Electrochemical measurement device for a fluid incorporating at least one electrochemical probe, in particular at the free end of a pole, and a protective element rotating around the probe, Application to monitoring in bioproduction.

Abstract

Electrochemical measurement device for a fluid incorporating at least one electrochemical probe, in particular at the free end of a pole, and a protective element rotating around the probe, Application to monitoring in bioproduction.The invention relates to an electrochemical measuring device for a non-gaseous fluid, in particular contained in a container, such as a tank, especially one with opaque walls, comprising: - a measuring pole in the form of a tube (2) with longitudinal axis X, one free end of which is intended to be immersed in the fluid; - at least one electrochemical probe, fixed to the free end of the measuring pole, and adapted to measure the electrochemical properties of the fluid; - an element (3) mounted for rotation around the tube and comprising at least one wall with a plurality of open holes (31 to 39) shaped such that the peripheral surface (300) of each hole is formed so that a flow of the fluid over the wall causes an asymmetry of the bearing forces on each peripheral surface of the hole and thus sets the element in rotation about the axis X. Figure for the abstract: Fig. 1.

Description

Title of the invention: Electrochemical measurement device for a fluid integrating at least one electrochemical probe, in particular at the free end of a pole, and a protective element rotating around the probe, Application to monitoring in bioproduction. technical field

[0001] The present invention relates to the field of knowledge of the state of a fluid, more particularly by means of an electrochemical probe.

[0002] It aims in particular to make the measurements carried out by such an electrochemical probe more reliable, in particular within a bioreactor, even in the case of non-turbulent flow of a fluid.

[0003] Although described by reference for an application within a bioreactor, the invention can be considered for any application of measuring the state of a fluid (liquid, gas) within a container such as a tank, more particularly one with opaque walls, whose operating conditions cause the fluid to be in general or local motion. For example, this could be a production or settling tank. Previous technique

[0004] Stirred tank reactors, like bioreactors, are widely used in many areas of the chemical industry.

[0005] In the field of bioproduction, the manufacture within bioreactors of biological products, which are living substances (vaccines, microalgae, biological pharmacological molecules, etc.) cannot be carried out by a completely pre-established protocol.

[0006] Indeed, it requires a permanent adaptation to adjust the physical parameters of the fluid, such as its viscosity, its mixing speed, its temperature, as well as its content of bubbles, gas, nutrients, etc... from imperfect measured parameters, which consist of indirect biochemical measurements, such as pH, and / or valid only locally and / or incomplete, etc....

[0007] The study of fluid flow in a bioreactor is essential in order to provide key information for choosing the best adaptation to be made in real time. In particular, viscosity and, by correlation, the Reynolds number, which defines the nature of a flow based on its velocity and also the viscosity of the flowing medium, is a parameter that must be known.

[0008] When reactor vessels have transparent walls, the flow velocity of a fluid can be measured by means of measurement by indirect observation carried out from outside. For velocity measurement, there can mainly be two optical methods, namely laser Doppler anemometry (LDA for "Laser Doppler Anemometry") and particle imaging velocimetry (PIV for "Particle Imaging Velocimetry").

[0009] Ideally, CFD (Computational Fluid Dynamics) numerical simulations should be compared with these experimental flow field data.

[0010] However, many bioreactors have opaque-walled tanks to prevent light from penetrating, or for reasons of equipment cost or robustness. In the case of an opaque fluid, such as kerosene, the droplets are not transparent and strongly scatter light. This therefore effectively rules out the aforementioned indirect measurement methods.

[0011] In addition, it is generally impossible or prohibited to use in bioreactors measuring capsules that move freely with the permanent or intermittent movements of the fluid.

