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Old 09-29-2019, 10:25 AM
am77494 is offline
Join Date: Mar 2012
Posts: 1,924
Originally Posted by purplehorseshoe View Post
. Please explain how dew point figures into this?
My Engineering mentor used to say - ďUnless you can explain it to your grandmother, you donít really understand itĒ

So in that spirit - let me give it try.

So imagine air to be tennis balls and water vapor to be marbles. Imagine you have a container with 100 tennis balls. Now imagine that you add the marbles to fill up the space between the tennis balls.

As you probably understand, the space between the tennis balls expands when the temperature goes up, so you can fit more marbles at a higher temperature.

So you do an experiment to fit in max marbles at different temperatures and find the following :

Temp = 60F, Max marbles = 20
Temp = 70F, Max marbles = 25
Temp = 80F, Max marbles = 30
Temp = 90F, Max marbles = 35
Temp = 100F, Max marbles = 40

The temperatures above are dew points. So at 70F, 25 marbles will be accommodated by the 100 tennis balls. Add one more and it will stick out like a sore thumb.

So if someone tells you, that there are 30 marbles per 100 tennis balls, you can immediately say : Hey that means the dew point is 80F. Now the actual temperature is 90F so there is room for 5 more marbles.

Now your body needs to lose water vapor (marbles) to the air (tennis balls) to keep cool. If the air is already at its dew point or It is maxed out, then it cannot accept the water from your skin. So it will feel muggy.

So letís take HOUSTON. The temperature is 100F and the dew point is 90F. So this means there are 35 marbles but it can accommodate 40. So there is room for only 5 marbles - so the sweat on your skin doesnít evaporate fast and it feels muggy.

Now letís take Arizona. The temperature is 100F and the dew point is 60F. So this means there are 20 marbles but the air can accommodate 40. So there is room for 20 more marbles. Your sweat evaporates fast and you feel good.

Please, let me know if my explanation worked for you.