Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
  • G01N17/008—Monitoring fouling
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N25/00—Investigating or analyzing materials by the use of thermal means
  • G01N25/18—Investigating or analyzing materials by the use of thermal means by investigating thermal conductivity

Definitions

• the invention relates to a sensor and a system for measuring or detecting the fouling of a reactor or a pipe containing a fluid.
• These installations comprise pipes in which fluids circulate and may also comprise reactors such as, for example, heat exchangers.
• fouling of such installations can be detrimental to the extent that it is likely to affect the performance of the installation (for example the efficiency of an industrial process).
• fouling when fouling is formed on the inner wall of a pipe or a reactor, it should be cleaned at the right time.
• the fouling irregularly cause the shutdown of the installation and this, for a sometimes indeterminate duration, which strongly penalizes the course of the industrial process.
• These interventions can be painful tasks for the staff, especially if the fouling has been detected only late and if its thickness is too great.
• This de-clogging has a significant economic cost since it is appropriate to include in the cost of maintenance operations the cost of the temporary shutdown of the operation.
• methods are used to measure the thickness of the fouling layer formed inside the walls of a pipe or a reactor using a measurement of the pressure drop that occurs between two points spaced in the direction of fluid flow. Methods that measure temperature differences between these points can also be used.
• Document FR 2 885 694 discloses a method for measuring the fouling in a reactor or pipe that uses two temperature probes. More particularly, these two probes are introduced into a pipe respectively through two stitching points and one of these probes measures the temperature of the fluid, while the other probe measures the wall temperature of a heat generator.
• the first step is to obtain a temperature difference between the wall temperature and the fluid temperature as close to zero as possible. Then, the heat generator emits a heat flux while the temperature difference between the wall temperature and that of the fluid is measured over time, the reactor fouling condition being determined from the measurement this temperature difference.
• two temperature probes even if they are of the same type, always have a certain operating drift relative to each other because of, for example, dispersions occurring during manufacture.
• the two probes do not have the same behavior relative to each other vis-à-vis the same temperature of the medium in which they are immersed.
• the temperature probe that serves as a reference (the one that measures the temperature of the fluid) can itself get dirty, which introduces an additional drift relative to the other temperature probe.
• the method used in the aforementioned document requires any lack of variation in the temperature of the fluid in which are plunged the two separate temperature measuring elements. This greatly reduces the scope of application since most industrial processes and / or water treatment processes constantly alter and disrupt the average temperature of the medium.
• the method used by imposing initial conditions, requires both a post-processing of the recorded information and a systematic verification of the conditions before any use. This makes this method unusable for continuous applications or for long-term operation (24 hours a day). At best, access to the temperature difference (thermal drift) is observable over the envisaged and programmed measurement period. The disadvantages just mentioned can thus lead to erroneous measurements of the fouling and therefore to a lack of reliability of the method used. In addition, due to the operating mode and constituent elements of the physical device the number of possible applications is limited.
• the subject of the present invention is therefore a micro-sensor for measuring or detecting fouling, which can be produced according to microelectronics manufacturing technologies (eg microsystems technologies). More particularly, the subject of the invention is a sensor for measuring and / or detecting a fouling forming directly or indirectly on a so-called front face of the sensor, characterized in that it comprises in the form of a plurality of superimposed layers:
• At least one heating element which is capable of diffusing, on command, a homogeneous controlled thermal flux whose thermal power is substantially less than 200 mW,
• thermal insulator disposed on the opposite side to the front face of the sensor to prevent dissipation of the heat flow of said opposite side
• At least one temperature measuring element which is placed in the homogeneous heat flow diffused by the at least one heating element and which offers a temperature measurement accuracy better than 0.1 ° C. a substrate on which are reported the layers of said at least one heating element and at least one temperature measuring element.
• a sensor whose heating element (s) generate a low thermal power for example less than or equal to 200 mW (preferably less than 100 mW, and for example between 1 and 50 mW) and whose temperature measuring element (s) placed in the homogeneous part of the heat flow (at the heart of the flow, that is to say as far as possible from the edges of the heating element or elements to overcome the edge effects) offer a high accuracy, for example better than 0.1 ° C (preferably better than 0.01 ° C, for example between 0.005 and 0.01 ° C) is particularly advantageous in that it is very sensitive, very reactive and very reliable.
• microsystem sensor The characteristics of the components of this sensor set out above are related to the fact that this sensor has very small dimensions (microsystem sensor). It can for example be manufactured by manufacturing technologies used in microelectronics and consisting of producing the functional elements in the form of layers deposited one above the other on a substrate or on both sides of the according to the desired arrangement.
• MEMS collective microelectronic manufacturing technologies
• the micro-sensor is more reactive to the heat flux diffused by the heating element (s) because the thermal losses are reduced;
• the microsystem sensor has a greater sensitivity to the measurement of the thickness of a fouling layer (for example of the order of a few microns instead of a few hundred microns).
• the heat flux diffused by the heating element (s) can be greatly reduced and is therefore very easily evacuated by the medium in which the sensor is placed.
• the flow rate of the latter may be very low, or even zero, and the heat flux generated by the sensor will still be dissipated satisfactorily by the fluid.
• Other manufacturing technologies can be used (screen printing, nanotechnology %) to manufacture a micro-sensor and obtain the same benefits or similar benefits.
• the senor according to the invention is capable of determining in a particularly efficient way the fouling formed on the external face of the latter when it is placed in a fluid or in contact with a fluid.
• determination of the fouling is meant the measurement of a fouling layer thickness formed on the sensor and / or the detection of a fouling layer being formed.
• the temperature measurement is local and not global because of the small dimensions of the measuring element and the temperature measuring element measures the temperature of the place where it is located.
• the sensor is thus faster and more sensitive than in the presence of the interface.
