Hello:

If you put a large tub of water in a 72 degree Fahrenheit room, what will the temp of the water settle to be, and WHY?

excon

After a long long long long time, the water of the tub will have the same temperature as the room.

Why the same temperature? Because there is heat transfer as long as there is a difference in temperature. If you want to go into more detail... just ask! :)

Why a long long time? That's because water has a very high value called specific heat capacity, which basically dictates how much energy the water should gain to get to a certain temperature, from a said temperature. The temperature that you measure is that of the air, and that gas' thermal energy might very well be less than the water itself since it's about 1000 times less massive.

And... why 'dew point' as title? :confused:

And... why 'dew point' as title? :confused:Hello Unky:

Thanks for that great explanation. I said dew point, because I though water was ALWAYS going to be colder than the ambient air no matter HOW long it was in the room, and I thought the REASON had to do with dew point.

Now, I see that I'm all wet.

excon

Ah no, water can be warmer or colder than the air.

In your question, I assumed that the temperature of the room was kept at 72 F. But what usually happens (when the temperature of the room is not maintained) is that:

If the water's warmer, the water will gradually heat up the air, not by much, since heat transfer causes the air to become warmer and the water become colder, until they are at the same temperature.

If the water's colder, the water will gradually cool down the air while the water gets warmer, until both are at the same temperature.

Using figures that you probably don't want to see, let's say the water is at 86 F and the room at 72 F, the temperature where there is no more heat transfer could be roughly 82 F.

And otherwise with water at 58 F, the final temperature can be something like 62 F.

As you can see, the water will change a little, while the air changes the most :)

EDIT: Dew point is the temperature at which air needs to be cooled to make water vapour condense. This depends on pressure and humidity :)

Hello again, Unky:

Thanks, again...

While I have your attention, it's been my long held belief that COLD air has LESS capacity for water, than warm air has...

In other words, if I had some jerky I wanted to dry, would it dry quicker in COLD air, or WARM air? I think cold. Am I all wet again?

excon

While I have your attention, it's been my long held belief that COLD air has LESS capacity for water, than warm air has...

Butting in here...

That's why Chicago (or the South) is so sweltering during the summer -- hot air holds water vapor.

Now, how does one explain the lush forests of the Pacific Northwest?

Hm... that actually depends on humidity. You can have warm humid air, as you can have warm dry air and the same with cold air.

So... your jerky will become dry quickier in dry air than in moist air. :)

Otherwise, the water capacity of air increases with temperature, meaning that hotter air can hold much more vapour than cold air. That's also why dew tends to form when hot vapour gets into contact with a cold surface :)

You might want a table... or not if figures scare you ;)

Climate/humidity table (http://www.tis-gdv.de/tis_e/misc/klima.htm)

So... your jerky will become dry quickier in dry air than in moist air. :)Hello again, Unky:

The table is great.. Hopefully, I can figure out what it's telling me...

But, let me ask my question another way.. Assuming whatever humidity it is, and it's cold in the room. Will the jerky dry faster if I heated up the room and the humidity stayed the same?

excon

Yes it will.

You can also picture it as you're heating your jerky and evaporating the water in it.

Also, in the table, the higher the absolute humidity, the better it is for your jerky to dry :)