Method and device for determining the pressure of a liquid flowing in a channel

Abstract

The invention relates to a measurement system (1) adapted to determine a pressure Pheq of a liquid of interest having compressibility km flowing in a channel having a radius rint, the liquid of interest and the channel being selected such that the product of km * rint is less than or equal to 12.5 * 10-11 mm / Pa, and comprising: a flow actuator (20) adapted to actuate the flow actuator (20); a channel (10) for flowing a liquid of interest in the channel (10) with a Mach number less than or equal to 0.3; a thermal measurement device (30) for measuring a temperature Theq of the liquid of interest flowing in the channel (10); and a processing unit (40) adapted to determine the pressure Pheq from the measured temperature Theq and a predetermined calibration function f.

Description

Technical Field

[0001] The field of the invention is the determination of the pressure of a liquid flowing in a channel, in particular in a millifluidic liquid channel or even a microfluidic channel. Background Art

[0002] Microfluidics involves the flow of liquids in channels with sub-millimeter lateral dimensions, and the applications of microfluidics generally cover physical, chemical, life, biological, medical, environmental, process and engineering sciences.

[0003] Depending on the application, it is known that the pressure of the liquid flowing in the microfluidic channel may be important. For this purpose, a pressure sensor is usually used, which may include a diaphragm or a deformable diaphragm, which separates two spaces, one where the liquid flows and the other brought to a reference pressure. The pressure difference between the two spaces causes the diaphragm to deform, and the pressure of the flowing liquid can be derived by measuring the deformation intensity (or vibration frequency). However, due to the size of the diaphragm, the pressure sensor is usually arranged upstream or downstream of the channel, in an area of ​​the fluid circuit with a sufficiently large lateral dimension. Therefore, the pressure is not measured in the microfluidic channel itself, which may result in providing erroneous values. In addition, the pressure sensor may experience measurement drift, especially in the case where it undergoes degradation of the membrane or gradual scaling, especially when used for a long time. Summary of the invention

[0004] An object of the present invention is to at least partially remedy the disadvantages of the prior art and more particularly to provide a measurement system and method for determining the pressure of a liquid flowing in a channel. Such a measurement system provides improved reliability because the pressure is determined from thermal measurements and a predetermined calibration function rather than indirectly from a value from a remote pressure sensor whose performance may be degraded.

[0005] To this end, an object of the present invention is a measuring system suitable for determining the int The flow in the channel has compressibility k m At least one pressure P of the liquid of interest heq , the liquid of interest and the channel are chosen so that the product k m × int Less than or equal to 12.5×10 -11 The measuring system comprises: a channel; a flow actuator adapted to cause the liquid of interest to flow in the channel so that the liquid of interest has a ratio V less than or equal to 0.3 m / c, where V mis the maximum velocity of the liquid of interest in the channel, and wherein c is the speed of sound in the liquid of interest; a thermal measurement device adapted to measure at least one temperature T of the liquid of interest flowing in the channel heq and a processing unit adapted to process the measured temperature T heq and the predetermined calibration function f to determine the pressure P heq , the calibration function f will be at pressure P heq and a predetermined reference pressure P of the liquid of interest at rest in the channel eq The evolution of the pressure difference ΔP between the measured temperatures T heq and a predefined reference temperature T of the liquid of interest at rest in the channel (10) eq is a function of the temperature difference ΔT between them.

[0006] Measured value T heq and a predefined value T eq The temperature difference ΔT between can be determined by the processing unit. eq Alternatively, the temperature difference ΔT can be determined by the thermal measurement device itself, which will then be converted to the predefined value T eq The value ΔT is added to the memory and provided directly to the processing unit.

[0007] The calibration function f represents the variation (i.e., course) of the pressure difference ΔP according to the temperature difference ΔT: ΔP=f(ΔT). Therefore, it should be understood that the terms "variation" and "course" have the same meaning. This variation or course can be positive or negative. In addition, the calibration function f can be an affine function defined by the following relationship: ΔP=β×ΔT, where β is a predetermined positive or negative (and, for example, positive) constant, where ΔP=P heq -P eq And ΔT=T heq -T eq .

[0008] The channel may have a length less than or equal to 5 cm.

[0009] The channel may be straight along its entire length and have a constant inner radius r int .

[0010] The flow actuator may include a conduit connecting the channel to a tank and a pump for the liquid of interest, the conduit having a flow greater than r int The inner radius of .

[0011] The thermal measurement device may be adapted to detect infrared radiation emitted by the liquid of interest and transmitted by the peripheral wall of the channel and to deduce the temperature T heq, the peripheral wall is made of a material that is transparent to infrared radiation.

[0012] The thermal measurement device may include at least one contact thermal sensor, which is arranged in contact with the peripheral wall of the channel.

[0013] The contact thermal sensor can be arranged to contact the outer surface of the peripheral wall, which is made of a thermally conductive material so that the temperature of the outer surface is equal to the temperature T of the liquid. heq .

[0014] The channel may have an inner diameter d between 10 μm and 1 mm. int .

[0015] The thermal measurement device may be adapted to acquire a thermal image of the liquid of interest, and the processing unit may be adapted to determine the pressure image from the acquired thermal image and the calibration function f.

