A method and system for measuring the thermal conductivity of a liquid based on a piezoelectric film

Abstract

The application relates to a kind of liquid thermal conductivity coefficient measurement method and system based on piezoelectric film, wherein the method comprises the following steps: the measured liquid is placed between light target composite layer and film detector layer;Pulse laser is applied to the light target composite layer, and the actual pyroelectric signal generated when pulse laser passes through the light target composite layer and acts on the measured liquid and then is transmitted to the film detector layer is collected;A heat transfer simulation model of multilayer structure is established;The thermal conductivity coefficient of the measured liquid and the equivalent thickness of the liquid are set as unknown parameters, the unknown parameters of the model are adjusted, the instantaneous response of the temperature in the polarized film under the action of thermal pulse is calculated, the simulation pyroelectric signal is calculated, and the actual and simulation pyroelectric signals are compared and fitted, and the thermal conductivity coefficient of the liquid is determined according to the best fitting result.Compared with the prior art, the application has the advantages of accurate measurement result, less liquid consumption, short test process and the like.

Description

Technical Field

[0001] This invention relates to the field of thermal conductivity measurement technology, and in particular to a method and system for measuring the thermal conductivity of liquids based on piezoelectric thin films. Background Technology

[0002] With the three major development trends of high performance, miniaturization, and integration in the electronics industry, the power consumption of core electronic device chips is rapidly increasing, and the problem of heat accumulation is becoming increasingly serious. Traditional forced air cooling heat exchange methods can no longer provide effective heat dissipation to maintain stable operating temperatures of devices. Miniature high-intensity refrigeration systems using working fluids as cooling media have become one of the hot topics in high-tech research. Working fluids, as efficient energy transport media with high heat transfer performance, can effectively improve the heat transfer performance of thermal systems and meet the high-load heat transfer and cooling requirements of thermal systems. Accurate and reliable data on fluid thermal conductivity are of great significance for studying the heat transfer mechanism of fluids and developing working media such as nanofluids with high thermal conductivity and high heat transfer efficiency.

[0003] Several techniques for measuring the thermal conductivity of fluids have been proposed, among which the most representative are the transient hot-wire method (THW), the transient planar source method (TPS), and the 3ω method. In the transient hot-wire method, a metal wire is immersed in the liquid being measured, acting as both a heating element and a resistance thermometer. The thermal conductivity of the liquid can be calculated based on the resistance data. The advantages of the transient hot-wire method are short testing time, wide measurement range, and simple operation, but it has some problems in measuring conductive fluids. The transient planar source (TPS) technique is an improved THW technique that uses a hot-film disk sensor instead of a metal wire. TPS can simultaneously obtain multiple thermal parameters such as thermal conductivity, specific heat, and thermal diffusivity, but it is accompanied by a longer measurement cycle and convection interference. The 3ω method is a commonly used technique for measuring the thermal conductivity of nanoscale solids (such as nanotubes, nanowires, and nanofilms). The extended 3ω method can measure the thermal conductivity of fluids the size of a single droplet, but the measurement accuracy is low when the thermal conductivity of the fluid is low.

[0004] CN116297657A discloses a method and system for measuring the thermal conductivity of a high thermal conductivity trace liquid, comprising the following steps: placing the liquid to be tested between a metallized dielectric film and a metal layer; collecting the experimental thermal response current generated by the metal layer-liquid-dielectric film under laser pulse action; establishing a heat transfer simulation model of the metal layer-liquid-dielectric film; adjusting the thermal conductivity of the liquid to be tested in the simulation model and calculating the theoretical thermal response current; using an iterative algorithm to adjust the thermal conductivity of the liquid to be tested in the simulation model to achieve the best fit between the theoretical thermal response current and the experimental thermal response current, and using the thermal conductivity of the liquid to be tested in the simulation model at this time as the measurement result. This method requires applying an electric field to the dielectric film through an external circuit to determine the thermal conductivity of the high thermal conductivity liquid. During the measurement process, the dielectric film may be subject to interference from space charge injection and the safety hazard of breakdown under external voltage. The liquid to be tested is placed between a metal foil and a dielectric film. If a metal foil larger than tens of micrometers is used, the metal foil itself will absorb a large amount of energy, directly affecting subsequent signal measurements. If a metal foil only a few micrometers thick is chosen, and the metal is relatively soft, it may deform under the influence of liquid surface tension, which will lead to some uncertainty in the uniformity of the liquid thickness. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for measuring the thermal conductivity of liquids based on piezoelectric thin films, enabling accurate measurement of the thermal conductivity of various liquids, including basic fluids, nanofluids, high or low thermal conductivity liquids, insulating or non-insulating liquids.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for measuring the thermal conductivity of a liquid based on a piezoelectric thin film includes the following steps:

[0008] The liquid to be tested is placed between the optical target composite layer and the thin film detector layer. The optical target composite layer includes quartz glass and an opaque metal target layer, and the thin film detector layer includes a piezoelectric thin film and two metal electrode layers that are in contact with the upper and lower surfaces of the piezoelectric thin film, respectively.

