MEASUREMENT ORDINANCES AND PROCEDURES FOR DETERMINING A LIMIT TERM VOLTAGE

Abstract

A measuring arrangement for determining interfacial tension comprises a vessel (10) with a chamber (11) for receiving a carrier liquid (31). A sample liquid (36) is fed dropwise into the chamber (11) via a feed device (20). A magnetic field source (40) generates an inhomogeneous magnetic field with a vertical magnetic field gradient in the chamber (11). A measuring device (50) detects at least a section of the contour of a droplet (37) of the sample liquid (36) formed in the chamber (11) during operation of the measuring arrangement.

Description

TECHNICAL AREA

[0001] The present application relates to measuring arrangements and a method for determining the interfacial tension between two liquids. In particular, the present application relates to an optical tensiometer that optically detects the contour of a droplet of liquid. BACKGROUND

[0002] Tensiometers for determining surface tension or interfacial tension allow for the monitoring of industrial processes and the determination of the flow behavior of liquids. Insights into flow behavior can be incorporated into the design and development of products, technical processes, and industrial plants. Optical tensiometers for droplet contour analysis measure the shape of a liquid droplet and deduce the surface or interfacial tension from these shape parameters.

[0003] In contact angle measurement, a drop of a liquid to be characterized is placed on a solid surface. The contact angle between the drop and the solid surface is determined using an optical method, and the surface tension of the liquid to be characterized is then calculated from this contact angle using Young's equation.

[0004] The captive bubble method generates a gas bubble in the liquid to be characterized, which adheres to the surface of a solid immersed in the liquid. Again, the contact angle between the droplet and the solid surface is determined using an optical method, and the surface tension of the liquid to be characterized is then deduced from this contact angle using Young's equation.

[0005] In the pendant drop method, the shape of a drop of the liquid to be characterized, suspended from a capillary, is optically recorded. The interfacial tension can be determined from the position of characteristic points on the drop's surface and / or the size of the detaching drop using the Young-Laplace equation.

[0006] According to publication WO 2004 / 070360A1, a liquid flows slowly through a capillary, at the end of which drops form. The drops fall into a closed chamber containing a gas. A measuring device, which may be optical, for example, records the first time at which a drop reaches a predetermined size and the second time at which a drop falls. From the time interval between the first and second time intervals for the first drop, as well as the time interval until the next drop reaches the predetermined size, the interfacial tension between the liquid and the gas can be calculated.

[0007] The sessile drop method records the shape of a drop of the liquid to be characterized placed on a semicircular, rigid surface. The surface tension is then determined using the Young-Laplace equation.

[0008] For the spinning-drop method, a drop of sample liquid is added to a heavier phase in a horizontally mounted, cylindrical cannula. As the cannula is rotated around its longitudinal axis, the contour of the drop changes. From this change in contour, the interfacial tension between the sample liquid and the heavier phase can be determined using the Vonnegut equation and the Young-Laplace equation.

[0009] US Patent 4,953,389 A determines the interfacial tension at the interface between a gas bubble and a liquid and aims to determine the interfacial tension of a lung surfactant film in an arrangement that closely approximates the conditions in the human lung. A liquid containing the surfactant is placed in a chamber, and a gas bubble is injected into the liquid. The liquid pressure is increased and decreased, thereby reducing or increasing the volume of the gas bubble. The effective interfacial tension is then determined from the shape of the gas bubble.

[0010] A method described in German patent application DE 103 55 504 A1 uses changes in interfacial tension between two immiscible liquids to detect substances that accumulate at the interface. Molecular complexes form at the interface as a result of the deposition of dissolved substances. The interfacial tension changes associated with these molecular complexes are quantifiably detected using a magnetically manipulated sample that deforms or penetrates the interface.

[0011] According to publication CN 1 14 965 176 A, the surface tension of a high-temperature liquid metal alloy is measured under electromagnetic suspension conditions. For this purpose, a sample is placed in an electromagnetic suspension device and a protective gas is supplied. The sample is gradually heated until its melting point is exceeded. A high-speed camera observes the transformation of the sample's shape into an ellipsoidal form. If suspended molten droplets are observed to be in a surface vibration state, the high-speed camera captures a sequence of surface vibration images of the suspended molten droplets. The surface tension of the suspended molten droplets is calculated from their surface vibration frequency.