[0012] Another problem arises in bioreactors, and more generally in mixed media, which are equipped with electrochemical probes, particularly in the form of electrochemical sensors that operate primarily by voltammetry, i.e., by voltammetric and / or amperometric methods, possibly combined with other methods exploiting impedance or other electrochemical properties, to measure various parameters. Indeed, the stability of the measurement performed by these probes can be disrupted by changes in the nature of the fluid flow, which induces slow drifts that are not representative of electrochemical phenomena.

[0013] Furthermore, these probes can become fouled if the fluid flow reaching them is not sufficiently turbulent or if a layer forms on them, also resulting in a disruption of the measurement. In other words, the fluid medium is likely to have adverse effects either through its flow properties, through fouling ("biofouling"), or through the formation of a biofilm or a surface layer that impairs the quality of the measurements.

[0014] There is therefore also a need to find a solution to guarantee the quality and stability of measurement of electrochemical probes immersed in a non-gaseous fluid, whether moving or not, within a volume, in particular of a tank, whatever its type, especially a settling or production tank.

[0015] The object of the invention is to meet, at least in part, this need(s). Description of the invention

[0016] To this end, the invention relates to an electrochemical measuring device for a non-gaseous fluid, in particular contained in a container, such as a tank, especially one with opaque walls, comprising: - a measuring pole in the form of a tube with a longitudinal axis X, one free end of which is intended to be immersed in the fluid;

[0017] - at least one electrochemical probe, attached to the free end of the pole measurement, and adapted to measure electrochemical properties of the fluid;

[0018] - an element mounted for rotation around the tube and comprising at least one wall with a plurality of through holes made in such a way that the peripheral surface of each hole is shaped so that a flow of fluid on the wall causes an asymmetry of the support forces on each peripheral surface of hole and thus sets the element in rotation around the X axis.

[0019] According to an advantageous embodiment, the electrochemical probe comprises at least one electrochemical sensor, fixed to the free end of the tube inside the element, comprising at least one pair of electrodes, including a so-called working electrode to which an applied electrical potential (equivalent voltage or current) can be varied as a function of time and a so-called auxiliary electrode in which the electrical signal flowing, as well as in the working electrode, is measured as a function of the electrical potential.

[0020] For the purposes of this invention, the term "electrochemical probe" refers to a device comprising at least one electrochemical sensor capable of converting one or more chemical quantities, such as concentration, pH, or electrochemical activity, into electrical output quantities with variable sensitivity depending on the channel and equipped with calibration relationships. This device may be single-electrode or multi-electrode and may be implemented on a PCB (Printed Card Board) or any equivalent integrated sensor. The probe may include a thin-walled, fragile capsule, e.g., made of glass, or a bare or functionalized surface in direct contact with the fluid.

[0021] By "electrochemical measurement" ("voltamperometry" or "voltammetry" or "impedance"), we mean here and within the framework of the invention an electroanalytical method based on the measurement of the electric current flow or electric potential resulting from the reduction or oxidation of the test compounds present in solution under the effect of a controlled variation of the potential difference between two specific electrodes ("voltamperometry"), or of the reduction or oxidation of the electrodes under the effect of the compounds present in solution ("voltammetry"), or of the variation of the electrical conductivity of the medium as a function of the compounds present in solution ("impedance").

[0022] According to another advantageous embodiment, the wall of the element is at least partly cylindrical, the holes being formed in the thickness of the cylindrical wall, each with an axis that does not intersect the axis of the cylinder of the wall. The holes are thus teardrop-shaped because their contour results from the intersection of two cylinders whose axes do not intersect.

[0023] The holes may be distributed uniformly or not on the periphery.

[0024] Advantageously, the holes are distributed in rows, preferably three or six in number, parallel to the X axis, preferably distributed uniformly angularly around the X axis, in order to improve the regularity of the rotation of the element.

[0025] Advantageously, the holes are of different diameters so as to broaden the Reynolds number range that characterizes the fluid and is capable of producing the rotation. Indeed, holes of different dimensions make it possible to adapt the rotation of the device to different ranges of fluid viscosity or turbulence effects.