[0016] Another object of the invention is a method for determining the pressure P of a liquid of interest moving in a channel of a measurement system according to any of the preceding features. heq The method comprises a measuring phase, the measuring phase comprising the following steps:

[0017] Choose a compressible k m The liquid of interest and has an inner radius r int channels, so that the product k m × int Less than or equal to 12.5×10 -11 mm / Pa;

[0018] The liquid of interest is caused to flow in the channel at a predefined flow rate by a flow actuator so that the liquid of interest has a ratio V less than or equal to 0.3. m / c, where V m is the maximum velocity of the liquid in the channel, and where c is the speed of sound in the liquid of interest;

[0019] The temperature T of the liquid of interest flowing in the channel is measured by a thermal measurement device heq , and determine the measured temperature T heq and a predefined reference temperature T of the fluid of interest at rest in the channel eq The temperature difference ΔT between them is non-zero;

[0020] The pressure P of the liquid of interest is determined by the processing unit from the determined temperature difference Δdifference and a predetermined calibration function f heq , the predetermined calibration function f will be the pressure P of the liquid of interest flowing in the channel heq and the pressure P of the fluid of interest at rest eqThe development of the pressure difference ΔP between them is expressed as a function of the temperature difference ΔT.

[0021] The method may include a calibration phase, which is performed before the measurement phase, and which includes the following steps:

[0022] Choose the inner radius of the calibration system to be r int The channel and the compressibility k c of liquid, so that the product k c × int Less than or equal to 12.5×10 -11 mm / Pa;

[0023] The liquid in the channel is caused to flow at a predetermined flow rate by a flow actuator of the calibration system so that the liquid has a ratio V less than or equal to 0.3. m / c, where V m is the maximum velocity of the liquid in the channel, and where c is the speed of sound in the liquid;

[0024] The temperature T of the liquid flowing in the channel is measured by the thermal measurement device of the calibration system. heq , and determine the measured temperature T heq and a predefined reference temperature T of the stationary liquid eq The temperature difference ΔT between them is non-zero;

[0025] The pressure P of the liquid flowing in the channel is measured by the pressure sensor of the calibration system. heq , and determine the measured pressure P heq and a predefined reference pressure P of the stationary liquid eq The pressure difference ΔP between them is non-zero;

[0026] Repeat for different flow rates of the liquid in the channel to measure the temperature T heq and pressure P heq Steps;

[0027] The calibration function f is determined by the processing unit of the calibration system from different values ​​of the temperature difference ΔT and the corresponding values ​​of the pressure difference ΔP.

[0028] The liquid of interest may be selected from water, alcohol and glycerol.

[0029] The liquid of interest may be the same liquid used during the calibration phase.

[0030] The flow of the liquid of interest can be performed by suction, so that the measured temperature T heq Below the reference temperature T eqand corresponds to cooling of the liquid of interest; or the liquid of interest flows through the discharge so that the measured temperature T heq Above the reference temperature T eq and corresponds to the heating of the liquid of interest.

[0031] The channel may be made of a thermally conductive material and in thermal contact with the external device, such that cooling or heating of the liquid of interest results in cooling or heating, respectively, of the external device. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other aspects, objects, advantages and features of the present invention will become more apparent on reading the following detailed description of a preferred embodiment of the invention given as a non-limiting example and made with reference to the accompanying drawings, in which:

[0033] Figure 1A is a schematic partial view of a measurement system suitable for determining the pressure of a liquid flowing in a channel according to one embodiment;

[0034] Figure 1B is a partial schematic longitudinal cross-sectional view of a channel of a measuring system;

[0035] Figure 1C is a schematic partial cross-sectional view of a channel and a thermal measurement arrangement of a measurement system;

[0036] Figure 2A An example of a calibration function f representing the progression of the pressure difference ΔP as a function of the temperature difference ΔT is shown;

[0037] Figure 2B is a schematic partial view of a calibration system suitable for determining a calibration function f according to one embodiment;

[0038] Figure 3 is a flow chart of a method for determining the pressure of a liquid flowing in a channel, here comprising a preliminary stage of determining a calibration function f. DETAILED DESCRIPTION

[0039] In the drawings and the rest of the specification, the same reference numerals represent the same or similar elements. In addition, in order to improve the clarity of the drawings, different elements are not shown to scale. In addition, different embodiments and alternatives are not mutually exclusive, but can be combined together. Unless otherwise specified, the terms "substantially", "about", "approximately" mean within 10%, preferably within 5%. In addition, unless otherwise specified, the terms "between ... and ..." and the like mean to include boundaries.

[0040] The present invention relates to the pressure P of a liquid flowing in a channel. heqThe determination of the pressure is not based on a dedicated pressure sensor, but on the measurement of the temperature of the liquid (more precisely the temperature difference ΔT) and with the aid of a predetermined calibration function f. The liquid whose pressure is to be determined is referred to here as the "liquid of interest" to distinguish it from the liquid used to establish the calibration function in advance. Like the calibration liquid, the liquid of interest is a liquid with a density ρ, a dynamic viscosity μ and a compressibility k.

