VERFAHREN UND MESSVORRICHTUNG ZUM BESTIMMEN DER KOMPRESSIBILITÄT EINES STRÖMENDEN FLUIDS

The method and measuring device for determining the compressibility of a fluid flowing

The present invention relates to a method for determining the compressibility of a flowing fluid.

The density of a fluid at reference conditions, in particular at a reference pressure of 1013 MPa, is on the evaluation of fluids of interest. However, it is not directly available in many applications. One way is to calculate the density at the reference pressure from a density measured value which has been detected at a higher pressure. In order to perform this calculation reliable, most accurate knowledge of the compressibility is required.

It is therefore the object of the present invention to provide a method and a measuring device having a simple and reliable as possible

allow determination of the compressibility of a fluid, particularly for determining the density of a medium at a reference pressure.

The object is inventively achieved by the method according to independent claim 1 and the apparatus according to independent

Patent claim. 9

The inventive method for determining the compressibility of a flowing fluid comprising the steps of:

Driving a flow rate of the fluid by means of a pump, through at least a measuring tube of a vibronic density meter at a first pressure which is maintained by means of a throttle;

Determining a first density measurement value of the flowing fluid at the first pressure;

Determining a first pressure reading of the fluid flowing in the first

Pressure;

Driving a volume flow of the flowing fluid by a pump, by a densitometer at a second pressure which is maintained by means of a throttle; Determining a second density measurement value of the fluid at the second pressure, different from said first pressure;

Determining a second pressure measurement value of the flowing fluid at the second pressure; Determining the compressibility of the fluid, based on the first density measurement value of the second density measuring value of the first pressure reading and the second pressure reading on the assumption that the composition of the fluid between the sensing of the first density measurement value and the second density measurement value is unchanged.

In a further development of the invention, the method further comprises calculating a third density value at a third pressure based on the determined compressibility and using at least one of the first and second density measurement values, said third pressure from the first pressure and the second pressure is different, the third pressure, especially outside a bounded by the first pressure and the second pressure interval.

In a further development of the invention, the method further comprises calculating a sound velocity value based on the compressibility and at least one of the density measurements.

In a development of the invention, the determination of the compressibility is performed under the assumption of a constant temperature of the fluid in the first

Pressure reading and the second pressure reading is carried out.

In a further development of the invention, a first temperature of the fluid in the measuring tube when detecting the first density measurement value from a second temperature of the fluid in the measuring tube in capturing the second density reading by no more than 5 ° C, especially not more than 2 ° C and preferably no more than 1 ° C from.

In a development of the invention, determining the first comprising

Density measured value, and determining the second density reading, in each case detecting a natural frequency value of at least one bending vibration modes of the measuring tube.

In a further development of the invention, the natural frequency of the at least one bending oscillation mode of a flexural rigidity of the flow tube depends on which has a cross-sensitivity to pressure of the fluid in the measuring tube, wherein the pressure-dependent bending stiffness of the measuring pipe enters into the determination of the density measured value on the basis of the detected natural frequency, being used to determine the pressure-dependent bending stiffness of at least one of the detected pressure measurement values.

The measuring arrangement according to the invention for determining the compressibility of a flowing fluid and or a quantity dependent on the compressibility size comprising: a fluid path for guiding a medium; a pump which is arranged in the fluid path for driving a volume flow of the medium in the fluid path; a density meter comprising at least one oscillator which at least an oscillating measuring tube, for guiding the medium, with at least one excitation device for exciting oscillations of the measuring tube, and at least one sensor arrangement for detecting at least one vibration characteristic of the oscillator, wherein the measuring tube or measuring tubes of the at least an oscillator is arranged in the fluid path, or are; a throttle arrangement with a variable flow resistance, wherein the density meter between the pump and the

, Throttling device is arranged in the fluid path in which the throttling device is used at a constant flow rate due to different

to cause flow resistances different static pressures in the densitometer; at least one pressure sensor for detecting a pressure reading of the fluid path, the pressure sensor between the pump and the throttle arrangement is disposed in the fluid path; an operation and evaluation unit which is set up on the basis of at least two measured density values ​​and the corresponding measured pressure values ​​acquired at different flow resistances of the throttling device to determine a value for the compressibility of the fluid.

