VORTEX FLOW METER WITH MICROMACHINED SENSING ELEMENTS

Abstract

The design and structure of a vortex flow meter with large dynamic range utilizing a micro-machined thermal flow sensing device for simultaneously measurement of volumetric flowrate via vortex street frequency as well as mass flowrate is exhibited in this disclosure. The micro-machined thermal flow sensing device is placed at the central point of a channel inside the bluff body where the channel direction is not perpendicular to the direction of fluid flow in the conduit. The thermal flow sensing device is operating in a time-of-flight principle for acquiring the vortex street frequency such that any surface conditions of the device shall not have significant impact to the measured values. With a temperature thermistor on the same micro-machined thermal flow sensing device, the vortex flow meter shall be able to output the fluid temperature as well as the fluid pressure.

Claims

1. A smart vortex flow meter having extended dynamic range and low pressure drop, which contains a bluff body in which the channel for measurement of vortex frequency by a thermal flow sensing device is not perpendicular to the fluid flow direction the thermal flow sensing shall further incorporate an integrated micro-machined flow sensing device with both time-of-flight sensing for the vortex street frequency measurement and calorimetric or thermal dissipative sensing elements for mass flow data acquisition; an additional thermistor on the sensing device substrate shall meter the fluid temperature the vortex flow meter shall be comprising A bluff body in the form of a trapezoid being placed in the middle of the fluid flow conduit of the said vortex flow meter; A channel inside the bluff body and is not perpendicular to the fluid flow direction but tilted towards the fluid flow direction; A micro-machined or MEMS silicon thermal flow sensing device that is used for the purpose of metering vortex street frequency as well as thermal mass flowrate of the fluid; An addition thermistor on the substrate of the micro-machined thermal flow sensing device for temperature measurement of fluid; A meter head housing the signal conditioning and data processing as well as user interface electronics and local display; A fluid flow conduit having a venturi structure; and A complete enclosure connects and houses the said components for being constituent into a complete and stand-alone meter system; such an enclosure shall also meet the safety requirements for industrial application domain.

2. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein said bluff body shall be in the form of a trapezoid where the front side dimension shall be from 0281×D×cos(α) to 0.281×D×cos(α/2); D is the fluid flow conduit diameter (D) and a is the tail angle of the said trapezoid; the preferred front side dimension shall be 0.281×D×cos(α); the tail side dimension of the bluff body shall be 0.03×D×cos(α) to 0.3×D×cos(α), but preferably 0.09×D×cos(α); and the tail angle shall be from 20 to 40°, but preferably 25 to 35°, and most preferably 26°.

3. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein the channel for measurement of the vortex street frequency shall be made inside and in the middle of the bluff body; the said channel shall not be perpendicular to the fluid flow direction but tilted with an angle; the angle with respect to the side of the bluff body shall be from 70 to 110%, but preferably 80 to 100° and most preferably 90°, the preferred far distance of the channel entrance to the front side of the bluff body shall be (½)×D×cos(α) to (⅓)×D×cos(α), but preferably (⅓)×D×cos(α).

4. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein the channel for measurement of the vortex street frequency shall made into a shape of circular or square, but preferably in a shape of square; the channel size is preferably from 1 to 5 mm in diameter but most preferably 2 mm in diameter; the channel is further preferably made into a venture shape or a trumpet shape.

5. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein said micro-machined thermal flow sensing device shall preferably have two pairs of sensing elements; one pair shall be operating in the principle of thermal time-of-flight and shall be utilize to measure the frequency variations of the vortex street generated by the bluff body and from the fluid flow through the channel via the differential pressure differences across the channel; the other pair of the sensing elements shall be operating in the principle of calorimetric sensing which shall be utilized to measure the mass flowrate of the fluid flow through the channel and further correlated to the mass flowrate of fluid in the main fluid flow conduit.

6. The vortex flow meter with extended dynamic range and low pressure loss of claim I wherein said micro-machined thermal flow sensing device shall preferably have an independent thermistor on the substrate of the device for measurement of the temperature of the fluid.

7. The vortex flow meter with extended dynamic range and low pressure loss of claim I wherein said micro-machined thermal flow sensing device shall have the capability to relay the data for processor to calculate the fluid pressure from the acquired volumetric flowrate, mass flowrate and temperature values of the fluid.

8. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein said micro-machined thermal flow sensing device shall be preferably installed at the channel wall and at the central point of the channel inside the bluff body.

9. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein said meter head shall house the signal conditioning, data process, as well as user interface electronics; the meter head shall further have a local display that shall display the desired metrology information including the volumetric flowrate, mass flowrate, temperature and pressure; if desired, the totalized flow shall also be displayed.

10. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein said user interface shall contain the software and hardware that can be locally accessed by the onsite users and shall also have the networking capability as well as remote data access and data safety considerations.

11. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein said meter signal conditioning and data process electronics shall work at a low power mode and shall be able to be powered by battery, which shall be further in compliance with the industrial standard safety regulations.

12. The vortex flow meter with extended dynamic range and low pressure loss of claim 1 wherein said fluid flow conduit shall be made in the venturi structure having the bluff body placed at the middle of the fluid flow conduit; the said fluid flow conduit shall further have installed a pair of flow conditioner including a flow straightener and a flow profiler at the entrance of the fluid flow conduit.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0017] FIG. 1 is the vortex flow meter with a thermal mass flow sensor to measure the vortex frequency exhibited in the prior arts. FIG. 1 is a direct measurement with the sensor being placed inside the bluff body while

[0018] FIG. 2 utilized an elevated channel inside the bluff body.

[0019] FIG. 3 is the detailed graphic presentation of the said bluff body with the asymmetrical channel where the two ends at the channel entrances shall have different pressure values creating a large pressure drop or differences.

[0020] FIG. 4 is an improved embodiment where the channel is made into a venturi or trumpet structure for better flow stability and sensitivity at the central of the channel where the sensor being placed.

[0021] FIG. 5 and FIG. 6 show top and side view of the said bluff body placed inside the fluid conduit and the corresponding positions of the channel for vortex frequency acquisition as well as for the mass flow measurement.

[0022] FIG. 7 is the preferred configuration of the said micro-machined flow sensor for the said vortex flow meter.

[0023] FIG. 8 is an example of the assembly of the said vortex flow meter.

[0024] FIG. 9 and FIG. 10 are shown the actual data for both the volumetric flowrate and mass flowrate simultaneously acquired by the said vortex flow meter from the single micro-machined sensor placed in the channel inside the bluff body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The two examples of utilizing thermal mass flow sensor to measure the vortex frequency are shown in FIG. 1 and FIG. 2 which are both from prior arts revealed by S. Kiguchi (Karman vortex flow meter, U.S. Pat. No. 5,708,214, Jan. 13, 1998) from some earlier unexamined Japanese patent publications. The conventional usage of the thermal mass flow for vortex frequency measurement was to place the sensor inside the bluff body in a channel perpendicular to the fluid flow direction. Although the traditional thermal mass flow sensor was normally a metal hot wire material which had a fast response time and it is excellent to meter the frequency generated by the vortex street, it is however easily got contaminated or damaged by the particles or other materials in the fluid which could adhere to the surface of the hot wire in the fluid, hence it suffers a reliability issue. The improvement of the art with an elevated passage as exhibited in FIG. 2 which shall be less prone to the contamination but the channel design had the problem to establish a stable differential pressure during the measurement which leads to large errors for the acquired data.

[0026] For the preferred embodiment, the present disclosure of a new vortex flow meter design that utilizes a micro-machined integrated thermal flow sensor inside an asymmetrical channel of a trapezoid bluff body is show in FIG. 3. The design has two crucial improvements to the current state-of-the art vortex flow meters. On the one hand, the asymmetrical design enables a significant improvement of the sensitivity to the measurement of the difference pressure as the pressure point of at the two ends of the channel is asymmetrical and thus the difference shall be larger than that in the case of the perpendicular configuration, which contributes in particular for the improvement of the low flowrate metrology. On the other hand, the design of the asymmetrical or non-perpendicular channel to the fluid flow direction leads to the pressure values at the two ends of the channel shall be different. In this configuration, the differences shall drive the flow passing through the channel alternatively but not equally due to the vortex street generated by the bluff body. However, the vortex frequency shall not be affected by the configuration which shall be further correlated to the volumetric flowrate of the fluid flowing in the conduit where the bluff body is placed. The asymmetrical channel arrangement shall allow the mass flow data be collected by comparison with the flow from the two sides of the channel. With the temperature of the fluid being simultaneously measured by the flow sensor, the pressure of the fluid in the conduit can also be calculated. Thus the present design discloses a new vortex flow meter that can use a single thermal flow sensor to measure both volumetric flowrate and mass flowrate while the other metrology parameters for the flow fluid of interest can also be obtained without additional sensing elements such as individual pressure and temperature sensors.