[0012] The effects of a homogeneous magnetic field on the shape of a liquid droplet were investigated in the publications Sudo, S., Hashimoto, H., Ikeda, A.: Measurements of the Surface Tension of a Magnetic Fluid and Interfacial Phenomena; JSME international journal (1989), Series II, Vol.1, pp.47-51, Flament C. et al.: Measurements of ferrofluid surface tension in confined geometry; Phys. Rev. E (1996), Vol.53, 4801, and Hayakawaab, M. et al.: Effect of moderate magnetic fields on the surface tension of aqueous liquids: a reliable assessment; RSC Adv., 2019, 9, 10030-100033.

[0013] The present application is based on the task of determining the interfacial tension between two liquids in a simple manner.

[0014] The problem is solved by the measuring arrangement and the method according to the dependent claims. Advantageous embodiments are described in the sub-claims.

[0015] The following figures show embodiments of the measuring arrangements and the method according to the invention. The elements and structures shown in the figures are not necessarily drawn to scale. Identical reference numerals refer to identical or corresponding elements and structures. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a schematic representation of a measuring arrangement for determining the interfacial tension between a carrier liquid and a sample liquid according to one embodiment. Fig. Figure 2 shows the contour of a drop of the sample liquid during operation of the measuring arrangement. Fig. 1 during measurement according to one embodiment. Fig. Figure 3 shows a perspective view of a vessel, a feeding device and a magnetic field source of the measuring arrangement according to Fig. 1. Fig. Figure 4 shows a perspective view of a detail of the measurement setup according to Fig. 1. Fig. Figure 5 shows a schematic representation of a measuring arrangement for determining the interfacial tension with a metering pump for dropwise supply of the sample liquid and with an optical device for determining the droplet shape according to one embodiment. Fig. Figure 6 shows a schematic perspective view of a measuring arrangement for determining the interfacial tension using sensors / electrodes for impedance / resistance measurement on the wall of a cuvette with a rectangular base according to one embodiment. Fig. Figure 7 shows a schematic perspective representation of a measuring arrangement for determining the interfacial tension using sensors / electrodes for impedance / resistance measurement on the wall of a cuvette with a circular base according to one embodiment. Fig. 8A to Fig. Figure 8D shows schematic representations of a chamber of a measuring arrangement filled with a carrier fluid in different phases of a method for determining the interfacial tension according to one embodiment. Fig. Figure 9 shows a schematic representation of a process line with a measuring arrangement arranged in a bypass for determining the interfacial tension according to a further embodiment. DETAILED DESCRIPTION

[0016] The following detailed description refers to the accompanying drawings. These drawings form part of the description and illustrate specific embodiments that can realize the invention. Directional terminology such as "top," "bottom," "front," "back," "anterior," "rear," etc., is used with reference to the orientation of the described figure(s). Since components of embodiments can be positioned in a number of different orientations, the directional terminology serves only for explanation and is in no way to be understood as restrictive. In addition to the embodiments shown, other embodiments exist. Structural or logical modifications can be made to the embodiments shown in the figures and / or described below without deviating from the claimed subject matter.Features of the described embodiments can be combined unless explicitly or implicitly stated otherwise. Vertical axes and directions are aligned parallel or approximately parallel to the direction of the gravitational force.

[0017] One aspect of the present disclosure relates to a measuring arrangement for determining the interfacial tension of a sample liquid. The measuring arrangement comprises a vessel with a chamber for receiving a carrier liquid, a feeding device, a magnetic field source, and a measuring device.

[0018] The vessel is, for example, a cuvette suitable for optical examination of its contents, with plane-parallel sides. The material of at least two opposing sides is transparent to the wavelength range used for the optical examination. The transparent material is glass, e.g., quartz glass, or a transparent plastic. The cuvette can be closed and sealed, except for an inlet opening, or open.