[0026] The element may comprise a plurality of protrusions arranged on the external and / or internal face of the element, each adapted to create a fluid bearing surface, advantageously in addition to the bearing surfaces formed by the periphery of the holes in the wall of the element, or replacing them if the fluid is gaseous. These protrusions constitute a bearing surface that can be combined with the peripheral surfaces, which are the primary bearing surfaces. This makes it possible to increase the efficiency of rotation, provided that the balance of added friction remains favorable.

[0027] The element is advantageously mounted for rotation around the tube by at least one bearing or ball bearing or ball cage.

[0028] The invention further relates to a settling, purification, or production medium or tank, particularly for a bioreactor, comprising a measuring device as described above or a system as described above. A tank can be any type of container, reservoir, bioreactor, vessel, or boiler containing a fluid. A bioreactor includes a tank used for the manufacture of drugs, pharmaceuticals, antibodies, vaccines, or other products that can be described as living.

[0029] The invention finally relates to the use of a measuring device as described above or a system as described above for monitoring bioproduction and / or for providing reference data in a digital twin.

[0030] A tank can be equipped with one or more tubes, for example, to implement means for stirring the fluid, or a means for introducing nutrients or a gas, or for any other function. Generally, the poles are fixed, but some They can be mobile in rotation or translation and driven by motors. A pole can be equipped with one or more measuring probes, including a probe capable of performing electrochemical measurements.

[0031] The invention proposes to use any one of these types of poles to carry out the measurements according to the invention, referred to for this purpose as a measuring pole.

[0032] A measuring pole can consist of a solid tube or hollow tube at least partially immersed in a fluid to be analyzed, and can be fixed or mobile in translation and / or rotation.

[0033] More generally, the invention can be implemented in certain agri-food productions and / or for applications where protection and performance improvement of already installed electrochemical probes are desired, particularly fixed probes immersed in tanks where the fluid medium is likely to have adverse effects, either through its flow properties, fouling ("biofouling"), or the appearance of a biofilm or surface layer that impairs the quality of measurements. These may include fish farming ponds or so-called natural ponds.

[0034] The invention can also be implemented in fluidic media that are currently uninstrumented or under-instrumented due to their nature, such as excessive turbidity, significant eddies or turbulence, or excessively rapid deposition of a layer unsuitable for electrochemical measurement. These may include settling tanks, particularly for wastewater, and micro-wastewater treatment plants for private individuals.

[0035] The invention therefore essentially consists of a measuring device with an electrochemical probe for a non-gaseous fluid around which is mounted in rotation an element, made asymmetric by through holes allowing the fluid flow to produce an asymmetric thrust which allows the element to rotate around the probe.

[0036] The perforated peripheral wall of the rotating element creates sufficiently large and asymmetrical bearing surfaces to produce a torque around the axis of the tube.

[0037] In other words, the rotating element of the measuring device can be likened to a paddle wheel, with passive rotation, fully immersed in the non-gaseous fluid medium. Its bearing surfaces, defined by the perforated peripheral wall, are very compact and contained within the thickness of the element to accommodate rotation in a non-gaseous fluid. The ratio of the peripheral surface area to the total surface area of ​​the rotating element is advantageously maximized to facilitate rotation by minimizing friction and to minimize the flow disturbance introduced by the presence of the rotating element. Care is, of course, taken to maintain the mechanical rigidity of the rotating element.

