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GEK Wiki: Union-based gas flow measurement
Union-based Gas Flow MeasurementPosted: 3/14/09
Updated: 8/4/09
IntroductionMeasurement of gas flow rates through a gasifier is
critical to better understanding and optimizing the operation of
the GEK.
There are many methods available to determine the flow rate of
gases . One of the most robust and easy to implement
techniques is the orifice flowmeter. An orifice flowmeter is
comprised of a flat constriction (orifice) plate placed within a
larg
pipe. Two taps, upstream and downstream (generally 1 pipe dia.
upstream of plate, and 1/2 pipe dia. downstream of plate),
are used to measure the pressure difference created by flow
through the pipe. The pressure differential follows a simple
equation, with dependencies on the fluid density, pipe diameter,
opening (orifice) diameter, orifice smoothness/design, and
flow rate.
An early, simple implementation of an orifice flowmeter. A
washer welded between a cut pipe.
After multiple calibration runs, this flowmeter has remained
consistently repeatable and accurate. The pipe is 1" NPT with
~0.5" orifice with 1/8" NPT barbs (avoid screwing the barbs past
the interior wall of the pipe) .
A quick summary of the math:
A calculator and description of the math is available
here:http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm
Flow can be found with:
Where:
is volumetric flow
http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfmhttp://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm
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is friction coeffient, dependent on design
is orifice area
is pres sure differential
is fluid density
There is an Excel spreadsheet below used to fit when calibrating
the flowmeter us ing another
accurate flowmeter (like a rotameter).
The new designBy using a union to hold the orifice plate, we can
provide a number of interchangable constrictions allowing for
measuremen
across a range of flows, either electronically or with a
manometer. The electronic pressure sensors that will ship with
the
GCU will allow high resolution measurement with very little
pressure drop, producing lower losses throughout the system.
Parts for a union-based orifice flowmeter
Further testing is required before we can deliver this as a
product.
UpdateTes ting and calibration of the union-bas ed flowmeter has
shown poor repeatability, likely owing to a number of alignment
issues introduced by the union. Practically, it is unlikely that
the orifice size will need to be changed often and unions
introduce a reasonable parts cost. Therefore, we recommend using
hard welded flowmeters of the type described at the top
of the page.
Resources:
Excel spreadsheet for calibrating your own flowmeter:
Orifice Flowmeter Calibration.xls
http://wiki.gekgasifier.com/f/Orifice+Flowmeter+Calibration.xls
