Meriam Laminar Flow Elements - Manual (Page 10)

10
Actual Volumetric Flow Rate
1) To obtain actual volumetric flow rate at inlet flowing temperature other than 70ºF, find
the flow rate (Q) that corresponds to the corrected DP. Multiply Q by the viscosity correction only.
See chart A-31986 for corrections.
2) At flowing inlet temperature of 70ºF read curve directly in actual volumetric flow rate.
Actual volumetric flow rate equals standard volumetric flow rate when flowing conditions are 70ºF
and 29.92" Hg.
Notify Meriam if your flowing gas is not air and/or standard conditions are different from 70ºF and
29.92" Hg absolute. A special curve/table can be provided listing the gas being flowed. The gas
viscosity correction, µstd / µf will reference the gas and/or new standard temperature value, if
applicable. Table A-32422 or A-31986 cannot be used for gases other than air.
Gas Flow Other Than Air/Standard Conditions From 70°F and 29.92” Hg ABS.
Select the proper flow curve/table for the LFE being used.
Standard Volumetric Flow Rate
1) To obtain standard volumetric flow rate if the inlet temperature and pressure are different from
standard, read the flow rate (Q) from the curve/table corresponding to the corrected differential
pressure (DP). Calculate the viscosity at the flowing temperature using the viscosity equation
for the flowing gas. Then calculate the viscosity correction factor (µcf) using
µcf =
୚୧ୱୡ୭ୱ୧୲୷ ୡ୭୬ୱ୲ୟ୬୲ ୤୰୭୫ ୡ୳୰୴ୣ/୲ୟୠ୪ୣ
୤୪୭୵୧୬୥ ୥ୟୱ ୴୧ୱୡ୭ୱ୧୲୷ ୟ୲ ୤୪୭୵୧୬୥ ୲ୣ୫୮ୣ୰ୟ୲୳୰ୣ
Locate the pressure correction factor (Pcf) for the flowing inlet pressure on chart A-31031 or
calculate the correction factor using
Pcf =
ୟୠୱ୭୪୳୲ୣ ୧୬୪ୣ୲ ୪୧୬ୣ ୮୰ୣୱୱ୳୰ୣ
ୟୠୱ୭୪୳୲ୣ ୱ୲ୟ୬ୢୟ୰ୢ ୮୰ୣୱୱ୳୰ୣ
Locate the temperature correction factor (Tcf) for the flowing temperature on chart A-35700 or
calculate using
Tcf =
ୟୠୱ୭୪୳୲ୣ ୱ୲ୟ୬ୢୟ୰ୢ ୲ୣ୫୮ୣ୰ୟ୲୳୰ୣ
ୟୠୱ୭୪୳୲ୣ ୤୪୭୵୧୬୥ ୲ୣ୫୮ୣ୰ୟ୲୳୰ୣ
Multiply Q from the curve/table by the viscosity correction factor (µcf), the pressure correction factor
(Pcf) and the temperature correction factor (Tcf). This product will give the flow rate of a particular
gas at the standard conditions.
2) At flowing inlet conditions equal to the standard conditions, read curve/table directly in standard
volumetric flow rate.