In a further development of the invention, the throttling arrangement comprising two parallel-connected check valves, of which a first check valve having a lower operating point as a second check valve, and the first check valve, a check valve-stop valve is connected upstream, which is in particular automatically controlled.

In an alternative development of the invention, the throttling device has a diaphragm with an adjustable aperture.

In a development of the invention further comprises the measuring arrangement at a second pressure sensor, wherein the density meter is arranged between the first pressure sensor and the second pressure sensor.

In a further development of the invention, the operating and evaluation unit is adapted to determine a measured pressure value for the fluid, which is assigned to a density measured value as an average of substantially simultaneously recorded pressure measurement values ​​of the first pressure sensor and the second pressure sensor.

In a further development of the invention, the operating and evaluation unit is adapted to determine a viscosity measured value for the fluid on the basis of the volume flow and a difference of substantially simultaneously recorded pressure measurement values ​​of the first pressure sensor and the second pressure sensor, and the density measurement value based on the vibration characteristic of the oscillator and of

to determine viscosity measured value.

In a further development of the invention, the operating and evaluation unit is configured to determine a density value at reference conditions, for example 1013 mbar, based on the density measured value of the associated pressure reading and the determined value for the compressibility.

The invention will now be explained in more detail with reference to the drawings shown in the embodiments. It shows:

Fig. V. a flow diagram of an embodiment of the inventive method;

FIG. 2a is a schematic representation of a first embodiment of a measuring arrangement according to the invention;

FIG. 2b shows a schematic representation of a detail of the first variant,

Embodiment of an inventive measuring arrangement; and

Fig. 3 is a schematic representation of a second embodiment of a measuring arrangement according to the invention.

The embodiment of a method 1 according to the invention shown in Fig. 1 in a first step 10 includes detecting a first density measurement value pi and an associated first pressure measuring value pi of a flowing fluid, wherein the first pressure of the flowing fluid is created by the fluid against a first flow resistance R-ι a choke assembly with a variable

Flow resistance is pumped.

After detecting the first density measurement value pi and the associated first

Pressure measurement value p-ι in a second step 20 on a second

Flow resistance R ₂ of the throttle arrangement sensing a second density measurement value p2 and an associated second pressure measurement value P2 of a flowing fluid, wherein the first flow resistance of the second flow resistance is different. At a substantially constant volume flow of the fluid through the throttling device according to this results in different values ​​for the first static pressure and the second static pressure of the flowing medium. For example, the first pressure be about 0.5 to 1 bar and the second pressure is 5 to 10 bar.

The density measurement can be performed for example by measurement of a density-dependent resonant frequency of a vibrating measuring tube, which is flowed through by the fluid.

In a third step 30 is finally based on the two density values pi, p ₂ and the associated measured pressure values pi, p ₂ is the compressibility of the fluid ß calculated according to:

Building on the determination of the compressibility of the fluid in a step 40a, the sound velocity can be calculated based on a density value p and a Kompressibilitätswerts determined to ß according to c of the fluid: The density value can, for example, the arithmetic mean of the two

Density measurements p-ι be p _2, on the basis of the compressibility was calculated ß.

Alternatively or additionally, a reference density at a reference pressure p _ref p _ref can be calculated by, for example 1013 mbar following on the determination of the compressibility of the fluid in a step 40b. Here, the reference density depends on the reference pressure p _ref, at least one pair of values of a pressure reading p, with its associated density measured value p ,, and the calculated value to the

ß compressibility of the fluid.