• the heating element (s) dissipates a very low thermal power in order not to heat the fluid, nor to cause a rise in parietal temperature likely to cause the formation of fouling (scale ).
• this low thermal power is naturally discharged into the fluid, which allows the sensor to be used in a stagnant environment or during the interruption of fluid flow.
• the thermal power must be sufficiently significant so that the temperature measuring element can deliver a useful signal.
• this sensor operates with one or several temperature measuring elements.
• the senor according to the invention is able to provide measurements in continuous and in real time, whatever the evolutions of the conditions of the measuring medium (temperature of the uncontrolled fluid).
• the senor is part of a system that comprises means for supplying energy to the functional elements of the sensor and means for processing the data provided by these elements.
• the system further comprises, optionally, means for displaying the results (example: measurement curve of the measured temperature as a function of time, curve of thickness of fouling as a function of time, etc.) and / or means remote transmission of information relating to the quantitative data (temperature, thickness, ...) and / or qualitative data (presence or absence of fouling ).
• the sensor according to the invention is part of a system which is intended to measure and / or to detect fouling formed or being formed inside a container containing a fluid.
• Such container is, for example, a reactor or a conduit carrying a fluid. It will be noted that the measurement and / or the detection of the level of fouling are carried out continuously and almost in real time, whatever the evolutions of the conditions of the measuring medium (for example the temperature of the uncontrolled fluid).
• the measurements are reliable over time.
• said at least one temperature measuring element has a surface whose size is at least substantially less than 2% of that of the surface of said at least one heating element.
• the surface ratio may even be less than 1%.
• the size of the surface that counts in the heating element is that of the active zone (heating zone) and not the total size including that of the non-active zone (non-heating zone, for example peripheral zone).
• the active surface of said at least one heating element has a size less than or equal to 25 mm 2 .
• This size is relatively small compared to the heating elements used in sensors of the prior art.
• the surface of said at least one temperature measuring element has a size less than or equal to 0.49 mm 2 .
• this measuring element gives the latter particularly small dimensions which allow it to measure a local and non-global parietal temperature and offers the possibility to the sensor to be particularly reactive.
• said at least one heating element and said at least one temperature measuring element are made in the form of tracks or resistive lines.
• These tracks or resistive lines are metal deposits made on a substrate or on a layer previously deposited on the substrate. These tracks are configured in a more or less complex form in order to obtain the desired physical characteristic (s) (for example obtaining a given heat flux as homogeneous as possible).
• These tracks are for example arranged so as to form one or more coils disposed on the substrate or on the layer which may for example be arranged concentrically.
• the thickness of the resistive tracks or lines can be adjusted in microsystem technology in order to obtain the desired properties, and, for example, for the heating element (s) to modify the heating power of the sensor.
• the functional characteristics of the temperature measurement element or elements can be varied, such as, for example, the sensitivity and / or response dynamics.
• the senor may comprise intermediate layers of electrical insulation between the different functional layers. This or these intermediate layers also smooth the surface of the layer to facilitate the subsequent deposition of an upper layer or contact with another element.
• said at least one heating element and said at least one temperature measuring element are, for example, each of the platinum resistors.
• the heating elements and temperature measurement made as well are particularly effective.
• the substrate has a first and a second opposite face, the thermal insulator being opposite the first face while the layer of said at least one heating element is opposite the second face. face, the layer of said at least one temperature measuring element being superimposed on the layer of said at least one heating element.
• the substrate has a first and a second opposite face, the thermal insulator being opposite the first face, the layer of said at least one heating element being arranged between the thermal insulator and the first face of the substrate, the layer of said at least one temperature measuring element being disposed opposite the second face of the substrate.
• the heating element layer and the temperature measuring element layer are arranged on either side of the substrate. This arrangement allows to separate said at least one temperature measuring element of said at least one heating element.
• the substrate placed between these two functional layers and which is a thermal conductor has a thickness less than or equal to 300 microns.
• the thickness of the substrate is chosen so that the temperature measuring element is closer to the fluid than to the heating element so that the wall temperature measured by the temperature measuring element is the same. more representative of the skin temperature and not too influenced by the heat flux generated by the heating element.
• the invention provides for using the sensor briefly described above to measure or detect the fouling formed (or being formed) on the sensor that is installed in a wall of a container (for example an industrial pipe or a industrial reactor containing a fluid.
• a container for example an industrial pipe or a industrial reactor containing a fluid.
• the fouling is formed on the outer face of the sensor which is exposed to the fluid.
• This outer face corresponds either to the outer face of said at least one interface element when the sensor is manufactured with such an element, the outer face of a separate interface material against which the sensor can be positioned.
• the senor measures the local wall temperature and determines the temperature difference when a low electrical power is applied to the at least one heating element.
• At least the outer face of the sensor is representative of the state of the surface of a wall of the container which is in contact with the fluid, for example by the nature of the material and / or by its roughness.
• the surface state of the outer face of the interface element or of the interface material depends on the internal surface condition of the wall or walls of the container, which surface state depends on the intended applications.
• the outer face of the sensor has an equivalent roughness (for example identical) to that of a wall of the container which is in contact with the fluid.
• This adaptation makes it possible to refine the resemblance between the external face of the sensor and the wall of the container.
• the interface element or the interface material may be made of stainless steel, for example of class 316L if the fluid is in a 316L stainless steel container or polyvinyl chloride (PVC) container if the fluid is in a PVC container.
• the interface element is made of the same material as the wall of the container to ensure the representativeness of the surface condition of the wall and the fouling phenomenon.
• a sensor or at least the interface element or the interface material of the sensor is thus dedicated to a given application and, at least, to a given situation.
