Sensor of a system for measuring inertial heat flux

Abstract

According to one aspect, the present invention relates to a sensor (200) for a system for measuring inertial heat flux, the sensor comprising: a solid-type calorimetric element (201) having a thermal conductivity greater than or equal to about 100 W / (m·K) and an electrical conductivity greater than or equal to about 105 S / m; a thermal insulation element (202) that partially covers the calorimetric element (201) to define a first planar portion that is not covered by the calorimetric element and a second portion of the calorimetric element (201) that is thermally insulated from the heat flux, the first planar portion being configured to be exposed to the heat flux contained in the front face (203); and two wire-based conduction elements (207a, 207b) that pass through the calorimetric element (201) and are arranged not to be in mechanical contact with each other, but rather the two wire-based conduction elements (207a, 207b) are in electrical contact via the calorimetric element (201), the two wire-based conduction elements (207a, 207b) being made of two different thermoelectric materials.

Description

Technical Field

[0001] This specification relates to sensors for an inertial heat flux measurement system, systems including such sensors, and methods for measuring heat flux by such systems. Background Art

[0002] Heat flux measurement has applications in many fields. For example, in the microelectronics field, accurately measuring the dissipated heat flux allows optimizing the architecture of devices including semiconductors and improving their energy efficiency.

[0003] In the field of hydraulics, complex processes including turbulence, supercritical fluid flow, or phase changes such as boiling can be optimized in their operation by characterizing the heat flux in action. This also allows correcting the models used in a standard way, which are not very suitable for complex processes.

[0004] In the aerospace field, structures such as combustion chambers of turbomachines or rocket engines, atmospheric reentry bodies, or even launch pads of launchers are subjected to strong heat fluxes. Therefore, it is usually necessary to accurately know the heat flux to estimate the thermomechanical strength of the structure and avoid any failures.

[0005] In the field of energy production and conversion processes (chemistry, steel industry, fluidized beds, etc.), the operating points of plants are closely related to the definition of a stable heat balance, which requires continuous control of the heat flux in action.

[0006] The measurement of heat flux is generally carried out indirectly based on the measurement of quantities other than the flux, particularly the temperature of an element subjected to the heat flux to be measured. This element can be part of a larger system, such as the metal wall or filling material of a reactor.

[0007] Among the sensors used to perform indirect measurements of heat flux, it is particularly known to use enthalpy flux meters, the principle of which is based on the measurement of the rise in temperature of a liquid circulating within the body of the entire flux meter.

[0008] The measured temperature rise at a given flow rate allows knowing the thermal power absorbed by the liquid and obtaining the desired heat flux. Generally, the results given by these devices are inaccurate.

[0009] It is also known to use Gardon gauges, Schmidt-Boelter gauges, and thermopiles, which indirectly measure heat flux by measuring the temperature difference in a solid medium contained in the gauge. Preferably, this type of sensor is used to measure radiative heat flux, i.e., the heat flux generated by electromagnetic radiation, and its limitations have been demonstrated when measuring convective or mixed heat fluxes.

[0010] Another example of an excellent device for indirectly measuring heat flux is an inertial fluxmeter, in which when a reference element (a so-called calorimetric element) is exposed to a heat flux, the heat flux is determined by measuring the rise in the temperature of the calorimetric element.

[0011] Figure 1 shows an inertial fluxmeter of the prior art, for example, disclosed in WO02 / 18890A2 [Reference 1] or JAYAPRAKASH, C. et al. [Reference 2]. Such an inertial fluxmeter generally includes a calorimetric element 101 and an insulating element 102 that partially wraps the calorimetric element 101. The surface of the calorimetric element 101 that is not covered by the insulating element 102 (i.e., the so-called front face 103) is configured to receive the heat flux. The fluxmeter also includes a thermocouple 107 that is used to determine the temperature of the calorimetric element 101 that is subjected to the heat flux. The thermocouple 107 includes two wire-based elements 107a, 107b made of two conductive materials with different Seebeck coefficients, and the two wire-based elements 107a, 107b are connected at a single hot junction 104, where the temperature of the calorimetric element 101 is measured. The hot junction 104 is in contact with the face of the fluxmeter that is opposite to the front face 103 (i.e., the so-called rear face 106).

[0012] It is known that a potential difference appears between the two wire-based elements 107a, 107b, and this potential difference is substantially proportional to the temperature difference that exists between the temperature at the hot junction 104 and the reference temperature at two cold junctions that are usually located at the ends of the wire-based elements 107a, 107b. The occurrence of this potential difference is the so-called Seebeck effect.

[0013] Therefore, by using the measuring unit 140 to measure the potential difference, the increase in the temperature of the rear face 106 over time can be inferred. Therefore, based on the temperature rise, the processing unit 150 can use thermodynamic theory and the known characteristics of the calorimetric element 101 (such as mass and heat capacity at constant pressure) to calculate the heat flux.

[0014] However, the calculation of the heat flux Φ is based on the assumption of a thin calorimetric element 101 so that the temperature measurement on the rear face 106 can be considered to be substantially equal to the temperature measurement on the front face 103.

[0015] The published patent application FR 2 706 610 [Reference 3] also describes a sensor for a heat flux measurement system; the sensor described in [Reference 3] includes two conductors that form a thermocouple and are fastened at different points on the rear face of a sheet made of a conductive material and having a reduced thickness (usually less than one-tenth of a mm).

[0016] Therefore, the devices described in [Reference 1], [Reference 2], or [Reference 3] do not allow for the accurate determination of strong heat fluxes, i.e., heat fluxes higher than or equal to a few MW / m 2 of heat flux.

[0017] In fact, in the presence of a high heat flux, the calorimetric element 101 should be strong enough not to melt during the measurement period, which is usually solved by increasing the size of the calorimetric element 101.

[0018] However, the increase in the size of the calorimetric element 101 leads to an increase in the distance between the front face 103 exposed to the heat flux and the rear face 106 where the temperature is measured. Therefore, the assumption of a thin calorimetric element 101 is usually no longer satisfied, and the accuracy of the temperature measurement and the accuracy of the heat flux calculated based on the temperature are greatly reduced.

[0019] Therefore, a sensor for an inertial heat flux measurement system is needed that enables the accurate measurement of high heat fluxes, such as heat fluxes higher than or equal to a few MW / m 2 of heat flux. Summary of the Invention

[0020] In this specification, the terms "comprising" and "including" or "containing" have the same meaning and are inclusive or open and do not exclude other elements not described or illustrated.

