Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a device for measuring the
flow of a fluid such as for instance air or other gas in a pipe
or bore and has been devised with the object of providing a
simple means for creating an easily measurable pressure different-
ial,, related to flow, with a low resistance to flow and readily
adaptable to suit various cross-sectional shapes and areas of
pipe or bore.
In the following description the term "air" should be
read to mean air or any other gas or fluid.
In accordance with the present invention there is
provided a fluid flow measuring device comprising a pipe or bore,
which transversely contains a diaphragm having a multiplicity of
closely spaced fluid flow holes which are so shaped as to increase
fluid flow velocity through the diaphragm and means for sensing
fluid pressure at or adjacent the upstream and downstream faces
of the diaphragm said means being intended to be connected to a
differential pressure indicating or recording instrument from
which a fluid flow measurement can be derived.
The internal profile of the holes is preferably such
that the change in velocity takes place smoothly with negligible
loss of total energy. One typical and preferred form of hole is
of nozzle form having a bell mouthed entrance leading to a
parallel cylindrical section.
The holes in the diaphragm may be of circular or other
cross-section and are disposed in any convenient pattern which
may take the form of a "honeycomb" or similar arrangement, so
that when the air emerges from the diaphragm at increased velocity
it is in the form of a multiplicity of closely spaced jets which
rapidly coalesce as they proceed downstream to form a reasonably
uniform flowing mass in the pipe or bore. This results in a
relatively high conversion of velocity energy back to static
pressure. It has thus been found, by use of temporary pressure
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sensors, that the overall pressure drop of the device as measured
between points of reasonably uniform flow on the upstream and
downstream sides is substantially less than the pressure differe-
; ntial measured as now proposed by means of a hole or series ofholes preferably facing the flow on the upstream face of the
diaphragm and a hole or series of holes at right angles to the
flGw or facing partially or wholly downstream or otherwise
arranged for static pressure measurement on the downstream face
of the diaphragm.
Thus, it was discovered in accordance with the present
invention, that if sensing tubes are placed immediately on the
upstream and downstream faces of a specially constructed dia-
phragm, in accordance with the invention, a pressure differential
is obtained between the upstream and downstream measuring points.
When a differential pressure indicating or recording
instrument such as a manometer is connected by any suitable
¦ arrangement of tubes to the sensing means on the upstream and
¦ downstream faces of the diaphragm its reading may be converted
J to one of velocity or mass flow by the use of a factor relating
to the characteristics of the diaphragm device and the fluid
flowing and if the fluid density and viscosi~y are substantially
¦ constant the scale of the instrument may be arranged to read
directly in velocity or mass flow units.
One other purpose of a diaphragm having a multiplicity
of closely spaced and shaped holes as already mentioned is to act
j as a flow straightening or smoothing device thus reducing
turbulence and, in some applications, pressure loss. For instance
when placed in a branch pipe of an air system at or near the
point where air enters it from a main air flow duct it can control
the flow so as to reduce, substantially, the turbulence and
¦ maldistribution which would otherwise occur downstream of the
~ junction. Furthermore, if placed slightly upstream from a grille
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or diffuser it can be so arranged as to ensure satisfactory entry
conditions to the grille or diffuser and therefore satisfactory
; dischar~e conditions from the grille or diffuser.
Yet another purpose of a diaphragm containing a
multiplicity of shaped holes as already described above is to
act as a sound attenuator if constructed of suitable materials.
Alternatively, the device may be used in conjunction with
another device, having a matching series of holes, designed for
sound attenuation.
The accompanying drawings illustrate alternative fluid
flow measuring devices according to the invention and their mode
of use. In these drawings:
Figure 1 is a diagrammatic cross-section of an air
flow pipe 1 equipped with a diaphragm 2 having a multiplicity of
holes 3;
Figure 2 is an enlarged fragmentary elevation of the
diaphragm;
Figure 3 is a transverse section corresponding to
Figure 2 showing a tapping point 4 on the upstream side of the
diaphragm facing the direction of fluid flow and a tapping point
4_ on the downstream side of the diaphragm lateral to the fluid
flow. Each tapping point has a connection 7 to a manometer, the
arrow F indicating the direction of intended air flow through the
diaphragm 2;
Figure 4 is a similar transverse section through
another form of a diaphragm 5 showing an alternative scheme of
tapping points 6 and 6_ with connections 8 to a manometer;
Figures 5 and 6 show two alternative modes of instal-
lation of a diaphragm device 9 including pressure sensing tubes
in a branch pipe from the side wall of a main air flow pipe 10.
In each instance there is an associated diffuser 11 downstream of
the diaphragm. It should be noted that in the Figure 6 instal-
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lation the diaphraqm device is recessed in the side branch 11which has a chamfered upstream corner or shoe 12.
; It should be understood that the diaphragm may be
formed by moulding or by casting or be otherwise fabricated and
that the holes neea not necessarily have a circular cross-section
or be of the same size. The perforations could, for instance,
be of elongated form or of hexagonal or other polygonal form.
Alternatively, the diaphragm could be constructed in any com-
bination of solid or hollow members arranged in "egg box",
j 10 parallel or other form to provide the necessary velocity increase
and to provide convenient means for connecting single or multiple
pressure tappings to a manometer or other differential pressure
j indicating or recording instrument.
3 It may be convenient in some circumstances to arrange
the fixing of the pressure tapping points for both upstream and
downstream pressure connections in one or more plugs which are
¦ inserted into the formed holes in the diaphragm, as shown in
¦ Fig- 3-
2a
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