The embodiment of a measuring device 101 illustrated in FIG. 2a comprises a withdrawal conduit 102, the first to a pipe 104 between a

Connection point 106 and a second connection point is guided parallel 108th The measuring arrangement 101 comprises in the sampling line 102 further comprises a Mikrozahnring- pump 114, such as is available from HNP, or other dosing pump with a delivery accuracy of better than 1%, in particular better than 0.5% for driving a defined volume flow through the formed by the withdrawal conduit 102 and the components arranged therein fluid path 116. the withdrawal conduit includes, for example, an inner diameter of 4 mm. In the sampling line 102 is a filter element 115 is in front of the gear pump 1 14 is still arranged, for example, μιη a maximum pore size of not more than 20, especially not more than 10 μιη and preferably not more than 5 μιη has to ensure that the following components not clog.

In the sampling line 102, a densimeter 120 is disposed with a vibratable measurement tube 122 which can be excited by means of an exciter to bending vibrations is dependent on their resonance frequency of the density of a medium contained in the measuring tube 122nd The measuring tube has a diameter of

For example, 160 μιη and is prepared by means of MEMS technology in silicon. The resonance frequency is a low-viscosity fluid having a density of about 10 ⁶ g / m ^3, for example of the order of 20 kHz.

The total length of a fluid-path portion through the measuring tube 122 and surrounding MEMS components having an internal diameter of 200 μιη is about 1 cm. This fluid path section has a relatively high flow resistance, so it is not practical to run the entire flow through the discharge line 102 through this fluid path section. The expected flow rates at pressure drops of a few bar above the liquid path portion through the measuring tube 122 would be so small that the medium in the sampling line 102, and in particular under changing properties of the medium in the pipeline 104 would not reliably representative. Therefore, the fluid path portion is guided parallel to an aperture 124 through the MEMS components 126 as a bypass, wherein the bypass 126 has a Bypasspf ad length of less than 20 mm, in particular less than 15 mm, for example 10 mm. The aperture 124 has a diameter of 0.5 to 2 mm on which is dimensioned so that due to the due to the flow in the

Withdrawal conduit 102, a pressure gradient is created which drives a portion of the volume flow of, for example 0.1% to 5% through the bypass 126th The MEMS components further comprise a temperature sensor 127, such as a semiconductor resistance element or a Pt resistor element, which extend, in particular a temperature of the measuring tube 122 at or near the measuring tube, which is representative of the temperature of the medium.

The measuring arrangement 101 further comprises a pressure sensor 130 for detecting a pressure measurement value at a Druckabgriffpunkt 132, which is arranged on the fluid path 1 16 between the ring gear pump 140 and a throttle arrangement 160a. More specifically, the Druckabgriffpunkt here is arranged in downstream of the density meter. However, since a pressure drop occurs through the diaphragm 124 and the measuring tube 122 which is proportional to the volume flow, in essence, the pressure at the Druckabgriffpunkt 132 is definitely lower than the average pressure in the measuring tube 122. In this respect, it is advantageous to another pressure sensor between the pump and provide the measuring tube, and a medium pressure for the fluid in the measuring tube from the measured values ​​of the two

under pressure sensors and calculate above the measuring tube. This is particularly advantageous when the actual pressure of the fluid in the measuring tube is of interest, for example, by assuming to calculate a density at a reference pressure. However, for the determination of the compressibility of a second

Pressure sensor expressly not necessary, because at a constant volume flow of the pressure drop across the measuring tube is constant, so that it does not contribute to the pressure differential in equation (1).

The throttle arrangement 160a comprises two parallel-connected check valves, of which a first check valve 162a has a lower operating point as a second check valve 164a. The first operating point of the first check valve 162a is for example 0,5 - 1 bar, while the second operating point of the second

is 10 bar - check valve 164a in the fifth The first check valve 162a is connected upstream of check valve 166a automatically controllable shut-off valve. If the check valve-stop valve is open 166a, the driven from the gear pump 114 flow through the first check valve 162a to flow, so that the static pressure of the flowing fluid is determined by the operating point of the first check valve 162a. In contrast, when the check valve is closed shutoff valve 166a, flows, the volumetric flow through the second check valve 164a, so that the static pressure on the second operating point is determined, and thus has a significantly higher value. may be alternately determined by the first working point and the second working point 166a by means of the shut-off valve thus, at a constant volume flow of the static pressure. The value of the static pressure of the fluid which can be determined with the pressure sensor 130 with the previously described limitations. The measuring arrangement 101 further comprises an operating and evaluation unit 140 which is adapted to the static reference value tuples for different