[0021] Furthermore, in this specification, the terms "about" or "substantially" are synonymous (have the same meaning) with a lower limit and / or an upper limit of 10% (e.g., 5%) of the corresponding value.

[0022] According to a first aspect, this specification relates to a sensor for an inertial heat flux measurement system, the sensor comprising:

[0023] - a solid-type calorimetric element having a given length, the calorimetric element including a front face and a rear face opposite the front face, the calorimetric element having a thermal conductivity higher than or equal to about 100 W / (m·K), preferably, the calorimetric element having a thermal conductivity higher than or equal to about 300 W / (m·K), the calorimetric element having an electrical conductivity higher than or equal to about 10 5 S / m, preferably, the calorimetric element having an electrical conductivity higher than or equal to about 10 7 S / m;

[0024] - a thermal insulation element that partially covers the calorimetric element to define a first part that is not covered by the calorimetric element and a second part that is covered by the calorimetric element, the first part being substantially planar and being configured to be exposed to the heat flux to be measured and form part of the front face, the second part being thermally insulated from the heat flux; and

[0025] - Two wire-based conduction elements that at least partially pass through the calorimetric element from the rear face, and the two wire-based conduction elements are arranged such that they do not mechanically contact each other, but the two wire-based conduction elements are in electrical contact via the calorimetric element over at least a portion of the length of the calorimetric element, and the two wire-based conduction elements are made of two different thermoelectric materials.

[0026] In the present specification, a thermoelectric material is a material whose electrical conductivity varies with temperature. In particular, such a material has the ability to convert thermal energy into electrical energy, and this ability is quantified by the Seebeck coefficient.

[0027] In the present specification, two different materials are materials having different chemical compositions, preferably having different Seebeck coefficients. The Seebeck coefficients of most materials are known and can be obtained by those skilled in the art by referring to tables. In addition, the measurement of the Seebeck coefficient can be performed by methods known in the prior art, which include the following method, which includes: measuring the potential difference that appears between two elements when an element made of the material to be characterized and a reference element (such as platinum) are in mechanical contact and subjected to a known temperature.

[0028] The applicant has demonstrated that the original arrangement of the two thermoelectric materials in the sensor according to the first aspect allows for a more accurate measurement of the heat flux than the prior art, especially when the heat flux is higher than or equal to a few MW / m 2 .

[0029] According to one or more examples of the specification, it is advantageous to use two thermoelectric materials having Seebeck coefficients, the absolute value of the difference between which is higher than or equal to about 5 μV / K, in order to be able to measure the temperature of the calorimetric element using the sensor according to the present specification. In particular, using two thermoelectric materials having Seebeck coefficients (the absolute value of the difference between which is higher than or equal to about 5 μV / K) allows for obtaining a sensor with sufficient resolution to measure the temperature of the calorimetric element.

[0030] In the present specification, the length of the calorimetric element is defined between the front face and the rear face in a direction substantially perpendicular to the first portion exposed to the heat flux.

[0031] The heat flux measured in W / m 2 at the said first portion of the calorimetric element is caused by the temperature difference between the external environment temperature of the sensor at a given time point and the temperature of the first portion of the calorimetric element at that time point. Due to this heat flux, the temperature of the calorimetric element rises over time.

[0032] Generally, the heat flux includes a radiative contribution (also known as radiative flux) and / or a convective contribution (also known as convective flux).

[0033] The radiative flux is due to electromagnetic radiation between the external environment of the sensor and the first part exposed to the heat flux. The convective flow is due to the movement of materials in the external environment of the sensor at the first part.

[0034] The applicant has demonstrated that in the sensor according to the present specification, two wire-based conduction elements that at least partially pass through the calorimetric element allow for the measurement of the average temperature of the calorimetric element at a given point in time, where the average temperature is the temperature averaged over the part of the calorimetric element that is passed through by the two wire-based conduction elements. This improves the accuracy of the temperature measurement of the calorimetric element compared to inertial heat flux sensors of the prior art.

[0035] Thus, the passing arrangement of the wire-based elements of the sensor according to the present specification advantageously allows, for example, to overcome the temperature measurement uncertainty of the calorimeter due to the temperature gradient existing between different regions of the part of the calorimetric element that is passed through by the two wire-based conduction elements.

[0036] In particular, the sensor according to the first aspect addresses some drawbacks of inertial heat flux sensors of the prior art, in particular inertial heat flux sensors having thermocouples at the rear face, where the thermocouple can only measure the temperature of the calorimetric element at one point on the rear face, and where therefore only calorimetric elements with a small thickness satisfy the assumption of a thin calorimetric element, which limits the use at high heat fluxes.

[0037] According to one or more examples, the length of the calorimetric element defined in a direction substantially orthogonal to the front face is strictly greater than 0.1 mm, advantageously longer than or equal to about 1 mm, advantageously longer than or equal to about 2 mm. Generally, the length can be chosen to be long enough to have good heat resistance when the sensor is subjected to high heat fluxes, and small enough to satisfy the assumption of a thermally thin calorimetric element.

[0038] According to one or more examples, the two wire-based conduction elements pass through the calorimetric element over at least about 30%, preferably 50%, even more preferably 90% of the length of the calorimetric element.

[0039] According to one or more examples, the two wire-based conduction elements pass through the entire calorimetric element so that the two wire-based conduction elements are flush with the first part of the calorimetric element exposed to the heat flux.

[0040] According to one or several examples, the two wire-based conduction elements are arranged to be substantially parallel.

[0041] According to one or more examples, the calorimetric element has a cylindrical shape, a conical shape, or a cylindrical-conical shape, and the calorimetric element includes a rotational axis that is substantially perpendicular to the first part.

[0042] According to one or more examples, the two wire-based conduction elements are arranged to be substantially parallel to the rotational axis, and the two wire-based conduction elements are symmetric about the rotational axis.

[0043] According to one or more examples, the calorimetric element includes a material having the following properties:

[0044] - A constant-pressure heat capacity that is greater than or equal to about 120 J / (kg·K) at 25 °C; and / or

[0045] - A melting temperature that is greater than or equal to about 500 °C; and / or

[0046] - A density that is greater than or equal to about 2500 kg / m 3 ³.