• the interface element of the sensor or its external face is not representative of the state of the surface of the walls of the container, the sensor can nevertheless be used to detect the fouling in a relative manner (for example in detecting growth and decay of deposits).
• the interface element or the external surface of the sensor need not be similar to the wall of the container in this mode of operation where the signal delivered by the sensor is used as an indicator.
• this additional interface material can be carried out separately from the sensor and in adequacy with the targeted application (s).
• This additional interface material will be assembled on the sensor but later in the manufacturing phase of said sensor. This approach makes it possible to manufacture in large numbers the micro-sensors according to their elementary structure, namely comprising the heating element (s), the temperature measuring element (s) and the thermal insulation.
• the presence of the interface material in contact with the fluid, flowing or not protects the sensor, at least mechanically, or even chemically, and makes it robust to external aggressions, in particular from the fluid.
• the senor comprises at least one thermal conductive interface element having two opposite faces, one of the faces, so-called interior, being disposed against the temperature measuring element.
• the other face, said external, is intended to be in contact with the fluid.
• Such an interface element protects the temperature measuring element, as well as the rest of the sensor, and is chosen (material and thickness) to provide as low a thermal resistance as possible.
• said at least one interface element has (between its two opposite faces) a thermal resistance of less than or equal to 10 ° C / W.
• This characteristic of the interface element makes it possible to ensure that the heat flux generated will be well diffused up to the outer face and discharged by the fluid, without encountering a strong thermal resistance which could cause a harmful temperature rise to the temperature. correct operation of the sensor. In addition, this makes the sensor more responsive, more responsive and more reliable.
• the thickness of the interface material is thus adapted as a function of the material itself, given the thermal resistance not to be exceeded.
• the invention relates to a system for measuring or detecting a fouling formed directly or indirectly on a front face of a sensor which is exposed to a fluid, the sensor comprising in the form of superposed layers:
• At least one heating element which is capable of diffusing, on command, a controlled homogeneous heat flow
• thermal insulator disposed on the opposite side to the front face of the sensor to prevent the dissipation of the heat flow of said opposite side; at least one temperature measuring element which is placed in the homogeneous heat flux diffused by the at least one heating element ,
• the system comprising: means for determining a difference in temperature between, on the one hand, the parietal temperature measured by said at least one measuring element of temperature when said at least one heating element diffuses a heat flow and, on the other hand, the temperature of the fluid,
• said at least one heating element generates a thermal power of less than 200 mW and said at least one temperature measuring element provides better measurement accuracy than 0.1 ° C.
• the invention also relates to a method for measuring and / or detecting fouling formed on the front face of a sensor which is exposed to a fluid when it is installed in a wall of a container containing the fluid. fluid, the sensor comprising sus the form of superimposed layers:
• At least one heating element which is capable of diffusing, on command, a controlled homogeneous heat flow, a thermal insulator disposed on the opposite side to the front face of the sensor to prevent the dissipation of the heat flux of said opposite side,
• At least one temperature measuring element which is placed in the homogeneous heat flux diffused by said at least one heating element
• a substrate on which are reported the layers of said at least one heating element and at least one temperature measuring element.
• the subject of the invention is also a method which comprises the following steps:
• the invention more particularly relates to a method in which the determination of a temperature difference comprises the following steps: alternation of control phases of the diffusion of a thermal power by said at least one heating element and non-diffusion of a thermal power,
• the measurement or detection of fouling is performed by determining the temperature difference provided by the parietal temperature measuring element when said at least one heating element generates a heat flow and when it does not generate it.
• the sensor that is particularly sensitive and responsive measures the temperature of the fluid.
• the temperature difference is less than 0.1 ° C, while it can reach 2 to 3 ° C in the presence of a heavy fouling.
• the step of controlling the diffusion of a heat flux by said at least one heating element comprises a step of generating a power modulation signal of said at least one heating element.
• the signal is alternating and for example is stationary.
• the stationary alternating signal is in slots.
• said at least one temperature measuring element provides a measurement accuracy of the temperature which is better or equal to 1% of the maximum temperature difference determined between the non-fouled state and the fouled condition of the sensor. .
• the measurement accuracy of said at least one temperature measuring element is on the order of 0.01 to 0.02 ° C. It should be noted that, according to the invention, the use of a temperature measuring element or of several very precise temperature measurement elements make it possible to use one or more heating elements generating a very low thermal power, whereas elements Uncertain temperature measurement would not allow the use of such a low thermal power.
• FIG. 1a is a general schematic view of a sensor according to a first embodiment of the invention and associated means for its implementation;
• FIG. 1b is a general schematic view of a sensor according to a second embodiment
• FIGS. 2a to 2f schematically illustrate the manufacturing steps of the sensor according to the first embodiment
• FIGS. 2a to 2c and 2g to 2i schematically illustrate the manufacturing steps of the sensor according to the second embodiment; - Figures 3 and 4 schematically illustrate respectively two embodiments of the heating element layer;
• FIG. 5a schematically illustrates the superposition of a temperature measuring element layer and the heating element layer of Figure 4
• FIG. 5b illustrates the superposition of a layer comprising two temperature measuring elements and the heating element layer of FIG. 4
• Figures 6 and 7 schematically illustrate respectively two embodiments of the temperature measuring element layer
• - Figure 8 is a schematic view showing the implantation of a sensor according to the invention in a body mounted on a wall of a container;
• FIG. 9 is a schematic view showing the implantation of a sensor according to the invention in a wall of a container;
• Figures 10 and 11 illustrate the temperature measurements taken by a sensor according to the invention, respectively in the presence and in the absence of fouling in relation to a supply signal S;
• FIG. 12 schematically illustrates the evolution of a fouling curve during the time formed on the sensor shown in FIGS. 2f and 9.
