CIRAS-3 Operation Manual V. 1.09 159 support@ppsystems.com
Summary of the Gas Exchange Equations Used in CIRAS-3
Mass Flow Equation
Calculate the mass flow of air (W) entering the cuvette per unit leaf area
(1.1) The CIRAS-3 mass flowmeter is calibrated to read the volume flow (V
0
) at 0 °C and 1013.25 mb.
The Ideal Gas molar volume is 22.414 L mol
-1
at 0 °C and 1013.25 mb (STP). Therefore:
(
)
=
×
×
.
×
Where: a is projected leaf area (cm
2
converted to m
2
). V
0
is converted above to cc sec
-1
, but displayed by
CIRAS-3 as cc min
-1
.
Transpiration
Calculate transpiration rate (E) from the partial pressures of water vapor of the air entering (e
in
) and
exiting (e
out
) the cuvette
(2.1) The molar flow of water vapor (mol m
2
s
-1
) into the cuvette is:
×
(2.2) The molar flow of air out of the cuvette (due to the addition of transpired water vapor) is (W+E).
Therefore, the molar flow of water vapor out of the cuvette is:
(
+
)
×
(2.3) However, the difference between the molar flows into and out of the cuvette must equal the
transpiration, so:
=
(
+
)
×
×
(2.4) Therefore:
(
)
=
×
(
)
(
)
×
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