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Psychrometric Chart

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					Psychrometric or Humidity Chart

Mixtures of Air & Water Vapor in Gas Phase
Treat Air as Pseudo Single Component

      Humidity (Kg H2O/Kg Bone Dry Air) = f(Dry Bulb & Wet Bulb Temperature)
Steady State Temp when thermometer end is surrounded by moist wick & spun in humid air

            Antoine Water(0-60oC)  Antoine Water(60-150 oC)
                              Mw(H2O)    Mw(Air)
                                     18    29
A           B     C                A     B      C                        P(Tot Press)
    8.108       1750              235               7.967   1668   228     760
P*=10^(A-B/(C+T))

                        Absolute Humidity=Sa= (P*)/(PT -P*)*(Mw(H2O)/Mw(Air))
o
 C          o
             C          mm Hg            Kg(H2O)/KgB.D. Air
T db        T wb        P*(H2O)          H(Sat)
        0           0      4.566931189   0.003752
       10          10      9.196562151   0.007603
       20          20      17.53005721   0.014655
       30          30      31.82710741   0.027129
       40          40      55.33165194   0.048738
       50          50      92.53278085   0.086048
                                                 H vs T
                               0.1
       H Kg H2O/Kg B.D. Air

                              0.08
                                                                               hr=30%
                                              Sat. Curve
                              0.06

                              0.04
                                                                    T wb =30
                              0.02
                                                           Twb=20
                                0
                                     0   10    20          30          40      50       60

                                                       TdboC


       How to Determine Humidity?
Select Dry Bulb Temp.
Move up to Wet Bulb Temp
Read across to Humidity Axis
        How to determine Dew Pt. Temp. oC?
Select Dry Bulb Temp.
Move up to Wet Bulb Temp
Move to Left to Saturation Curve
Read Dew Pt. On T db axis
Use Wet Bulb & Dry Bulb Temp to locate point within Chart
Interpolate using the Relative Humidity Lines that bracket the above point
                          Humidity Chart & Volume Calculations

Humid Volume=Volume occupied by 1 Kg of B.D. Air
           & the Water that Accompanies it

      Look for a few lines with Large negative slope
Labeled at bottom of T db axis 0.75, 0.80, 0.85 and 0.90 M3/Kg B.D. Air

                                                         H vs T

                                     0.1
                                    0.09
                                    0.08
             H Kg H2O/Kg B.D. Air




                                    0.07               Sat. Curve
                                    0.06
                                    0.05
                                    0.04
                                    0.03
                                                                      T wb =30
                                    0.02
                                    0.01                         Twb=20
                                      0
                                           0      10    20       30       40         50   60
                                                          VH=                  V H =0.
                                               TdboC
                                                                                   .9
                                                          0.85
                           Humidity Chart & Enthalpies
         Enthalpy of Humid Air                   Enthalpy of Humid Air
Reference Conditions for Figure 8.4-1   Reference Conditions for Figure 8.5-1
         Liquid Water at 0OC & 1 am              Liquid Water at 32OF & 1 am
         Dry Air at 0oC & 1 atm                  Dry Air at 0oF & 1 atm

Be careful- Cannot use these tables interchangeably with Steam tables
Unless make adjustments for Different Reference State for Zero Enthalpy
          To read & Determine Humid Enthalpy
Find Humidity Point based on Dry & Wet Bulb Temperatures
Follow the Constant Wet Bulb Temperature Line Up & to the Left to Saturation Curve
Interpolate to Read Saturation Enthalpy
Go Back to the Humidity Point & Enterpolate the find Enthalpy Deviation
Humid Enthalpy = Staturation Enthalpy + Enthalpy Deviation KJ/Kg B.A. Air

				
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posted:6/8/2014
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