[0038] An advantageous variant for creating larger peripheral surfaces that are asymmetrical from the point of view of fluid flow around the drilled element is to produce the holes, either by machining or by additive manufacturing, in a perforation direction that is not directed towards the axis of symmetry of the rotating element. This promotes the accumulation of tangential forces produced by the portion of fluid flowing on one side or the other of the cylindrical surface of the rotating element, causing it to move at the fluid velocity by generating a rotational torque. The term "bearing surface" refers to the cumulative sum of all the peripheral surfaces of the drilled holes that contribute to the rotational torque. The effective bearing surface is derived from the geometric bearing surface, slightly corrected by a coefficient that depends on the fluid flow conditions and can be calibrated.The diameter of the rotating element is chosen to maximize the rotational torque according to principles known to those skilled in the art. The good capacity of the fluid to pass through the openings increases the forces exerted on the bearing surface. In turbulent flow, more numerous and smaller holes are preferable in order to sum the useful contributions and minimize the forces produced by internal turbulence orientations that are not directed in the overall flow direction and therefore do not contribute to the rotational torque.

[0039] In fact, to minimize the equilibrium of the two supports, which are radial and antagonistic in nature, created by the flow splitting in two around the rotating element, rows of open holes are preferably created within it. In certain specific cases, a break in the element's symmetry may suffice to generate a rotational torque corresponding to a small tangential force produced from the imbalance between the radial forces, thus obtaining a slight rotation that can sometimes be regular or even stable.

[0040] But for the operation of the device to be guaranteed, more particularly in many usage configurations and fluids and Reynolds number ranges, correlated with viscosity, it is necessary to partition the liquid into two contributions around the rotation element so that the liquid enters holes that are both well organized and well made such that the summation of the fluid forces on the peripheral surfaces of the holes is tangential in nature and maximized to increase the rotational torque in the chosen direction and minimize it in the other direction.

[0041] For this reason, according to this advantageous variant, the axes of the holes do not intersect with the longitudinal axis X of the tube. Indeed, with the axes of the holes intersecting the X axis, the resulting rotational torque is less optimized, with a resultant rotation that could be irregular or, in certain turbulent fluid situations, could randomly switch from one direction of rotation to the other.

[0042] Therefore, the wall thickness of the rotating element and the number, size, drilling angle, and distribution of the plurality of holes are parameters to be precisely adjusted.

[0043] This rotating element forms a protective ring for the electrochemical probe for determining the chemical properties of the fluid.

[0044] Thanks to this active and permanent protection provided by the rotation of the element, the adverse effects associated with the slow evolution of the flow nature are minimized, such as highly localized microcirculations of fluid around the probe, which can lead to slow drifts in the probe measurement that are not representative of electrochemical phenomena. While not limited in generality, this advantage is particularly relevant to very slow flow conditions or the effects of permanent drag induced by the presence of the probe in a slow or very low-turbulence flow. Furthermore, the perforated rotating element not only facilitates the renewal of contact between the electrochemical probe and the non-gaseous fluid medium in which it is immersed, but also ensures a flow regime conducive to improving the stability of the measurement performed by the electrochemical probe.

[0045] The peripheral surface of the rotating element of the measuring device can advantageously be structured, in particular by means of grooves and / or asperities, or functionalized, in particular by a hydrophilic or hydrophobic coating to improve the operation of the device, according to methods known to those skilled in the art. This allows for more effective uniformization of the fluid flow in contact with the electrochemical probe.

[0046] In conclusion, the invention offers several advantages, including: a more precise estimation of the impact of flow physics on the quality of electrochemical measurements before their calibration, and / or on the accuracy or short-, medium-, or long-term stability of the portion of the calibration that is linked to potential changes in the fluid flow properties. This makes it possible to resolve potential ambiguities in the analysis of electrochemical dynamics based on the results measured by the probe.

[0047] Other advantages and features will become clearer upon reading the detailed description, given by way of illustration and not limitation, with reference to the following figures. Brief description of the drawings

[0048] [Fig-1] [Fig. 1] is a schematic perspective view of the implementation at the end of a pole of a first example of an electrochemical measurement device for a non-gaseous fluid, according to the invention.

[0049] [Fig.2] [Fig.2] is a side view of the device according to [Fig.1].

[0050] [Fig.3] [Fig.3] is a schematic front view of a flat blank of a rotation element according to the first example of Figures 1 and 2, produced by flat additive manufacturing before being finalized.

