A method and system for measuring the thermal conductivity of a high thermal conductivity micro-liquid

Abstract

The application relates to a kind of high thermal conductivity micro liquid thermal conductivity coefficient measurement method and system, comprising the following steps: the liquid to be measured is placed between the medium film of metallization processing and metal thin layer;Collect the experimental thermal response current generated by metal thin layer-measured liquid-medium film under the action of laser pulse;Establish the heat transfer simulation model of metal thin layer-measured liquid-medium film;Adjust the thermal conductivity coefficient of measured liquid in simulation model, calculate to obtain theoretical thermal response current;Using iterative algorithm to adjust the thermal conductivity coefficient of measured liquid in simulation model, so that the theoretical thermal response current and experimental thermal response current best fitting degree, the thermal conductivity coefficient of measured liquid in simulation model at this time is used as measurement result.Compared with prior art, the application provides a simple and effective means capable of high-precision measurement of high thermal conductivity coefficient liquid, convenient operation, fast measurement speed, and can effectively measure the thermal conductivity coefficient of micro liquid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal conductivity measurement, and particularly relates to a method and system for measuring thermal conductivity of high-thermal-conductivity micro-liquid. BACKGROUND

[0002] With the increasing growth of high-throughput electronic products, it is necessary to improve the effective heat dissipation in electronic devices to meet the performance and life expectancy of electronic devices. In many practical scenarios, heat accumulation in heat-generating devices is removed by cooling liquid. Therefore, accurate thermal conductivity information is of great significance for effective thermal management of electrical equipment. In addition, the thermal conductivity data of the liquid has been used to calculate and improve the heat transfer efficiency of the working fluid for effective thermal management. Therefore, accurate and reliable liquid thermal conductivity data is very important for developing fluids with high efficient heat transport performance.

[0003] At present, many conventional methods have been developed to measure the thermal conductivity of various liquids, which are generally divided into steady-state method and transient method. The steady-state method mainly includes flat plate method, cylindrical unit method and spherical method. When measuring the thermal conductivity of the sample by using the steady-state method, the measured sample needs to be heated by a continuous stable heat source to maintain long-term thermal equilibrium. The thermal conductivity of the sample is calculated by the stable temperature gradient in the sample. Therefore, the steady-state method generally requires a large amount of liquid, and cannot avoid the heat convection during the measurement of the liquid, which is not conducive to the improvement of the measurement accuracy. Compared with the steady-state method, the transient method can more accurately and quickly measure the thermal conductivity of the liquid. The transient method is based on the transient thermal response of the sample, and the representative transient methods include transient hot wire method (THW), laser flash (LF) and photon correlation spectroscopy (PCS) and the like. The transient hot wire method has good test effect on the thermal conductivity of the liquid, and has high test precision, but it is difficult to measure the high-conductivity liquid. Laser flash is suitable for complex fluids and small-volume samples, and the measurement precision depends on the sensitivity of the temperature probe. Photon correlation spectroscopy is a high-precision non-contact measurement that is not limited by the size and conductivity of the sample, but it involves a very complex analysis model, and the precision of the secondary measurement instrument is very strict.

[0004] Chinese patent CN114264695A discloses a kind of micro liquid thermal conductivity measurement method and system, uniform distribution of electric field is applied on the medium film of metallization processing, one side of medium film is excited by laser pulse, the other side is in close contact with liquid of half infinite thickness, experimental displacement current generated by medium film-half infinite thick liquid under the action of laser pulse is collected;Combining the parameters of medium film with the actual model structure to establish heat transfer simulation model, according to the temperature distribution change in medium film, calculate the theoretical displacement current;Extract the characteristics of theoretical displacement current and experimental displacement current to compare and fit, the thermal conductivity of liquid is regarded as the only unknown variable, the thermal conductivity of liquid in simulation model is adjusted using iterative algorithm to make the fitting degree of experimental curve and simulation curve best, the thermal conductivity in simulation model at this time is regarded as measurement result.But, in practice, it is found that the measurement scheme has the following shortcomings: with the increase of the thermal conductivity of the measured liquid, the measurement precision decreases obviously, especially when the thermal conductivity of the measured liquid is as high as 1W / (m·K) or more, although the thermal conductivity of the measured sample increases by several times, the temperature distribution of medium film detector hardly changes, which leads to the characteristics of displacement current not changing very obviously, so the thermal conductivity obtained by fitting displacement current has great error.