• the object of the present invention is to propose, particularly by means of the collective manufacturing processes of microelectronics in general, and by the microsystems technology manufacturing processes in particular, a small sensor capable of determining a fouling in a fluid in flow or at rest.
• a miniaturized sensor according to the invention may alternatively be manufactured according to other techniques such as screen printing.
• a sensor 10 made using microsystem manufacturing technologies according to a first embodiment of the invention comprises several functional elements assembled with each other on a substrate 12 having two opposite faces 12a, 12b , namely: at least one heating element 14 made in the form of a layer deposited on the face 12b of the substrate 12 and diffusing, on command, a controlled homogeneous heat flow,
• the at least one temperature measuring element 16 made in the form of a layer deposited on the layer 14 and which is arranged so as to be in the most homogeneous part of the dissipated heat flow (when the element 16 is unique there is is in the center of the active zone of the heating element or elements), a thermal insulator 11 in contact with the face 12a of the substrate (the insulator is, for example, a Teflon block of 400 ⁇ m thickness and 0.25 W / mK of thermal conductivity),
• At least one thermal conductive interface element 18 made in the form of a layer deposited on the layer 16 and which protects the sensor vis-à-vis external aggressions.
• the senor is thus produced in the form of a plurality of superposed heterogeneous layers.
• the temperature measuring element 16 is for example in a surface ratio with the heating element 14 (more precisely with the active zone of the heating element) less than 2%, that is to say that the size of the element 16 is at least 50 times smaller than that of the element 14.
• Figure 1a does not show the functional elements within the layers for reasons of scale and readability.
• the temperature measuring element is characterized by a high measuring accuracy better than 0.1 ° C, more particularly between 0.005 and 0.01 ° C, which allows it to cooperate with one or more heating elements generating a low power.
• the thermal power generated is between 1 and 50 mW. This power is, on the one hand, sufficient for the highly sensitive measuring element 16 to measure a temperature and, on the other hand, sufficiently low so as not to influence the measurement medium (fluid).
• the low power value and high measuring accuracy allow the sensor to be very sensitive, highly reactive and very reliable in measuring and / or detecting fouling, without being disturbed by the measuring conditions in general and by the circulation of the fluid in particular.
• the layer of said at least one heating element 14 which is powered by electrical power supply means 20 (example: current or voltage generator capable of supplying electrical power on control), via connection means 22, diffuses a homogeneous and controlled heat flow illustrated by the vertical arrow in the figure.
• electrical power supply means 20 example: current or voltage generator capable of supplying electrical power on control
• This flow is dissipated towards the front face of the sensor (face which is intended to be in direct or indirect contact with the fluid and which is either the free face of the layer 18 or the free face of the layer 16) opposite to the rear face the sensor where the thermal insulation is located because of the presence of this insulation.
• the dissipation of the flux is prevented on the rear face of the sensor by the thermal insulation.
• the layer of said at least one interface element 18 When the layer of said at least one interface element 18 is present, it transmits the thermal flux towards the outside of the sensor, towards the fluid medium in which it is placed and dissipates this heat.
• the data (for example parietal temperature measured by element 16 and induced power in element 14) are collected by unit 26.
• This unit 26 samples and translates in physical quantities (temperature, %) the measurements and information from the sensor, as well as the power generated. It will be noted that the fouling determination system formed by the sensor and in particular elements 20 and 26 comprises means
• unit 26 for determining a temperature difference between the temperatures measured by the measuring element and calculation means (unit 26) of the thickness of the fouling formed on the sensor surface from this difference of temperature thus determined and physical formulas of known sensor geometry.
• the determination means measure a temperature difference between, on the one hand, the wall temperature measured by the temperature measuring element when the heating element dissipates a heat flow and, on the other hand, the temperature of the fluid.
• the system further comprises, optionally, a display 28 and / or means 30 for transmitting information to distance.
• the display 28 makes it possible, for example, to continuously display the temperature (measured) and fouling (calculated) values as will be seen below, for example in the form of curves representing the time evolution of the temperature and / or the fouling thickness.
• the means 28 (example: transmitter) make it possible to remotely send the data measured and / or processed by the unit 26 and / or alerting information and / or other information relating to the sensor and / or its state of being. operation.
• FIG. 1b illustrates a sensor 10 made using, for example, microsystem manufacturing technologies according to a second embodiment of the invention.
• the arrangement of the sensor of FIG. 1b is different from that of FIG. 1a insofar as the heating element 14 and the temperature measuring element 16 are arranged, not on the same side of the substrate 12, but on both sides of it.
• the temperature measuring element 16 is disposed facing the face 12b of the substrate and for example in contact with it (although one or more intermediate layers may be arranged between these two elements) and the heating element 14 is disposed between the face 12a of the substrate and the thermal insulator 11.
• the two functional elements 14 and 16 of the sensor are spaced from each other by a distance corresponding substantially to the thickness of the substrate 12.
• This thickness can be of the order of several hundred microns and by example of 300 microns.
• This arrangement makes it possible to reduce the direct influence of the heating element on the temperature measuring element in order to improve the performance of the sensor.
• the one or more temperature measuring elements 16 will measure a wall temperature that is closer to that of the fluid than that of the heating element. The resulting measurement of fouling will therefore be more reliable. Moreover, the sensor is thus more sensitive.
• the temperature measuring element is always in the homogeneous part of the heat flow generated by the heating element despite this spacing between the two elements.
• Figures 2a to 2f illustrate a manufacturing method of the sensor of Figure 1a
• Figures 2a to 2c and 2g to 2i illustrate a method of manufacturing the sensor of Figure 1b. Steps 2a to 2c are common to both methods and will now be described.
• an electrically insulating layer 40 is first deposited on a reception substrate 42, for example made of silicon, of a given thickness (for example 300 ⁇ m).