[0019] The feeding device is designed for the dropwise introduction of the sample liquid into the chamber. For example, the feeding device includes a cannula suitable for connection to a dosing pump, with an outlet opening at one free end inside the chamber. The feeding device may have a guide that fixes the free end of the cannula in a working position within the cuvette chamber.

[0020] The magnetic field source is designed to generate an inhomogeneous magnetic field with a vertical magnetic field gradient within the chamber. The magnetic field source is, for example, an electromagnet or a permanent magnet with a fixed position relative to the vessel. The magnetic field source can be permanently and forcefully connected to the vessel, or the vessel and the magnetic field source can be temporarily and forcefully connected.

[0021] The magnetic field source can be positioned above the chamber if the density ρ0 of the sample liquid is lower than the density ρf of the carrier liquid. Conversely, the magnetic field source can be positioned below the chamber if the density ρ0 of the sample liquid is higher than the density ρf of the carrier liquid.

[0022] The measuring device is configured to detect at least one section of the contour of a droplet of the sample liquid formed in the chamber during operation of the measuring arrangement. The droplet is at least approximately point-symmetric in the horizontal cross-sectional planes. The contour is the parallel projection of the largest vertical cross-sectional area of ​​the droplet onto a vertical plane. The measuring device can detect one or more sections of the contour, or the entire contour of the droplet, in one plane or in several non-parallel planes.

[0023] To operate the measuring setup, the vessel is filled with a paramagnetic carrier fluid. The feed device injects at least one drop of the sample fluid into the carrier fluid. If several drops are injected successively, they coagulate into a single drop.

[0024] The position of the droplet on a vertical axis parallel to the direction of the gravitational force results from the equilibrium condition for weight force, buoyancy force and magnetic gradient force.

[0025] In an inhomogeneous magnetic field, the droplet visibly deforms in its contour, with the droplet's shape depending on the local magnetic field strengths and the material properties of the carrier fluid and sample fluid. The side of the droplet exposed to the stronger magnetic pressure flattens more than the side exposed to the weaker magnetic pressure. Depending on the droplet's orientation relative to the magnetic field source, either the top or the bottom may be exposed to the stronger magnetic pressure.

[0026] The measuring device detects at least sections of the contour and the position of the droplet relative to the magnetic field. From the contour, the local magnetic field strength, and the material properties of the carrier liquid and the sample liquid, the interfacial tension between the carrier liquid and the sample liquid can be determined.

[0027] The measuring setup allows for the simple determination of interfacial tension. The droplet's contour can be captured in a state where the droplet is completely enclosed by the carrier liquid and not directly adjacent to a third, solid phase. The influence of such a third phase on the measurement result is thus eliminated. Measurement errors due to temperature changes, vibrations, and air movement, as often observed with other optical tensiometers, are minimal or nonexistent.

[0028] According to one embodiment, the measuring arrangement has an evaluation unit which is configured to determine significant contour parameters (contour parameters) from the sections of the drop's contour detected by the measuring device.

[0029] Such significant contour parameters include, for example, the maximum vertical extent of the drop, the vertical distance between a geometric upper edge and a geometric lower edge of the drop, the vertical extent of the drop along the vertical axis of symmetry, the maximum horizontal diameter of the drop, and local curvatures between the drop and surrounding liquid at selected locations, e.g., in the region of the vertical axis of symmetry and in the plane of maximum horizontal extent.

[0030] According to one embodiment, the evaluation unit is designed to determine the interfacial tension between the drop and the carrier liquid from the significant parameters and the magnetic field strengths acting locally on the drop.

[0031] The interfacial tension can be calculated, for example, using the Young-Laplace equation from the significant parameters, taking into account the magnetic pressure acting in the vertical direction, the susceptibility of the carrier fluid, and the densities of the carrier fluid and sample fluid.

[0032] According to one embodiment, an outlet opening of the feeding device, positioned in the chamber, is closed with an open capillary. The diameter of the capillary is sufficiently narrow so that the amount of sample liquid required to form a small-volume droplet completely fills a longitudinal section of the capillary.