Pressure measurement values ​​to determine with the respectively associated density and optionally temperature measurements of the flowing fluid, the compressibility of the fluid and thus to determine a density value of the at reference conditions, for example 1013 mbar

Similarly, the operating and evaluation unit controls the check-valve shutoff valve 166a to lock the first check valve 162a. The electrical circuits of the differential pressure measuring arrangement of the densitometer 120, as well as the operation and evaluation unit are preferably embodied in the protection type Ex-i (intrinsically safe). The electronic circuit gear pump 114 is preferably also implemented in a type of protection, for example in a flameproof enclosure according to the class Ex-d.

In Fig. 2b, a throttle arrangement is shown 160b, which can be used as an alternative to in Fig. Drosselanaordnung illustrated 2a 160a in the embodiment shown in Fig. 2a. The choke assembly 160b includes a shutter 166b having a variable flow cross section, said flow cross-section with an actuator is adjustable, which is controlled from the operating and evaluation unit 140th By varying the Stromungsquerschnitts the pressure drop across the orifice at constant volume flow rate can for setting be varied between 0.1 and 10 bar.

The embodiment of a measurement according to the invention shown in Fig. 3 arrangement 201 includes all components of the first embodiment. Detailed explanations of the components of the first embodiment shall apply to the second embodiment. The second embodiment also includes other components which enables a determination of the viscosity of the fluid and thus correction of viscosity-dependent errors in the density measurement. Along with the determination of the compressibility of the invention an even more accurate value of the density may be indicated by reference conditions and for higher viscosity fluids.

The measuring arrangement 201 comprises an extraction line 202, which is guided parallel to a pipe line 204 between a first connection point 206 and a second terminal point 208th The measuring arrangement 201 further comprises in the sampling line 202, a micro annular gear pump 214 to drive a defined volume flow through the arranged from the extraction line 202 and components therein fluid path 216 formed in the withdrawal conduit 202 a filter element is also arranged 215 in order to ensure in front of the gear pump 1 14 that subsequent components do not become clogged. In the sampling line 202, a densimeter 220 is provided with a vibratable

arranged measuring tube 222 which can be excited by means of an exciter to bending vibrations is dependent on their resonance frequency of the density of a medium contained in the measuring tube 222nd The fluid path through the measuring tube section 222 and the subsequent MEMS components is performed as a bypass 226 in parallel with an iris 224th The aperture 224 has a diameter of 0.5 to 2 mm on which so dimensioned that is generated by the flow in the sampling line 202, a pressure gradient due to the a portion of the volume flow of, for example 0.1% to 5% by bypass 226 drives. The MEMS components further comprise a temperature sensor 227, such as a semiconductor resistance element or a Pt resistor element, which extend, in particular a temperature of the measuring tube 222 at or near the measuring tube, which is representative of the temperature of the medium.

The measuring arrangement 201 further comprises a first pressure sensor 230a for detecting a pressure measurement value at a first Druckabgriffpunkt 232a, which is disposed on the fluid path 216 between the ring gear pump 240 and the densimeter 220, and a second pressure sensor 230b for detecting a pressure measured value at a second Druckabgriffpunkt 232b at which the fluid path 16 between the 1

Density meter 220, and a throttle arrangement 160a is disposed.

The purpose of the two pressure sensors 230a and 230b is two-fold here. First, the discussion in the context of the first embodiment of the pressure measurement weaknesses are overcome with only one pressure sensor, by performing an averaging of the measured values ​​of the Duck first and the second pressure sensor.

Furthermore, the pressure drop across the densitometer 220 may be calculated by a difference between the pressure values ​​of the first pressure sensor 230a and the second pressure sensor 230b, from which can be determined the viscosity of the fluid at a given volume flow rate.

