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Series 820 Instruction Manual Appendix A
IM-82-C A-3
Where:
H = The constant amount of heat applied to the sensor tube,
m = The mass flow rate of the gas (gm/min)
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Cr = The coefficient of specific heat of the gas (Cal/gm);
Cr is given in the Table (at 0°C),
DT = The temperature difference between the downstream and
upstream coils, and
N = A correction factor for the molecular structure of the gas
given by the following table:
Number of Atoms in the Gas Molecule N
Monatomic 1.040
Diatomic 1.000
Triatomic 0.941
Polyatomic 0.880
The mass flow rate, m, can also be written as:
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m = Q
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r
(3)
Where:
r = The gas mass density at standard conditions (g/l); r is given
in the tables (at 0°C, 760 mm Hg).
Furthermore, the temperature difference, DT, is proportional to the
output voltage, E, of the mass flow meter, or
DT = aE (4)
where:
a = A constant.
If we combine equations (3) and (4), insert them into equation (2),
and solve for Q, we get
Q = (bN/rC
p
) (5)
where:
b = H/aE = a constant if the output voltage is constant.