[0033] According to one embodiment, the measuring arrangement comprises a metering pump, wherein the metering pump is connected to an inlet opening of the feed device and the metering pump is configured to dispense the sample liquid dropwise into the chamber of the vessel.

[0034] According to one embodiment, the measuring device has a radiation source for electromagnetic waves and a radiation sensor for the electromagnetic waves emitted by the radiation source, wherein the vessel is arranged in a beam path between the radiation source and the radiation sensor.

[0035] The radiation source emits a measurement radiation. The radiation sensor detects the portion of the measurement radiation passing through the vessel with spatial resolution. For example, the measurement radiation is broadband or narrowband radiation in the visible, infrared, and / or ultraviolet wavelength range. The radiation sensor can include a camera with a high-resolution image sensor, such as a far-field optical microscope. The image sensor can be configured to capture sections of the contour relative to a horizontal plane from at least one side. In another example, the radiation source is an X-ray source and the radiation sensor is an X-ray image sensor.

[0036] According to one embodiment, the measuring device has a plurality of electrodes arranged on the vessel and an impedance measuring device, wherein the impedance measuring device is configured to determine electrical impedances between any two of the electrodes.

[0037] The electrodes can be mounted on the inside of the chamber or embedded in the chamber wall. The electrodes can be arranged in two or more rows, with electrodes in the same row positioned at the same height above the base of the chamber along its circumference.

[0038] The impedance measuring device can transmit a periodic signal as an excitation signal to at least some of the electrodes and determine the complex impedance between two electrodes located at different points on the chamber wall. Alternatively or additionally, the impedance measuring device can include a resistance measuring device, which is configured to determine the electrical resistance between any two electrodes.

[0039] For each electrode, an impedance measurement and / or resistance measurement can be performed with exactly one other electrode, with several other electrodes, or with all other electrodes.

[0040] Due to the different conductivities and / or dielectric properties of the carrier fluid and the sample fluid, the impedances between the electrodes change depending on the shape and size of the droplet. Different droplet shapes and sizes result in different signatures of the measured impedances or resistance values.

[0041] The impedances or electrical resistances between each pair of electrodes provide information about the contour of the droplet. Based on a tomographic reconstruction, the curvatures on the top and bottom of the droplet can be determined, and the interfacial tension can be calculated using the Young-Laplace equation.

[0042] According to one embodiment, a device for processing or using a process fluid comprises a measuring arrangement, wherein the process fluid can be supplied to and removed from the measuring arrangement as the carrier fluid permanently, at predefined intervals, or by user intervention. A controllable process unit of the device can be controlled depending on the interfacial tension determined by the measuring arrangement.

[0043] The process fluid can be a liquid that is the subject of the process or an auxiliary fluid that contributes to the process but is not consumed. The measuring arrangement enables the continuous monitoring of a process acting on the carrier fluid or dependent on the interfacial tension of the carrier fluid during operation.

[0044] Another aspect of the present disclosure relates to a measuring arrangement for determining the interfacial tension of a sample liquid in an operational state. Such a measuring arrangement comprises a paramagnetic carrier liquid in a chamber of a vessel, a drop of sample liquid in the carrier liquid, a magnetic field source, and a measuring device. The magnetic field source is configured to generate an inhomogeneous magnetic field with a vertical magnetic field gradient in the chamber. The sample liquid is less paramagnetic than the carrier liquid. The sample liquid and the carrier liquid are immiscible. The measuring device is configured to detect at least sections of a contour of the drop.

[0045] According to one embodiment, the sample liquid contains a diamagnetic liquid or, apart from impurities, consists entirely of a diamagnetic liquid.

[0046] According to one embodiment, the carrier liquid is an aqueous solution and the sample liquid is a hydrophobic liquid, or the sample liquid is an aqueous solution and the carrier liquid is a hydrophobic liquid. The carrier liquid and the sample liquid can have different densities.

[0047] According to one embodiment, the carrier fluid is an aqueous solution containing one or more rare earth salts. The anionic component of the dissolved salt(s) includes, for example, chloride ions, nitrate anions, sulfate anions, hydrogen sulfate anions, phosphate anions, hydrogen phosphate anions, dihydrogen phosphate anions, carbonate anions, and / or hydrogen carbonate anions.