[0041] Within the usual theoretical scope of fluid mechanics, a liquid is considered incompressible when its volume and therefore the density of each liquid particle remains constant during motion. So the density ρ is constant throughout the flow and at any time. This is especially true when the corresponding Mach number is low, usually less than 0.3, or even less than 0.1, or even smaller. The Mach number is defined by the following relationship: Ma = V m / c, where V m is the maximum velocity of the flowing liquid and c is the speed of sound in the liquid in question.

[0042] Therefore, in an incompressible liquid, since the velocity field is by definition of zero divergence, the expansion and compression effects of the liquid are assumed to be non-existent. Therefore, the equations of the conventional fluid mechanics model for an incompressible liquid (continuity, dynamics and energy equations) lead to a decoupling of the dynamic problem (velocity, pressure) from the thermal problem. Therefore, in an incompressible flow, it is usually assumed that the pressure of the liquid has no thermodynamic influence, and the dynamic and thermal problems can be solved independently of each other.

[0043] However, the inventors have noticed that when verifying the compressibility k of the liquid and the characteristic transverse dimension r of the channel int This conventional theoretical framework is not always correct in the case of making liquids flow, even though the condition of the product of π / π (which will be explained later) is met. This is especially true in channels with millimeter, micrometer or even nanometer dimensions. Therefore, they demonstrated that liquids that are usually considered incompressible in flow exhibit some compressibility, namely related to elasticity (called shear elasticity), whose physical effects vary with the characteristic size r of the channel. int Smaller and bigger.

[0044] Therefore, moving such a liquid in a channel while obeying the product k×r intThe conditions are equivalent to inducing shear elasticity of the liquid and thus causing it to depart from thermodynamic equilibrium through a thermoelastic effect (which can also be called an "elasto-caloric" effect). In fact, there is a thermoelastic coupling such that making the liquid flow leads to heating (mechanical compressive stress) or cooling (mechanical tensile stress). An introduction to thermoelasticity related to mesoscopic shear elasticity can be found in particular in the article entitled Strain-induced violation of temperature uniformity in mesoscale liquids by Kume et al. in SciRep, 10, 13340 (2020).

[0045] The inventors have developed a measurement system and method for determining the pressure of a liquid that utilizes a characteristic dimension r applied to the liquid. int Satisfies the product k×r int This measuring system avoids the above-mentioned disadvantages of the pressure sensors of the prior art, since the pressure of the flowing liquid is determined in situ in the measuring zone in the channel based on thermal measurements (thus by measurements that do not disturb the liquid flow) and a predetermined calibration function.

[0046] Furthermore, it should be noted that this temperature change of the liquid of interest due to thermoelastic effects is different from the heating due to effects of viscous friction type (which, moreover, cannot cause cooling of the liquid). In fact, when the liquid flows at a speed close to the speed of sound (Ma≈1), heating by viscous dissipation is usually expected, which does not correspond to the scope of the present invention.

[0047] Figure 1A is a partial schematic diagram of a measurement system 1 according to an embodiment, which is suitable for determining the pressure of a liquid of interest flowing in a channel 10 . Figure 1B and Figure 1C yes Figure 1A Schematic partial longitudinal and transverse cross-sectional views of a channel 10 of a measuring system 1 .

[0048] In general, the measurement system 1 comprises a channel 10, a device 20 for moving a liquid of interest in the channel 10 (referred to as a flow actuator), a thermal measurement device 30 suitable for measuring the temperature of the liquid in the channel 10, and a processing unit 40 suitable for determining the pressure of the liquid in the channel 10 from the measured temperature (and more precisely from the temperature difference ΔT) and a predetermined calibration function f.

[0049] The channel 10 is a flow conduit formed by a peripheral wall 11 having an inner surface 12 defining a cross section for the flow of the liquid and an outer surface 13 opposite the inner surface. The channel 10 extends longitudinally between a first end 10.1 and a second end 10.2 with a length L. The fluid flow transverse cross section of the channel 10 can be circular (tube) or elliptical, or polygonal, such as square, octagonal, etc. The channel 10 preferably has an aspect ratio equal to 1, which is defined by the inner dimensions of the two mutually orthogonal transverse axes of the channel 10. The transverse inner dimension d of the channel 10 is int (also called the inner diameter or equivalent inner diameter) is defined as the diameter of a disk having the same area as the fluid flow cross section of the channel 10. The inner radius r int Equal to diameter d int In the following description, the channel 10 is, by way of example, a cylindrical tube having a circular cross section.

[0050] inner radius r int According to the compressibility value k of the liquid m To select such that the following conditions are met: m × int ≤12.5×10 -11 The inventors have noticed that when this condition is met, the liquid flowing in the pipe 10 has a thermoelastic effect, which causes the temperature T of the liquid to heq Relative to the temperature T of the stationary liquid eq In addition, when the compressibility k of the liquid m In 10 -9 Pa -1 Up to 10 -11 Pa -1 When (here in the case of liquid), the inner radius r of the channel 10 int It can be of the order of a few micrometers, or even of the order of tens or hundreds of micrometers, or even of the order of one millimeter or ten millimeters. Therefore, in the context of microfluidics or millifluidic flows, the inner diameter d int It may be between 1 μm and 10 mm, or even between 10 μm and 1 mm.

[0051] The channel 10 can extend along its entire length in a straight line or even in a curved manner. In the thermal measurement region, the channel can also be straight or curved. The diameter d of the channel int It may be constant over the entire length of the channel, or may vary. If it is desired to limit or avoid thermal instabilities along the longitudinal axis of the channel 10, the length L may be less than or equal to 5 cm.

