CH705730A1 - Flow sensor, particularly for single use for dosing device for dosing fluid, has three measuring chambers, which are arranged one behind other and are interconnected by flow resistance - Google Patents

Abstract

The flow sensor (10) has three measuring chambers (11,15,19), which are arranged one behind the other and are interconnected by a flow resistance. The two of the flow resistances have a different coefficient of pressure loss. Pressure measuring units (12,16,20) are provided for each measurement chamber, where pressure measuring unit is suitable for measuring the pressure in the measurement chamber. An electromagnetically actuated valve arrangement (50) is connected downstream of the flow sensor. Independent claims are included for the following: (1) a dosing device with a feed chamber; and (2) a method for measuring a volume flow and a viscosity of the fluid.

Description

TECHNICAL AREA

The invention relates to flow sensors with at least three successively arranged measuring chambers, which are each connected by a flow resistance flowing together, wherein at least two of the flow resistances have a different pressure loss coefficient. The invention further relates to metering devices having such flow sensors, and to methods for determining a volume flow and / or a viscosity of a fluid with such flow sensors.

STATE OF THE ART

In the cultivation of microorganisms, it is important to supply nutrient media exactly and with certain dosing to the reaction vessel. For larger bioreactors (> 500 L, dosing rate> 1 kg / h) dosing pumps or scales are used.

In the applicant's international application no. PCT / EP2011 / 052 545 an advantageous metering system for metering fluids into reaction vessels is described. The content of said application is hereby incorporated by reference as part of this specification. In the dosing system mentioned, the metered addition into reaction vessels is effected dropwise with the aid of a suitable metering device, for example an electromagnetically controlled precision valve. The required dosing accuracy is achieved by controlling the differential pressure across the dosing unit very precisely by additionally monitoring the actual dosing rate via a dosing rate determination means such as a balance or a flow sensor and adjusting the differential pressure accordingly. The very precise control of the differential pressure is necessary, among other things, because the droplet size resulting from a certain opening duration of the valve and a certain fluid pressure is dependent on the viscosity of the fluid, and thus also on the temperature.

Further, in this dosing system, the dosing device and the Dosierratenbestimmungsmittel are arranged separately and not necessarily in a spatially constant position to each other, which influences the differential pressure control by the resulting undefined hydrostatic pressure differences. In order to ensure exact dosing rates over longer periods of time, these effects must be taken into account if necessary. This leads to a complex regulation.

A known from the prior art flow sensor for measuring small flow rates in the microliter range, for example, the so-called. MEMS flow sensor from. Seyonic, CH-2000 Neuchâtel, Switzerland. This flow sensor is used in pipetting systems and includes a measuring channel, a piezoresistive pressure sensor and a temperature sensor. The disadvantage of this flow sensor is that the measured flow rates are dependent on the temperature due to dynamic viscosity influences and in addition to the flow, the temperature or the viscosity of the fluid to be measured must be taken into account. It is accordingly necessary to calibrate the flow sensor before the measurement.

In the thesis "flow sensors made of plastic for very small volume flows based on the AMANDA method" by Dipl. Ing. Dirk Maria Dittmann, Forschungszentrum Karlsruhe GmbH, Karlsruhe, 2002, a temperature-independent flow sensor is presented. In this flow sensor two measuring chambers are connected in series, wherein in each of the two measuring chambers, an elastic membrane is arranged, which has a center hole. The two successively arranged membranes are movably arranged in the measuring chamber, of different thickness and act as flow resistances. The fluid volume flow to be measured enters the first measuring chamber, passes through the center hole of the first diaphragm, passes into the second measuring chamber and passes through the center hole of the second diaphragm. The pressure drop across each membrane is determined by electronically measuring the elongation of the membrane and determining the pressure difference from this strain. The influence that the first membrane exerts on the second membrane as it flows through the liquid is not considered. The pressure loss coefficients £ 1 and £ 2 for the flow through the membrane openings are equated. By connecting the two membranes in series, which serve as flow resistances, the fluid volume flow should be able to be measured independently of the viscosity, and thus independently of the temperature. The derivation of the theoretical formula for the relationship of the temperature-independent flow measurement is explained in the previously mentioned dissertation, from p. The content of this document is hereby incorporated by reference into this specification.