[0009] A pulsed laser is applied to the optical target composite layer, and the actual pyroelectric signal generated by the pulsed laser passing through the optical target composite layer and acting on the liquid under test is collected and transmitted to the thin film detector layer.

[0010] A heat transfer simulation model of a multilayer structure is established, which is used to calculate the instantaneous temperature response of the polarized thin film under the action of a thermal pulse.

[0011] Using the thermal conductivity and equivalent thickness of the liquid under test as unknown parameters, the unknown parameters in the heat transfer simulation model are adjusted to calculate the instantaneous response of the temperature inside the polarized film under the action of a thermal pulse. Based on the polarization distribution of the polarized film and the calculated instantaneous temperature rise, the simulated pyroelectric signal is calculated using the pyroelectric calculation formula. The actual pyroelectric signal and the simulated pyroelectric signal are compared and fitted. If the fitting degree between the two meets the preset convergence condition, the thermal conductivity of the liquid in the heat transfer simulation model at this time is taken as the final measurement result to obtain the thermal conductivity of the liquid. Otherwise, this step is repeated.

[0012] The formula for calculating pyroelectricity is:

[0013]

[0014] Where I is the pyroelectric current, x is the spatial position of the piezoelectric film along the laser pulse direction, x5 and x6 are the spatial positions of the upper and lower surfaces of the piezoelectric film along the laser pulse direction, t is the heat conduction time, ΔT5 is the internal temperature change of the polarized film, P(x) is the polarization distribution of the polarized film, A and d are the heating area and the thickness of the polarized film, respectively, and x6-x5=d.

[0015] The heat transfer simulation model is as follows:

[0016] Heat conduction equation:

[0017]

[0018] Boundary conditions:

[0019]

[0020]

[0021]

[0022] T i (x, t) = T i+1 (x, t)(x = x) i+1 (i = 2, 3, 4, 5) (6)

[0023]

[0024] Initial conditions:

[0025] T i (x, t = 0) = T room (0≤x≤l i )(i=1, 2, 3, 4, 5, 6, 7) (8)

[0026] Where x represents the spatial position of the piezoelectric film along the laser pulse direction, and x = x1, x2, x3, x4, x5, x6, x7 correspond to the surface of the quartz glass receiving the pulsed laser, the surface of the quartz glass in contact with the opaque metal target layer, the surface of the opaque metal target layer in contact with the liquid being tested, the surface of the liquid being tested in contact with the first metal electrode layer, the surface of the first metal electrode layer in contact with the piezoelectric film, the surface of the piezoelectric film in contact with the second metal electrode layer, and the surface of the second metal electrode layer not in contact with the piezoelectric film, respectively. t represents the time of heat conduction, and layers i = 1, 2, 3, 4, 5, 6 represent the quartz glass, the opaque metal target layer, the liquid being tested, the first metal electrode layer in contact with the upper surface of the piezoelectric film, the piezoelectric film, and the second metal electrode layer in contact with the lower surface of the piezoelectric film, respectively. T i (x, t) represents the temperature distribution of the i-th layer, D i Let k represent the thermal diffusivity of the i-th layer. i Let f(t) represent the thermal conductivity of the i-th layer, f(t) be the absorption power density along the direction of the incident pulsed laser, and T be the thermal conductivity of the i-th layer. room The ambient temperature.

[0027] The solution to the temperature distribution is:

[0028]

[0029] Among them, the Green function G i，k (x, t|x′, τ) represents the effect of the unit pulse at x′ in interval i at time τ on x in interval i at time t.

[0030]

[0031] Where modulus N(β) m )for:

[0032]

[0033] X i (β m (x) and X j (β m Let x′ be the eigenfunction of equation (2-8) under the homogeneous problem. The eigenvalue β is the root of the eigenfunction, and there are infinitely many of them, i.e., β = β′. m (m = 1, 2, ...).

[0034] The specific steps for comparing and fitting the actual pyroelectric signal and the simulated pyroelectric signal are as follows:

[0035] The actual pyroelectric time-domain signal and the simulated pyroelectric time-domain signal are converted into frequency-domain signals respectively, and the real and imaginary parts of the signals are extracted respectively.