[0047] According to one or more examples, the calorimetric element includes graphite, a metal, or a metal alloy, preferably copper or silver.

[0048] According to one or more examples, the two different thermoelectric materials are a pair of materials selected from the following: chromel / constantan, iron / constantan, chromel / alumel, nicrosil / nisil, nickel-molybdenum / nickel-cobalt (nickel-molybdenum / nickel-cobalt), platinum-rhodium / platinum, tungsten-rhenium / tungsten.

[0049] According to one or more examples, the sensor further includes an adhesive material that encapsulates each of the two wire-based conduction elements to ensure mechanical contact between each of the two wire-based conduction elements and the calorimetric element.

[0050] According to one or more examples, the adhesive material includes:

[0051] - An electrical conductivity that is greater than or equal to about 10 6 S / m; and / or

[0052] - A thermal conductivity that is greater than or equal to about 200 W / (m·K).

[0053] According to one or more examples, the adhesive material includes a material selected from at least one of the following materials: silver, gold, copper-phosphorus alloy, copper-silver alloy, copper-zinc alloy.

[0054] According to one or more examples, the thermal insulation element has a thermal conductivity of less than or equal to about 2 W / (m·K), preferably less than or equal to about 0.5 W / (m·K).

[0055] According to one or more examples, the thermal insulation element is in particular a solid, which is preferably selected from the following: aerogels, porous ceramics, refractory cements, cement-ceramic composites, epoxy resins, phenolic resins, ceramic-ceramic composites, and technical corks.

[0056] According to one or more examples, the sensor further includes a heat exchanger in contact with a part of the calorimetric element, and the heat exchanger is configured to cool the calorimetric element.

[0057] In such a configuration, a part of the heat flux stored in the calorimetric element is dissipated by the heat exchanger, so that the calorimetric element can be exposed to a high heat flux, for example, a high heat flux of higher than or equal to several W / m 2 without reaching the melting temperature of the calorimetric element. Therefore, this allows the measurement of high heat fluxes without any time limit and without ever reaching the melting point of the material forming the calorimetric element.

[0058] According to one or more examples, the first part is at least partially covered with a reflective film that has an emissivity of less than or equal to about 0.1, preferably less than or equal to about 0.05, in a wavelength range between about 0.5 micrometers and about 10 micrometers.

[0059] According to one or more examples, the first part is at least partially covered with a reflective film that has an emissivity of less than or equal to about 0.1, preferably less than or equal to about 0.05, in a wavelength range between about 0.8 micrometers and about 3 micrometers.

[0060] According to one or more examples, the front face is at least partially covered with an absorption film that has an emissivity of higher than or equal to 0.9, preferably higher than or equal to about 0.95, in a wavelength range between about 0.5 micrometers and about 10 micrometers.

[0061] According to one or more examples, the front face is at least partially covered with an absorption film that has an emissivity of higher than or equal to 0.9, preferably higher than or equal to about 0.95, in a wavelength range between about 0.8 micrometers and about 3 micrometers.

[0062] According to one or more examples, the sensor further includes a window section that is configured to be arranged between the heat flux to be measured and the calorimetric element, but the window section is not in mechanical contact with the absorption film.

[0063] In such a configuration, the convective contribution of the heat flux to be measured is neutralized by the window section, so that the sensor can be used to measure only the radiative contribution of the heat flux.

[0064] According to one or more examples, the porthole portion has a transmittance higher than about 0.9, preferably 0.95, in a wavelength range based on between about 0.8 and about 3 microns.

[0065] According to one or more preferred examples, the porthole portion has a transmittance higher than about 0.9, preferably 0.95, in a wavelength range based on between about 0.5 and about 10 microns.

[0066] This allows for good transmission of the radiant flux from the external environment of the sensor towards the front face of the calorimetric element.

[0067] According to a second aspect, the present specification relates to an inertial heat flux measurement system, the inertial heat flux measurement system comprising:

[0068] - a sensor according to the first aspect;

[0069] - means for measuring the potential difference between two wire-based conduction elements when a first portion of the calorimetric element is exposed to the heat flux to be measured; and

[0070] - a processing unit configured to calculate the value of the heat flux based on the potential difference.

[0071] According to a third aspect, the present specification relates to a method for measuring heat flux by means of a system according to the second aspect:

[0072] - exposing a first portion of the calorimetric element of the sensor to the heat flux to be measured;

[0073] - measuring the potential difference between two wire-based conduction elements of the sensor using the potential difference measuring means; and

[0074] - calculating the value of the heat flux using the processing unit based on the potential difference. Description of the Drawings

[0075] Other advantages and features of the present invention will become apparent after reading the description shown in the following drawings:

[0076] [Figure 1] shows a diagram illustrating a heat flux measurement system including an inertial fluxmeter according to the prior art, which has been described in Figure 1;

[0077] Figure 2 shows a diagram illustrating an example of a heat flux measurement system including a sensor according to the present specification;

[0078] Figure 3 shows a diagram illustrating the operation of a sensor for an inertial heat flux measurement system according to the present specification; ​​

[0079] Figure 4 The figure showing the principle of measuring the average temperature of the calorimetric element in the sensor according to the present specification is shown by an equivalent diagram.

[0080] Figure 5A The figure showing a thermocouple according to the prior art and a part of the sensor according to the present specification is shown;

[0081] Figure 5B The graph showing the variation of the potential difference generated by the thermocouple with opposite Seebeck coefficients with temperature is shown;

[0082] Figure 6 The figure showing the inertial heat flux measurement system including a second example of the sensor according to the present specification is shown;

[0083] Figure 7 The figure showing the inertial heat flux measurement system including a third example of the sensor according to the present specification is shown;

[0084] Figure 8 The figure showing the inertial heat flux measurement system including a fourth example of the sensor according to the present specification, the sensor being particularly provided with a heat exchanger is shown. DETAILED DESCRIPTION

[0085] In the figures, for better visibility, the elements are not always drawn to scale.

[0086] Figure 2 A cross-sectional view of an example of an inertial heat flux measurement system is shown, the inertial heat flux measurement system including: a sensor 200 exposed to a heat flux, a device 240 for measuring a potential difference (also referred to as a measurement unit 240), and a processing unit 250.