[0005] Therefore, according to the deficiencies of the prior art, it is necessary to provide a measurement method for thermal conductivity of high-thermal-conductivity, insulating or non-insulating liquid with higher discrimination. SUMMARY

[0006] The purpose of the present application is to overcome the deficiencies of the prior art and provide a measurement method for thermal conductivity of high-thermal-conductivity micro liquid.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] According to the first aspect of the present application, a measurement method for thermal conductivity of high-thermal-conductivity micro liquid is provided, comprising the following steps:

[0009] The medium film with known parameters is subjected to double-sided metallization treatment, and the measured liquid is placed between the medium film and the metal thin layer with known parameters;

[0010] An external circuit is connected to the medium film to make the medium film have a uniform distribution of electric field, as a medium detector, the metal thin layer is used as an absorbing light target, a laser pulse is applied to the metal thin layer, and the thermal response current generated by the metal thin layer-measured liquid-medium film under the action of laser pulse is collected, recorded as experimental thermal response current;

[0011] A heat transfer simulation model of metal thin layer-measured liquid-medium film is established by combining the parameters of medium film and metal thin layer, and the simulation model is used to calculate the temperature distribution change in medium film;

[0012] The thermal conductivity of the measured liquid is taken as an unknown variable, the thermal conductivity of the measured liquid in the simulation model is adjusted, the corresponding temperature distribution change in the medium film is calculated, the theoretical thermal response current is calculated according to the temperature distribution change, and the characteristics of the theoretical thermal response current and the experimental thermal response current are extracted for comparison and fitting; if the fitting degree of the two meets the pre-set convergence condition, the thermal conductivity of the liquid in the simulation model at this time is taken as the final measurement result, the thermal conductivity of the liquid is obtained, otherwise, the step is repeated.

[0013] Further, there is no air residue between the measured liquid and the medium film and the metal thin layer, the laser spot diameter of the laser pulse applied to the metal thin layer is 1-2 orders of magnitude higher than the thickness of the measured liquid, the thickness of the measured liquid is 50-100 microns, and the thickness of the metal thin layer is 1-10 microns.

[0014] Further, the calculation formula of the theoretical thermal response current is:

[0015]

[0016]

[0017] wherein I sim is the theoretical thermal response current, x is the spatial position along the thickness direction of the metal thin layer-measured liquid-medium film structure, t is the time, ΔT3(x,t) is the temperature change inside the medium film, χ is the coefficient of the medium film, A and d are the laser irradiation area and the thickness of the medium detector respectively, E(x) is the electric field distribution, ε0 and ε r are the vacuum dielectric constant and the relative dielectric coefficient of the sample respectively, α ε and α x are the temperature coefficient of the relative dielectric coefficient and the thermal expansion coefficient of the sample respectively.

[0018] Further, the simulation model is established as:

[0019] Heat conduction equation:

[0020]

[0021] Boundary condition:

[0022]

[0023]

[0024] T i (x,t)=T i+1 (x,t)(x=x i+1 )(i=1,2) (5)

[0025]

[0026] Initial conditions:

[0027] T i (x,t=1)=T rm (x i ≤x≤x i+1 (i = 1, 2, 3) (7)

[0028] Where x represents the spatial position along the thickness direction of the metal thin layer-liquid under test-dielectric thin film structure, t represents time, x = x1, x2, x3, x4 correspond to the surface of the metal thin layer receiving the laser pulse, the surface of the metal thin layer in contact with the liquid under test, the surface of the dielectric thin film in contact with the liquid under test, and the surface of the dielectric thin film not in contact with the liquid under test, respectively, and the i = 1, 2, 3 layers represent the metal thin layer, the liquid under test, and the dielectric thin 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 heat source boundary of the laser pulse, and T be the thermal conductivity of the i-th layer. rm The ambient temperature.