[0052] In the case where the thermal measurement device 30 is based on measurements by infrared detection, the peripheral wall 11 of the channel 10 can be made of a material that is transparent to infrared light radiation (e.g. Long Wavelength Infrared (LWIR)). Alternatively, in the case where the thermal measurement device 30 comprises one or more thermistors positioned in contact with the outer surface 13 of the peripheral wall 11, the peripheral wall 11 is made of a material having sufficient thermal conductivity so that the outer surface 13 has a temperature equal to the temperature of the liquid. Therefore, the material of the peripheral wall 11 (and therefore its optical and thermal properties) depends on the type of thermal measurement device 30 used, as described in detail later.

[0053] The liquid of interest is a material that can flow in the channel. This can be, for example, a viscous Newtonian or non-Newtonian liquid such as water, glycerol, alcohol, molten polymer, physiological or body fluids (blood, lymph, serum, etc.), colloidal solutions, etc. The liquid of interest has a dynamic viscosity μ m , density ρ m and compressibility k m . Compressibility k m Can be equal to a few units or hundreds of 10 -11 Pa -1 For example, k m For mercury, it is 3.7×10 -11 Pa -1 , for water it is 45.8×10 -11 Pa -1 , and for ethanol it is 110×10 -11 Pa -1 .

[0054] As mentioned before, with compressibility k m The liquid of interest and has an inner radius r int The channel 10 is selected so that the following conditions are met: m × int ≤12.5×10 -11 mm / Pa. When this condition is met, the liquid flowing in the channel 10 exhibits a uniform thermoelastic effect, which causes the liquid temperature T heq Relative to the temperature T of the stationary liquid eq changes have occurred.

[0055] The measuring system 1 comprises a flow device 20 (also called a flow actuator) adapted to ensure that the liquid of interest flows in the channel 10 at a predetermined flow rate D, which may or may not be constant. Thus, the flow may be continuous in one direction or time-dependent and may have a flow rate that may vary or remain constant.

[0056] Thus, the flow actuator 20 comprises at least one pump 21 (i.e. a device suitable for moving a liquid by discharge or suction), at least one tank 22 for the liquid of interest, and connecting pipes 23 ensuring fluid connections between the channel 10 and the pump 21 and between the channel 10 and the tank 22. The pump or pumps 21 are directly connected to the pipes 23 and are not located in the pipe 10, so as to avoid disturbing the flow of the liquid in the pipe 10 and thus reducing the quality of the temperature measurement of the liquid.

[0057] In this example, the measuring system 1 comprises a single pump 21 arranged between the tank 22 and the first end 10.1 of the channel 10. This may be a micropump, such as a peristaltic micropump, or any equivalent means (such as a syringe drive). The pump 21 is adapted to ensure that the liquid flows in the channel 10 at a predetermined flow rate D, which may or may not be constant.

[0058] The flow meter 24 is preferably connected to the channel 10 and is here located between the pump 21 and the first end 10.1 of the channel 10. The flow rate D of the liquid in the channel 10 can be deduced from the value measured by the flow meter 24. Preferably, the pump 21 is configured such that the flow rate D of the liquid in the channel 10 is less than or equal to a predetermined maximum value D if it is desired to avoid thermal instabilities along the longitudinal axis of the channel 10. m . Maximum flow rate D m Depends particularly on the nature of the liquid and in the case of water is approximately 416 mm 3 / s, while for alcohol it is about 2.5 mm 3 / s.

[0059] A tank 22 for liquid is connected here to both ends of the channel 10. The liquid has a predefined pressure, which may be atmospheric pressure P in this case. atm This pressure also corresponds to the reference pressure P of the liquid when it is at rest in the channel 10. eq .

[0060] Thus, the connecting pipe 23 provides a fluid connection between the tank 22, the pump 21 and the channel 10. The connecting pipe has a diameter d which may be greater than the channel 10. int The inner diameter of the channel 10 is, for example, int 2x, 5x, 10x or even greater ratios.

[0061] Of course, other configurations are possible. Thus, the second pump may be located between the tank 22 and the second end 10.2. Furthermore, multiple tanks may be used. One or more tanks may also contain the liquid of interest under overpressure, in which case one or more pumps may not be required, and valves may be provided to allow or block the flow of the liquid.

[0062] It should be noted that the arrangement of the pump 21 relative to the channel 10 and the direction of the applied flow define the type of mechanical stress to which the liquid in the channel 10 is subjected, ie compressive or tensile, and therefore the sign of the temperature change ΔT (heating or cooling).

[0063] Thus, in this example where the pump 21 is located between the tank 22 and the first end 10.1 of the pipe 10, the flow direction directed from the first end 10.1 to the second end 10.2 causes the liquid in the pipe 10 to be subjected to compressive mechanical stresses, resulting in heating due to thermoelastic effects. The liquid then has a temperature difference ΔT=T with a positive sign. heq -T eq And the pressure difference ΔP=P also with a positive sign heq -P eq . T eq and P eq Here, T represents the temperature and pressure of the liquid at rest in the channel 10 (“eq” stands for “in thermodynamic equilibrium”), and T heq and P heq represents the temperature and pressure of the liquid flowing in the channel 10 ("heq" stands for "non-thermodynamic equilibrium").