[0087] In particular, the sensor 200 includes: a calorimetric element 201 having a front face 203 and a rear face 206 opposite to the front face 203, a thermal insulation element 202, and two wire base elements 207a, 207b passing through the calorimetric element 201 from the rear face 206. The sensor 200 is electrically connected to the measuring device 240 through the wire base elements 207a, 207b, and the sensor 200 may be electrically connected to the measuring device 240 via two connection elements 208a, 208b respectively electrically connected to the wire base elements 207a, 207b.

[0088] As will be described in more detail below, when the sensor 200 is subjected to a heat flux, the sensor 200 generates a potential difference through the Seebeck effect, which is measured by the potential difference measuring device 240. Then the potential difference is transmitted to the processing unit 250, which calculates the heat flux value.​​​​​​

[0089] Typically, the potential difference measuring device 240 may include a voltmeter and a unit for shaping the electrical signal measured by the voltmeter. The shaping unit includes, for example, a voltage amplifier.

[0090] In the present specification, the processing unit 250 may be a computer that includes a memory for storing instructions and a processor capable of executing the instructions stored in the memory, particularly for controlling the calculation of the heat flux value based on the potential difference received from the potential difference measuring device 240. The processing unit 250 may also be in the form of an integrated circuit including electronic components adapted to implement the functions described in the present specification. The processing unit 250 may also be implemented by one or more physically distinct devices.

[0091] In the heat flux sensor 200, the calorimetric element 201 is partially wrapped by the insulating element 202. Thus, the insulating element 202 allows for defining: an uncovered first portion of the calorimetric element 201, which is configured to be exposed to the heat flux to be measured and forms part of the front face 203; and a second portion of the calorimetric element 201 that is thermally insulated from the heat flux. The uncovered first portion of the calorimetric element 201 is substantially planar.

[0092] In Figure 2 In the example shown, the first portion of the calorimetric element configured to be exposed to the heat flux coincides with the front face 203. In other examples not shown, the front face 203 includes the first portion of the calorimetric element but does not coincide with the first portion.

[0093] In this example, the calorimetric element 201 includes a rotation axis 209 and the calorimetric element 201 is a straight cylinder with one base being the front face 203 and the other base being the rear face 206.

[0094] The sensor 200 also includes two wire-based conduction elements 207a, 207b, which are made of two different thermoelectric materials and partially pass through the calorimetric element 201 along the length direction of the calorimetric element 201 from the rear face 206. As will be explained in detail below, the applicant has demonstrated that the two wire-based conduction elements 207a, 207b allow for measuring the average temperature of the calorimetric element 201.

[0095] In the inertial heat flux measurement system according to the present specification, the applicant has demonstrated that the heat flux Φ to be measured can be obtained from the temperature change obtained based on the change in the potential difference measured between the two wire-based conduction elements 207a, 207b by the formula in the following paragraph.

[0096] [Mathematical formula 1]

[0097]

[0098] In the formula, m is the mass of the calorimetric element 201 of the sensor, S is the cross-section exposed to the first part of the heat flux, Cp is the isobaric heat capacity of the constituent material of the calorimetric element 201, T is the temperature of the calorimetric element 201, and t is the time, i.e., the time point at which the temperature measurement is made. Usually, the user obtains a series of temperature measurement values (T1, T2... Tn) at regular time intervals (t, t+Δt... t+n.Δt). Then, the discrete derivative of this time series is calculated through the equation on the front face to obtain the experimental value of the heat flux.

[0099] The improvements (evolution) made by the applicant to the technology of the inertial heat flux measurement system are mainly based on the possibility of performing full-temperature measurements in the calorimetric element 201, which was previously only possible on the rear face 206. Secondly, this improvement is based on the use of a thermocouple formed by two elements (207a, 207b) that are not connected but electrically connected through the calorimetric element 201, instead of the thermocouple 107 (as shown in Figure 1), where the two elements (107a, 107b) of the thermocouple 107 are connected at a single thermal junction 104 fixed at a point on the calorimetric element 101. The combination of these two aspects allows for a significant improvement in the accuracy of the temperature measurement of the calorimetric element, and thus in the heat flux value derived therefrom.

[0100] In the sensor according to the present specification, two wire-based conduction elements 207a, 207b are arranged substantially parallel to the rotational axis 209 of the calorimetric element 201. The two wire-based conduction elements 207a, 207b partially pass through the calorimetric element 201 from the rear face 206 in a direction substantially orthogonal to the front face 203, which is also the direction defining the length of the calorimetric element 201. In a preferred example, the two wire-based conduction elements 207a, 207b pass through the calorimetric element 201 by at least about 90% of the length of the calorimetric element 201.

[0101] In Figure 2 the example, the two wire-based elements 207a, 207b are arranged parallel to each other and symmetric about the rotational axis 209. The two wire-based elements 207a, 207b extend through two orifices 205a, 205b from the rear face 206 of the calorimetric element 201, respectively.

[0102] According to some examples, the two wire-based elements 207a, 207b are connected to the potential difference measuring device 240 through connection elements 208a, 208b. The connection elements 208a, 208b can be parts of the extensions of the two wire-based elements 207a, 207b to connect to the device 240 for measuring the potential difference.

[0103] As Figure 2As shown in the example of , the connecting elements 208a, 208b can pass through the insulating element 202 to connect the two wire base elements 207a, 207b to the potential difference measuring device 240.

[0104] Although Figure 2 a single pair of wire base elements 207a, 207b is shown in , some examples of the sensors according to this specification may include multiple pairs of wire base elements 207a, 207b inserted into the calorimetric element.

[0105] In some embodiments, the wire base elements 207a, 207b are single strands with a diameter less than about 1 mm, for example, a diameter equal to about 0.5 mm.

[0106] According to some examples, the wire base elements 207a, 207b are inserted into the calorimetric element 201 through microholes formed along the length of the calorimetric element 201. For example, if the wire base elements 207a, 207b are single strands of wire with a diameter of about 0.5 mm, the diameter of the microholes can be 0.55 mm, thus providing a small gap to enable the insertion of the wire base elements 207a, 207b into the calorimetric element 201.

[0107] For example, the microholes can be made by electrical discharge machining. These holes can be diametrically opposite with respect to the rotational axis 209 of the calorimetric element 201. For example, the microholes can be arranged on a circle concentric with the diameter of the calorimetric element 201, with a diameter equal to about 1.5 mm and longitudinally passing through the calorimetric element 201. Therefore, these holes are parallel to each other throughout their path.

