Meriam Laminar Flow Elements - Manual (Page 7)

7
Be sure to use the same absolute units for pressure (i.e. PSIA, mm Hg absolute,...) and temperature
(ºK or ºR). The result is the standard volumetric flow rate at the given standard conditions.
Standard volumetric flow rate = Actual volumetric flow rate x
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୘ୱ୲ୢ
୘୤
ቁ
x
ቀ
୔୤
୔ୱ୲ୢ
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This equation can be rewritten: (B x DP + C x DP²) x
ቀ
ஜୱ୲ୢ
ஜ୤
ቁ
x
ቀ
୘ୱ୲ୢ
୘୤
ቁ
x
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୔୤
୔ୱ୲ୢ
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Table A-31031 lists the values of Pf/Pstd absolute line pressures from 26”Hg at 0.05” Hg intervals.
The standard pressure is 29.92” Hg absolute for this table. Table A-32422 lists the values of
(Tstd / Tf) x (µstd / µf) for air from 50 to 159ºF in 1º intervals. The standard temperature is 70ºF
(529.67ºR) for this table.
Note: If you are flowing wet air, a humidity correction factor for standard volumetric flow rate must
be used. The difference between wet-air density (Pwet) and dry-air density (Pdry) increases with
temperature and humidity. At 80°F and 80% relative humidity, the ratio of Pwet / Pdry is .990. Table
A-35600 lists the ratio Pwet / Pdry of air from 40 to 100°F and from 20 to 100% relative humidity.
The equation for standard volumetric flow rate of flowing wet air becomes:
Standard Volumetric Flow Rate
Wet Air =
(B x DP + C x DP²) x
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ஜୱ୲ୢ
ஜ୵ୣ୲ ୟ୧୰
ቁ
x
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୘ୱ୲ୢ
୘୤
ቁ
x
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୔୤
୔ୱ୲ୢ
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x
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୔୵ୣ୲
୔ୢ୰୷
ቁ
Mass Flow Rate
Multiply the standard volumetric flow rate by the density of the flowing gas at standard conditions to
obtain the mass flow rate of that gas.
Mass Flow rate = Standard volumetric flow rate x density @ standard conditions
Summary
Curve/table value @ DP = (B x DP + C x DP²)
Actual volumetric flow rate = (B x DP + C x DP²) x
ቀ
ஜୱ୲ୢ
ஜ୤
ቁ
Standard volumetric flow rate = Actual volumetric flow rate x
ቀ
୔୤
୔ୱ୲ୢ
ቁ
x
ቀ
்௦௧ௗ
்௙
ቁ
Mass flow rate = Standard volumetric flow rate x density @ standard conditions