[0064] In contrast, in the case of a flow direction from the second end 10.2 to the first end 10.1 imposed by the pump 21, the liquid flowing in the channel 10 is subjected to tensile mechanical stresses, resulting in cooling by thermoelastic effects. The liquid then has a temperature difference ΔT with a negative sign and a pressure difference ΔP also with a negative sign.

[0065] Finally, note that the thermoelastic effect causes the temperature T of the liquid flowing in the channel 10 to heq and pressure P heq The temperature in the pipe 23 can be substantially equal to the reference temperature (room temperature) along the longitudinal axis of the channel 10, and the flow of the liquid is induced by the pressure difference between the high pressure applied by the pump 21 and the ambient pressure of the tank 22. In fact, the pressure of the liquid flowing in the channel 10 is substantially constant due to the fact that, when the pump 21 is started, the liquid present in the channel 10 initially resists the flow up to a threshold value due to the interaction with the peripheral wall 11 and is then moved. There is then a thermoelastic coupling, so that the liquid has a temperature T that is substantially constant in space along the longitudinal axis of the channel 10. heq and pressure P heq , which corresponds to a non-thermodynamic equilibrium state of the liquid.

[0066] The measurement system 1 further comprises a thermal measurement device 30 suitable for determining the value of the temperature of the liquid in the channel 10. The thermal measurement device may be of the contactless type, for example by optical detection of infrared radiation, or may be of the contact type.

[0067] Preferably, the thermal measurement device 30 is of the non-contact type and comprises a photodetector 31 for detecting optical radiation emitted from or originating from the liquid present in the channel 10 (e.g. infrared radiation). The photodetector 31 may be a matrix photodetector (imager) or a non-matrix photodetector (photodiode). The photodetector may be a bolometer or microbolometer, a CCD or CMOS sensor (or equivalent, such as BS-CMOS, etc.) or an optical pyrometer. The optical radiation to be detected may be in the infrared range, i.e. with a wavelength between about 0.7 μm and 16 μm. It can be included in the near infrared (NIR) range of about 0.78μm to 1μm, in the short wave infrared (SWIR) range of about 1μm to 2.7μm, in the middle wave infrared (MWIR) range of 3μm to 5μm, or even in the long wave infrared (LWIR) range of 7μm to 14μm.

[0068] In this example, a matrix photodetector 31 (imager) is used, which comprises a matrix of microbolometers forming 382×288 detection pixels. The size of each detection pixel on one side of the focal plane is 20 μm. In the nominal range of about 15°C-25°C, the thermal sensitivity is about ±0.02°C. The thermal measurement device 30 also includes one or more optical elements 32 for shaping the incident light radiation, such as one or more lenses. The depth of field depends in particular on the liquid and can be of the order of about one hundred micrometers or even more. In addition, the detected thermal image corresponds to a measurement area in the channel 10, the height H of the measurement area zm may be at least equal to the diameter d of the channel 10 int , length L zm can be equal to d int One or more times of, for example, equal to about 5 mm.

[0069] Based on the detected thermal image, the thermal measurement device 30 determines a temperature value for the liquid in the channel 10. This value may be an average value calculated from the values ​​of the thermal image or detailed thermal mapping, and may be a weighted average value. This means that values ​​far from the peripheral wall 11 may be given more weight, or not given more weight. The value thus determined corresponds to the temperature T of the liquid in the channel 10 (i.e. the temperature T when the liquid is stationary). eq and the temperature T of the liquid when it flows heq ). This temperature value is sent to the processing unit 40. Alternatively, a thermal image (thermal map) is sent to the processing unit 40, which derives a pressure image (pressure map) therefrom.

[0070] In the case where the thermal measuring device 30 is of the optical type, the peripheral wall 11 is formed of a material that is transparent to the optical radiation to be detected (i.e., the transmission coefficient is at least equal to 50% or even 75% or even 90% of the optical radiation to be detected), or is formed of a material that is opaque to the optical radiation to be detected but has a high thermal conductivity, so that the optical radiation is the optical radiation emitted by the outer surface 13 of the peripheral wall 11. Transparent materials include calcium fluoride (CaF2), germanium (Ge), potassium bromide (KBr) and some plastics. In the case of an opaque material, the thickness of the peripheral wall 11 is preferably less than or equal to the inner diameter d int .

[0071] Alternatively or complementary, the thermal measurement device 30 may comprise one or more contact thermal sensors, each formed by a thermistor material positioned in contact with the peripheral wall. In the case where the thermistor material is in contact with the inner surface 12 of the peripheral wall 11, the thermistor material is in contact with the liquid and is connected to the processing unit 40 by a cable passing through the peripheral wall 11 in a sealed manner. Preferably, however, the thermistor material is in contact with the outer surface 13 of the peripheral wall 11, in which case the peripheral wall 11 is made of a thermally conductive material, so that the temperature of the outer surface 13 of the peripheral wall 11 is substantially equal to the temperature of the liquid, or so that the temperature of the liquid can be derived from the temperature of the peripheral wall 11 by means of a predefined physical model of thermal conductivity.