[0048] The cation fraction of the dissolved salt(s) contains, for example, dysprosium(III) ions, holmium(III) ions, erbium(III) ions, and / or gadolinium(III) ions. The carrier fluid may be, for example, a dysprosium(III) chloride solution (DyCl3).

[0049] The sample liquid is, for example, a diamagnetic oil, such as paraffin or naphthene. The sample liquid can be chosen from the following group of organic solutions: carbon tetrachloride, chlorobenzene, cyclohexane, heptane, hexane, pentane, toluene, and triethylamine.

[0050] In another example, the carrier fluid is a superparamagnetic fluid, e.g. a ferrofluid, and the sample fluid is a liquid elemental metal, e.g. mercury, or a liquid metal alloy, e.g. Galinstan.

[0051] Another aspect of the present disclosure relates to a method for determining interfacial tension. The method comprises generating a magnetic field, wherein the magnetic field in a chamber of a vessel has a vertical magnetic field gradient; generating a drop of sample liquid in the chamber filled with a carrier liquid, wherein the sample liquid is less paramagnetic than the carrier liquid, and wherein the sample liquid and the carrier liquid are immiscible; and acquiring significant parameters of the drop's contour. The sample liquid may be diamagnetic.

[0052] According to one embodiment, the method also includes determining the interfacial tension from the significant parameters and magnetic field strengths acting locally on the droplet.

[0053] According to one embodiment, the droplet is generated by first dispensing a small volume of the sample liquid into the chamber and forming a precursor droplet, then dispensing more sample liquid into the chamber and coagulating it with the precursor droplet until the droplet resulting from the precursor droplet reaches a size at which the contour of the droplet meets a predetermined criterion.

[0054] The predetermined criterion can be a maximum height difference of the flat side of the droplet over a minimum horizontal area. With a sufficiently flat side of the droplet, the significant parameters of the droplet's contour can be determined with high precision.

[0055] Fig. Figure 1 shows a measuring setup with a cuvette 15 as a vessel 10 with a chamber 11 for holding a carrier liquid 31. The cuvette 15 has a rectangular base plate and two pairs of plane-parallel side surfaces made of transparent plastic. The transparent plastic is, for example, a polyimide, polytetrafluoroethylene (PTFE), or polymethyl methacrylate (acrylic glass). The horizontal cross-sectional area of ​​the chamber 11 can be approximately 1 cm². 2 for example, within a range of 0.5cm 2 up to 2cm 2 The height of chamber 11 perpendicular to the base plate can be at least 0.5 cm up to 5 cm, e.g. about 1 cm.

[0056] A feeding device 20 with a tube- or hose-like cavity 25 (cannula) is inserted into the cuvette 15. The feeding device 20 has a connector 26 suitable for connection to a flexible hose or a dosing pump at an inlet opening accessible from outside the chamber 11 and an upwardly directed outlet opening 27 inside the chamber 11. The outlet opening 27 is closed with a capillary 29. The cannula 25 extends continuously from the inlet opening to the outlet opening 27 with a constant diameter. The feeding device 20 comprises, for example, a 3D-printed plastic part that is form-fittingly fitted into the lower part of the chamber 11.

[0057] A magnetic field source 40 of the measuring arrangement comprises a ring magnet with a central opening. The ring magnet is, for example, a neodymium magnet of grade N45. The ring magnet closes off the chamber 11 at the top or rests on a lid of the cuvette 15. The longitudinal axis of the ring magnet and the longitudinal axis of the capillary 29 are coaxial and lie on the same straight line. The ring magnet generates an inhomogeneous magnetic field with a vertical magnetic field gradient in the chamber 11.

[0058] At least a portion of chamber 11 above the outlet opening of capillary 29 is filled with a carrier fluid 31. The carrier fluid 31 contains a paramagnetic phase with a magnetic susceptibility χ and a density ρf. The paramagnetic phase can, for example, contain or consist of a paramagnetic salt in an aqueous solution, several paramagnetic salts in an aqueous solution, an ionic liquid, an organic solvent, and / or a silicon-based oil.