[0036] For each frequency point, the difference between the real and imaginary parts of the actual pyroelectric signal and the simulated pyroelectric signal is calculated and the absolute value is taken. The absolute values ​​of all differences are summed. When the sum is less than a preset threshold, it indicates that the fitting degree between the actual pyroelectric signal and the simulated pyroelectric signal meets the preset convergence condition.

[0037] A liquid thermal conductivity measurement system based on piezoelectric thin film, comprising:

[0038] A test stand is provided, on which a phototarget composite layer and a thin film detector layer are placed. The liquid to be tested is placed between the phototarget composite layer and the thin film detector layer. The phototarget composite layer includes quartz glass and an opaque metal target layer. The thin film detector layer includes a piezoelectric thin film and two metal electrode layers that are in contact with the upper and lower surfaces of the piezoelectric thin film, respectively.

[0039] The measuring device includes a laser unit and a data acquisition unit. The laser unit emits pulsed laser light and applies it to the optical target composite layer. The data acquisition unit acquires the actual pyroelectric signal generated by the pulsed laser light acting on the liquid under test through the optical target composite layer and then being transmitted to the thin film detector layer.

[0040] The simulation and calculation unit establishes a heat transfer simulation model of a multilayer structure, which is used to calculate the instantaneous temperature response of the polarized thin film under the action of a thermal pulse.

[0041] The fitting unit uses the thermal conductivity and equivalent thickness of the liquid under test as unknown parameters to adjust the unknown parameters in the heat transfer simulation model, calculates the instantaneous response of the temperature inside the polarized film under the action of a thermal pulse, and calculates the simulated pyroelectric signal based on the polarization distribution of the polarized film and the calculated instantaneous temperature rise and polarization distribution of the polarized film using the pyroelectric calculation formula, and compares the fitted actual pyroelectric signal with the simulated pyroelectric signal.

[0042] The judgment unit determines whether the fitting degree between the actual pyroelectric signal and the simulated pyroelectric signal meets the preset convergence condition. If the condition is met, the thermal conductivity of the liquid in the heat transfer simulation model at this time is taken as the final measurement result to obtain the thermal conductivity of the liquid. Otherwise, the fitting unit is called again to perform fitting.

[0043] The formula for calculating pyroelectricity is:

[0044]

[0045] Where I is the pyroelectric current, x is the spatial position of the piezoelectric film along the laser pulse direction, x5 and x6 are the spatial positions of the upper and lower surfaces of the piezoelectric film along the laser pulse direction, t is the heat conduction time, ΔT5 is the internal temperature change of the polarized film, P(x) is the polarization distribution of the polarized film, A and d are the heating area and the thickness of the polarized film, respectively, and x6-x5=d.

[0046] The heat transfer simulation model is as follows:

[0047] Heat conduction equation:

[0048]

[0049] Boundary conditions:

[0050]

[0051]

[0052]

[0053] T i (x, t) = T i+1 (x, t)(x = x) i+1 (i = 2, 3, 4, 5) (6)

[0054]

[0055] Initial conditions:

[0056] T i (x, t = 0) = T room (0≤x≤l i )(i=1, 2, 3, 4, 5, 6, 7) (8)

[0057] Where x represents the spatial position of the piezoelectric film along the laser pulse direction, and x = x1, x2, x3, x4, x5, x6, x7 correspond to the surface of the quartz glass receiving the pulsed laser, the surface of the quartz glass in contact with the opaque metal target layer, the surface of the opaque metal target layer in contact with the liquid being tested, the surface of the liquid being tested in contact with the first metal electrode layer, the surface of the first metal electrode layer in contact with the piezoelectric film, the surface of the piezoelectric film in contact with the second metal electrode layer, and the surface of the second metal electrode layer not in contact with the piezoelectric film, respectively. t represents the time of heat conduction, and layers i = 1, 2, 3, 4, 5, 6 represent the quartz glass, the opaque metal target layer, the liquid being tested, the first metal electrode layer in contact with the upper surface of the piezoelectric film, the piezoelectric film, and the second metal electrode layer in contact with the lower surface of the piezoelectric film, respectively. T i (x, t) represents the temperature distribution of the i-th layer, D i Let k represent the thermal diffusivity of the i-th layer. i Let f(t) represent the thermal conductivity of the i-th layer, f(t) be the absorption power density along the direction of the incident pulsed laser, and T be the thermal conductivity of the i-th layer. room The ambient temperature.

[0058] The solution to the temperature distribution is:

[0059]

[0060] Among them, the Green function G i，j (x, t|x′, τ) represents the effect of a unit pulse at x′ in interval j at time τ on x at interval i at time t.

[0061]

[0062] Where modulus N(β) m )for:

[0063]

[0064] X i (β m (x) and X j (β m Let x′ be the eigenfunction of equation (2-8) under the homogeneous problem. The eigenvalue β is the root of the eigenfunction, and there are infinitely many of them, i.e., β = β′. m (m = 1, 2, ...).

