Appendix A | Series 830/840/860 Instruction Manual |
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Where:
H = The constant amount of heat applied to the sensor tube,
m• = The mass flow rate of the gas (gm/min)
Cρ = The coefficient of specific heat of the gas (Cal/gm);
Cρ is given in the Table (at 0°C),
∆T = 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:
• | (3) |
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m = !Q |
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Where:
ρ= The gas mass density at standard conditions (g/l); ρ is given in the tables (at 0°C, 760 mm Hg).
Furthermore, the temperature difference, ∆T, is proportional to the output voltage, E, of the mass flow meter, or
∆T = 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/ρCp) | (5) |
where:
b = H/aE = a constant if the output voltage is constant.