[0051] [Fig.4] [Fig.4] illustrates the positioning of the drilling tool to produce a rotating element according to the example of figures 1 and 2.

[0052] [Fig.5] [Fig.5] is a perspective view of a second example of an electrochemical measurement device for a non-gaseous fluid, according to the invention.

[0053] [Fig.6] [Fig.6] is a side view of the device according to [Fig.5].

[0054] [Fig.7] [Fig.7] is a partial longitudinal cross-sectional view of the system along the [Fig.5].

[0055] [Fig.8] [Fig.8] is a schematic perspective view of a third example of an electrochemical measurement device for a non-gaseous fluid, according to the invention.

[0056] [Fig.9] [Fig.9] is a cyclic voltamogram, that is to say a so-called canard curve of the current density as a function of the potential, characteristic of a detection by cyclic voltammetry of an oxidized species free to diffuse in solution as implemented by an electrochemical probe of a device capable of measuring the electrochemical properties of a fluid, according to the invention. Detailed description

[0057] For the sake of clarity, the same references designating the same elements according to the invention are used for all figures 1 to 8.

[0058] The drawings and the arrangement of the different elements in relation to each other are not shown to scale.

[0059] Throughout this application, the terms "above", "below", "lower" and "upper" are to be understood by reference to the measuring system according to the invention as it is in an installation configuration with a measuring pole arranged vertically.

[0060] Figures 1 and 2 illustrate a first example of a device for measuring the flow velocity of a non-gaseous fluid contained in a vessel, such as a tank, particularly one with opaque walls. This could be the tank of a bioreactor containing a bioproduction fluid whose mixing conditions one seeks to determine and control.

[0061] The device 1 includes first of all a tube 2 with longitudinal axis X forming a measuring pole.

[0062] An element 3, mounted for rotation around the tube 2, comprises at least one wall 30 with a plurality of open holes 31, 32, 33 arranged such that the peripheral surface 300 of each hole is shaped so that a flow of fluid on the wall causes an asymmetry of the support forces on each peripheral surface of the hole and thus puts element 3 in rotation around the X axis.

[0063] In other words, the surface of the wall 30 is made mechanically asymmetric about the X axis, that is to say, it can easily be subjected to a rotational torque about the X axis and with the preferred characteristic that the holes are made as small hollow cylinders in the thickness of the cylindrical wall with for each small cylinder an axis not intersecting with the X axis.

[0064] An example of the fabrication of a blank 3 of a rotating element produced flat by additive manufacturing is shown in [Fig. 3]. To finalize the rotating element 3, this blank is rolled onto itself and then sealed at its two adjoining edges. The blank 3 can be produced in several sub-parts with successive assembly of the adjoining edges.

[0065] Fig. 4 shows the presence of drilling tools PI, P2, P3 which each extend along a non-secant axis with the central axis X of the tube 2 so as to respectively make holes 31, 32, 33 with asymmetric peripheral surface.

[0066] Due to the asymmetry of each peripheral surface 300 of hole, a flow of fluid on the wall 30 causes support forces on the peripheral surfaces of the holes such that an overall rotational torque results and thus sets the element 3 in rotation around the X axis.

[0067] In the illustrated example, element 3 is in the form of a cylindrical ring, with holes 31 to 33 made in the thickness of the cylindrical wall, each with an axis that does not intersect the X-axis of the cylinder. The diameter of the ring and the thickness of its wall are chosen to maximize this torque according to rules known to those skilled in the art, and beyond this initial dimensioning, the through holes are adapted to the intended use.

[0068] This element 3 can be mounted in rotation on the measuring pole 2 by means of a ball cage 4 which can be integrated directly into the element 3 or interposed between it and the pole 2.