[0108] The two wire base elements 207a, 207b are formed of two different thermoelectric materials. In this way, the applicant has demonstrated that the arrangement of the two wire base elements 207a, 207b passing through the calorimetric element 201 then forms a thermocouple for measuring the temperature of the calorimetric element. The two thermoelectric materials used in the sensor 200 can be different, but are preferably selected from the material pairs commonly used for K-type, J-type, E-type, or N-type thermocouples.

[0109] Thus, in the case of a K-type thermocouple, one of the materials of the two wire base elements 207a, 207b is chromel, and the other material is alumel. The two selected materials can also be the material pairs commonly used to form other types of thermocouples (such as B-type, R-type, S-type, T-type, G-type, C-type, D-type thermocouples).

[0110] Preferably, the insulating element 202 is ceramic. In particular, it can be prepared in liquid form and injected between the calorimetric element and its support ([ Figure 2A porous insulating ceramic based on alumina (Al2O3) (not shown in the figure). During the fabrication of such a ceramic, special attention should be paid to avoid trapped air that may form cavities within the insulating element 202. According to some examples, if necessary, the process of manufacturing the ceramic may include degassing under a vacuum hood before curing. Once the ceramic has hardened, fresh ceramic can be added to compensate for any shrinkage at the front face of the sensor. Once cured, the ceramic can be polished to fine grains (e.g., 240-grit grains) to perfectly align with the front face 203 of the calorimetric element 201.

[0111] According to one or more examples, the insulating element 202 is assembled with the calorimetric element 201 by in-situ casting in a support including the calorimetric element 201, by pressure injection, by machining and fitting into the support, by in-situ sintering, by in-situ manufacturing via an additive method, or by any other process known to those skilled in the art.

[0112] The calorimetric element 201 includes a material whose thermal properties (e.g., thermal conductivity and heat capacity at constant pressure) are known and can be represented by an equation depending on the temperature of the calorimetric element 201. According to a preferred example, the calorimetric element 201 is made of copper.

[0113] In Figure 2 the example shown, the calorimetric element 201 is a straight cylinder, which is characterized by a rotational axis 209. Thus, in Figure 2 a cross-sectional view, the cross-section of the calorimetric element 201 appears rectangular, and the front face 203 is shown by a straight edge as it includes a planar surface.

[0114] According to other examples, the calorimetric element 201 can be a frustum of a cone with the bottom as the rear face 206, the side opposite the bottom of the frustum as the front face 203, or a cylinder with a shoulder at the front face such that the surface area of the front face 203 is less than the average cross-section of the cylinder. These two alternative geometries allow for an extended measurement time without changing the material forming the calorimetric element 201. Figure 3 A schematic diagram of a sensor for an inertial heat flux measurement system according to this specification is shown, which sensor includes a calorimetric element 201 penetrated by two elements 207a, 207b of a thermocouple.

[0115] Due to the through measurement of the thermocouple and the unconnected elements 207a, 207b, the potential difference caused by the Seebeck effect occurring between the elements 207a, 207b corresponds to the average temperature Tm of the calorimetric element 201 over the length it traverses. Thus, this arrangement is like multiple thermocouples (107a, 107b) with a single junction 104 distributed along the length of the calorimetric element 201, thereby producing an accurate average value of the temperature of the calorimetric element 201 over that length. By the so-called accurate average value, it should be understood that the obtained temperature is the continuous average value of the temperature over the entire length of the calorimetric element 201, rather than a discrete average value, as Figure 3 schematically shown for illustration.

[0116] Therefore, the sensor for the heat flux system according to this specification allows the measurement of the temperature of the calorimetric element 201 at multiple points distributed along the length of the calorimetric element 201, which enables, for example, taking into account the temperature gradient within the calorimetric element 201. For example, such a gradient is due to the high heat flux on the front face 203 of the calorimetric element 201 resulting in non-uniform temperature within the calorimetric element 201.

[0117] In contrast, the main drawback of the fluxmeter according to the prior art is that it measures the temperature of the calorimetric element at only a single point, and thus cannot take into account the possible temperature gradient in the calorimetric element, which reduces the accuracy of such a fluxmeter.

[0118] Size setting of the calorimetric element

[0119] In a preferred embodiment, the size of the calorimetric element 201 is set to meet at least two generally opposing criteria, as described below.

[0120] Assumption of thermally thin medium

[0121] On the one hand, the size of the calorimetric element 201 can be set such that its temperature is almost uniform when it is subjected to a heat flux, which allows it to be considered "thermally thin", and thus enables the use of thermodynamic theory to calculate the value of the heat flux based on the potential difference caused by the temperature rise of the calorimetric element 201. In fact, this first criterion gives the maximum length of the calorimetric element beyond which the calorimetric element can no longer be considered thermally thin. The applicant has demonstrated that a dimensionless number including the sensor parameters and the experimental conditions of the heat flux measurement can be used to determine the said maximum length of the calorimetric element 201. In particular, the applicant has demonstrated that when the dimensionless number to be considered is less than about 0.1, then the calorimetric element 201 can be considered a thermally thin medium.

[0122] The dimensionless number to be considered depends on the type of heat flux to be measured by the sensor.

[0123] In the case where the heat flux to be measured is substantially a convective flow, the dimensionless number to be considered is the Biot number.

[0124] The Biot number is defined by the formula in the following paragraph.

[0125] [Mathematical formula 2]

[0126]

[0127] In the formula for the front face, h is the convective coefficient under the measurement conditions, H is the length of the calorimetric element 201, and X is the thermal conductivity of the material forming the calorimetric element 201.

[0128] In the case where the heat flux to be measured is substantially a radiative flux, the dimensionless number to be considered is the radiation number N R .

[0129] The radiation number is defined by the formula in the following paragraph.

[0130] [Mathematical formula 3]

[0131]

[0132] In the formula for the front face, G is the Stefan - Boltzmann constant, T gas is the temperature of the external environment of the sensor, H is the length of the calorimetric element, X is the thermal conductivity of the material forming the calorimetric element 201, and T ini is the initial temperature (before measurement) of the calorimetric element 201.

[0133] In the case where the heat flux is a flux that includes a radiative contribution and a convective contribution (i.e., the so - called "total flux"), the dimensionless number to be considered is the sum of the Biot number and the radiation number.