[0065] The specific steps for comparing and fitting the actual pyroelectric signal and the simulated pyroelectric signal are as follows:

[0066] The actual pyroelectric signal and the simulated pyroelectric signal are converted into frequency domain signals respectively, and the real and imaginary parts of the signals are extracted respectively.

[0067] For each frequency point, the difference between the real and imaginary parts of the actual pyroelectric signal and the simulated pyroelectric signal is calculated and the absolute value is taken. The absolute values ​​of all differences are summed. When the sum is less than a preset threshold, it indicates that the fitting degree between the actual pyroelectric signal and the simulated pyroelectric signal meets the preset convergence condition.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] 1. This invention provides a simple and effective method for high-precision measurement of various commonly used liquids. During the measurement process, only the piezoelectric film is connected to the measurement circuit, and the pyroelectric signal depends solely on the temperature response of the piezoelectric film under a thermal pulse. Changes in the liquid's conductivity do not affect the temperature distribution of the subsequent piezoelectric film or the characteristics of the pyroelectric signal. Therefore, this measurement method is not limited by the conductivity of the liquid; it can be either insulating or conductive.

[0070] 2. The highly polarizable piezoelectric thin film in this invention has a good thermoelectric effect, and the generated pyroelectric signal has a high signal-to-noise ratio and the signal features are easy to extract, which is beneficial to the post-processing of the signal and makes the measurement results more accurate.

[0071] 3. This invention uses a piezoelectric thin film, which eliminates the need for an external high voltage to the detector layer, avoids interference from space charge injection, and also eliminates the safety hazards of external voltage.

[0072] 4. In this invention, after the laser energy is absorbed, it first passes through the liquid layer being measured, and then is transmitted to the piezoelectric thin film. The piezoelectric thin film is heated, generating pyroelectricity in the external circuit. To ensure that the piezoelectric thin film can receive sufficient laser energy to generate a pyroelectric signal with a good signal-to-noise ratio, the thickness of the liquid should be as small as possible. Generally, the thickness of the liquid can be controlled within a few micrometers, which is suitable for determining the thermal conductivity of trace liquids.

[0073] 5. In this invention, a metal electrode with a thickness of several hundred nanometers evaporated on the surface of quartz glass is used as the optical target. This not only effectively reduces the absorption of laser energy by the metal layer, but also effectively ensures the uniformity of the thickness of the liquid sample being tested. Attached Figure Description

[0074] Figure 1 This is a schematic diagram of the sample structure;

[0075] Figure 2 This is a polarization distribution diagram of a polarized PVDF (28 μm) sample in one embodiment;

[0076] Figure 3 This is a graph showing the fitting result of pyroelectricity in the frequency domain in one embodiment;

[0077] The figures are labeled as follows: ① Quartz glass, ② Opaque metal target layer, ③ Liquid under test, ④ and ⑥ Metal electrodes, ⑤ Piezoelectric thin film. Detailed Implementation

[0078] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0079] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer and show the mating relationships between the components, some parts in the drawings have been appropriately scaled down, and the distances between the components have been increased or decreased.

[0080] In the description of the embodiments of this application, it should be understood that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly placed when the product of this application is used, or the orientation or positional relationship commonly understood by those skilled in the art. They are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0081] In the description of the embodiments of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0082] Example 1:

[0083] The structure of the experimental measurement sample used in this embodiment is as follows: Figure 1 As shown, the sample under test has a multilayer thin-layer structure, mainly consisting of: a phototarget composite layer (①+②), a liquid layer ③, and a thin-film detector layer (④+⑤+⑥). An opaque metal target layer ② is sputtered or evaporated onto a free-polished surface of quartz glass ①, forming the phototarget composite layer structure (①+②). The thin-film detector layer (④+⑤+⑥) is a composite structure formed by double-sided metallization of a piezoelectric thin film ⑤. Metal electrodes (④+⑥) serve as electrical contacts with the external circuit, electrode ④ is the grounding terminal, and electrode ⑥ is connected to the measurement circuit, forming a closed-loop circuit. The liquid under test is placed between the phototarget composite layer (①+②) and the thin-film detector layer (④+⑤+⑥). Applying a certain pressure to the outside of the quartz glass effectively fixes the sample, controls the thickness of the liquid under test, and enables the measurement of trace liquid samples. Simultaneously, it avoids air residue at the contact interface, effectively reducing the interference of interfacial thermal resistance on the experimental measurement. A thermal pulse acts on the sample, passes through the quartz glass, and acts on the opaque metal target layer ②. Part of the pulsed laser energy is absorbed by the target layer and then transferred bidirectionally layer by layer. At this point, the target layer can be considered a transient internal heat source. According to the second law of thermodynamics, heat always spontaneously flows from a high-temperature object to a low-temperature object. When heat passes through the measured liquid in the form of a pulse and is transferred to the detector layer, the thermal disturbance causes a transient temperature change within the polarized thin film. The displacement of charges will result in a detectable current signal (pyroelectric) on the measurement circuit.

