Method of Determining a Flow Rate and Related Apparatus

Abstract

A method of determining a flow rate of a liquid includes collecting the liquid in a container; monitoring the collection of liquid in the container with respect to time; and determining a first value of the flow rate based on the monitored collection of liquid in the container with respect to time. An apparatus for determining a flow rate of a liquid is also provided.

Claims

1. A method of determining a flow rate of a liquid, the method comprising: collecting the liquid in a container; monitoring the collection of liquid in the container with respect to time; determining a first value of the flow rate based on the monitored collection of liquid in the container with respect to time; and automatically draining the liquid collected from the container.

2. A method as claimed in claim 1 comprising providing a substantially continuous supply of liquid to the container and repeatedly draining the liquid collected from the container.

3. A method as claimed in claim 1, comprising using a flow meter to determine a second value of the flow rate, the method comprising calibrating the flow meter based on a comparison of the first flow rate value to the second flow rate value.

4. A method as claimed in claim 1, wherein monitoring the collection of liquid in the container comprises determining the mass of liquid collected in the container with respect to time.

5. A method as claimed in claim 1, wherein determining the first flow rate value comprises calculating the derivative of the determined mass of collected liquid with respect to time.

6. A method as claimed in claim 1, wherein monitoring the collection of liquid in the container comprises measuring the pressure of the liquid collected in the container with respect to time.

7. A method as claimed in claim 6, wherein determining the first flow rate value comprises calculating the derivative of the measured pressure of the liquid collected in the container with respect to time.

8. A method as claimed in claim 1, wherein the liquid is drained from the container when a predetermined quantity of liquid has collected in the container.

9. An apparatus for determining a flow rate of a liquid, the apparatus comprising: a container for collecting the liquid; means for monitoring the collection of liquid in the container with respect to time; processing means configured to determine a first value of the flow rate based on the monitoring of the collection of liquid in the container with respect to time; and draining means for automatically draining liquid from the container.

10. An apparatus as claimed in claim 9, wherein the apparatus is configured to provide a substantially continuous supply of liquid to the container and repeatedly to drain the liquid collected from the container.

11. An apparatus as claimed in claim 9, wherein the processing means is configured to calibrate a flow meter, said flow meter being adapted to determine a second value of the flow rate, wherein the processing means is configured to calibrate said flow meter based on a comparison of the first flow rate value to the second flow rate value.

12. An apparatus as claimed in claim 10, wherein the monitoring means comprises means for determining the mass of liquid collected in the container.

13. An apparatus as claimed in claim 12, wherein the processing means is configured to calculate the derivative of the determined mass of the collected liquid in the container with respect to time to determine the first flow rate value.

14. An apparatus as claimed in claim 9, wherein the monitoring means comprises means for measuring the pressure of the liquid collected in the container.

15. An apparatus as claimed in claim 14, wherein the processing means is configured to calculate the derivative of the determined pressure of the collected liquid in the container with respect to time to determine the first flow rate value.

16. An apparatus as claimed in claim 9, wherein the draining means is configured to drain the liquid from the container when a predetermined quantity of liquid has collected in the container.

17. An apparatus as claimed in claim 14, wherein the draining means comprises a siphon or a solenoid valve.

18. A method as claimed in claim 2, comprising using a flow meter to determine a second value of the flow rate, the method comprising calibrating the flow meter based on a comparison of the first flow rate value to the second flow rate value.

19. A method as claimed in claim 18, wherein the liquid is drained from the container when a predetermined quantity of liquid has collected in the container.

20. An apparatus as claimed in claim 10, wherein the processing means is configured to calibrate a flow meter, said flow meter being adapted to determine a second value of the flow rate, wherein the processing means is configured to calibrate said flow meter based on a comparison of the first flow rate value to the second flow rate value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which:

[0038] FIG. 1 shows a schematic view of a prior art system for calibrating a flow meter;

[0039] FIG. 2 shows a schematic view of an apparatus for calibrating a flow meter in accordance with an embodiment of the present invention;

[0040] FIG. 3 shows a graph representing the mass of liquid determined with respect to time with the apparatus shown in FIG. 2, in the case of a pulsed flow;

[0041] FIG. 4 shows a graph representing the mass of liquid determined with respect to time with the apparatus shown in FIG. 2, in the case of a continuous (i.e. uninterrupted) flow;

[0042] FIG. 5 shows a graph representing the first and second flow rate values determined with the apparatus shown in FIG. 2 during a calibration process of a flow meter, and the difference between the first and second determined flow rate values;

[0043] FIG. 6 shows a schematic view of a draining means of the apparatus in accordance with a first variant of the present invention;

[0044] FIG. 7 shows a graph representing the mass of liquid determined with respect to time with the apparatus according to the first variant of the present invention;

[0045] FIG. 8 shows a schematic view of a draining means of the apparatus in accordance with a second variant of the present invention;

[0046] FIG. 9 shows a graph representing the mass of liquid determined with respect to time with the apparatus according to the second variant of the present invention; and

[0047] FIG. 10 shows a schematic view of means for measuring the pressure in the container with respect to time according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0048] An apparatus 101 for determining a flow rate of a liquid in accordance with an embodiment of the present invention will now be described with reference to the accompanying Figures, and in particular with reference to FIGS. 2 to 10.