[0072] The processing unit 40 is suitable for determining the pressure of the liquid in the channel 10, on the one hand as a function of the temperature T measured by the thermal measuring device 30. eq (and more precisely from the temperature difference ΔT), on the other hand, from the calibration function f, the pressure of the liquid in the channel 10 is determined. Therefore, the processing unit comprises a calculator comprising at least one microprocessor and at least one memory storing the calibration function f. As previously mentioned, the processing unit 40 can receive at least one temperature value, for example one or more thermal values, and for example a thermal image (thermal map), in order to derive therefrom at least one corresponding pressure value, or even a pressure image (pressure map).

[0073] The calibration function f converts the pressure difference ΔP = P heq -P eq The development (ie change) of is expressed as the temperature difference ΔT=T of the liquid in the channel 10 heq -T eq Function: ΔP=f(ΔT). The standard function is a continuous function, which is preferably an affine function, but can also be a polynomial, a logarithmic function or even an exponential function. As described in detail later, the standard function is parameterized in a preliminary calibration phase. Therefore, when the temperature difference ΔT is zero, the pressure difference ΔP is also zero. As mentioned above, the temperature difference ΔT can have a positive value (heating), so that the pressure difference ΔP is also positive (the liquid is in compression), but the temperature difference ΔT can also have a negative value (cooling), so that the pressure difference ΔP is also negative (the liquid is in tension).

[0074] Figure 2A An example of such a calibration function f determined for water flowing in a tubular channel 10 with a diameter of 0.3 mm is shown, where the temperature T of the stationary liquid is eq is a room temperature of about 20°C. The temperature is measured by a contact thermal sensor, and the peripheral wall of the channel 10 is made of a material with high thermal conductivity that is opaque to infrared radiation, which material is silicate glass in this context. In addition, the peripheral wall 11 has an outer diameter of 0.8 mm. It is observed that a change ΔT of 0.34°C±0.02°C results in a change |ΔP| of 0.68 bar. The calibration function f herein is an affine function ΔP=β×ΔT, where β is a constant equal to about 2 bar / °C. Preferably, the pressure difference ΔP is between -1 bar and +1 bar, and more preferably between -0.5 bar and +0.5 bar.

[0075] Figure 2B is a schematic partial view of an example of a calibration system 100 which is adapted to determine a calibration function f which is then recorded in a processing unit 40 of a measuring system 1 .

[0076] The calibration system 100 is similar to the measurement system 1, and includes a channel 110, a flow actuator 120, a thermal measurement device 130, and a processing unit 140. However, unlike the measurement system 1, the calibration system 100 includes at least one pressure sensor 150, which is suitable for measuring the pressure of the liquid in the channel 10. The pressure sensor 150 can be a strain gauge, a capacitive, a piezoelectric sensor, etc. A plurality of pressure sensors 150 can be arranged along the channel 10 in order to obtain a more accurate pressure value of the liquid. In addition, it should be noted that the size of the channel 110 is the same as that of the measurement system 1.

[0077] Advantageously, the calibration system 100 and the measuring system 1 are two different systems, so that the calibration system 100 is used to determine the calibration function f once, and then the measuring system 1 is used to determine the pressure of the liquid flowing in the channel 10 according to the calibration function f thus determined. This can be the same system, wherein the measuring system 1 corresponds to the calibration system 100 in which one or more pressure sensors 150 are removed. It is worth noting that the liquid whose pressure is determined by the measuring system 1 can be different from the liquid used to determine the calibration function f, of course, both liquids satisfy the product k×r int Preferably, the two liquids have the same compressibility value k (within 10%, or even within 5%, or even less), and preferably, the two liquids are the same liquid.

[0078] Figure 3 The method for determining the pressure of a liquid flowing in a channel 10 of a measuring system 1 and the different steps of a preliminary phase of determining a calibration function f are shown.

[0079] The calibration phase 10 is first performed by the calibration system 100 .

[0080] During step 11, a c , viscosity μ c and compressibility k c In addition, the inner radius is chosen to be r int The liquid and the channel 110 are selected so that the product k c × int Less than or equal to 12.5×10 -11 mm / Pa. In addition, the channel 110 has a length L less than or equal to 5 cm and an inner diameter d int Less than or equal to 1 mm, preferably between 10 μm and 1 mm.

[0081] During step 12, the liquid is stationary in channel 110. The temperature of the stationary liquid is T eq and pressure P eq are defined and recorded in the processing unit 140 of the calibration system 100. These values ​​may simply be defined by the user (without measurement) or may have been pre-measured, for example by means of the thermal measurement device 130 or another temperature sensor (not shown), or by means of the pressure sensor 150 or another pressure sensor (not shown).

[0082] During step 13, the flow actuator 120 causes the liquid to flow in the channel 110 (at a constant flow rate in this example). More precisely, the pump 121 ensures that the liquid flows from the tank 122 so that the liquid flows in the pipe 123 and the channel 110 and returns to the tank. The flow rate D of the liquid in the channel 110 is measured to ensure that the flow rate does not exceed a predetermined maximum value D m , which depends on the properties of the liquid. Thus, for water, the flow rate does not exceed about 416 mm 3 / s occurs in channel 110.