• a passivation layer 40 may be formed on the two opposite faces of the substrate (FIG. 2a).
• This insulating layer 40 may be a monolayer of silicon oxide deposited thermally, or a monolayer of silicon nitride with a thickness of about one micron. It may be alternately composed of a bilayer which is generally composed of a first layer of silicon oxide on which a second layer of silicon nitride is deposited.
• the thicknesses currently used are, for SiO2, 0.7 ⁇ m and 0.8 ⁇ m for silicon nitride.
• a layer 14 consisting of one or more heating elements (only one heating element is shown in this embodiment) is formed by a metal deposit on one of the insulating layers 40 (for example, the upper layer).
• the heating element 14 is configured to optimize and promote the creation of the heat flow.
• the metal is deposited in the form of a or of several tracks or resistive lines of small width forming a more or less complex geometrical figure according to the physical characteristics sought (here, the thermal flux to be produced by the heating element), by covering one or more zones, or even almost all of the layer 40. These lines are similar to resistive metal tracks formed, for example, by screen printing on a printed circuit substrate. These lines are designed to form one or coils 40a (Fig.3) or concentric lines 40b (Fig.4).
• the heating element consists of either a platinum-type metal monolayer (Pt) or a titanium / platinum-type (Ti / Pt) bilayer.
• the first layer of titanium is a layer of hanging that allows the platinum layer to increase its adhesion. It also has the role of increasing, during a heating phase, its mechanical resistance which is caused by the variation of stress in this layer. The aim is to minimize the effects of delamination and thereby increase the service life of the heating element.
• This heating element can also be made of doped silicon.
• the heating element of FIGS. 3 and 4 comprises connecting tracks or pads which make it possible to supply this element with the necessary electrical energy coming from the device 20.
• the heating element of FIG. electrical connection pads which are for example used for test or measurement purposes by implementing the known technique of the four points.
• the dimensioning of the heating element is performed by determining the heat flow necessary to be able to detect a fouling on the surface of the sensor according to the intended application.
• the injection of an electric current or a voltage into the heating resistor generates an overheating thereof.
• a heat flux is then generated and varies according to the power injected into the heating element.
• the value of its resistance to rest is calculated according to the power of the heat flow to be generated.
• the power injected into the heating element is very low, for example of the order of 10 mW (which corresponds to a current of intensity of between 0.1 and 10mA), which is particularly advantageous.
• the heating element is for example made in the form of platinum resistive tracks of 40 .mu.m width and 2 .mu.m thickness and whose electrical resistance is 3.2 k ⁇ at 20 ° C.
• the size of the active surface of the heating element is for example 25 mm 2 (corresponding to a square of 5 mm side).
• the thermal power generated by such an element is between 5 and 50 mW and more particularly between 5 and 10 mW.
• the power density is between 0.2 and 2 mW / mm2.
• An electrically insulating layer 44 is deposited on the layer of the heating element 14 (FIG. 2c).
• This dielectric layer for example made of silicon nitride, is deposited according to the deposition technique known as PECVD.
• PECVD the deposition technique
• the first role of this layer is to eliminate any risk of short circuit between the heating element 14 and the next layer to be deposited (measuring element), during the operation to be described later.
• the second role of this layer is to planify the topography generated by the presence of the heating element to facilitate the deposition of the measuring element.
• Steps 2d and 2f of the manufacturing method of the sensor of Figure 1a will now be described.
• a layer 16 comprising one or more temperature measuring elements is deposited on the insulating layer 44 previously described. (Fig.2d).
• This layer is configured to optimize the variation of its resistive characteristics as a function of temperature.
• the distribution of a heat flow during a heating phase of a heating element is homogeneous in the center of it and becomes discontinuous when one moves away from its center. Therefore the temperature measuring element is deposited above the heating element 14, made for example according to the configuration 40b of FIG. 4, on the dielectric layer 44.
• the measuring element 16 is arranged centrally on the heating element and it is much smaller than that of said heating element to be placed in the most homogeneous flow part of the heart of that of the heat flow, thus avoiding the disturbances caused by edge effects.
• Figure 5a shows the centered and superimposed position of a temperature measuring element 16 above a heating element.
• thermometers 16a and 16b are arranged in the central part of the heating element to be at the heart of the homogeneous flow and known but spaced from each other to be able to determine the fouling in two distinct places. of the sensor surface. More than two elements can be used according to needs and applications.
• the geometry retained to create this measuring element is known to those skilled in the art.
• One or more resistive metal lines arranged in the form of coils (FIG. 6) or concentric lines (FIG. 7) may be used in the same manner as described above for the heating element with reference to FIGS.
• the temperature measuring element or elements consist of either a monolayer of metal, for example platinum or a Ti / Pt type bilayer.
• the first layer of Titanium is the layer of hooked.
• the temperature measuring element 16 is thus for example made in the form of platinum resistive tracks of 20 .mu.m width and 2 .mu.m thickness and whose electrical resistance is 3 k ⁇ at 20 ° C.
• the precision for example measuring 0.005 ° C with a suitable electronics (having for example a precision of 20 bits).
• the size of the surface of the temperature measuring element is, for example, 0.49 mm 2 (which corresponds to a square of 700 ⁇ m on the side). It will be noted that the measuring element of FIGS. 5a and 5b, 6 and 7 comprises connecting tracks or pads which make it possible to supply this element with the necessary electrical energy coming from the device 20 and to collect, at the level of the unit 26, the temperature data.
• the measuring element such as that of FIG. 7 can be implemented using, for example, the well-known technique of the two tips which makes it possible, knowing the voltage and the electrical intensity, to deduce therefrom in a direct way the value of resistance.
• This measurement is used when the measurement noise or associated measurement is not too high and it is the one used in the assembly of Figures 5a and 5b.