[0084] The theoretical expression for pyroelectricity, i.e., the calculation formula, is as follows:

[0085]

[0086] Where I is the pyroelectric current, x is the spatial position of the piezoelectric film along the laser pulse direction, x5 and x6 are the spatial positions of the upper and lower surfaces of the piezoelectric film along the laser pulse direction, t is the heat conduction time, ΔT5 is the internal temperature change of the polarized film, P(x) is the polarization distribution of the polarized film, A and d are the heating area and the thickness of the polarized film, respectively, and x6-x5=d.

[0087] From formula (1), it can be seen that, given a fixed polarization distribution, heating area, and thickness of the thin film, the characteristics of pyroelectricity will depend on the temperature change of the polarized thin film. In cases such as... Figure 1 In the structure shown, the temperature distribution of the polarized thin film depends on multiple physical parameters, including laser parameters, the film's thermal conductivity, and the thermal conductivity of the liquid being tested. The unknown and uncertain parameters are the thermal conductivity and thickness of the liquid being tested; the other relevant parameters are known. Therefore, the pyroelectric signal can be treated as a function containing the thermal conductivity and thickness of the liquid being tested as unknown variables. By analyzing the characteristics of the fitted pyroelectric signal, the thermal conductivity and thickness of the liquid can be deduced.

[0088] Will Figure 1 The multi-layered sample was fixed on the experimental measurement device, and heated by thermal pulses. The pyroelectric current signal generated by the piezoelectric thin film was acquired by the measurement circuit. The target parameters were obtained by analyzing the characteristics of the fitted pyroelectric signal.

[0089] Based on such Figure 1 The structure shown in this embodiment provides a method for measuring the thermal conductivity of a liquid based on a piezoelectric thin film, including the following steps:

[0090] The liquid to be tested is placed between the optical target composite layer and the thin film detector layer;

[0091] A pulsed laser is applied to the optical target composite layer, and the actual pyroelectric signal generated by the pulsed laser passing through the optical target composite layer and acting on the liquid under test is collected and transmitted to the thin film detector layer.

[0092] A heat transfer simulation model of a multilayer structure is established, which is used to calculate the instantaneous temperature response of the polarized thin film under the action of a thermal pulse.

[0093] Using the thermal conductivity and equivalent thickness of the liquid under test as unknown parameters, the unknown parameters in the heat transfer simulation model are adjusted to calculate the instantaneous response of the temperature inside the polarized film under the action of a thermal pulse. Based on the polarization distribution of the polarized film (see CN110244138A for specific solution methods) and the calculated instantaneous temperature rise, the simulated pyroelectric signal is calculated using the pyroelectric calculation formula (1). The actual pyroelectric signal and the simulated pyroelectric signal are compared and fitted. When the simulated current curve and the actual current curve reach the best fit, the thermal conductivity of the liquid set in the model is the measured value. In this embodiment, for ease of practice, if the fit between the simulated current curve and the actual current curve meets the preset convergence condition, it is considered that the best fit has been reached. The thermal conductivity of the liquid in the heat transfer simulation model at this time is taken as the final measurement result to obtain the thermal conductivity of the liquid. Otherwise, this step is repeated.

[0094] The establishment of a multilayer heat transfer simulation model is a necessary condition for measurement. The heat transfer simulation model satisfies the following assumptions: (1) During the measurement process, the heating diameter is much larger than the thickness of the liquid and the polarized film, and the heat conduction equation can be approximated as a one-dimensional heat transfer model. (2) During the heating process, the local temperature rise of the polarized film is less than 1K, and the influence of temperature on polarization distribution and other thermophysical properties can be ignored. (3) During the sample preparation process, by adjusting the pressure applied to the surface of the quartz glass, the air at the interface is eliminated as much as possible, and the interference of interface thermal resistance can be ignored.