[0083] In step 14, when the liquid flows in channel 110 at a flow rate D (i) When flowing, the temperature T of the liquid in the channel 110 is heq(i) The pressure P of the liquid in the channel 110 is measured by the thermal measuring device 130. heq(i) The temperature difference ΔT is then determined. (i) =T heq(i) -T eq and pressure difference ΔP (i) =P heq(i) -P eq . So we get a pair (ΔT (i) ; ΔP (i) ), and for different flow rate values ​​D (i) The measurement is repeated by increasing the value of i. The number N is at least 1, assuming that the pair (ΔT=0; ΔP=0) exists by definition, but the number N can be at least 6, with at least 3 measurements for Δt>0 and at least 3 measurements for ΔT<0.

[0084] During step 15, the processing unit 140 determines the calibration function f, i.e. the processing unit 140 determines the parameters of the function (e.g. the constant β in the case of an affine function) from the measured values ​​of the temperature difference and the pressure difference by, for example, linear regression. Thus, the calibration system 100 has determined the calibration function f, which is then transmitted to the processing unit 40 of the measurement system 1, if necessary.

[0085] A phase of measuring 20 the pressure of the liquid of interest may then be performed by the measurement system 1 .

[0086] During step 21, a liquid of interest is selected. The liquid of interest is similar to the liquid used for calibration. The liquid of interest has a density p m , viscosity μ m and compressibility k m , compressibility k m equal to k within 10% (i.e. within 10% or even smaller range)c Preferably, the liquid of interest is the same as the liquid used for calibration. Therefore, since channel 10 is the same as the channel of the calibration system, the product k m × int Satisfy the condition k m × int ≤12.5×10 -11 mm / Pa, and the product is equal to the product k c × int (Within 10% or even smaller range).

[0087] During step 22, the liquid is present in the channel 10 at rest and at a temperature T eq and pressure P eq are defined and recorded in the processing unit 40. These values ​​may be retrieved directly from the values ​​recorded in the calibration system 100. Alternatively, these values ​​may be defined and recorded by the user in the processing unit 40 without direct measurement. In another alternative, the temperature T eq The pressure P can be measured by means of a thermal measuring device 30 (or another temperature sensor not shown). eq The pressure may be measured by a pressure sensor (not shown) disposed at, for example, the tank 22 or the pipe 23 .

[0088] During step 23, the flow actuator 20 moves the liquid in the channel 10 (in this example at a constant flow rate). The flow rate D is less than or equal to a predefined maximum value D m Thus, the liquid of interest is heated (ΔT>0) or cooled (ΔT<0) along the flow direction imposed by the flow actuator 20 by the thermoelastic effect.

[0089] During step 24, the temperature T of the liquid in the channel 10 is measured by means of the thermal measuring device 30 while the liquid flows in the channel 10 at a flow rate D. heq Then, the processing unit 40 determines the temperature difference ΔT=T heq -T eq .

[0090] During a step 25 , the processing unit 40 determines the pressure difference ΔP as a function of the calibration function f and of the value obtained for the temperature difference ΔT.

[0091] Finally, during step 26 , the processing unit 40 processes the pressure difference ΔP according to the pressure value P of the stationary liquid. eq To determine the value P of the pressure of the liquid flowing in the channel 10 eq :P heq =ΔP-P eq .

[0092] The measurement system 1 thus makes it possible to determine the non-equilibrium pressure P of the liquid flowing in the channel 10 by exploiting the thermoelastic effect demonstrated by the inventors. heq , without having to measure the pressure of the flowing liquid in the channel. Therefore, not only is the flow of the liquid in the channel not disturbed by the pressure sensor, but the reliability of the measurement system 1 is improved, because the pressure is not determined by a local and possibly degraded dedicated remote pressure sensor, but by thermal measurement and calibration functions.

[0093] Note that flow instabilities may occur during the measurement phase and therefore an image of the pressure variations of the flowing liquid is obtained via the measurement of the thermal image.

[0094] It should also be noted that the heating or cooling of the flowing liquid can be used to heat or cool the channel and thus heat or cool an external device that will be in thermal contact (heat exchange) with the channel.

[0095] Having just described specific embodiments, various variations and modifications will become apparent to those skilled in the art.

Claims

1. A measuring system (1) adapted to determine a int The flow in the channel (10) has a compressibility k m At least one pressure P of the liquid of interest heq , the liquid of interest and the channel (10) are selected so that the product k m × int Less than or equal to 12.5×10 -11 mm / Pa, the measuring system (1) comprises: The channel (10); A flow actuator (20) adapted to cause the liquid of interest to flow in the channel (10) such that the liquid of interest has a ratio V less than or equal to 0.3 m / c, where V m is the maximum velocity of the liquid of interest in the channel (10), and wherein c is the speed of sound in the liquid of interest; Thermal measuring means (30) adapted to measure at least one temperature T of the liquid of interest flowing in the channel (10) heq ; A processing unit (40) adapted to process the measured temperature T heq and a predetermined calibration function f to determine the pressure P heq , the calibration function f makes ΔP = f(ΔT), which will be heq and a predetermined reference pressure P of the liquid of interest at rest in the channel (10) eq The evolution of the pressure difference ΔP between the measured temperatures T heq and a predefined reference temperature T of the liquid of interest at rest in the channel (10) eq is a function of the temperature difference ΔT between them.

