A flow meter suitable for the measurement of the mass flow rate
of two phase flows. The flow meter has an S-shaped flow tube located
within a housing. The housing has an inlet and outlet which are
in register with the inlet and outlet of the flow tube. The flow
tube has force transducers fitted at the bends of the tube which
measure the reaction forces during fluid flow and enable a mass
flow reading to be obtained.
1. Flow meter comprising a housing having an inlet and an outlet
for a fluid, a flow tube located within the housing and allowing
fluid from the inlet to the outlet, the flow tube having an S bend
geometry comprising a pair of symmetrical bends, one in a first
direction and another in an opposite direction, each of said bends
having a midpoint, the ends of the flow tube being slightly spaced
apart from the respective housing inlet and outlet to enable fluidic
communication between the flow tube and the housing, the flow tube
being rigidly mounted on means for measuring the reaction forces
generated by fluid flow through the flow tube, and said means being
disposed normal to the midpoints in the bends of the flow tube.
2. Flow meter according to claim 1 in which there is a narrow circumferential
gap or slot between the ends of the flow tube and the respective
housing inlet or outlet.
3. Flow meter according to claims 2 or 1 wherein said bends are
90 bends and are disposed in the same plane.
4. Flow meter according to claim 1 in which the fluid flow path
at the outlet has the same direction and is parallel to the fluid
flow at the inlet.
5. Flow meter according to claim 1 in which the bore of the flow
tube is substantially the same as the bores of the housing inlet
6. Flow meter according to claim 1 in which the means for measuring
generated reaction forces comprises a force transducer or load cell.
7. Flow meter according to claim 6 in which the force transducer
or load cell is in the form of a strain gauge or piezo-electric
8. Flow meter according to claim 6 or 7 in which the means for
measuring generated reaction forces is located between the flow
tube and the housing.
The present invention relates to a flow meter and more particularly
relates to a flow meter for measuring flow rates of single or multi
Flow meters are well known and are available in a number of forms
such as mass flow meters, mechanical flow meters, vortex shedding
meters etc. Most of these meters are unsuitable for the measurement
of multiphase fluid flow without previous separation or homogenisation
and the present invention relates to a novel flow meter capable
of measuring the flow of single or multi phase fluids.
Thus according to the present invention there is provided a flow
meter comprising a housing having an inlet and an outlet for fluid,
a flow tube located within the housing and adapted to allow fluid
flow from the inlet to the outlet, the flow tube being adapted to
deflect the direction of fluid flow whereby reaction forces are
generated on the flow tube and means for measuring the generated
The flow tube adapted to deflect the fluid flow direction may have
a number of configurations. It is desirable that the flow tube has
sufficient curvature so that all the components of the fluid flow
impart force to the flow tube while changing the direction of flow.
Preferably the flow tube has an S-bend geometry (most preferably
having two 90.degree. bends) in one plane. It is preferred that
the total orientation change is from 90.degree. to 180.degree. and
it is most preferred that the direction of flow is the same at the
inlet and outlet of the housing. It is preferred that the bore of
the flow tube is the same as that of the inlet and outlet of the
housing and that they are co-axial.
It is preferred that the interior of the flow tube is in fluidic
communication with the housing for example by the use of a narrrow
circumferential gap or slot between the ends of the tube and the
respective inlet or outlet. This arrangement allows rapid pressure
equalisation between the interior of the tube and the housing which
obviates the need for corrections of meter output during pressure
variations occurring during multiphase flow, and the need for a
pressure balancing system whilst allowing a flow meter construction
having relatively few parts thereby promoting more reliability and
ease of manufacture. The tube is preferably of a rigid construction
and may be made from erosion and corrosion resistant materials such
as ceramics, composites, metals etc.
The means for measuring the reaction force is preferably a force
transducer or a load cell. It may be in the form of a strain gauge
or piezo electric device. For a stable configuration it is desirable
to use a tube having a pair of symmetrical bends there being a load
cell arranged normal to each of the bends. The load cell is connected
between the tube and the housing. The sum of the signals from the
load cells is proportional to the couple generated by the change
of fluid momentum. Combination of the signals with those from a
velocity, density or other forms of sensor gives a continuous mass
flow reading which may be processed as required.
For two phase gas-liquid flow it is necessary to measure the phase
hold ups and phase velocities, or to known one phase velocity as
a function of the other velocity, the phase holdup and flow regime.