[0059] A sample liquid 36 is fed dropwise into chamber 11 via the feed device 20. The sample liquid 36 and the carrier liquid 31 are immiscible. The sample liquid 36 emerging from the capillary 29 forms one or more drops that detach from the capillary 29, or which detach from the capillary 29 and, oscillating along the vertical axis, eventually reach a final position above the capillary 29 and at a distance from both the capillary 29 and the magnetic field source 40. Several drops coagulate into a single drop 37. The shape of the drop 37 at its final position depends on the susceptibility χ and the density ρf of the carrier liquid, the density ρ0 of the sample liquid, the magnetic field densities at the lower and upper edges of the drop 37, and the interfacial tension between the carrier liquid 31 and the sample liquid 36.

[0060] A measuring device 50 comprises a radiation source 51 on a first side of the cuvette 15 and a radiation sensor 52 on the side of the cuvette 15 opposite the radiation source 51. The radiation sensor 52 is, for example, an image sensor.

[0061] An evaluation unit 70 is connected to the measuring device 50 via data transmission and receives image data from the measuring device 50, which describes a contour of the drop 37. The evaluation unit 70 determines significant parameters of the contour from the received image data, for example, the curvature at the geometric upper edge κ. Top of the drop 37 and the curvature κ Bot at the geometric lower edge of the drop 37. The geometric upper edge can be determined by the highest point of the drop surface, the geometric lower edge by the lowest point of the drop surface relative to the Earth's surface.

[0062] From the significant parameters, the difference χ of the magnetic susceptibilities of the sample liquid and the carrier liquid, the density ρf of the carrier liquid, the density ρ0 of the sample liquid, the magnetic flux densities B Top and B Bot at the upper and lower edges of the drop 37 and the local curvatures κ Top and k Bot At the geometric upper and geometric lower edges of the drop 37, the evaluation unit 70 calculates the interfacial tension σ between the sample liquid 36 and the carrier liquid 31, e.g. according to equation #1: σ=12(κBot−κTop)⋅[(BTop2−BBot2)⋅χ⋅c2μo+(ρo−ρf)⋅gh]

[0063] Here, µ0 is the vacuum magnetic permeability, g is the free fall acceleration, h is the vertical distance between the top and bottom of droplet 37, or the vertical distance between the geometrically upper and lower edges of droplet 37, and c is the molar concentration of paramagnetic salts dissolved in the carrier phase. For example, for an aqueous dysprosium(III) chloride solution (DyCl3), c is the concentration of dysprosium(III) ions in water.

[0064] Fig. Figure 2 shows on the left an image of a droplet 37 of the process fluid 36, taken by a radiation sensor 52 designed as an image sensor. The droplet 37 floats in the carrier fluid 31 at a distance z0 from the lower edge of the magnetic field source 40. The droplet 37 originates from a multitude of smaller precursor droplets 32, which successively detach from the capillary 29 and coagulate to form the droplet 37.

[0065] In the illustrated case, the upper surface of droplet 37 is subjected to a stronger magnetic pressure and flattens out considerably. The lower surface of droplet 37 is subjected to a weaker magnetic pressure, and the curvature of droplet 37 decreases only slightly.

[0066] The right side of the Fig. Figure 2 shows parameters that can be obtained from the image on the left side of the figure to calculate the interfacial tension σ, e.g. the curvatures κ. Top and k Botat the upper and lower edges of the drop 37. From the distances of the upper and lower edges of the drop 37 to the lower edge of the magnetic field source 40, the magnetic field densities B can be determined if the magnetic field generated by the magnetic field source 40 is known. Top and B Bot Determine at the top and bottom edges of drop 37.

[0067] Fig. Figure 3 shows the coaxial arrangement of the longitudinal axis of the capillary 29 and the longitudinal axis 49 of the ring magnet 45.

[0068] Fig. Figure 4 shows typical dimensions for the outer diameter of the ring magnet 45, the diameter of the opening in the ring magnet 45, the distance between the opening of the capillary 29 and the lower edge of the ring magnet 45, and a typical hydrodynamic length of the drop 37.