• the measuring element such as that of Figure 6 can be implemented using for example the well known technique of the four points.
• this indirect measurement technique the value of the voltage imposed on the terminals is known, the value of the intensity is measured and the value of the resistance is deduced therefrom.
• An insulating layer 46 is deposited on the layer of the temperature measuring element (FIG. 2e). This electrically insulating layer is deposited on the measuring element. The first role of this layer is to eliminate any risk of short circuit between the measuring element and the next layer to be deposited (interface element (s)), during the operation to be described later.
• the second role of this layer is to flatten the topography of the microsystem during manufacture.
• the deposition of a dielectric layer according to the known technique known as PECVD makes it possible to limit excessive profile variations.
• the thickness of this layer must, as explained above, be of sufficient thickness to, on the one hand, eliminate any risk of a short circuit between the measuring element and the interface layer when it is present and, on the other hand, significantly reduce the reliefs produced by the topography generated by the presence of the measuring element and thus offer as flat a surface as possible.
• a protective layer 18 formed of at least one interface element is deposited on the insulating layer 46 (FIG. 2f) by techniques well known to those skilled in the art (eg PEVCD).
• This layer may consist, for example, of a metal layer or a dielectric layer.
• FIG. 2g corresponds to the step of applying or depositing a layer 16 comprising one or more temperature measuring elements on the insulating layer 40 situated under the substrate 42 of FIG. 2c.
• FIG. 2g reverses the arrangement of FIG. 2c and the heating element 14 is found at the bottom, under the substrate 42.
• the step of depositing the element or the elements for measuring the temperature 16 is identical to what has been described with reference to FIG. 2d, except that the temperature measuring element or elements are thus arranged on the side of the substrate which is opposed to the side on which the heating element is arranged.
• the step illustrated in Figure 2h corresponds to the application or deposition of an insulating layer 46 identical to that described in relation to Figure 2e previously described.
• an optional protective layer 18 acting as an interface element is deposited on the insulating layer 46, above the temperature measuring element or elements 16.
• FIG. 8 illustrates an exemplary embodiment in which the microsystem sensor 10 according to the invention is associated with a wall 50 of a container 52 (for example a chemical reactor or a vessel) in which a fluid, here stagnant, symbolized by the reference F is present.
• a container 52 for example a chemical reactor or a vessel
• a fluid here stagnant, symbolized by the reference F is present.
• the container 52 containing the fluid may be of another type such as a pipe or pipe of an industrial plant, .... It will also be noted that the fluid present in the container is not necessarily at rest but may be in flow.
• the microsystem sensor 10 as shown schematically in FIG. 1a or 1b, is mounted in one of the walls of the container as shown in FIG. 8 via a body 54 in which the microsystem 10 is integrated. .
• the senor 10 is arranged in a hollow cylindrical envelope 56 provided at one of its longitudinal ends 56a of a plate 58 forming a shoulder and which has for example a disc or pellet shape.
• This plate is for example welded to the cylindrical casing 56. It will be noted that other body shapes can be envisaged without calling into question the operation of the sensor.
• the plate 58 forming the shoulder is intended to be inserted in a corresponding arrangement provided in the wall 50 of the container to be mounted flush with respect thereto.
• the plate 58 forming a shoulder may also be assembled on a cylinder which is to be inserted into the wall 50 of the container having a hole (or stitching point) already existing and provided for this purpose.
• This plate 58 is thinned in its central part, where the sensor is positioned, and is a material or interface element which is in contact with the fluid F by its outer face 58a.
• the face 58a and the surface 50a can be arranged on the same side in order not to introduce a disturbance in the flow.
• the interface element 18 of the sensor of FIGS. 1a and 1b is not present, the plate 58 acting as an interface element.
• a heat-transmitting element 60 such as a thermal paste with a high coefficient of thermal conductivity, can be used and placed in contact with the microsystem. More particularly, this element 60 is disposed on the active zone of the microsystem consisting of almost all of its outer face except for a small peripheral zone (the sensitive elements of the microsystem being rather centrally arranged). This assembly is then placed against the rear or internal face 58b of the interface material 58.
• the microsystem sensor 10 is mounted on a support 62 such as a printed circuit board whose role is to create the necessary electrical contacts between this microsystem sensor and the part of the associated system which ensures power supply and information processing of this sensor. These electrical contacts cooperate with the tracks or pads shown in Figures 3 to 7 and briefly described above.
• This part of the measuring system has been represented in FIGS. 1a and 1b by elements 20, 26, 28 and 30 connected to the sensor via connections 22 and 24.
• an element of Additional thermal insulation 64 is introduced into the body 54 through the rear end 56b.
• This element 64 such as a paste with a low coefficient of thermal conductivity, is arranged against the rear face of the support 62 in order to form an additional heat shield at the rear of the body and thus favor the dissipation of the heat flow towards the before said body. It will be noted, however, that the thermal insulation 11 of FIGS. 1a and 1b already provides a satisfactory barrier function to the heat flux on the rear face of the sensor.
• thermal insulation is also provided between the plate 58 and the cylindrical envelope 56 of the body 54.
• the role of this thermal insulation is to eliminate any risk of thermal bridge between the interface material 58 and the casing 56 during a heating phase.
• the plate 58 acting as an interface material with the fluid is adapted at least so that its outer face 58a is representative of the surface state of the wall 50 of the container so that the deposition of a fouling layer on the face 58a is made almost identical to the deposition of a fouling layer on the inner face 50a of the wall of the container.
• the determination of fouling formed on the face 58a determination which corresponds to either a fouling measurement or to a fouling detection, will be particularly reliable given the nature of this external face and also given the micro sensor which is particularly sensitive and generates very few disturbances likely to modify the phenomenon of fouling.