[0095] Heat conduction equation:

[0096]

[0097] Boundary conditions:

[0098]

[0099]

[0100]

[0101] T i (x, t) = T i+1 (x, t)(x = x) i+1 (i = 2, 3, 4, 5) (6)

[0102]

[0103] Initial conditions:

[0104] T i (x, t = 0) = T room (0≤x≤l i )(i=1, 2, 3, 4, 5, 6, 7) (8)

[0105] Where x represents the spatial position of the piezoelectric film along the laser pulse direction, and x = x1, x2, x3, x4, x5, x6, x7 correspond to the surface of the quartz glass receiving the pulsed laser, the surface of the quartz glass in contact with the opaque metal target layer, the surface of the opaque metal target layer in contact with the liquid being tested, the surface of the liquid being tested in contact with the first metal electrode layer, the surface of the first metal electrode layer in contact with the piezoelectric film, the surface of the piezoelectric film in contact with the second metal electrode layer, and the surface of the second metal electrode layer not in contact with the piezoelectric film, respectively. t represents the time of heat conduction, and layers i = 1, 2, 3, 4, 5, 6 represent the quartz glass, the opaque metal target layer, the liquid being tested, the first metal electrode layer in contact with the upper surface of the piezoelectric film, the piezoelectric film, and the second metal electrode layer in contact with the lower surface of the piezoelectric film, respectively. T i (x, t) represents the temperature distribution of the i-th layer, D i Let k represent the thermal diffusivity of the i-th layer. i Let f(t) represent the thermal conductivity of the i-th layer, f(t) be the absorption power density along the direction of the incident pulsed laser, and T be the thermal conductivity of the i-th layer. room The ambient temperature.

[0106] By solving equations (1)-(8) using the method of separation of variables, the homogeneous solution of the equation is obtained. Then, the non-homogeneous solution with the pulsed laser heat source as the outer boundary is obtained by using the Green's function. Thus, the solution for the temperature distribution is obtained as follows:

[0107]

[0108] Among them, the Green function G i，j (x, t|x′, τ) represents the effect of a unit pulse at x′ in interval j at time τ on x at interval i at time t.

[0109]

[0110] Where modulus N(β) m )for:

[0111]

[0112] X i (β m (x) and X j (β m x′) is the eigenfunction of equation (2)-(8) under homogeneous problem, and the eigenvalue β is the root of the eigenfunction. There are infinitely many eigenvalues, i.e., β = β. m (m = 1, 2, ...).

[0113] In a preferred embodiment, the comparison and fitting of the actual pyroelectric signal and the simulated pyroelectric signal specifically involves:

[0114] The actual pyroelectric time-domain signal and the simulated pyroelectric time-domain signal are converted into frequency-domain signals respectively, and the real and imaginary parts of the signals are extracted respectively.

[0115] For each frequency point, the difference between the real and imaginary parts of the actual pyroelectric signal and the simulated pyroelectric signal is calculated and the absolute value is taken. The absolute values ​​of all differences are summed. When the sum is less than a preset threshold, it indicates that the fit between the actual pyroelectric signal and the simulated pyroelectric signal meets the preset convergence condition.

[0116] This embodiment uses common dimethyl silicone oil as the test liquid for verification. The thin-film detector layer is a double-sided aluminum-coated polarized PVDF (28μm) film with a surface aluminum layer thickness of 180nm as the contact electrode with the external circuit. The glass is a 1mm thick transparent quartz glass sheet with an opaque copper oxide layer sputtered to its surface for a thickness of approximately 200nm as the target electrode. The pulse width of the infrared pulsed laser is 7ns. Figure 2 The polarization distribution of the polarized PVDF thin film was calculated using the method described in patent CN110244138A. By fitting the experimentally acquired current curves with simulated current curves, the thickness of the dimethyl silicone oil layer was calculated to be 1 μm, and the thermal conductivity of the silicone oil was 0.131 W / (m·K), with a deviation of approximately 1% from the reference value, thus verifying the accuracy of the measurement method described in this invention.

[0117] Example 2:

[0118] This embodiment provides a liquid thermal conductivity measurement system based on a piezoelectric thin film, including:

[0119] A test stand is provided, on which a phototarget composite layer and a thin film detector layer are placed. The liquid to be tested is placed between the phototarget composite layer and the thin film detector layer. The phototarget composite layer includes quartz glass and an opaque metal target layer. The thin film detector layer includes a piezoelectric thin film and two metal electrode layers that are in contact with the upper and lower surfaces of the piezoelectric thin film, respectively.

[0120] The measuring device includes a laser unit and a data acquisition unit. The laser unit emits pulsed laser light and applies it to the optical target composite layer. The data acquisition unit acquires the actual pyroelectric signal generated by the pulsed laser light acting on the liquid under test through the optical target composite layer and then being transmitted to the thin film detector layer.

[0121] The simulation and calculation unit is used to establish a heat transfer simulation model of a multilayer structure, which is used to calculate the instantaneous temperature response of the polarized thin film under the action of a thermal pulse.