[0069] In Fig. A metering pump 60 is connected via a hose 65 to the connector 26 of the feed device. The cuvette 15 is arranged in the beam path between a radiation source 51 and a radiation sensor 52.

[0070] The drop 37 is imaged onto a radiation-sensitive sensor surface of the radiation sensor 52.

[0071] Fig. 6 and Fig. Figure 7 shows a measuring device 50 with a plurality of electrodes 55 arranged on the vessel 10. Excitation signals can be output and / or measurement signals can be received via the electrodes 55. An impedance measuring device 56 determines the electrical impedances between two electrodes 55 (electrode pairs) arranged at different locations on the chamber wall from the measurement signals received by the electrodes 55.

[0072] The electrodes 55 are attached to the inside of the chamber 11 or embedded in the wall of the chamber 11. The electrodes 55 are arranged in at least two rows, with electrodes 55 in the same row being positioned at the same height above the base of the chamber 11 along the circumference of the chamber 11.

[0073] The floor area of ​​chamber 11 in Fig. 6 is rectangular. The base area of ​​chamber 11 in Fig. 7 is circular.

[0074] For impedance measurement, the impedance measuring device 56 outputs a periodic excitation signal to at least one electrode pair and determines the complex impedance between the electrodes of an electrode pair. Alternatively or additionally, the impedance measuring device can determine the electrical resistance between electrode pairs.

[0075] For each electrode 55, an impedance measurement and / or resistance measurement can be performed with exactly one other electrode 55, with several other electrodes 55, or with all other electrodes 55. The impedances or electrical resistances between each pair of electrodes provide information about the contour of the droplet 37.

[0076] Fig. 8A to Fig. Figure 8D shows the process of measuring the interfacial tension between a carrier liquid 31 and a sample liquid using schematic longitudinal sections through a cuvette 15.

[0077] Fig. Figure 8A shows a cuvette 15 filled with the carrier liquid 31. Fig. Figure 8B schematically shows the activation of a magnetic field source 40, which generates a magnetic field with a vertical magnetic field gradient in the cuvette 15. Fig. Sample liquid 36 is dispensed into the cuvette 15 via a cannula 25 sealed with a capillary 29. The sample liquid 36 forms a drop 37. Fig. Figure 8D shows a droplet 37 that is flattened on its upper side, oriented towards the magnetic field source 40.

[0078] Fig. Figure 9 shows a device for processing or using a process fluid 81. A line 82 supplies the process fluid 81 to a controllable process unit 80. Via a bypass 83, a portion of the process fluid 81 is continuously, as needed, or at regular intervals diverted and supplied as a carrier fluid 31 to the cuvette 15 of a measuring arrangement described above. After determining the interfacial tension, the carrier fluid can be drained from the cuvette 15 and, for example, returned to the line 82.

[0079] An evaluation unit 70 transmits the determined interfacial tension to the controllable process unit 80. The process unit 80 can control a process dependent on the interfacial tension of the carrier fluid in such a way that fluctuations in the interfacial tension are at least partially compensated, process parameters are adapted to the last determined interfacial tension, and / or a process is terminated if the interfacial tension falls below or exceeds a predetermined value.

[0080] If, for example, line 82 transports a Dy(III) solution from which process unit 80 extracts dysprosium, then an interfacial tension measurement with a standardized oil of known density and magnetic susceptibility provides information on how far the extraction process has progressed.

[0081] Alternatively, the phase under investigation, e.g., an oil, can be introduced via inlet 29 into a chamber 15 filled with a standardized carrier fluid of known density and magnetic susceptibility. The determined interfacial tension provides information about the current composition of the oil phase in a reactor. In the case of a rare-earth extraction / stripping process, the rare-earth content of the oil phase can be deduced from the interfacial tension.