[0069] As can be seen in Figures 1 and 2, the holes 31 to 33 are of different diameters, for example, with the larger holes 31 on the lower and upper end portions, the intermediate-diameter holes 32 inside the wall 30, and on either side a smaller-diameter hole 33. The arrangement of these holes 31 to 33 can be symmetrical with respect to the median plane of the height of the cylindrical ring 3. As also shown, these holes 31 to 33 are arranged in rows regularly spaced at an angle of 60° around the X-axis. Having different diameters for the holes 31 to 33 allows for a wider range of Reynolds numbers that characterize the fluid, enabling the ring 3 to rotate around the X-axis.

[0070] The device 1 includes a volt-amperometric sensor 5 fixed to or protruding from the free end of the tube 2 inside the rotating element 3. This electrochemical sensor 5 includes a pair of electrodes, including a so-called working electrode to which an applied electrical potential can be varied as a function of time and a so-called auxiliary electrode in which the electrical signal flowing, as well as in the working electrode, is measured as a function of the electrical potential.

[0071] The example of device 1 according to figures 5 and 7 differs from that of figures 1 and 2 by holes 34 to 36 of larger to smaller diameter respectively which are made with a random arrangement in the peripheral wall 30 of the rotating ring 3.

[0072] Figure 8 illustrates another example of device 1 with vertical rows of same hole diameters 37 to 39, from largest to smallest respectively, arranged adjacent to each other, also being angularly separated from each other by 60°.

[0073] The volt-amperometric sensor 5 is advantageously that of an electrochemical probe which allows the electrochemical properties of the fluid to be measured. The device 1 is thus a device for measuring the electrochemical properties of the fluid.

[0074] The rotating element 3 prevents the electrochemical sensor 5 from becoming fouled because the fluid flow reaching this sensor is sufficiently stable. The rotating element 3 also prevents the formation of a biofilm or surface layer. Thus, the stability and quality of the electrochemical measurements by the sensor 5 are ensured.

[0075] We now describe the operation of the measuring device.

[0076] Figure 9 illustrates an example of a cyclic voltamogram for a redox process. electrochemically reversible obtained with probe electrodes 5. The illustration shows the key points and portions of the so-called canard characteristic curve useful for analyzing the properties, with values ​​that are only indicative.

[0077] The scan begins at -0.4 V and progresses towards more positive oxidative potentials. Initially, the potential is insufficient to oxidize the analyte (a). When the potential approaches several kT from the standard potential, the onset (Eonset) of oxidation is reached. Following this, the current increases exponentially (b) as the analyte begins its oxidation at the surface of the working electrode. For a reversible process, the current initially increases as if there were no change in the oxidant concentration. The current is dictated by the diffusion rate of the oxidant towards the electrode, as well as by the proportion converted to the reduced form. This can be understood according to the Nernst equation. As the analysis continues, more oxidant is depleted. The concentration gradient adjusts accordingly. It is this change that causes a peak in the voltammogram.

[0078] It is observed that the decrease in current due to oxidant depletion outweighs the increase due to the change in the proportion of oxidant oxidized at the electrode. The current reaches its maximum at point c (anodic tip current (ipa)) for oxidation at the anodic tip potential (Epa). Here, more positive potentials cause an increase in current, which is compensated by a decrease in analyte flux from increasingly greater distances from the electrode surface.

[0079] From this point onward, the current is limited by the massive transport of the analyte from the ground to the DDL interface, which is slow on the electrochemical timescale. This results in a decrease in current (d) as the potentials are swept more positively. This continues until a steady state is reached, where further increases in potential have no effect. Reversing the sweep to negative potentials (reductive sweep) continues to oxidize the analyte. This continues until the applied potential reaches the value at which the oxidized analyte (which has accumulated on the electrode surface) can be re-reduced (e). The reduction process mirrors that of oxidation. The only difference is that it occurs with an opposite sweep direction and a cathode peak potential (ipc) at the cathode peak potential (Epc) (f).The anodic and cathodic peak currents must be of the same amplitude but opposite sign. This is only true if the process is reversible (and if the cathodic peak is measured relative to the baseline after the anodic peak).

