# Psychometric chart question.

1. Nov 30, 2013

### SherlockOhms

1. The problem statement, all variables and given/known data
The air emerging from a hot aqueous process at a temperature of 45°C, passes over a surface which is gradually cooled. It is found that the first traces of moisture appear on this surface when it is at 40°C. Estimate the relative humidity of the air leaving the dryer.

2. Relevant equations
None.

3. The attempt at a solution
I'm just wondering, is it possible using the psychometric chart I've attached to answer the above problem? To me, it just seems like the wet bulb line ends at 30 C and you can't read off the value of 40 C.

2. Nov 30, 2013

Here.

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3. Dec 1, 2013

### Staff: Mentor

It doesn't look like you can. So...., what's the saturation vapor pressure of water at 40 C and at 45 C. The partial pressure of the water vapor in the air is the saturation vapor pressure of water at 40C, since this is the temperature at which water starts to condense out. Do you know the definition of RH?

4. Dec 1, 2013

### SherlockOhms

Thanks for the reply. RH is the defined as the ratio of partial pressure to saturation partial pressure at a given temperature (multiplied by 100 for a percentage). I could always just use this, knowing the saturation pressure of water at the given temps, to find my final value of RH. I was really just looking to see if I wasn't using the psycho chart correctly though. I don't actually have to solve this problem. Thanks again for the help.