Dipl.-Ing. Götz Schnell, Darmstadt, 1995. In the dissertation «Flow Measurement of Smallest Liquid Quantities» by Dipl. Ing. Götz Schnell, Darmstadt, 1995, various measuring methods for applicability in the measurement of the flow of very small amounts of liquid were investigated. In chapter 8.4 of the dissertation "Flow Measurement by Measuring the Pressure Drop in Straight Pipes", the derivation of the theoretical formula for the pressure loss via a channel-shaped flow resistance is presented. The content of this chapter should hereby be incorporated by reference as part of this specification. The dissertation discusses various possible solutions to reduce the influence that throttling of the flow has as a proportion of the pressure drop over a pipe section, in order to allow a more accurate measurement. In the proposed measuring principle, a straight pipe section is designed so that two capillaries are arranged one behind the other. The first capillary serves to form the flow profile, and thus and to reduce the pressure drop due to the throttling when entering the second capillary. The second capillary represents a measuring capillary, via which the pressure drop is measured. The total pressure drop across the pipe is made up of the largest possible reduction in throttling and the amount of friction. This friction pressure is a viscosity-dependent or temperature-dependent variable. The proposed in the thesis configuration allows to minimize the pressure component of the throttling of the fluid to be measured, so as to measure substantially only the friction effect. The measured pressure drop is still dependent on the viscosity and the temperature.

In biotechnology very high demands are placed on the sterility. All components must be sterilized (e.g., autoclaved) before a new batch. To avoid this and to reduce the effort for cleaning and the necessary quality control while maintaining the same high quality, the focus is increasingly on disposable components (single-use or disposables). These are provided sterile, installed and then disposed of. Precise metering systems are not yet available as disposable components, making their use as disposable components uneconomical.

PRESENTATION OF THE INVENTION

The object of the invention is to provide a flow sensor available, which can be produced inexpensively, preferably as a disposable product, and with which small amounts of liquid can be precisely measured.

Another object of the invention is to provide a flow sensor with which a flow rate of a fluid can be measured without knowledge of the exact viscosity and / or temperature of the fluid, or in which no prior calibration is necessary.

It is also an object of the invention to provide a metering device which can be manufactured as a cost-effective disposable product, and with which small amounts of fluid can be precisely metered. Advantageously, a metering device according to the invention should allow the volume of a single metered drop to be measured.

It is a further object of the invention to provide a method with which it is possible to measure a volume flow of a fluid without knowledge of the viscosity and / or the temperature of the fluid, or without prior calibration.

These and other objects are achieved by a flow sensor, a metering device and a method according to the independent claims. Preferred embodiments of the invention are given in the dependent claims.

A flow sensor according to the invention comprises at least three measurement chambers arranged one behind the other, each of which is fluidly connected to one another by a flow resistance. At least two of the flow resistances have a different pressure loss coefficient ζ. For each measuring chamber, a pressure measuring means is provided, which is adapted to measure the pressure p in the corresponding measuring chamber.

The inventive flow sensor is provided in particular for single use.

In an advantageous embodiment of a flow sensor according to the invention, three measuring chambers are arranged serially one behind the other. Particularly advantageously, the middle of the three measuring chambers has a smaller volume than the other two measuring chambers.

Due to this arrangement, it is possible to bring an outlet openings of the first flow resistance as close as possible to an inlet opening of the second flow resistance. The first flow resistance influences the subsequent flow resistance in such a way that the exiting fluid flow does not completely propagate in the second measuring chamber and thus can partially maintain its flow profile. Since the fluid flow is directed to the second frictional channel, as a result, the throttling effect of the inlet opening decreases accordingly, and the pressure loss coefficient is lower.

The flow resistances are advantageously designed so that they each have a friction channel with a certain length L1, L2 and a certain cross-sectional area A1, A2. The lengths L1 and L2 and / or the cross-sectional areas A1 and A2 of the friction channels can be chosen the same or different. In an advantageous embodiment, the cross-sectional areas A1, A2 have a value between 0.03 and 0.3 mm <2>, alternatively or additionally, the length L1, L2 of the friction channels is smaller than 2 mm.

To be able to produce the flow sensor cost-effectively, cost-effective yet precise pressure sensors are needed. Semiconductor pressure sensors, in particular the pressure sensors MPX2300DT1 and MPX2301DT1 from Freescale, Austin TX, USA (http://www.freescale.com) are suitable as pressure measuring means in a flow sensor according to the invention.

Due to the simple construction of the sensor, the flow sensor according to the invention can be injection-molded, preferably in one piece, and thus manufactured as inexpensively. Advantageously, the flow sensor is made of plastic.

In a particularly advantageous embodiment of the invention, the flow sensor on a last measuring chamber downstream valve device, preferably an electromagnetically operable valve. This advantageous arrangement makes it possible to measure the flow of a fluid to be metered as close to the inlet to the valve device, and optionally readjust the metering device, should a user set by the metering rate does not correspond to the actual metering rate.