[0027] The bluff body front side dimension 110 is normally constrained by the fluid conduit diameter and the stable output requires that it is limited by 0.281 times of the fluid conduit diameter (D). This constrain in many cases contributes to the large pressure drop or loss for vortex flow meters. With the differential pressure channel 114 tilted, the effective length of the channel is also increased compared to the perpendicular one accounting from the pressure point of the larger distance from the bluff body front side. In the case that the angle 115 between the channel 114 and the sidewall of the bluff bode 112 is 90°, the present disclosure found that the front side dimension 110 can be reduced. Let the bluff body tail angle 116 be α, the front side dimension could be reduced to 0.281×D×cos(α/2) to 0.281×D×cos(α) without loss the reproducibility in the vortex street frequency measurement. This reduction shall reduce the pressure loss compared to those by the conventional vortex flow meters for a significant factor. As the measurement of the vortex frequency is from the channel inside the bluff body, this leaves a better freedom for the dimension of the parallel side 111 with respect to the front dimension 110. In the present disclosure, the integrated thermal flow sensor 130 is placed at the center of the pressure measurement channel 114. The channel size is also critical for the measurement sensitivity. A small one shall limit the low flow detection capability as the small differential pressure at low flowrate comparably to large pressure drop across the channel shall prevent fluid flow from traveling through while a large dimension shall generate flow instability resulting in inaccurate measurement. It is therefore an improvement to the embodiment exhibited in FIG. 3 is to configure the channel 124 into a venturi type as exhibited in FIG. 4. Further, the channel 124 may not be made with the exact dimensional constrains according to a venturi structure due to the size and space limitations, it is nonetheless that the dimension of the entrance of the channel shall be larger than that at the center where the flow sensor is placed such that the compression shall increase the flow stability and the acceleration of the flow speed that shall increase the sensitivity at the low flowrate for the flow sensor.

[0028] FIG. 5 and FIG. 6 exhibit the position of the bluff body 500 inside a fluid flow conduit 100, where FIG. 5 is a top view and FIG. 6 is a side view. In the preferred embodiment, the bluff body shall be placed at the middle of the fluid flow conduit, and it shall fill the conduit from top to bottom for the better vortex street stability. For the same reason, the channel 114 for measurement of the vortex frequency shall also be aligned to the center of the fluid flow conduit. This is in particular important for the low flowrate measurement as the profile of the flow in the conduit shall have the highest flowrate at the center of the conduit.

[0029] Thermal mass flow sensor has not been a conventional sensor for the vortex flow meters. Instead the pressure sensor placed at a distance to the tail of the bluff body is widely used. The main reason is the reliability of the thermal flow sensor. The traditional hot wire thermal flow sensor is prone to be fragile and even heavy vibration could result in damage. The late improved thermal sensors made on a substrate make it more robust but it could as well suffer from the surface contamination which shall make the data acquisition very unreliable. Therefore, it is the objective of the present disclosure to have the significantly improvement in the embodiment. FIG. 7 is the preferred micro-machined thermal flow sensor device that shall be utilized as the sensing elements for the disclosed vortex flow meter. The said device has the sensing elements deposited on a silicon substrate 700, or alternatively they can be deposited on a glass or ceramic or other solid state substrate. A thermal isolation membrane 705 can be made on the substrate for better thermal response. In the middle of the membrane it is the micro-heater 710, which provides the thermal source for the thermal sensing principles. A pair of thermistors, 721 and 722, shall be served as the calorimetric sensing elements which can measure the mass flowrate of the fluid via the measurement of the amplitude changes of the sensed heat variation due to the heat Migration carried by the fluid flow. The second pair of thermistors, 731 and 732, is a time-of-flight sensor that senses the thermal pulse or time of the heat carried away from the micro-heater to the sensing thermistor(s). This time lapse is directly proportional to the fluid flow speed. The time-of-flight sensors are used to measure the oscillation or frequency changes inside the channel that is corresponding to the vortex street frequency generated by the bluff body. The time-of-flight sensing is a frequency detection approach that is less prone to the changes in the surface conditions of the sensing chip. It is therefore more reliable in an environment where contamination is likely to be present. Use of a frequency measure instead of amplitude as it is in conventional approaches to meter the vortex frequency changes then effectively solves the current reliability issues for the thermal flow sensor applications in the vortex metering technology. The thermistor 740 is made on the substrate such that it has a better accuracy for measurement of the environment (fluid) temperature. The pads 770 that connect each thermistor can be distributed uniformly on two sides of the substrate or at one side which provide the interface for sensors to the signal conditioning and control electronics circuitry. The said complete thermal flow sensing device can then measure the volumetric flowrate, the mass flowrate as well as the temperature data acquired simultaneously via the single device, the pressure of the fluid is calculated based on the acquired data. Therefore, the present disclosure shall meter all of the desired metrology values with a single device.

