Download - Using a Psychrometric Chart
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Using the Psychrometric Chart
Problem Statement
The air in a room has a dry‐bulb temperature of 80oF and a
wet‐bulb temperature of 65oF. Assuming a pressure of
14.7 sia use the s chrometric chart to determine:
1. The specific humidity.
2. The relative humidity.
3. The dew point temperature.
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Given: TDB = 80oF; TWB = 65
oF; 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 =
o = o
WB .
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Solution (cont’d):
Draw a vertical line from TDB = 80oF which crosses the TWB = 65
oF diagonal line.
e n ersec on o ese wo nes n ca es
the state of the atmospheric air.
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.
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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 .
⎟⎟ ⎠
⎜⎜⎝
=air drylbm
mo s urem
,
,010.0ω
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.
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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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.
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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 ,
be 100%
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Solution (cont’d):
raw a or zon a ne rom e a mosp er c
air state point to the “Saturation o ” = o . . .
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the saturation temperature line.
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Summary:
ω = 0.010
Φ = 45%DP = .