The throttle assembly 260 includes two parallel-connected check valves, of which a first check valve 262 has a lower operating point as a second check valve 264. The first operating point of the first check valve 262 is, for example 0.5 - bar 1, while the second operating point of the second

is 10 bar - check valve 264 in the fifth The first check valve 262 is connected upstream of check valve 266 automatically controllable shut-off valve. If the check valve-stop valve is open 266 driven from the gear pump 214 flow via the first check valve 262 can flow, so that the static pressure of the flowing fluid is determined by the operating point of the first non-return valve 262nd In contrast, when the shutoff valve 266 is closed to flow the volumetric flow through the second check valve 264, so that the static pressure on the second operating point is determined, and thus has a significantly higher value. By means of the shut-off valve 266 may thus alternately at a constant volume flow of the static pressure through the first working point and the second

Working are determined. comprises the value of the static pressure of the fluid in the measuring tube 222, can be determined by averaging the measured pressure values ​​of the first pressure sensor 230a and the second pressure sensor 230b.

The measuring arrangement 201 further comprises an operating and evaluating unit 240, which is adapted to determine an actual viscosity measurement value of the fluid based on the values ​​for the volume flow, and the corresponding pressure difference, and a reference to a measured resonance frequency of the measuring tube or a derivative thereof density measurement to calculate the corrected with respect to a viscosity influence density measurement. Furthermore, the operating and evaluating unit 240 is adapted, based on tuples for different averaged static pressure measurements in the measuring tube, with the respectively associated with respect to the

Viscosity influence corrected density measured values ​​and, if necessary, temperature measurement values ​​of the flowing fluid to determine the compressibility of the fluid. a density of the fluid at a reference pressure, for example 1013 mbar are calculated based on these values. Similarly, the operating and evaluation unit controls the check valve

Check valve 266 to lock the first check valve 262a.

The measuring arrangement 201 may further comprise a reservoir 250 and a waste container 252 for an auxiliary medium. The auxiliary medium may be the one hand be a cleaning fluid, such as gasoline, or a reference medium with a defined viscosity or density to calibrate the measuring device 201. Thus, the auxiliary medium can not be discharged into the pipe 204, are in the withdrawal conduit 202 near the first and second connection point 206, 208 or a first check valve 210, provided 212th The reservoir 250 is connected between the first check valve 210 and the filter 215 by means of a branch line to the extraction line, wherein a check valve is disposed in the branch line 254. The waste container 252 is between the second pressure sensor 230b and the

is connected by means of a choke assembly 260 branch line to the removal line, wherein arranged in the branch line, a check valve 256th LIST OF REFERENCE NUMBERS

1 Kompressibilitätsbestimmung

10 first density and pressure measurement

20 Second density and pressure measurement

30 calculate the compressibility

40a calculating the speed of sound

40b calculating a reference density

101 measuring arrangement

102 withdrawal line

104 pipe

106 connection point

108 terminal

1 14 pump

1 15 Filter Element

1 16 fluid path

120 densimeter

122 meter tube

124 aperture

126 bypass

127 temperature sensor

130 pressure sensor

132 Druckabgriffpunkt

140 evaluation unit

160a throttle arrangement

162a check valve with a lower threshold value

Check valve 164a with a higher threshold

166a check valve 160b check valve restrictor assembly

166b throttle with continuously variable flow cross-section

201 measuring arrangement

202 withdrawal line

204 pipe

206 terminal 208 terminal

210 check valve

214 pump

215 filter element

216 fluid path

220 densitometer

222 meter tube

224 aperture

226 bypass

227 temperature sensor

230a first pressure sensor

230b second pressure sensor

232a first Druckabgriffpunkt

232b second Druckabgriffpunkt

240 evaluation unit

250 Reservoir

252 waste containers

254 check valve

256 check valve

Check valve 262 with a lower threshold value

Check valve 264 with a higher threshold

Check valve 266 check valve