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

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Discussion Overview

The discussion revolves around the use of a psychometric chart to determine the relative humidity (RH) of air in a cooling process. Participants explore whether the chart can provide the necessary information given the temperatures involved and the conditions under which moisture begins to condense.

Discussion Character

  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant questions the ability to use the psychometric chart for temperatures above 30°C, noting that the wet bulb line does not extend to 40°C.
  • Another participant suggests that the saturation vapor pressure of water at 40°C and 45°C is relevant for determining the partial pressure of water vapor in the air.
  • There is a clarification on the definition of relative humidity, described as the ratio of partial pressure to saturation partial pressure at a given temperature, multiplied by 100.
  • One participant expresses a desire to confirm the correct use of the psychometric chart rather than seeking a complete solution to the problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the use of the psychometric chart for this problem, with some expressing uncertainty about its applicability to the given temperatures.

Contextual Notes

The discussion highlights limitations in the psychometric chart's range and the need for saturation vapor pressure values, which are not provided in the thread.

SherlockOhms
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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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Attachments

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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