FORM 2
THE PATENT ACT 1970
[39 OF 1970]
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
[See section 10; rule 13]
“FLOW MEASUREMENT SYSTEM AND A METHOD THEREOF”
Name of the Applicant: Indian Institute of Science; Bangalore 560012, Karnataka, India.
Nationality: IN
The following specification particularly describes the invention and the manner in which it is to be performed
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TECHNICAL FIELD
The present disclosure relates to flow measurement.
BACKGROUND
Accurate mass flow measurement is essential in many industrial processes for various monitoring and flow control applications. Different types of flowmeters are available based on various properties of the fluid. These can be classified into two major types namely, disruptive type and non disruptive. Disruptive type of flow meter causes change in the operating point, whereas the operating point is not disrupted by the inclusion of the non-disruptive type of flow meter.
Differential pressure flowmeters employ the Bernoulli equation which describes the relation between pressure and velocity of flow. Elbow, flow nozzle, orifice plate, venturi tube, pitot tube, segmental wedge, V-cone and Dall tube work based on this principle. In variable area flowmeters like rotameter, movable vane meter cross sectional area available to the flow varies with the flow rate. Positive displacement flowmeters measure volumes of fluid flowing through by counting repeatedly the filling and discharging of known fixed volumes. Variety of designs exists like nutating disc, rotating valve, oscillating piston, oval gear, rotating impeller, etc. Turbine flowmeters, like windmills, utilize their angular velocity to indicate the flow velocity. A good turbine flowmeter requires well designed and placed aerodynamic or hydrodynamic blades that are suitable for the fluid and flow condition and bearings that are both smooth and durable to survive the sustained high-speed rotation of the turbine. Coriolis meters typically consist of one or two vibrating tubes with an inlet and an outlet and mass flow is determined based on the action of the fluid on the vibrating tubes called as Coriolis Effect. Vortex flowmeters also know as vortex shedding flowmeters, measure the vibrations of the downstream vortexes caused by the barrier placed in a moving stream. The vibrating frequency of vortex shedding can then be related to the velocity of flow.
Non-disruptive type of meter does not disturb the operating point in the system in which flow rate has to be measured. Electromagnetic flowmeters or magnetic flowmeters obtain the flow velocity by measuring the changes of induced voltage of the conductive fluid passing across a controlled magnetic field. Ultrasonic flowmeters pass
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ultrasonic waves in a pre-configured acoustic field. Transit time type of ultrasonic flowmeter makes use of the difference in the time for a sonic pulse to travel a fixed distance, first against the flow and then in the direction of flow. Doppler Ultrasonic flowmeters rely on the Doppler Effect to relate the frequency shifts of acoustic waves to the flow velocity. Thermal flowmeters measure the heat carried away from the sensor by the passing flow to determine the mass flow rate.
Limitations of the prior art
Disruptive type of meters have a medium or high pressure drop across the meter, which causes significant change in operating point especially where the flow rate is very small. In case of differential pressure meters, since pressure drop is proportional to square of the flow rate, scale is non-linear and depends on the type of the flow (laminar or turbulent). Variable area flowmeters cannot be used in non/low gravity environment and for low flow rate measurement. Though positive displacement meters are linear, compensation for variation in fluid properties due to temperature is not possible. Magnetic flow meters are not used for low flow measurement due to low signal to noise ratio (SNR) since induced voltage is very small. Fluid has to be conductive for using magnetic flow meter. Ultrasonic flow measurement highly depends on the Reynolds number. None of the existing meters give null-deflection measurement technique.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the bock diagram of proposed flow measurement system.
Figure 2 shows control bock diagram of proposed flow measurement system.
Figure 3 shows linearized flow measurement system characteristic.
Figure 4 show the experimental results of the flow measurement system.
DETAILED DESCRIPTION
The primary embodiment of the disclosure is a flow rate measurement system (1) comprising means for introducing flow resistance (2) in a pipe (6) to oppose flow of fluid; pressure sensor (3) mounted across the measurement system (1), said sensor measures pressure drop across the measurement system (1); controller (4) receives pressure difference from the sensor and generates control voltage, and pump (5)
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integrated into the pipe is adapted to receive the control voltage from the controller (4) to nullify the pressure drop.
In yet another embodiment of the disclosure the resistance introduced in the pipe (6) is friction of the pipe (6), venturi, orifice or any other standard structure that introduces pressure drop.
In still another embodiment of the disclosure the pressure sensor (3) is a differential pressure sensor.
In still another embodiment of the disclosure the controller (4) is Proportional-Integral controller or any other standard controller.