[0049] The apparatus 101 is configured to determine a flow rate of a liquid. At least in certain embodiments, the apparatus 101 can be used to test the accuracy of a flow meter 103, and can be used to calibrate said flow meter 103. The flow meter 103 is disposed downstream of a flow generator 105 and the apparatus 101 is configured to determine the flow rate of liquid through the flow meter 103. In use, the flow meter 103 generates a signal representative of a measured flow rate therethrough.

[0050] The flow generated by the flow generator 105 can be either a pulsed flow or a continuous (i.e. uninterrupted) flow. The flow rate can be steady-state or variable with time (i.e. increase or decrease). In the present embodiment, the flow generator 105 is a fuel injector for delivering fuel to an internal combustion engine (not shown), particularly a compression ignition combustion engine. The fuel injector is operable to generate a pulsed flow representative of a series of fuel injection cycles.

[0051] With reference to FIG. 2, the apparatus 101 comprises a container 107 for collecting liquid after it has flowed through the flow meter 103, monitoring means 109 for monitoring the collection of liquid in the container 107 with respect to time, and processing means 111 for calculating the liquid flow rate based on the monitored collection of liquid in the container 107 with respect to time. The apparatus 101 further comprises means 113 for draining liquid from the container 107. The apparatus 101 is connected downstream of the flow meter 103. The flow generator 105, the flow meter 103 and the container 107 are in fluid communication with each other. The container 107 is a beaker in the illustrated arrangement, but it will be appreciated that other types of container could be used.

[0052] The monitoring means 109 is configured to measure the mass of liquid collected in the container 107 with respect to time. The monitoring means 109 in the present embodiment is in the form of an electronic weighing scale 109 configured to continuously measure the mass of liquid collected in the container 107. The measured mass can optionally be output in real-time to a display screen 115. In use, the electronic weighing scale 109 measures the mass of the liquid collected in the container 107 throughout a measurement cycle. The electronic weighing scale 109 generates time-related (temporal) mass data which is transmitted to the processing means 111 as a signal. The time-related mass data is represented schematically as a saw-tooth signal in FIG. 2, but it will be appreciated that the form of the signal will depend on the characteristics of the flow generated by the flow generator 105. The electronic weighing scale 109 can have a relatively high precision, for example 1 milligram, to enable a relatively short measurement cycle. Alternatively, a relatively long measurement cycle can be implemented with a relatively low precision electronic weighing scale 109, for example having a precision of 1 gram.

[0053] The processing means 111 is configured to calculate a first value of the liquid flow rate based on the measured mass of the liquid collected in the container 107 with respect to time. The processing means 111 comprises a receiver 117 and at least one processor 119 (only one of which will be described herein). The receiver 117 is coupled to the electronic weighing scale 109, and is adapted to record the measurement of the mass of collected liquid in the container 107 with respect to time. The processor 119 receives the time-related mass data and is configured to calculate a first value of the liquid flow rate by calculating the derivative of the measured mass of the liquid collected in the container 107 with respect to time. The processor 119 can thereby determine an instantaneous flow rate of the liquid. Thus, the flow rate of the liquid can be determined at any given time.

[0054] The processor 119 is also coupled to the flow meter 103 to receive a signal from the flow meter 103. The processor 119 calculates a second value of the flow rate based on the signal received from the flow meter 103.

[0055] The processor 119 calculates the difference between the first flow rate value and the second flow rate value. The processor 119 can generate a calibration factor based on this difference which can be used to calibrate the flow meter 103.

[0056] The draining means is in the form of a siphon 113 in the present embodiment. The siphon 113 comprises a liquid inlet 121 and a liquid outlet 123. The liquid inlet 121 is disposed within the container 107. The liquid outlet 123 is disposed outside the container 107 and is in fluid communication with a reservoir (not shown) for collecting the liquid. The siphon 113 drains the liquid collected in the container 107 when the liquid reaches a predetermined threshold.

[0057] A method of using the apparatus 101 to determine a flow rate of a liquid and to calibrate a flow meter 103 in accordance with an embodiment of the present invention will now be explained in detail with reference to FIGS. 2 to 10.

