using the psychrometric chart - university of alabama worksheets/module 4/psychrometric...
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Using the Psychrometric Chart
Problem StatementThe air in a room has a dry‐bulb temperature of 80oF and a wet‐bulb temperature of 65oF. Assuming a pressure of 14.7 psia, use the psychrometric chart to determine:p , p y
1. The specific humidity.
2. The relative humidity.
3. The dew point temperature.
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Given: TDB = 80oF; TWB = 65oF; p = 14.7 psia
To Find: a) ω; b) φ; c) TDP
Solution:
Locate the properties TDB = 80oF and TWB= 65oF on the psychrometric chart.
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Psychrometric chart with TDB = 80oF and TWB = 65oF indicated80 F and TWB = 65 F indicated.
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Solution (cont’d):
Draw a vertical line from TDB = 80oF which crosses the TWB = 65oF diagonal line.
Th i t ti f th t li i di tThe intersection of these two lines indicates the state of the atmospheric air.
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Psychrometric chart with lines drawn inPsychrometric chart with lines drawn in.
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Solution (cont’d):
To determine ω, draw a horizontal line from the “state point” to the right and read the humidity ratio .
⎞⎛ i tlb⎟⎟⎠
⎞⎜⎜⎝
⎛=
airdrylbmmoisturelbm,
,010.0ω
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Psychrometric chart with ω indicatedPsychrometric chart with ω indicated.
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Solution (cont’d):
To determine Ф, note the curved line (indicated in green) that passes through the state point.
Ф = 45%
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Psychrometric chart with green linePsychrometric chart with green line.
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Solution (cont’d):
The dew point temperature is defined as the temperature at which condensation commences from the atmospheric air. The TDP state point will have the same ω as the atmospheric air state point but the Ф willatmospheric air state point, but the Ф will be 100%
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Solution (cont’d):
D h i t l li f th t h iDraw a horizontal line from the atmospheric air state point to the “Saturation temperature oF” line TDP = 57 5oFtemperature F line. TDP 57.5 F.
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Psychrometric chart with horizontal line toPsychrometric chart with horizontal line to the saturation temperature line.
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Summary:
ω = 0.010Φ = 45%T 57 5oFTDP = 57.5oF