In still another embodiment of the disclosure the pump nullifies the pressure drop by matching the pump pressure to the pipe pressure drop.
Another embodiment of the disclosure is a method for determining mass flow rate of a fluid flowing in a pipe (6), said method comprises: introducing flow resistance (2) in a pipe (6) for opposing flow of fluid; measuring pressure drop across the measuring system (1); generating control voltage using the pressure drop and applying control voltage onto a pump (5) for nullifying the pressure drop across the flow measurement system (1), wherein the control voltage gives measure of flow rate.
In yet another embodiment the introduced resistance in the pipe is friction of a pipe (6), venturi or orifice construction.
In still another embodiment the pressure difference is measured using a differential pressure sensor (3).
In still another embodiment the pressure difference is applied to a controller (4) as a feedback to generate the control voltage.
In still another embodiment the pump (5) nullifies the pressure drop by matching the pump pressure with the pipe pressure drop.
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The flow measurement system (1) of the instant disclosure is non-disruptive and null deflection. The flow measurement system is shown in figure 1. The system (1) consists of two air columns at the ends of the meter and a centrifugal pump (5) and flow resistance in between them. An artificial resistance is introduced to the flow of fluid. This is done by constricting the cross sectional area of the pipe (6), increasing the friction in the pipe, smoothly varying constriction like venturi, orifice constriction or or any standard structure that introduces pressure drop.
Each air column is made of T-shape having 3 terminals. Outlet at the top of the air columns are connected to the terminals of the differential pressure sensor (3). Other two terminals of the air columns are interconnected to the flow resistance and the centrifugal pump (5) through the pipes (6) of corresponding diameter. There will be pressure drop due to this flow resistance. Differential pressure sensor (3) is used to measure the pressure drop across this flow resistance. Pressures at these two points are represented as P1 and P2. Most of the existing differential pressure flow meters have a medium or high pressure drop though they are simple and easy in design.
Inclusion of this type of meter causes significant pressure drop in a system and changes the operating point especially where the flow rate is very small. In order to reduce this obstruction to flow of fluid, a pump (5) is being introduced that has smoothly variable pressure head. Input voltage to this pump (5) is decided according to the pressure drop across flow resistance. For a given flow rate, at one particular input voltage to pump (5), pressure head due to pump (5) cancels pressure drop due to the flow of fluid. At this point the pressure difference P1−P2 becomes zero.
As the flow rate increases, pressure drop across the flow resistance also increases depending on the type of flow. So more voltage has to be applied to the pump (5) in order to compensate (balance) the pressure drop. The voltage applied to this pump (5) will directly give the measure of mass flow rate. Dynamic response of the flow meter can be improved by automatically controlling the pressure drop to zero using any standard controller (4) as shown in the figure 2. Whenever there is a small change in the flow rate, the controller (4) should vary the output signal according to the pressure drop and finally adjust P2 to P1.
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Figure 2 shows the block diagram of the control system. The function of the controller (4) is to keep the output at zero. Output y is the pressure difference P1−P2 between the two ends of flow meter. This is sensed using a pressure transducer and fed back as feedback signal. Since the controller has to make the output to zero, reference signal is also kept zero. Error signal e obtained is given to a Proportional-Integral controller or any other standard controller can be used. Output of this controller which is called as control voltage Vc is fed to the pump. Corresponding to the control voltage, pump generates pressure Pc in opposite direction to the pressure drop in the flow meter system.
The pump (5) exerts an influence on the measured system so as to oppose the effect of the pressure drop due to flow rate which is being measured. This influence and the quantity to be measured are balanced until they are equal in magnitude but opposite in direction, yielding a null measurement. For any flow rate, the controller (4) adjusts its output such that pressure drop P1−P2 is made zero. Under steady state, pressure drop across the meter is made zero (minimized). Therefore, inclusion of this type of meter does not affect the functioning of the system. Hence, it is non-disruptive type of meter. Major advantage of non-disruptive type of measurement is that one can measure very small flow rates limited only by the resolution of the pressure sensor (3).
Centrifugal pump is used for compensating the pressure drop across the flow resistance (2). This is a rotodynamic pump that uses a rotating impeller to increase the pressure of a fluid. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward and exits from the outlet piping. Impeller is rotated by an electrical motor, which is driven the control voltage obtained from the controller (4).
