balanced by the number of molecules returning to it. |
I can understand a molecule going from state A to state B, I can understand a molecule that goes from B to A, but what kind of molecule goes both uphill and downhill just because Chad says it's OK?
|
|
| |
|
|
|
Chad
In: Ramsbottom
|
|
|
|
1) Take an empty room and fill it to a depth of about a metre with fine eider down.
2) Enter room armed with a hand operated rotary fan.
3) Aim fan at surface of down... observe feathers float into the air... (Analogue water vapour).
4) Turn up fan until shit loads of feathers fly into the air and an equal number are falling back to the surface of the down... (Analogue saturated vapour).
And there in a nutshell...
|
|
| |
|
|
|
Mick Harper
Site Admin
In: London
|
|
|
|
|
Come off it, Chad, where's the membrane?
|
|
| |
|
|
|
Chad
In: Ramsbottom
|
|
|
|
1.a) Suspend net approximately six inches above eider down... (Select mesh size such to allow individual feathers to pass through).
|
|
| |
|
|
|
Mick Harper
Site Admin
In: London
|
|
|
|
|
Let me put it another way. Is this a "model" that physicists tell one another or is it an observed fact?
|
|
| |
|
|
|
Brian Ambrose
|
|
|
|
| In a closed system, eventual saturation is inevitable |
er... be careful. It depends what you mean by saturation. If saturation means 'a point at which no more evaporation takes place', that's one thing (and I agree). But if saturation means the air is literally 100% (ie maximally) loaded with water molecules, that would surely depend on various factors and not be inevitable.
|
|
| |
|
|
|
|
The Library Index 
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in 