• the outer face 58a is representative of the surface state of the wall of the container, it is preferable that this face has a roughness equivalent to that of the wall, or identical.
• the wall 50 may be made of stainless steel, for example class 316L, and the face 58a of the sensor may be made to have a roughness of equal or less surface area at 0.8 ⁇ m, just like that of the face 50a of the wall.
• the outer face 58a is made of a material of the same nature as that of the wall of the container. If this material is not identical, it must at least be of a nature compatible with that of the material constituting the wall.
• the simplest solution is that the interface material 58 is made of a material identical to that of the wall of the container.
• the plate 58, as the cylindrical casing 56 are made of stainless steel, material that is the one used for the wall 50 and in particular its inner surface 50a.
• the plate 58 is a thermal conductor which has a thermal resistance of less than or equal to 10 ° C / W in order to give the sensor good sensitivity and a high signal-to-noise ratio.
• the material used and its thickness are thus chosen to offer the heat flow a very low thermal resistance.
• the thickness is, for example, 300 ⁇ m.
• the sensor according to the invention may comprise only one element for measuring temperature.
• the temperature of the fluid, and more generally of the industrial process involving the container, is generally not known.
• the method makes it possible to overcome any variations in this temperature over time.
• the microsystem sensor according to the invention may comprise more than one temperature measuring element according to the applications envisaged. Similarly, it may also include several heating elements in cooperation with a single temperature measuring element or with several of these elements.
• FIG. 9 schematically illustrates the direct installation of a microsystem sensor such as that of FIGS. 1a, 1b, 2f and 2i in a wall 50 of a container 52.
• the senor 10 is in direct contact with the fluid F via the external face 18a of its interface element 18 instead of using the interface material 58 of FIG. 8.
• the sensitivity of the sensor thus arranged is thus increased, thereby providing better results than in the case of FIG. 8.
• the senor 10 is not quite flush mounted relative to the wall but is very slightly recessed relative thereto. This withdrawal was intentionally exaggerated to illustrate it in the figures. In practice, it is for example a few hundred microns, for example
• a seal 61 is provided at the periphery of the outer face of the sensor to seal the mounting.
• This method makes it possible to measure and / or detect the fouling that forms on the outer face 58a of the interface material 58 of FIG. 8 or on the outer face 18a of the interface element 18 of FIG. 9.
• Clogging is understood to mean any adherent deposit forming on the surface of the element under consideration from bodies that are in the fluid temporarily or permanently (fouling of organic nature, such as a biofilm, or inorganic, such as scaling). .
• the method according to the invention makes it possible to measure and / or detect fouling on site, online and continuously, and almost in real time.
• the method according to a first embodiment provides for alternating phases for controlling the diffusion of a heat flux by the heating element (s) 14 of the sensor and non-diffusion of a heat flux over a given period of time. Furthermore, the method provides during this time to continuously measure the surface temperature of the interface element in contact with the measuring medium by means of the temperature measuring element (or only the local temperature of the place where is positioned the temperature measuring element in the absence of interface element). For example, this alternation of heating and non-heating phases of the sensor can be performed throughout the course of an industrial process, or only during certain stages thereof.
• the fouling measurement function makes it possible to know at any time the thickness of the fouling layer formed on the surface of the interface material or directly of the sensor and which reproduces in a very reliable manner, the fouling formed on the surface. inside the container in which the sensor is installed.
• the senor when used to fulfill a detection function, it can be used to trigger an alarm signal in the event of detection of a formation fouling layer or exceeding a predetermined threshold.
• the device 20 generates an electric power which is transmitted to the heating element, for example in the form of a power modulation signal which is, for example, of the alternative type.
• This signal is preferably stationary, that is to say that it defines perfectly determined stable states during which either a given electrical power is supplied to the heating element, or no power is supplied to this element.
• Figure 10 illustrates a stationary alternating signal in the form of slots.
• FIG. 10 illustrates, on the one hand, in the lower part the crenellated power signal S which is applied to the element heating and, on the other hand, in the upper part, the temperature measured by the measuring element during each of the heating and non-heating phases.
• the various temperature measurements show that they remain substantially constant (around a value Ti), which reflects a non-fouled condition of the sensor and therefore of the inner wall of the container.
• the temperature T1 corresponds to the temperature of the fluid.
• the heat flux produced by the heating element is transferred to the measuring element and the interface element, then diffused into the measuring medium and the temperature measured by the element. measurement remains substantially constant and equal to the temperature of the medium.
• the heat flux generated by the heating element will cause a rise in temperature at the level of the interface element or interface material.
• the fouling layer being formed acts as a thermal insulator (thermal barrier) which thus reduces the heat exchange with the measuring medium and thus the dissipation of the flow.
• the difference in temperature between the temperature measured on the bearing (T 2 ) and the temperature measured in the absence of fouling (Ti) is representative of the fouling formed at the instant corresponding to the measurements made and, more particularly, of the the thickness of the fouling layer.
• This thickness is obtained by formulas well known to those skilled in the art and which depend on the geometric configuration of the sensor, namely a planar geometry for the sensor 10 of FIG. 1. More generally, the thickness of the layer fouling is given by the following equation: or :
• P denotes, in W, the electrical power supplied to the heating element and which corresponds substantially to the power generated by the heat flux
• h denotes, in WIm 2 IK, the convective thermal transfer coefficient
• D denotes, in m, the diameter of the heating element when it is of cylindrical shape or, in surface equivalence, the side of the heating element when it is square,
• Ti and T 2 respectively denote, in K, the temperature measured in the non-heating and heating phase, ⁇ denotes, in W / m / K, the coefficient of thermal conductivity of the fouling layer which is deposited on the surface of the sensor, and, finally, e denotes, in m, the measured thickness of the fouling layer which is deposited on the surface of the sensor. Note that the greater the thickness of the deposit formed on the surface of the sensor increases, the higher the temperature rise will be important for a given power.