2. The measuring system (1) according to claim 1, wherein: The channel (10) has a length less than or equal to 5 cm.

3. The measuring system (1) according to claim 1 or 2, wherein: The channel (10) is straight over the entire length of the channel and has a constant inner radius r int .

4. The measuring system (1) according to any one of claims 1 to 3, wherein: The flow actuator (20) comprises a conduit (23) connecting the channel (10) to a tank (22) for the liquid of interest and to a pump (21), the conduit (23) having a flow path greater than r int The inner radius of .

5. The measuring system (1) according to any one of claims 1 to 4, wherein: The thermal measurement device (30) is adapted to detect infrared radiation emitted by the liquid of interest and transmitted by the peripheral wall (11) of the channel (10), and to deduce the temperature T heq , the peripheral wall (11) is made of a material that is transparent to infrared radiation.

6. The measuring system (1) according to any one of claims 1 to 4, wherein: The thermal measurement device (30) comprises at least one contact thermal sensor, which is arranged to be in contact with the peripheral wall (11) of the channel (10).

7. The measuring system (1) according to claim 6, wherein: The contact thermal sensor is arranged to contact the outer surface (13) of the peripheral wall (11), and the peripheral wall is made of a heat-conducting material so that the temperature of the outer surface (13) is equal to the temperature T of the liquid. heq .

8. The measuring system (1) according to any one of claims 1 to 7, wherein: The channel has an inner diameter d between 10 μm and 1 mm int .

9. The measuring system (1) according to any one of claims 1 to 8, wherein: The thermal measurement device (30) is adapted to acquire a thermal image of the liquid of interest, and the processing unit (40) is adapted to determine a pressure image from the acquired thermal image and the calibration function f.

10. A method for determining the pressure P of a liquid of interest moving in the channel (10) of a measuring system (1) according to any one of the preceding claims heq The method comprises a measuring phase, wherein the measuring phase comprises the following steps: Choose a compressible k m The liquid of interest and has an inner radius r int The channel (10) makes the product k m × int Less than or equal to 12.5×10 -11 mm / Pa; The liquid of interest is caused to flow in the channel (10) at a predefined flow rate by the flow actuator (20), so that the liquid of interest has a ratio V less than or equal to 0.3 m / c, where V m is the maximum velocity of the liquid in the channel (10), and wherein c is the speed of sound in the liquid of interest; The temperature T of the liquid of interest flowing in the channel (10) is measured by the thermal measuring device (30) heq , and determine the measured temperature T heq and a predefined reference temperature T of the liquid of interest at rest in the channel (10) eq A temperature difference ΔT between the two, wherein the temperature difference ΔT is non-zero; The pressure P of the liquid of interest is determined by the processing unit (40) based on the determined temperature difference ΔT and a predetermined calibration function f heq , the predetermined calibration function f converts the pressure P of the liquid of interest flowing in the channel (10) heq and a predetermined reference pressure P of the liquid of interest at rest in the channel (10) eq The progression of the pressure difference ΔP between is expressed as a function of the temperature difference ΔT.

11. The method according to claim 10, comprising a calibration phase, which is performed before the measuring phase, the calibration phase comprising the following steps: The inner radius of the calibration system (100) is chosen to be r int The channel (110) and the compressibility k c of liquid, so that the product k c × int Less than or equal to 12.5×10 -11 mm / Pa; The liquid in the channel (110) is caused to flow at a predetermined flow rate by a flow actuator (120) of the calibration system (100) so that the liquid has a ratio V less than or equal to 0.

3. m / c, where V m is the maximum velocity of the liquid in the channel (110), and wherein c is the speed of sound in the liquid; The temperature T of the liquid flowing in the channel (110) is measured by the thermal measurement device (130) of the calibration system (100). heq , and determine the measured temperature T heq and a predefined reference temperature T of the liquid at rest eq A temperature difference ΔT between the two, wherein the temperature difference ΔT is non-zero; The pressure P of the liquid flowing in the channel (110) is measured by the pressure sensor (150) of the calibration system (100). heq , and determine the measured pressure P heq and a predefined reference pressure P of the liquid at rest eq The pressure difference ΔP between them is non-zero; The method for measuring the temperature T is repeated for different flow rates of the liquid in the channel (110). heq and the pressure P heq Steps; The calibration function f is determined by a processing unit (140) of the calibration system (100) according to different values ​​of the temperature difference ΔT and corresponding values ​​of the pressure difference ΔP.

12. The method according to claim 10 or 11, wherein: The liquid of interest is selected from the group consisting of water, alcohol and glycerol.

13. The method according to any one of claims 10 to 12, wherein: The liquid of interest used during the measurement phase is the same as the liquid used during the calibration phase.

14. The method according to any one of claims 10 to 13, wherein: The liquid of interest is made to flow by suction so that the measured temperature T heq Below the reference temperature T eq and corresponds to cooling the liquid of interest; or causing the liquid of interest to flow through the discharge so that the measured temperature T heq Above the reference temperature T eq and corresponds to heating of the liquid of interest.

15. The method according to claim 14, wherein: The channel (10) is made of a thermally conductive material and is in thermal contact with an external device, so that cooling or heating of the liquid of interest results in cooling or heating of the external device, respectively.

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