[0134] Material's resistance to melting

[0135] On the other hand, in order to prevent any irreversible degradation of the calorimetric element 201, it can be required that the temperature reached at the end of the heat flux measurement does not exceed the melting temperature of the calorimetric element 201. In fact, this second criterion gives the minimum length of the calorimetric element 201 of a given material, below which the calorimetric element may melt during the heat flux measurement.

[0136] The applicant has demonstrated that the minimum length of the calorimetric element can be determined by an energy balance involving the physical parameters of the calorimetric element and the parameters of the heat flux measurement, said parameters including in particular:

[0137] - the constant - pressure heat capacity of the calorimetric element and its dependence on temperature, i.e., the function C p (T);

[0138] - The mass (m) of the calorimetric element, which depends in particular on the density (ρ) of the calorimetric element and the volume of the calorimetric element;

[0139] - The initial temperature T of the calorimetric element ini , i.e., before measurement, for example, the conventional ambient temperature is 20 °C;

[0140] - The acceptable final temperature T of the calorimetric element end , i.e., a temperature strictly lower than the melting temperature of the calorimetric element. In particular, a safety thermal margin can be defined, for example, about 10%, to ensure that the final temperature is lower than about 90% of the melting temperature of the calorimetric element, thereby ensuring the robustness of the sensor.

[0141] - The average maximum flux φ to be measured by the sensor average , which includes, for example, fluxes in the range of 8 MW / m 2 ; and

[0142] - The maximum measurement duration, Δt, i.e., the maximum time during which the sensor will be exposed to the heat flux to measure the heat flux.

[0143] The applicant has demonstrated that the thermal balance gives the minimum length of the calorimetric element, particularly in the case of a calorimetric element in the form of a straight cylinder, and the minimum length of the calorimetric element is expressed by the formula in the following paragraph.

[0144] [Mathematical formula 4]

[0145]

[0146] In the formula on the front face, C p,av is the integrated average of the heat capacity at constant pressure of the calorimetric element, with the lower limit being the initial temperature T ini of the calorimetric element and the upper limit being the final temperature T end of the calorimetric element. The applicant has observed that other types of averages (e.g., the semi-sum of the heat capacities at the final temperature and the initial temperature) can be used, but the integrated average is particularly advantageous due to its simple calculation.

[0147] For example, when the dimensions of the sensor are set to measure a substantially convective heat flux equal to about 8 MW / m 2 originating from a gas source at 2,500 °C with a duration of at least about 5 seconds and an initial ambient temperature of about 20 °, and the calorimetric element is a straight cylinder made of copper (pure copper of grade CuC2) with a density of about 8,920 kg / m 3 , it is acceptable for the length of the cylinder to be between about 10.9 mm and about 11.5 mm, so that on the one hand, the Biot number is substantially less than or equal to 0.1, and on the other hand, the final temperature reached does not exceed the melting temperature of the calorimetric element 201, with a safety margin of 10%.

[0148] Size of the front surface

[0149] In equation [Math. 4], the surface of the first portion not covered by the insulating element (which in some examples may coincide with the front face 203 of the calorimetric element) does not appear. Therefore, in the case of a calorimetric element 201 in the form of a right circular cylinder, the size setting of the surface of the front face 203 of the calorimetric element 201 can in principle be selected arbitrarily. However, some constraints may be considered when selecting this value, including, for example:

[0150] - the space requirement of the sensor with respect to the environment in which the sensor is specifically studied. In particular, the surface of the front face 203 can be reduced in order to facilitate the implantation of the sensor;

[0151] - Manufacturing and handling constraints. In particular, if the surface of the front face 203 is too small, this may make the sensor more difficult to manufacture (in particular due to being less easy to grip);

[0152] - Heat loss minimization constraint. In particular, the total outer surface of the calorimetric element 201 causes heat loss, which can generally be reduced if the surface of the front face 203 is reduced. For example, for a right circular cylinder, the larger the diameter of the cylinder, the larger the surface of rotation of the cylinder, and the greater the lateral heat loss, which is disadvantageous for the accuracy of the measurement because such losses are difficult to measure.

[0153] Furthermore, the size of the surface of the front face 203 can also be set to meet specific experimental conditions, such as increasing the measurement duration of the heat flux without any desire to change the material of the calorimetric element 201. Therefore, according to some examples, the calorimetric element 201 can include a shoulder, the end of which forms the front face 203, so as to reduce the surface area of ​​the front face 203 relative to the size of the calorimetric element 201, so as to avoid the calorimetric element 201 from melting too quickly. For example, in the case of a calorimetric element 201 of a right cylindrical shape, the surface of the front face 203 can be reduced by a factor of 2 relative to the surface of the cylinder by the shoulder, so as to be able to extend the measurement duration of the heat flux by a factor of 4, without affecting the state of the thermally thin medium.

[0154] Figure 4 Shown by including such Figure 3 The equivalent diagram of the thermocouple shows the principle of through-measurement based on the thermoelectric analogy between the thermal circuit (Th) and the electrical circuit (E1).

[0155] exist Figure 4 In the embodiment, the longitudinal average temperature of the linear calorimetric element 50 is measured by three thermocouples 10, 20, 30, each thermocouple comprising two elements (12, 13, 22, 23, 32, 33). The applicant has demonstrated that if the thermocouples are asFigure 4 With the connections shown, the potential difference measured between conductor A and conductor B at the end 40 allows the mean longitudinal temperature Tm to be deduced, which corresponds to the mean of the temperatures (T1, T2, T3) measured respectively with the thermocouples 10, 20, 30. This can be demonstrated in particular by the thermoelectric analogy between the thermal circuit Th and the equivalent electrical circuit E1. Thus, by measuring the temperature at several levels in the calorimetric element, the direct measurement allows the mean longitudinal temperature Tm of the calorimetric element to be measured.

[0156] Figure 5A There is shown a thermocouple 107 with a single thermal junction 104 according to the prior art and a thermocouple 207 formed by the wire base elements (207a, 207b) of the sensor according to the present specification.

[0157] The applicant has demonstrated that the temperature of the calorimetric element 201 can be measured by means of a thermocouple 207 with a specific arrangement, in which the two elements 207a, 207b are not directly mechanically connected by a single thermal junction but are connected via the calorimetric element 201. Thus, this specific arrangement includes two thermal junctions 64, 65, since a junction exists between the calorimetric element 201 and each of the two elements 207a, 207b of the thermocouple 207.