Measurement of phase holdup may be achieved, for example, by using
either gamma ray densitometry or capacitance sensing. For densitometry
the system required would be two gamma-ray sources mounted 90.degree.
apart on the outside pipe wall, and a scintillation counter mounted
diametrically opposite each source and also on the outside of the
pipe. The devices would be required to measure the complete 0-100%
holdup range. Such equipment is commercially available.
The capacitance sensor is an alternative way of determining phase
hold up, the principle of which is to measure the combined dielectric
constant of the fluids in the pipe. This sensor has, however, to
be mounted on electrically non-conducting pipe. Both of these methods
provide a possible means of measuring the time dependent liquid
holdup in a line.
Preferably the means for measuring the reaction force is located
inside the housing. Preferably the tube has two or more rigid supports
at least one of which has a means for measuring the reaction force.
Most preferably each support has an associated means for mesuring
the reaction force. These arrangements enable bearing friction effects
to be reduced or eliminated and secondary parameters related to
fluid/wall friction e.g. viscosity, may be inferred by differential
measurement of the two output signals.
The invention will now be described by way of example only and
with reference to the accompanying drawings.
FIG. 1 shows a schematic diagram of a flow meter according to the
FIG. 2 is an exploded diagram of the flow meter housing.
A plenum chamber or housing 1 has an inlet 2 and an outlet 3 for
a fluid. Liquid and gas phase input to the inlet 2 is controlled
by valves and measured by sensors 4 to provide the complementary
velocity, density or hold up parameters necessary for mass flow
calculation. The housing 1 is fabricated from mild steel and forms
the main structural element of the assembly. The comparatively massive
plenum frame absorbs mechanical loading due to pipe distortion,
A reaction tube 5 having a pair of opposed right angle bends is
located within the housing and is located in fluid flow relationship
with the inlet and outlet.
The inlet and outlet pipe inner ends are faced off radially to
closely fit the ends of the reaction tube. Axial clearances at these
points are between 0.5 mm and 1 mm depending on flow direction,
the smallest clerance being at the inlet end. The gaps 6 are not
sealed, allowing pressure equalisation between tube 5 and housing
6 to take place.
The reaction tube 5 was mounted on a flexure suspension to keep
its end axes aligned with the inlet and outlet pipe axes, whilst
still allowing free independent axial movement at each end.
The load cells 7 were mounted outside the plenum frame, reaction
tube forces being transmitted by probes passing through positive
clearance ptfe bushes. The preferred embodiment is with the reaction
tube 5 mounted directly onto load cells inside the housing. This
eliminates the need for a reaction tube suspension and probes and
enables the flow meter to be less complex and more accurate.
The load cells fitted to the flow meter were of the "Pye Ether"
UF2-0-101b compression type and an equivalent "Pioden Controls"
The meter assembly was completed by two plenum covers of 12 mm
perspex clamped up with soft rubber gaskets to the flange faces
of the plenum frame.
The sum of the readings from the loadcells 7 is proportional to
the couple generated by the momentum change. Combination of the
signal with that from a velocity or other form of sensor gives a
continuous mass flow reading, which may be sampled, integrated,
or otherwise processed as required.
The difference between the two load cell signals is proportional
to the wall friction/turbulence, etc effects of the fluid path.
If upstream turbulence is allowed for, combination of the difference
signal with velocity and temperature information may give a good
continuous bulk viscosity output.
With two-phase flow, forces measured will have high short-term
variability, due to individual slugs, etc. It is possible that continuous
automatic analysis of characteristic waveforms might be used to
identify the type of flow existing, and an estimate of the gas/liquid
proportions made. For instance, a high reaction reading relative
to the velocity will indicate a high proportion of liquid, and vice
versa. For intermittent flow regimes such as slug flow, intensity
and ratio of slug to gas might be identifiable.
The reaction tube is rigid and fabricated from erosion and corrosion
resistance materials such as ceramics and composites. The reaction
tube is suspended on two load cells inside a pressure tight enclosure.
This arrangement eliminates or reduces pivot friction.
During use, single or multi phase fluid is passed into the housing
through inlet tube 1 into the reaction tube and through the outlet.
The fluid also fills the housing allowing pressure equalisation
between the tube and the housing to take place.
The change in momentum vector caused by the change of direction
of the fluid flow at the bends of the reaction tube results in a
turning couple to be set up about the tube midpoint. The signal
generated by the load cells is proportional to the instantaneous
momentum of fluid passing through the tube. Combination of the load
cells signals with those from other sensors enables mass flow to
be calculated. The fluid phase hold up measurement is made downstream
of the housing/flow tube unit.