Laminar flow element and method for metering fluid flow

DETAILED DESCRIPTION These objects and other objects are obtained with the instant invention of an adjustable laminar flow element.
In the current state of the art rigidly defined, non-adjustable geometries are utilized to fabricate laminar flow elements.
In a typical thermal mass flow meter calibrations are accomplished by comparing a known primary flow indicating instrument with a voltmeter (or ammeter) connected to the output terminals of the process transmitter (i.
e.
the complete thermal mass flow meter instrument).
An adjustable potentiometer ("zero" adjustment) is used to adjust the output at zero flow conditions to zero reading on the voltmeter.
Another potentiometer ("span" adjustment) is used to adjust the output at maximum desired flow rates (usually 5 volts direct current reading).
Alternatively, when desired, an ammeter is used to adjust the "span" to 20 milliamps, or some other value.
A desirable linear response would then be sought by verifying the resultant flow reading at various percentages of the maximum flow to correspond to similar percentages of the maximum voltage (or current) readings.
At present these rigid, non-adjustable laminar flow elements cause non-linear conditions.
To compensate, manufacturers build two or more additional "trimmer" potentiometers into the control circuits of their thermal mass flow meters to permit two or more points to be "pulled" into linearity within stated tolerances.
In the instant invention a porous, open celled, flexible material partially or completely fills a conduit to be used as a laminar flow element.
This material can be a plastic or rubber foam, for example, or an inorganic or organic aerogel.
Other suitable materials include "Fiberglas" (a registered trademark of Owens-Corning Fiberglas), and metal meshes such as copper and steel wool.
A steel wool type mesh made up out of type 316 stainless steel has been found to be a preferred embodiment, since type 316 stainless steel is well accepted by the semiconductor industries.
The stainless steel mesh is placed within the laminar flow element partially or completely filling the laminar flow element depending on proposed applications