By the inventive arrangement of the flow sensor with the valve device succeeds when using a suitable valve device, inter alia, to dose individual drops of the fluid, while measuring the volume of each dosed drop or to check. These values can also be recorded, for example for quality control.

An inventive metering device for metering fluids comprises a supply channel for supplying the fluid to be metered; a flow sensor according to the invention as previously discussed for determining the volume flow through the sensor, wherein the supply channel is fluidly connected to the first measuring chamber of the flow sensor; and a valve device for metering the fluid, preferably an electromagnetically operable valve, wherein the last metering chamber is connected to the inlet of the valve device.

In a method according to the invention for measuring a volume flow [V / t] M and / or a viscosity Hm of a fluid, a flow sensor according to the invention is provided as discussed above, and for at least two flow resistances of the flow sensor with different pressure loss coefficients ζ, a characteristic field of one Are provided plurality of isobaric characteristics, said isobaric characteristics represent flow-viscosity-value pairs, which cause a certain differential pressure at the corresponding flow resistance. The differential pressures Δp are determined via the corresponding at least two flow resistances by measuring the pressures in the corresponding measuring chambers with the pressure measuring means and calculating the differential pressures therefrom. The determined at least two differential pressures are assigned the corresponding isobaric characteristic curve with the same differential pressure in the respective characteristic fields, and the point of intersection of the associated at least two isobaric characteristic curves is determined. From this specific point of intersection, the associated volume flow [V / t] M and / or the associated viscosity η M is then determined.

According to the theory, the pressure drop Δp between two measuring chambers, which are connected by a friction channel with radius rR and length lR: Δp = [ζp / (π <2> rR <4>)] [V / t] <2> + [8 η lR / (πrR <4>)] [V / t]. The pressure loss coefficient ζ takes into account the flow profile at the inlet into the friction channel, p is the density of the fluid. This three-dimensional function can be reshaped so that with ζ, p, lR, rR as fixed parameters the pressure drop Δp can be represented as a three-dimensional function of the volume flow [V / t] and the viscosity η. From this function, characteristic curves for a specific Δp can be calculated.

Instead of determining the characteristic curves with mathematical models, these can also be obtained by numerical simulations. Also advantageous are the experimental determination of a plurality of measured value triples, and the subsequent numerical interpolation of a three-dimensional function.

Such a method according to the invention thus makes it possible to determine a flow or volumetric flow without the viscosity having to be known. Viscosity even results in flow measurement as an additional measurement.

In an advantageous variant of such a method, the isobaric characteristics of the characteristic curves of the flow resistances are extrapolated from suitable characteristic values, preferably from characteristic values determined by measurements.

Additionally or alternatively, in such a method according to the invention, the differential pressures can be determined as a function of time. This allows a precise integration, for example, of individual drop volumes.

Due to the underlying physical effects characteristic curves apply only to certain fluid densities p. The density of the fluid must therefore be known. However, the density is usually known, or at least easy to determine. Alternatively, four-dimensional functions can also be used, with density as an additional function parameter. From these three-dimensional isobaric characteristics can then be determined. Correspondingly, for the one-to-one determination of the volumetric flow (as well as the viscosity and the density), three intersecting isobaric characteristics are required, that is also three flow resistances with different pressure loss coefficients.

BRIEF EXPLANATION OF THE FIGURES

The invention will be explained in more detail with reference to embodiments in conjunction with the drawings. <Tb> FIG. 1 <sep> shows schematically the use of a flow sensor according to the invention in a dosing system. <Tb> FIG. 2 <sep> shows a schematic representation of the flow sensor according to the invention in cross section. <Tb> FIG. 3 <sep> schematically shows a metering device according to the invention with a flow sensor according to the invention and a valve device. <Tb> FIG. 4 <sep> schematically shows (a) a first characteristic field of a first flow resistance, with an isobaric characteristic belonging to a first measured pressure difference, (b) a second characteristic field of a second flow resistance, with an isobaric characteristic associated with a second measured pressure difference, (c) determining the intersection of the first and second isobaric characteristics, and based thereon determining the volume flow and viscosity; and (d) determining volumetric flow and viscosity in a variant embodiment with three measured pressure differences and three isobaric characteristics.

WAYS FOR CARRYING OUT THE INVENTION

In a preferred embodiment of the invention according to FIG. 1, the flow sensor 10 according to the invention is used in a dosing system 90, for example for a bioreactor 94. The fluid 96 to be metered is transported by a reservoir 93 via a transfer line 95 to a metering device 92, which comprises the flow sensor 10 according to the invention and a valve device 50. With the aid of the metering valve 50, the fluid to be metered is supplied to the bioreactor 94 in individual drops 97. The flow sensor 10 and the metering valve 50 are advantageously formed in one piece, preferably as a disposable unit.