[0080] It is therefore the effect of the two sweeps of the electrical potential that allows us to analyze a chemical equilibrium called "redox".

[0081] The invention is not limited to the examples just described; in particular, features of the illustrated examples can be combined in unillustrated variants.

[0082] Other variants and improvements may be envisaged without departing from the scope of the invention.

[0083] If in the illustrated examples the holes are of circular or elliptical cross-section, any shape of through holes can very well be considered, such as triangular, square, rectangular, etc. cross-sections.

[0084] If in the illustrated examples the holes are arranged in rows regularly spaced at 60° from each other, other variants can be considered such as arrangements in pairs, in three rows at 120° from each other, etc. and / or a non-regular distribution around the X axis.

[0085] More generally, the ability of the fluid to pass through the holes instead of simply being deflected by the wall of the rotating element increases the forces produced on the bearing surfaces defined by these peripheral walls. In the case of turbulent flow More numerous and smaller holes are preferable in order to sum up useful contributions and minimize the efforts produced by internal orientations to turbulences that are not directed in the direction of the overall flow.

[0086] The rotating element and the holes are designed to minimize significant frictional forces, so that the angular velocity is acquired with very low effort in order to be directly related to the free flow of the unconfined fluid. When frictional forces allow, if they are sufficiently low, the surface area of ​​the peripheral walls can be increased by means of protrusions arranged on the outer and / or inner face of the rotating element.

[0087] Although the advantageous method described is voltamperometry, the number and choice of electrodes, whether those for measuring current or those applying voltage, is free.

Claims

Demands

1. Electrochemical measuring device for a non-gaseous fluid, in particular contained in a container, such as a tank, especially one with opaque walls, comprising: - a measuring pole in the form of a tube (2) with longitudinal axis X, one free end of which is intended to be immersed in the fluid; - at least one electrochemical probe, fixed to the free end of the measuring pole, and adapted to measure electrochemical properties of the fluid; - an element (3) mounted for rotation around the tube and comprising at least one wall with a plurality of through holes (31 to 39) made such that the peripheral surface (300) of each hole is shaped so that a flow of the fluid over the wall causes an asymmetry of the bearing forces on each peripheral surface of the hole and thus sets the element in rotation about the axis X.

2. A measuring device according to claim 1, the electrochemical probe comprising at least one electrochemical sensor, fixed to the free end of the tube inside the element, comprising at least one pair of electrodes, including a so-called working electrode to which an applied electrical potential (equivalent voltage or current) can be varied as a function of time and a so-called auxiliary electrode in which the electrical signal flowing, as well as in the working electrode, is measured as a function of the electrical potential.

3. Measuring device according to claim 1 or 2, the wall of the element (3) being at least partly cylindrical, the holes being made in the thickness of the cylindrical wall with each one having an axis not intersecting with the axis of the cylinder of the wall.

4. Measuring device according to claim 3, the holes being distributed uniformly or not on the periphery.

5. A measuring device according to any one of claims 3 or 4, the holes being distributed in rows, preferably three or six in number, parallel to the X axis, preferably distributed uniformly angularly around the X axis.

6. A measuring device according to any one of claims 3 to 5, the holes being of different diameters so as to broaden the Reynolds number range that characterizes the fluid.

7. A measuring device according to any one of the preceding claims, the element comprising a plurality of protrusions arranged on the external face and / or the internal face of the element, each adapted to create a fluid support surface.

8. Measuring device according to any one of the preceding claims, the element being mounted for rotation around the tube by at least one bearing or ball bearing or ball cage (4).

9. Settling, purification, or production medium or tank, in particular of a bioreactor, comprising a measuring device according to any one of claims 1 to 8.

10. Use of a measuring device according to any one of claims 1 to 8 for monitoring bioproduction and / or for providing reference data in a digital twin.

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