[0158] In order to be able to measure the temperature of the calorimetric element 201 by means of such an arrangement, it is useful for the calorimetric element 201 to conduct sufficient electric power. To this end, the applicant has observed that it is satisfactory for the calorimetric element with a conductivity higher than or equal to about 10 5 S / m, preferably 10 7 S / m to be able to measure the temperature of the calorimetric element 201.

[0159] The applicant has demonstrated that this arrangement is equivalent to the arrangement commonly used in the prior art, in which the two elements 107a, 107b are directly connected at a single junction 104, which is placed in point contact with the point of the calorimetric element 201 where the temperature is measured. This equivalence is due to the compensation of the contribution of the calorimetric element to the Seebeck effect at the two junctions 64, 65. In particular, since the Seebeck coefficients of the two junctions 64, 65 have opposite signs.

[0160] Figure 5B There is shown a graph containing experimental data, which graph shows an example of the evolution of the potential difference appearing at each of the two junctions 64, 65 due to the Seebeck effect as the temperature of the calorimetric element 201 rises. This data corresponds to the case where the calorimetric element 201 is made of copper and the two elements 207a, 207b are made of chromel and F - alumel respectively. In particular, Figure 5B it is shown that the potential differences appearing at each of the junctions 64, 65 are opposite and have substantially equal absolute values, such that they almost completely compensate each other.

[0161] Figure 6 Shows an example of a sensor for an inertial heat flux measurement system according to this specification. In particular, as shown in this example, two wire-based elements 207a, 207b can pass through the entire length of the calorimetric element 201 so as to be flush with the front face 203 of the calorimetric element 201. In addition, as Figure 6 shown in the example of the sensor, each of the two wire-based elements 207a, 207b can be embedded in an adhesive material 211 to ensure mechanical contact between the two wire-based elements 207a, 207b and the calorimetric element 201.

[0162] Preferably, the adhesive material 211 has an electrical conductivity greater than or equal to about 10 6 S / m and / or a thermal conductivity greater than or equal to about 200 W / (m K) to ensure electrical contact and thermal contact between the wire-based elements 207a, 207b and the calorimetric element 201.

[0163] According to some examples, the wire-based elements 207a, 207b are implanted into the calorimetric element 201 by soldering such that the function of the adhesive material 211 is ensured by a soldering paste (e.g., a paste containing silver).

[0164] Before soldering, the soldering paste is usually injected into the microholes using a syringe with a needle. The presence of excess paste at the channel outlet is checked to ensure that the microholes are saturated with the paste. The wire-based elements 207a, 207b (e.g., one made of nichrome alloy and the other made of alnico alloy) are inserted into the microholes from the rear face 206 of the calorimetric element 201 until slightly protruding from the front face 203. Subsequently, the soldering operation is performed by heating the calorimetric element to red (e.g., using an "oxybutane" type blowtorch). During heating, the silver paste migrates within the microholes by capillary action and wets both the calorimetric element 201 and the wire-based elements 207a, 207b substantially uniformly. After cooling, the front face of the calorimetric element (exposed to the flux) is usually polished with fine particles (e.g., P240 type particles) to obtain a very good reflectivity and also the ends of the wire-based elements 207a, 207b that may protrude from the surface of the front face 203 are cut off.

[0165] Figure 7 The example shown indicates that the wire-based elements may be parallel to each other rather than straight in some cases. In particular, the two wire-based elements 207a, 207b can describe two mathematically conformal or substantially conformal helices in the manner of two deoxyribonucleic acid (DNA) strands.

[0166] In Figure 8In the example shown, the sensor for the inertial heat flux measurement system includes a heat exchanger 210 that is arranged to contact at least a portion of the rear face 206 of the calorimetric element 201. The heat exchanger is configured to discharge thermal energy from the calorimetric element 201 in a controlled and predetermined manner. Thus, the heat flux measurement can be extended for a long duration without the risk of the temperature in the calorimetric element 201 exceeding the melting temperature.

[0167] In particular, according to some examples, the heat exchanger 210 is a liquid exchanger, and the inlet temperature and mass flow rate of the liquid exchanger are known and controlled, or measured during the operation of the sensor. The applicant has demonstrated that by measuring the outlet temperature of the exchanger, the incident heat flux can be determined by performing an energy balance on the calorimetric element 201. In this case, as Figure 8 shown, generally no thermal insulation element is applied on the rear face 206 of the calorimetric element 201. On the contrary, the rear face 206 should effectively discharge the heat flux.

[0168] In some examples, including the examples described previously, the front face 203 can be covered with a coating configured to perform different functions.

[0169] In particular, the coating can be an absorption film configured to absorb the radiation contribution of the incident flux, thereby allowing to ensure the measurement of the total flux including the sum of the radiation contribution and the convection contribution of the heat flux. For example, such an absorption film can be a high-temperature "matte black" colored paint with an average infrared absorptivity of 0.95 and an acceptable maximum temperature of 700 °C. The latter is usually manually deposited on the front face 203 of the calorimetric element 201 by a round-tipped precision brush. On the other hand, the outer peripheral surface of the insulator 202 should not be painted.

[0170] The coating can also be a reflective film configured to reflect the radiation contribution of the incident flux, thereby facilitating the measurement of the convection contribution of the heat flux. For example, such a reflective film can be configured to give the front face 203 an emissivity lower than about 0.1, preferably lower than about 0.05. According to some examples not shown in the figures, the sensor can also include a porthole configured to cancel the convection contribution of the heat flux but transmit the radiation contribution of the heat flux. In fact, the porthole forms a mechanical barrier between the heat flux outside the sensor and the front face 203 of the calorimetric element 201 to prevent the movement of materials associated with the heat flux at the front face 203. When the sensor according to the present specification is provided with such a porthole, only the radiation contribution of the heat flux can be measured because only this contribution reaches the front face 203 while the convection contribution is canceled by the porthole.

[0171] For example, such a porthole typically has a transmittance of higher than about 90% for electromagnetic radiation with wavelengths between about 0.7 micrometers and about 5 micrometers. Although a porthole with a transmittance higher than 90% is preferred, a porthole with a transmittance higher than 70% can also be used. In this case, all that is required is to measure the transmittance in a laboratory beforehand so that the heat flux measurements obtained in the presence of the porthole can be corrected subsequently.