[0122] The fitting unit uses the thermal conductivity and equivalent thickness of the liquid under test as unknown parameters, adjusts the unknown parameters in the heat transfer simulation model, calculates the instantaneous response of the temperature inside the polarized film under the action of a thermal pulse, and calculates the simulated pyroelectric signal based on the polarization distribution of the polarized film and the calculated instantaneous temperature rise using the pyroelectric calculation formula. The actual pyroelectric signal and the simulated pyroelectric signal are then compared and fitted.

[0123] The judgment unit determines whether the fitting degree between the actual pyroelectric signal and the simulated pyroelectric signal meets the preset convergence condition. If the condition is met, the thermal conductivity of the liquid in the heat transfer simulation model at this time is taken as the final measurement result to obtain the thermal conductivity of the liquid. Otherwise, the fitting unit is called again to perform fitting.

[0124] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the described module can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0125] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for measuring the thermal conductivity of a liquid based on a piezoelectric thin film, characterized in that, Includes the following steps: The liquid to be tested is placed between the optical target composite layer and the thin film detector layer. The optical target composite layer includes quartz glass and an opaque metal target layer, and the thin film detector layer includes a piezoelectric thin film and two metal electrode layers that are in contact with the upper and lower surfaces of the piezoelectric thin film, respectively. A pulsed laser is applied to the optical target composite layer, and the actual pyroelectric signal generated by the pulsed laser passing through the optical target composite layer and acting on the liquid under test is collected and transmitted to the thin film detector layer. A heat transfer simulation model of a multilayer structure is established, which is used to calculate the instantaneous temperature response of the polarized thin film under the action of a thermal pulse. Using the thermal conductivity and equivalent thickness of the liquid under test as unknown parameters, the unknown parameters in the heat transfer simulation model are adjusted to calculate the instantaneous response of the temperature inside the polarized film under the action of a thermal pulse. Based on the polarization distribution of the polarized film and the calculated instantaneous temperature rise, the simulated pyroelectric signal is calculated using the pyroelectric calculation formula. The actual pyroelectric signal and the simulated pyroelectric signal are compared and fitted. If the fitting degree of the two meets the preset convergence condition, the thermal conductivity of the liquid in the heat transfer simulation model at this time is taken as the final measurement result to obtain the thermal conductivity of the liquid. Otherwise, this step is repeated. The heat transfer simulation model is as follows: Heat conduction equation: Boundary conditions: Initial conditions: in, The spatial position of the piezoelectric thin film along the laser pulse direction. These correspond to the following surfaces: the surface of the quartz glass receiving the pulsed laser; the surface of the quartz glass in contact with the opaque metal target layer; the surface of the opaque metal target layer in contact with the liquid being tested; the surface of the liquid being tested in contact with the first metal electrode layer; the surface of the first metal electrode layer in contact with the piezoelectric film; the surface of the piezoelectric film in contact with the second metal electrode layer; and the surface of the second metal electrode layer not in contact with the piezoelectric film. t For the time of heat conduction, the first The layers represent quartz glass, an opaque metal target layer, the liquid being tested, a first metal electrode layer in contact with the upper surface of the piezoelectric film, the piezoelectric film itself, and a second metal electrode layer in contact with the lower surface of the piezoelectric film, respectively. Indicates the first Temperature distribution of the layer Indicates the first The thermal diffusivity of the layer, Indicates the first The thermal conductivity of the layer, The absorption power density is along the direction of the incident laser pulse. The ambient temperature; The solution to the temperature distribution is: Green's function for time interval unit pulse pair at the location time interval The impact of the location, Among them, the mold for: and Let be the eigenfunctions of equations (2)-(8) under homogeneous problems, and eigenvalues ​​be... The roots of the eigenfunctions have infinitely many eigenvalues, i.e. .

2. The method for measuring the thermal conductivity of a liquid based on a piezoelectric thin film according to claim 1, characterized in that, The formula for calculating pyroelectricity is: in, For pyroelectric current, The spatial position of the piezoelectric thin film along the laser pulse direction. , These represent the spatial positions of the upper and lower surfaces of the piezoelectric thin film along the laser pulse direction. t The time of heat conduction. This refers to the temperature change inside the polarized thin film. P This represents the polarization distribution of the polarized thin film. A , d These represent the heating area and the thickness of the polarization film, respectively. .

3. The method for measuring the thermal conductivity of a liquid based on a piezoelectric thin film according to claim 1, characterized in that, The specific steps for comparing and fitting the actual pyroelectric signal and the simulated pyroelectric signal are as follows: The actual pyroelectric time-domain signal and the simulated pyroelectric time-domain signal are converted into frequency-domain signals respectively, and the real and imaginary parts of the signals are extracted respectively. For each frequency point, the difference between the real and imaginary parts of the actual pyroelectric signal and the simulated pyroelectric signal is calculated and the absolute value is taken. The absolute values ​​of all differences are summed. When the sum is less than a preset threshold, it indicates that the fit between the actual pyroelectric signal and the simulated pyroelectric signal meets the preset convergence condition.

