Can a Psychometric Chart Determine Relative Humidity in a Cooling Process?

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The discussion revolves around estimating the relative humidity (RH) of air exiting a drying process, where the air temperature drops from 45°C to 40°C, the latter being the temperature at which moisture begins to condense. Participants question the applicability of a psychometric chart for this problem, noting that the wet bulb line does not extend to 40°C. The saturation vapor pressures of water at both 40°C and 45°C are essential for calculating the partial pressure of water vapor in the air. RH is defined as the ratio of the partial pressure of water vapor to its saturation pressure at a specific temperature, multiplied by 100 for a percentage. Ultimately, while the psychometric chart may not provide direct answers, using saturation pressures allows for the calculation of RH.
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Homework Statement


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.


Homework Equations


None.


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.
 
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SherlockOhms said:

Homework Statement


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.


Homework Equations


None.


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.
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?
 
Chestermiller said:
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?

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.
 
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