The flow meter 10 according to the invention measures the current metering rate directly at the metering valve 50. A control device 91 controls the opening time and / or the frequency of the actual metering rate measured by the user according to the target metering rate and the second metering rate measured by the flow meter according to the invention Metering valve 50, so that the actual metering rate of the desired metering rate corresponds.

Fig. 2 shows a simplified simplified flow sensor 10 according to the invention with a first measuring chamber 11, a second measuring chamber 15 and a third measuring chamber 19. The measuring chambers are connected by a first flow resistance 13 and a second flow resistance 17 with each other. In the particularly advantageous embodiment shown, the flow resistances 13 and 17 are formed by a first 14 and a second 18 friction channel with a cross-sectional area A1, A2 and a length L1, L2. The pressure loss coefficients ζ for the flow resistances are designed differently. The second measuring chamber 15 is smaller, in particular shorter, designed as, for example, the first measuring chamber 11. The measuring chamber 15 is designed such that an outlet opening of the first friction channel 14 is arranged at a suitably small distance from an inlet opening of the second flow channel 18. As a result, the airfoil has no time to spread evenly in the measuring chamber. The fluid flow is directed as it were to the inlet opening. As a result, the throttling effect of the inlet opening decreases in relation to the theoretically expected value due to the geometry. This results in different pressure loss coefficients for the two flow resistances 13 and 17.

Optimal geometries for the measurement chambers and friction channels may be determined based on a preferred range of viscosity, density, and volume flow through mathematical models and / or numerical simulations. Can be optimized in particular with regard to the accuracy of the determination of the volume flow according to the inventive method.

Per measuring chamber per a pressure measuring means 12, 16, 20 is provided. In a preferred embodiment, for example, it is a one-way pressure sensor from Freescale Semiconductor, http://www.freescale.com, the type MPX2300DT1 and / or type MPX2301 DT1. The differential pressures Δp1 and Δp2 are determined by determining the difference from the pressure values p1, p2, p3 in the measuring chambers.

FIG. 3 shows a flow sensor 10 according to the invention as part of a metering device according to the invention, the flow sensor being fluidly connected to a valve device 50. In the embodiment shown, this is an electromagnetically actuated valve. In this type of valves, a magnetic armature 51 is displaced in a valve chamber 55 with a specific clock frequency with a magnetic coil 51, thereby opening an outlet opening 57 of a valve nozzle during a likewise determinable duration and then resealing it. In this way, a specific volume of the pressurized fluid can be specifically conveyed into the outlet nozzle 57, thus delivering a drop of a certain volume at the end of the nozzle. The armature 52 of the metering valve 50 is preferably arranged in a capsule that protects it from aggressive media, such as dilute acids.

The flow sensor 10, which is connected upstream of the metering valve 50, is the same flow sensor as described in FIG. 2. In the preferred embodiment of Fig. 3, the flow sensor 10 and the metering valve 50 are integrally formed.

For a first flow resistance, a characteristic field is created, which represents the relationship between volume flow, viscosity and pressure drop across the flow resistance. Such a characteristic field is shown symbolically in FIG. 4 (a), with a plurality of characteristic curves a1-a5, which represent different pressure differences across the flow resistance. The same is done for a second flow resistance (Fig. 4 (b)). However, since this second flow resistance has a different pressure loss coefficient, the characteristics b1 to b5 are tilted in comparison with those of the first flow resistance. If the actual pressure differences .DELTA.p1, Ap1 are now determined experimentally, they can be assigned the corresponding characteristic curves a3, b3 in the respective characteristic fields. Since, of course, the viscosity of the fluid remains unchanged, and the volumetric flow must also be identical due to the experimental setup, then a pair of values of volume flow [V / t] oral viscosity ηM can be determined unambiguously by cutting the two characteristic curves a3, b3 (FIG (c)).

Fig. 4 (d) shows a variant in which three differential pressures over three flow resistances are measured with different pressure loss coefficient ζ, and cut according to three characteristics. The additional measurement increases the measuring accuracy.