• the method provides for imposing a power heating setpoint (example: 10 mW) by imposing an electric current whose intensity can vary from 0.1 to 10 mA, to determine the temperature difference that results (increase), then calculate the thickness of the fouling layer.
• a power heating setpoint example: 10 mW
• an electric current whose intensity can vary from 0.1 to 10 mA
• the duration of the heating period varies from several seconds to several minutes, as shown in Figures 10 and 11 where the elapsed time is expressed in seconds.
• the duration of the heating period is not necessarily equal to the duration of the non-heating but, for practical reasons of implementation of the invention, equal time periods of heating and non-heating will be preferred.
• the duration of the heating and / or non-heating period may vary over time in order to adapt dynamically to the operating conditions of the industrial process, but in practice an optimum duration will be determined, set and maintained according to the application and the industrial process.
• the temperature difference T2-T1 is determined using linear and / or nonlinear regression algorithms between two non-heating periods that frame a heating period.
• an upper limit of power supply can be provided in the control phase, so that in case of non-fouling, the power required, to generate the desired temperature difference, does not exceed the physical limit of power of the electronic system.
• Such information may for example give rise to the sending of an alarm signal to prevent an operator or maintenance personnel of the installation.
• This detection function can of course be coupled to the fouling measurement function in order to also be able to give quantitative information on the thickness of the fouling layer thus formed.
• the temperature measuring element has a very high sensitivity and temperature accuracy which is, for example, better than 0.05 ° C.
• FIG. 12 represents a measurement curve of fouling thickness obtained by successively realizing, over time, deposits on the external active surface of a sensor according to the invention, and by using a polymer resin spray whose thermal conductivity is known.
• the sensor used is that shown in Figures 2f and 9 with the arrangement of the heating and measuring elements of Figure 5a.
• the heating element (layer 14) is formed of a Ti / Pt bilayer with 500 ⁇ thickness for the first layer and 2000 ⁇ for the second.
• the insulation layer 44 is Si3N4.
• the measuring element (layer 16) is formed of a Ti / Pt bilayer with 500 ⁇ thickness for the first layer and 3000 ⁇ for the second one.
• Insulation layer 46 is Si3N4.
• the interface element (layer 18) is formed of a Ti / Au bilayer with 500 ⁇ thickness for the first layer and 1000 ⁇ for the second.
• the experimental procedure consists in carrying out a first series of measurements with the sensor without any deposit on its surface (calibration phase).
• a first polymer resin deposit is made on the surface of the sensor layer 18, annealing at 100 ° C for 60s is performed to solidify the resin and a series of thickness measurements are made with the sensor connected to its sensor. electronic measuring system. The first step of the curve is thus obtained.
• the successive deposits do not follow a linear growth because of the successive anneals suffered by the layers formed in the previous step. It is found that the measured thicknesses are of the order of a few micrometers, which shows the high sensitivity of the sensor.
• the sensors of the preceding embodiments can be used according to two methods of operation, the first of which has already been presented above and which will be repeated hereinafter more generally.
• a first method (first embodiment of the method according to the invention) consists in using periodic time slots as shown in FIGS. 10 and 11 (typically from 30 s to several minutes) in order to carry out regular heating of the heating element. and rest periods.
• the temperature being measured continuously and supplied by the unit 26, this temperature is the temperature of the fluid during the rest period (identified by T1 in FIGS. 10 and 11).
• T1 the temperature of the fluid during the rest period
• this measured temperature stabilizes at the value T2 which is the skin temperature (or parietal temperature) resulting from the heat transfer from the heating element to the measurement medium through the interface element (or directly when there is no interface element) and, potentially, through a fouling layer.
• the parietal temperature in the heating phase is equal to the fluid temperature (to the measurement errors and according to the thermal resistance generated by the thickness of the interface element 18 when it is present) because the entire heat flux is dissipated in the measuring medium.
• an additional thermal resistance comes to oppose the heat transfer to the measuring medium and the skin temperature (T2) takes a value greater than T1.
• the fluid temperature (T1) and the skin temperature ⁇ 12) are known.
• the formulas and equations presented above are applied to provide information to the display 28 (typically the fouling thickness and the fluid temperature) and / or to the transmitter 30 in order to deliver a signal standardized (typically 4-2OmA) to integrate with a supervision or signal recorder.
• the fouling thickness forming on the surface of the measuring device (sensor) is continuously evaluated in order to deliver information to the user on the state of cleanliness.
• This method does not require any preliminary calibration of the measuring device according to the conditions of use (flow rate or nature of the fluid), nor any subsequent treatment of the information to determine the fouling thickness.
• variations in operating conditions to a certain extent, such as temperature, flow rate, pressure
• the device regularly recalculates the temperature of the fluid.
• the system can deliver a fouling thickness signal in units of ⁇ m or mm; otherwise, the system relies on a default value of thermal conduction of the fouling layer that can be formed and the measurement signal is ultimately an indicator according to an arbitrary unit.
• the temperature does not vary, or does not vary when it is desired to carry out the measurements, in which case the temperature is known and can be known from the unit 26 (T1 is thus fixed),
• the constant heating of the device makes it possible to obtain a more dynamic information of the fouling thickness, from the difference T2-T1, or a quasi-real-time information with regard to the kinetics of formation and disappearance by treatment of the fouling. (typically less than 0.5s).
• this mode of operation makes it possible to follow rapid phenomena of growth or decay of fouling, such as the monitoring of cleaning phases in the food industry, for example. This is therefore useful for optimizing these cleaning phases (often long and always expensive) knowing that no current device (nor any global method) can follow in real time the effectiveness of these cleanings.

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