[0058] During a measurement cycle, liquid flows from the flow generator 105 through the flow meter 103. The flow meter 103 measures the flow rate of the liquid through the flow meter 103 and the measured flow rate is recorded by the processor 119. The liquid is collected in the container 107. Throughout the measurement cycle, the electronic weighing scale 109 continuously measures the mass of fluid collected in the container 107. The measured mass is recorded by the receiver 117. Once the mass of collected fluid reaches a predetermined value, the siphon 113 drains the collected fluid from the container 107 (for example to a reservoir). The mass measured with respect to time by the apparatus 101 is represented by the curves A and B in FIGS. 3 and 4, respectively for a pulsed flow and a continuous flow. The processor 119 selects measurement time regions M corresponding to the time during which liquid is collected in the container 107, i.e. corresponding to the or each measurement cycle. The selection of the measurement time regions M is based on a measured minimum mass of liquid in the container 107. In a variant, the measurement time regions M are determined by the profile of the measured curve. In these regions, the processor 119 calculates the derivative of the mass of collected liquid with respect to time. The calculated derivatives are represented by the curves A and B in FIGS. 3 and 4, respectively for a pulsed flow and a continuous flow. A correction factor can be introduced to take into account the force of the liquid acting on the apparatus. The correction factor can be dependent on the calculated flow rate. The correction factor can be determined empirically. The corrected mass is represented by the curve C in FIG. 4.

[0059] The processor 119 calculates a first flow rate value based on the measurement of the mass of liquid collected in the container 107. The processor 119 calculates a second flow rate value based on the signal output from the flow meter 103. A comparison is then made of said first and second flow rate values to determine a difference therebetween. The flow meter 103 is then calibrated based on the difference between the first flow rate value and the second flow rate value. The siphon 113 is used to drain the container 107. FIG. 5 shows the first flow rate values (represented by squares) and the second flow rate values (represented by diamonds) determined during the calibration process of the flow meter 103, and the difference between the first and second determined flow rate values (represented by triangles).

[0060] Variants of the draining means are described with reference to FIGS. 6 to 9. A first variant is illustrated in FIGS. 6 and 7. FIG. 6 shows draining means in the form of a solenoid valve 125 disposed in a drainage line. The solenoid valve 125 comprises a liquid inlet 127 and a liquid outlet 129. The liquid inlet 127 is connected to the container 107, and the liquid outlet 129 is in fluid communication with the reservoir. This arrangement is an alternative to the siphon 113 described herein. FIG. 7 shows a graph representing the mass of liquid measured with respect to time with the solenoid valve 125 (curve D), and the corresponding derivative with respect to time (curve D).

[0061] A second variant is illustrated in FIGS. 8 and 9. As shown in FIG. 8, the draining means is in the form of an automatic priming siphon 131. The automatic priming siphon 131 can be used when a low flow rate is to be determined by the apparatus 101. (The siphon 113 described in the previous embodiment may not be able to drain the container 107 automatically due to the low flow rate.) The automatic priming siphon 131 comprises a siphon portion 133 and an additional source of liquid 135 connected to the siphon portion 133 for priming the draining of liquid in the siphon portion 133. The siphon portion 133 comprises a liquid inlet 137 and a liquid outlet 139. The liquid inlet 137 is disposed in the container 107, and the liquid outlet 139 is in fluid communication with the reservoir (not shown). FIG. 9 shows a graph representing the mass of liquid measured with respect to time with the automatic priming siphon 131 (curve E), and the corresponding derivative with respect to time (curve E).

[0062] An alternative monitoring means 141 is represented in FIG. 10. The monitoring means 141 is configured to measure the pressure of a liquid collected in a vertical column 143 connected to the flow meter 103. The pressure is then used to determine the mass of liquid collected in the container 107. The vertical column 143 comprises an upper end 145 and a lower end 147. The upper end 145 is open to atmosphere. Means for measuring the pressure in the vertical column 143 is connected to the lower end 147 of the vertical column 143. The means for measuring the pressure in the vertical column 143 is for example in the form of a pressure sensor 149. The vertical column 143 comprises a liquid inlet 151 and a liquid outlet 153. The liquid inlet 151 is intended to receive liquid from the flow meter 103. A draining means such as a solenoid valve 155 as described above is disposed at the liquid outlet 153 to drain the liquid from the vertical column 143. The arrows shown in FIG. 10 represent the liquid flow. In operation, liquid flows from the flow meter 103 to the vertical column 143, through the liquid inlet 151. At the same time, the pressure sensor 149 measures the pressure within the vertical column 143, while the liquid is flowing into the vertical column 143. The pressure is measured with respect to time. As the pressure in the vertical column 143 is proportional to the mass of liquid in the vertical column 143, the flow rate can be deduced from the measurement of the pressure with respect to time.

[0063] It will be appreciated that various changes and modifications can be made to the apparatus 101 described herein without departing from the scope of the present invention, as set out in the appended claims. For example, the electronic weighing scale 109 has been described as continuously measuring the mass of fluid collected in the container 107. In a modified arrangement, the electronic weighing scale 109 could be configured to measure the mass of the collected liquid intermittently, for example to take a measurement at predefined time intervals, such as 0.1 seconds.

[0064] The apparatus 101 described herein is configured to determine the flow rate of a liquid, but it will be appreciated that the apparatus 101 could be modified to determine the flow rate of a gas. Also, rather than monitor the collection of fluid in a container, the method could comprise monitoring the fluid in a reservoir provided upstream of the flow generator.