LIST OF REFERENCE NUMBERS

[0041] <Tb> 10 <sep> Flow Sensor <tb> 11 <sep> first measuring chamber <tb> 12 <sep> first pressure measuring means <tb> 13 <sep> first flow resistance <tb> 14 <sep> first friction channel <tb> 15 <sep> second measuring chamber <tb> 16 <sep> second pressure measuring means <tb> 17 <sep> second flow resistance <tb> 18 <sep> second friction channel <tb> 19 <sep> third measuring chamber <tb> 20 <sep> third pressure measuring means <Tb> 21 <sep> supply channel <tb> 50 <sep> Valve device, metering valve <Tb> 51 <sep> solenoid <Tb> 52 <sep> armature <Tb> 53 <sep> valve seat <Tb> 54 'sep> valve part <Tb> 55 <sep> valve chamber <Tb> 56 <sep> sealing element <Tb> 57 <sep> outlet nozzle <Tb> 90 <sep> dosing <Tb> 91 <sep> control device <Tb> 92 <sep> dosing <Tb> 93 <sep> reservoir <Tb> 94 <sep> bioreactor <Tb> 95 <sep> transfer line <Tb> 96 <sep> Fluid <tb> 97 <sep> drops, added volume <tb> Δp1, Δp2, Δp3 <sep> differential pressure <tb> p1, p2, p3 <sep> Pressure in the measuring chamber <tb> ζ1, ζ2 <sep> pressure loss coefficients <tb> a1 ... a5, b1-b5 <sep> isobaric curves <Tb> S <sep> Intersection

Claims (12)

1. flow sensor (10), in particular for single use, with at least three successively arranged measuring chambers (11, 15, 19), each by a flow resistance (13, 17) are fluidly connected to each other, wherein at least two of the flow resistances a different pressure loss coefficient ( ζ1, ζ2), characterized in that a pressure measuring means (12, 16, 20) is provided for each measuring chamber, which is adapted to measure the pressure (p1, p2, p3) in the corresponding measuring chamber. 2. Flow sensor according to claim 1, characterized by serially three successively arranged measuring chambers (11, 15, 19). 3. flow sensor according to claim 1 or 2, characterized in that the flow resistances (13, 17) each have a friction channel (14, 18) with a certain length (L1, L2) and a certain cross-sectional area (A1, A2). 4. flow sensor according to claim 3, characterized in that the cross-sectional areas (A1, A2) of the friction channels (14, 18) have a value between 0.03 and 0.3 mm <2>. 5. Flow sensor according to claim 3 or 4, characterized in that the length (L1, L2) of the friction channels (14, 18) is smaller than 2 mm. 6. Flow sensor according to one of the preceding claims, characterized in that it is the pressure-measuring means (12, 16, 20) to semiconductor pressure sensors. 7. Flow sensor according to one of the preceding claims, characterized in that the flow sensor (20) is made of plastic and / or injection molded. 8. Flow sensor according to one of the preceding claims, characterized by one of the last measuring chamber (19) downstream valve device (50), preferably an electromagnetically operable valve. 9. dosing device (92) for metering fluids, comprising a supply channel (21) for supplying the fluid to be metered; a flow sensor (10) according to any one of claims 1 to 8, for determining the volume flow through the sensor, wherein the supply channel with the first measuring chamber (11) of the flow sensor is fluidly connected; and a valve device (50) for metering the fluid, preferably an electromagnetically operable valve, wherein the last metering chamber (19) is connected to the inlet of the valve device. 10. A method for measuring a volume flow ([V / t] M) and / or a viscosity (ηM) of a fluid, wherein - A flow sensor (10) according to one of claims 1 to 8 is provided; for at least two flow resistances (13, 17) of the flow sensor with different pressure loss coefficients (ζ1, ζ2), a characteristic field is provided from a plurality of isobaric characteristics (a1 ... a5, b1 ... b5), said isobaric Characteristics represent volume flow viscosity value pairs, which cause a certain differential pressure at the corresponding flow resistance; - The differential pressures (.DELTA.p1, .DELTA.p2) are determined via the corresponding at least two flow resistances by using the pressure measuring means (12, 16, 20) the pressures (p1, p2, p3) in the corresponding measuring chambers (11, 15, 19) measured and from this the differential pressures are calculated; - The particular at least two differential pressures in the respective characteristic curves, the corresponding isobaric characteristic (a3, b3) is assigned to the same differential pressure; - The intersection point (S) of the associated at least two isobaric characteristics is determined; - From the specific intersection of the associated volume flow ([V / t] M) and / or the associated viscosity (ηM) is determined. 11. The method according to claim 10, characterized in that the isobaric characteristics of the characteristic curves of the flow resistances are extrapolated from suitable characteristic values, preferably from characteristic values determined by measurements. 12. The method according to claim 10 or 11, characterized in that the differential pressures (Δp1, Δp2) are determined as a function of the time (t).