4. A liquid thermal conductivity measurement system based on piezoelectric thin films, characterized in that, include: A test stand is provided, on which a phototarget composite layer and a thin film detector layer are placed. The liquid to be tested is placed between the phototarget composite layer and the thin film detector layer. The phototarget composite layer includes quartz glass and an opaque metal target layer. The thin film detector layer includes a piezoelectric thin film and two metal electrode layers that are in contact with the upper and lower surfaces of the piezoelectric thin film, respectively. The measuring device includes a laser unit and a data acquisition unit. The laser unit emits pulsed laser light and applies it to the optical target composite layer. The data acquisition unit acquires the actual pyroelectric signal generated by the pulsed laser light acting on the liquid under test through the optical target composite layer and then being transmitted to the thin film detector layer. The simulation and calculation unit establishes a heat transfer simulation model of a multilayer structure, which is used to calculate the instantaneous temperature response of the polarized thin film under the action of a thermal pulse. The fitting unit uses the thermal conductivity and equivalent thickness of the liquid under test as unknown parameters, adjusts the unknown parameters in the heat transfer simulation model, calculates the instantaneous response of the temperature inside the polarized film under the action of a thermal pulse, and calculates the simulated pyroelectric signal based on the polarization distribution of the polarized film and the calculated instantaneous temperature rise using the pyroelectric calculation formula. The actual pyroelectric signal and the simulated pyroelectric signal are then compared and fitted. The judgment unit determines whether the fitting degree between the actual pyroelectric signal and the simulated pyroelectric signal meets the preset convergence condition. If the condition is met, the thermal conductivity of the liquid in the heat transfer simulation model at this time is taken as the final measurement result to obtain the thermal conductivity of the liquid. Otherwise, the fitting unit is called again to perform fitting. The heat transfer simulation model is as follows: Heat conduction equation: Boundary conditions: Initial conditions: in, The spatial position of the piezoelectric thin film along the laser pulse direction. These correspond to the following surfaces: the surface of the quartz glass receiving the pulsed laser; the surface of the quartz glass in contact with the opaque metal target layer; the surface of the opaque metal target layer in contact with the liquid being tested; the surface of the liquid being tested in contact with the first metal electrode layer; the surface of the first metal electrode layer in contact with the piezoelectric film; the surface of the piezoelectric film in contact with the second metal electrode layer; and the surface of the second metal electrode layer not in contact with the piezoelectric film. t For the time of heat conduction, the first The layers represent quartz glass, an opaque metal target layer, the liquid being tested, a first metal electrode layer in contact with the upper surface of the piezoelectric film, the piezoelectric film itself, and a second metal electrode layer in contact with the lower surface of the piezoelectric film, respectively. Indicates the first Temperature distribution of the layer Indicates the first The thermal diffusivity of the layer, Indicates the first The thermal conductivity of the layer, The absorption power density is along the direction of the incident laser pulse. The ambient temperature; The solution to the temperature distribution is: Green's function for time interval unit pulse pair at the location time interval The impact of the location, Among them, the mold for: and Let be the eigenfunctions of equations (2)-(8) under homogeneous problems, and eigenvalues ​​be... The roots of the eigenfunctions have infinitely many eigenvalues, i.e. .

5. The liquid thermal conductivity measurement system based on piezoelectric thin film according to claim 4, characterized in that, The formula for calculating pyroelectricity is: in, For pyroelectric current, The spatial position of the piezoelectric thin film along the laser pulse direction. , These represent the spatial positions of the upper and lower surfaces of the piezoelectric thin film along the laser pulse direction. t The time of heat conduction. This refers to the temperature change inside the polarized thin film. P This represents the polarization distribution of the polarized thin film. A , d These represent the heating area and the thickness of the polarization film, respectively. .

6. The liquid thermal conductivity measurement system based on piezoelectric thin film according to claim 4, characterized in that, The specific steps for comparing and fitting the actual pyroelectric signal and the simulated pyroelectric signal are as follows: The actual pyroelectric time-domain signal and the simulated pyroelectric time-domain signal are converted into frequency-domain signals respectively, and the real and imaginary parts of the signals are extracted respectively. For each frequency point, the difference between the real and imaginary parts of the actual pyroelectric signal and the simulated pyroelectric signal is calculated and the absolute value is taken. The absolute values ​​of all differences are summed. When the sum is less than a preset threshold, it indicates that the fit between the actual pyroelectric signal and the simulated pyroelectric signal meets the preset convergence condition.

Images