[0030] For the preferred embodiments, the assembly of the said vortex flow meter is shown in FIG. 8. The meter head 810 shall house the signal conditioning and control electronics as well as the display of the said meter. The bluff body 850 is placed at the middle of the fluid conduit 860 which is made in a venturi structure that shall be effective for enhanced flow stability. A flow conditioner 870, preferably to be composed of a flow straightener and a flow profiler shall be installed at the entrance of the fluid conduit of the said vortex flow meter for assurance of the stable flow. The 820 shall be the connection support house for the cables that connect the sensors and the electronics. The size of 820 is preferred to be made in certain length that shall effectively isolate any high temperature fluid that the meter may measure, for example in case of steam metrology. The cable channel 830 and sensor interface cable house 840 are preferred to be made via metal for the protection as well as temperature isolation via high temperature materials such as high temperature polymer or epoxy. Finally the interface 880 shall provide the user access to the meter as well as communication port for networking or remote data management.

[0031] For the preferred embodiment, the data acquired from the said vortex flow meter are exhibited in FIG. 9 and FIG. 10. The volumetric flowrate are linear in an extended dynamic range starting from the onset of turbulence at the Reynold number of 2300 which is far lower than those by the current state-of-the art vortex flow meters where the lowest detecting limit is above 10000 Reynold number. The extended, range shall be critical in metering applications for custody transfer or tariff. The mass flowrate data (FIG. 10) from the same sensing element device can also be acquired at the same time. As the vortex frequency meters the volumetric flowrate of the fluid in the conduit, the mass flowrate can be acquired via the thermal mass flow sensor in the asymmetrical channel, this shall enable to derive the desired pressure data from the said vortex flow meter without additional pressure sensor. With the mass flowrate, V.sub.mass, and volumetric flowrate, V.sub.vol, and the acquired temperature value, T, the pressure of the fluid, P, can then be obtained by

P=K×T×(V.sub.mass/V.sub.vol)   (1)

where the parameter K=P.sub.0/T.sub.0. And it is a constant obtained at the desired calibration fluid conditions (P.sub.0, T.sub.0). Therefore the present disclosure shall have the advantage of acquiring all flow metrology data with a single sensor device.

[0032] For the preferred embodiment, in case that the fluid media is identical but the density shall vary during the measurement even without the changes of the fluid pressure such as for the steam metrology where the steam can be in the form of saturated or non-saturated media. In such cases, the density measurement shall be critical for an acquisition of accurate metrology values which are however not available with the existing technology. In the present disclosure, as the sensor device used to measure the vortex frequency can also meter the mass flowrate. The said vortex meter for steam measurement with various densities could then be viable. During the calibration, the meter can register both the volumetric and mass flowrate and at the same pressure and temperature conditions. When the density changes while the temperature and pressure are kept the same, the metered volumetric and mass flowrate data shall then be deviated with which the compensation scheme shall be able to be applied based on the pre-set density values.

[0033] For the preferred embodiment, in case that a substantial contamination covers the sensor device surface, while the vortex frequency measurement shall not be impacted due to the time-of-flight signal frequency will not be eliminated but becomes weaker or stronger depending on whether the contamination materials is a thermal sensing value booster or a thermal value suppressor. The mass flowrate values however shall be substantially deviated from those by calibration register. The said vortex meter can then promote to an alarm status that alert the users to have the said vortex meter being placed for maintenance.

[0034] For the additional preferred embodiment, the said vortex flow meter for those in the art shall become readily and apparently could be further incorporated with additional features such as a gas composition sensor and the data shall be available for use for full spectrum metrology data analysis. It shall also be readily and apparently that the fluid applicable shall not be limited to the steam but also for those containing multiphase fluid flow media.