[0172] The porthole is arranged between the heat flux and the front face 203 but does not contact the front face 203 to avoid transferring heat energy due to conduction from the porthole towards the front face 203. For example, the porthole comprises sapphire. The shape of the porthole can be a circular plate with a thickness of about 0.5 mm to 1.5 mm.

[0173] Generally, such a porthole advantageously covers the absorption film as described above in order to improve the measurement of the contribution of the heat flux radiation by the sensor.

[0174] Although described through some embodiments, the methods and sensors for an inertial heat flux measurement system according to this specification include different variations, modifications, and improvements that will be apparent to those skilled in the art. It should be understood that these different variations, modifications, and improvements fall within the scope of the present invention as defined by the appended claims.

[0175] References

[0176] [Reference 1] W002 / 18890A2, HEAT SENSING DEVICE FOR THERMAL AND SKIN BURNEVALUATION, Hamouda et al., published on March 7th, 2002.

[0177] [Reference 2] JAYAPRAKASH, C., KUMAR, P. Pratheesh, SRINIVAS, I, et alDevelopment of copper slug calorimeter for heat flux measurements. In: ProcAsian Congr. Gas Turbines (ACGT). 2016. p. 1 - 6. [Reference 3] FR 2 706 610.

Claims

1. A sensor (200) for an inertial heat flux measurement system, the sensor comprising: - Solid-type calorimetric element (201), the calorimetric element having a given length, the calorimetric element including a front face (203) and a rear face (206) opposite the front face (203), the calorimetric element (201) having a thermal conductivity higher than or equal to about 100 W / (m.K) and an electrical conductivity higher than or equal to about 10 5 S / m; - A thermal insulation element (202) that partially covers the calorimetric element (201) to define a first portion not covered by the calorimetric element and a second portion covered by the calorimetric element (201), the first portion being substantially planar and configured to be exposed to the heat flux to be measured and form part of the front face (203), and the second portion being thermally insulated from the heat flux; And - Two wire-based conduction elements (207a, 207b) that at least partially pass through the calorimetric element (201) from the rear face (206), and the two wire-based conduction elements are arranged not to mechanically contact each other, but the two wire-based conduction elements are in electrical contact via the calorimetric element (201) over at least a portion of the length of the calorimetric element (201), and the two wire-based conduction elements are made of two different thermoelectric materials.

2. The sensor (200) according to claim 1, wherein, The two wire-based conduction elements (207a, 207b) pass through the calorimetric element (201) over at least about 30% of the length of the calorimetric element.

3. The sensor (200) according to claim 1 or 2, wherein, The two wire-based conduction elements (207a, 207b) pass through the calorimetric element (201) in a manner that penetrates the calorimetric element (201) such that the two wire-based conduction elements (207a, 207b) are flush with the first portion.

4. The sensor (200) according to claim 1 or 2, wherein, The two wire-based conduction elements (207a, 207b) are arranged to be substantially parallel.

5. The sensor (200) according to claim 1 or 2, wherein, The calorimetric element (201) has a cylindrical shape, a conical shape, or a cylindrical-conical shape, and the calorimetric element (201) includes a rotational axis (209) that is substantially perpendicular to the first portion.

6. The sensor (200) according to claim 5, wherein, The two wire-based conduction elements (207a, 207b) are arranged to be substantially parallel to the rotational axis (209), and the two wire-based conduction elements (207a, 207b) are symmetric about the rotational axis (209).

7. The sensor (200) according to claim 1 or 2, wherein, The calorimetric element (201) includes a material having the following properties: - A constant pressure heat capacity of at least about 120 J / (kg.K) at 25°C; and / or - A melting temperature of at least about 500°C; and / or - A density of higher than or equal to about 2500 kg / m 3 .

8. The sensor (200) according to claim 1 or 2, wherein, The calorimetric element (201) includes graphite, a metal, or a metal alloy.

9. The sensor (200) according to claim 1 or 2, wherein, The two different thermoelectric materials are a pair of materials selected from the following: chromel / constantan, iron / constantan, chromel / alumel, nicrosil / nisil, nickel-molybdenum / nickel-cobalt, platinum-rhodium / platinum, tungsten-rhenium / tungsten.

10. The sensor (200) according to claim 1 or 2, the sensor (200) further comprising an adhesive material (211) that encapsulates each of the two wire-based conduction elements (207a, 207b) to ensure mechanical contact between each of the two wire-based conduction elements (207a, 207b) and the calorimetric element (201).

11. The sensor (200) according to claim 10, wherein, The bonding material (211) includes at least one material selected from the following materials: silver, gold, copper-phosphorus alloy, copper-silver alloy, copper-zinc alloy.

12. The sensor (200) according to claim 1 or 2, wherein the sensor (200) further includes a heat exchanger (210) in contact with a part of the calorimetric element (201), and the heat exchanger (210) is configured to cool the calorimetric element (201).

13. The sensor (200) according to claim 1 or 2, wherein, The first part is at least partially covered with a reflective film, and the emissivity of the reflective film in the wavelength range between about 0.5 micrometers and about 10 micrometers is less than or equal to about 0.

1.

14. The sensor (200) according to claim 1 or 2, wherein, The first part is at least partially covered with an absorption film, and the emissivity of the absorption film in the wavelength range between about 0.5 micrometers and about 10 micrometers is greater than or equal to about 0.

9.

15. The sensor according to claim 14, wherein the sensor further includes a porthole portion configured to be disposed between the heat flux to be measured and the calorimetric element (201), but the porthole portion is not in mechanical contact with the absorption film.

16. An inertial heat flux measurement system, the inertial heat flux measurement system comprising: - The sensor (200) according to any one of the preceding claims; - A potential difference measurement device (240) for measuring the potential difference between the two wire-based conduction elements (207a, 207b) when the first part of the calorimetric element is exposed to the heat flux to be measured; and - A processing unit (250) configured to calculate the value of the heat flux according to the potential difference.

17. A method for measuring heat flux by the system according to claim 16, the method comprising: - Exposing the first part of the calorimetric element of the sensor (200) to the heat flux to be measured; - Measuring the potential difference between the two wire-based conduction elements (207a, 207b) of the sensor (200) by using a potential difference measurement device (240); and - Calculating the value of the heat flux according to the potential difference by using the processing unit (250).

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