Claims

[1] Measuring setup for determining the interfacial tension of a sample liquid (36), comprising: a vessel (10) with a chamber (11) for receiving a carrier fluid (31); a feeding device (20) which is designed to feed the sample liquid (36) into the chamber (11); a magnetic field source (40) configured to generate an inhomogeneous magnetic field with a vertical magnetic field gradient in the chamber (11); and a measuring device (50) which is designed to detect at least one section of a contour of a drop (37) of the sample liquid (36) formed in the chamber (11) during the operation of the measuring arrangement. [2] Measuring arrangement according to one of the preceding claims, further comprising: an evaluation unit (70) which is set up to determine significant parameters of the contour from the sections of the contour of the drop (37) detected by the measuring device (50). [3] Measuring arrangement according to the preceding claim, wherein the evaluation unit (70) is configured to determine the interfacial tension between the carrier liquid (31) and the sample liquid (36) from the significant parameters and magnetic field strengths acting locally on the drop (37). [4] Measuring arrangement according to the preceding claim, wherein an outlet opening of the feed device (20) positioned in the chamber (11) is closed with a capillary (29). [5] Measuring arrangement according to one of the preceding claims, further comprising: a metering pump (60) connected to an inlet opening of the feed device (20), wherein the metering pump (60) is configured to dispense the sample liquid (36) dropwise into the chamber (11). [6] Measuring arrangement according to one of the preceding claims, wherein the measuring device (50) comprises a radiation source (51) and a radiation sensor (52) and the vessel (10) is arranged in a beam path between the radiation source (51) and the radiation sensor (52). [7] Measuring arrangement according to one of the preceding claims, wherein the measuring device (50) comprises a plurality of electrodes (55) arranged on the vessel (10) and an impedance measuring device (56) and the impedance measuring device (56) is configured to determine electrical impedances between any two of the electrodes (55). [8] Device for processing a process fluid (81), comprising: the measuring arrangement according to one of the preceding claims, wherein the process fluid (81) can be supplied to and removed from the measuring arrangement as the carrier fluid (31) permanently, by user intervention or at predefined time intervals, and a controllable process device (80) for processing or using the process fluid (81), wherein the process device (80) is controllable depending on an interfacial tension determined by the measuring arrangement. [9] Measuring setup for determining interfacial tension, comprising: a paramagnetic carrier fluid (31) in a chamber (11) of a vessel (10), a magnetic field source (40) which is configured to generate an inhomogeneous magnetic field with a vertical magnetic field gradient in the chamber (11); a drop (37) of a sample liquid (36) in the carrier liquid (31), wherein the sample liquid (36) is less paramagnetic than the carrier liquid (31), and the sample liquid (36) and the carrier liquid (31) are immiscible and have different densities; and a measuring device (50) which is configured to detect at least sections of a contour of the drop (37). [10] Measuring arrangement according to claim 9, wherein the sample liquid (36) contains a diamagnetic liquid. [11] Measuring arrangement according to one of claims 9 or 10, wherein the carrier liquid (31) is an aqueous solution and the sample liquid (36) is a hydrophobic liquid, or the sample liquid (36) is an aqueous solution and the carrier liquid (31) is a hydrophobic liquid. [12] Measuring arrangement according to one of claims 9 to 11, wherein the carrier fluid (31) comprises an aqueous solution containing a salt of a rare earth element. [13] Method for determining interfacial tension, comprising: Generating a magnetic field wherein the magnetic field in a chamber (11) of a vessel (10) has a vertical magnetic field gradient; Generating a droplet (37) of a sample liquid (36) in the chamber (11) filled with a carrier liquid (31), wherein the sample liquid (36) is less paramagnetic than the carrier liquid (31), and wherein the sample liquid (36) and the carrier liquid (31) are immiscible and have different densities; and Capturing significant parameters of the droplet contour (37). [14] Method according to claim 13, further comprising: Determining the interfacial tension from the significant parameters and magnetic field strengths acting locally on the drop (37). [15] Method according to one of claims 13 and 14, wherein the drop (37) is produced by first dispensing a small volume of the sample liquid (36) into the chamber (11) and forming a precursor drop (32) with an initial volume, and further dispensing sample liquid (36) into the chamber (11) and coagulating with the precursor drop (32) until the drop (37) resulting from the precursor drop (32) reaches a size at which the contour of the drop (37) meets a predetermined criterion.

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