The flow measurement system (1) can be used for any type of liquid or gas. The flow meter is unaffected by the changes in properties of the fluid like temperature, pressure, viscosity and density. The system can be designed for any type of flow i.e. both laminar and turbulent. The system can be used for very low flow measurement applications as following:
• Fuel flow measurement in vehicles, which can be used to get instantaneous mileage or optimal speed at which fuel consumption is minimum.
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• Fluid flow monitoring and control in thermal and solar applications like water heating, space heating and cooling, cooking, etc.
• Flow measurement in a system where flow is not explicitly controlled. (Disruptive flow meter would change the operating point if it is used).
• Custody transfer of oil and gas.
• Accurate chemical dosing in chemical treatment, pharmaceuticals.
• Biomedical applications.
For a given range of flow rate, it is possible to design a flow resistance R2 such that the non-linearity of the compensating pump (5) is canceled by the non-linearity of R2. This ensures the linearity of the meter as shown in figure 3.
The experimental results of the flow measurement system are tabulated below and diagrammatically shown in figure 4.
Voltage
in V
Mass flow rate in kg/s
Voltage
in V
Mass flow rate in kg/s
Voltage
in V
Mass flow rate in kg/s
1.3
.006988
1.84
.014286
2.74
.024027
1.32
.007181
1.85
.013888
2.77
.025240
1.37
.00884
1.9
.013509
2.79
.025063
1.38
.007775
1.92
.015037
2.86
.026192
1.41
.008329
1.95
.014992
2.95
.027233
1.46
.008297
1.97
.015852
2.97
.027352
1.49
.009421
2.01
.016334
3
.027159
1.53
.009417
2.03
.016377
3.06
.027996
1.55
.009747
2.08
.016667
3.09
.028201
1.61
.010469
2.15
.017618
3.17
.027964
1.63
.010967
2.15
.017642
3.18
.028703
1.64
.011098
2.23
.018403
3.26
.028620
1.64
.011279
2.24
.018622
3.26
.029481
1.69
.011579
2.32
.019470
3.3
.029011
1.7
.012398
2.34
.018918
3.39
.030469
1.72
.012330
2.42
.021240
3.4
.030845
1.73
.011879
2.45
.021044
3.41
.031056 7
1.77
.012150
2.48
.021053
3.43
.031536
1.77
.013273
2.49
.021195
3.51
.032341
1.78
.013319
2.58
.022114
3.58
.032873
1.78
.012201
2.66
.023031
3.6
.032362
1.82
.012616
2.72
.023419
3.63
.032175
Finally, while the disclosure has been described with reference to a few specific embodiments, the description is illustrative of the disclosure and is not to be construed as limiting the disclosure. Various modifications may occur to those skilled in the art without departing from the true spirit and scope of the disclosure as defined by the appended claims.
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We claim:
1. A flow rate measurement system (1) comprising:
a. means for generating resistance (2) in a pipe (6) to oppose flow of fluid;
b. pressure sensor (3) mounted across the resistance (2) of the pipe (6), said sensor measures pressure drop across the flow resistance;
c. controller (4) receives pressure difference from the sensor and generates control voltage, and
d. pump (5) integrated into the pipe (6) is adapted to receive the control voltage from the controller (4) to nullify the pressure drop.
2. The system as claimed in claim 1, wherein the resistance generated in the pipe (6) is friction of the pipe, venturi, orifice.
3. The system as claimed in claim 1, wherein the pressure sensor (3) is a differential pressure sensor.
4. The system as claimed in claim 1, wherein the controller (4) is Proportional-Integral controller.
5. The system as claimed in claim 1, wherein the pump nullifies the pressure drop by matching the pump pressure to the pipe pressure drop.
6. A method for determining mass flow rate of a fluid flowing in a pipe (6), said method comprising acts of:
a. generating resistance in a pipe (6) for opposing flow of fluid;
b. measuring pressure drop across the resistance;
c. generating control voltage using the pressure drop and
d. applying control voltage onto a pump (5) for nullifying the pressure drop in the pipe (6), wherein the control voltage gives measure of flow rate.
7. The method as claimed in claim 6, wherein the generated resistance in the pipe (6) is friction of a pipe, venturi or orifice construction.
8. The method as claimed in claim 6, wherein the pressure difference is measured using a differential pressure sensor.
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9. The method as claimed in claim 6, wherein the pressure difference is applied to a controller (4) as an input to generate the control voltage.
10. The method as claimed in claim 6, wherein the pump (5) nullifies the pressure drop by matching the pump pressure with the pipe pressure drop.
Dated this 31st day of August, 2009.
P.H.D. RANGAPPA
IN/PA-1538
OF K & S PARTNERS
AGENT FOR THE APPLICANT