[0029] Furthermore, the temperature distribution change within the dielectric thin film was calculated using a simulation model as follows:

[0030] I. Assume f(f) = 0, and solve the homogeneous solution of the equation using the method of separation of variables;

[0031] (1) T i (x, t) can be separated into the product of a time function and a space function, as follows:

[0032] T i (x, t) = X i (x)Γ i (t) (8)

[0033] Among them, X i (x) is the spatial function of the i-th layer, Γ i (t) is the time function of the i-th layer;

[0034] (2) Substituting equation (8) into the heat conduction equation (2) and the boundary conditions (3)-(6), we get:

[0035]

[0036] -k1X1′=0,(x=x1) (10)

[0037] -k i Xi i = -k i+1 X i+1 i+1 (x = x i+1 )(i = 1, 2) (11)

[0038] X i i = X i+1 i+1 (x = x i+1 )(i = 1, 2) (12)

[0039] -k3X3' = 0, (x = x4) (13)

[0040] According to equations (11)-(12), the time function of the ith layer is:

[0041]

[0042] (3) Since the time functions of each layer are equal, equations (10)-(14) are an eigenvalue problem about the space function, and the eigenfunction of the space function is:

[0043] X(β m , x) = X i (β m , x) (15)

[0044] where β = β m is the eigenvalue of the eigenfunction;

[0045] where the orthogonal relationship of the eigenfunction is:

[0046]

[0047] where the modulus N(β m ) is:

[0048]

[0049] The superposition coefficient c m is obtained from the initial condition (7) and the orthogonal relationship (16):

[0050]

[0051] The solution of the temperature distribution is:

[0052]

[0053] Substituting c m into equation (19) and simplifying, we get:

[0054] ​​​​

[0055] Eigenfunction X i The general solution of (beta, x) is:

[0056]

[0057]

[0058]

[0059] The boundary conditions (10)-(13) are obtained by bringing the formula (21)-(23) into the boundary conditions (10)-(13) to obtain the coefficient matrix of the eigenfunction:

[0060]

[0061] Wherein, A1, A2, A 3, , B1, B2, B3 are the coefficients of the eigenfunction equation;

[0062] II. Let f(t) be a function of laser pulse, according to the homogeneous solution of temperature distribution, the temperature distribution of the sample under the action of heat pulse is solved by Green function;

[0063] Let the Green function be:

[0064]

[0065] The solution of the temperature distribution is obtained as:

[0066]

[0067] The theoretical thermal response current can be obtained by substituting formula (25) into the calculation formula of the theoretical thermal response current.

[0068] According to the second aspect of the present application, a system for measuring the thermal conductivity coefficient of high thermal conductivity trace liquid is provided, comprising:

[0069] A test table is provided on which a medium film with known parameters and a metal thin layer with known parameters are placed, and the measured liquid is placed between the medium film and the metal thin layer, and the medium film is a medium film subjected to double-sided metallization treatment;

[0070] A measuring device, comprising a voltage unit, a laser unit and a collection unit, the voltage unit is used to apply a direct current voltage outside the medium film to make the medium film have a uniform distribution of electric field inside, the laser unit is used to apply a laser pulse to the metal thin layer, and the collection unit is used to collect the thermal response current generated by the metal thin layer-measured liquid-medium film under the action of the laser pulse, which is recorded as the experimental thermal response current;

[0071] The simulation model unit is used to combine the parameters of the medium film and the metal thin layer to establish a heat transfer simulation model of the metal thin layer-measured liquid-medium film, and the simulation model is used to calculate the temperature distribution change in the medium film.

[0072] The fitting unit adjusts the thermal conductivity coefficient of the measured liquid in the simulation model as an unknown variable, calculates the corresponding temperature distribution change in the medium film, calculates the theoretical thermal response current according to the temperature distribution change, and extracts the characteristics of the theoretical thermal response current and the experimental thermal response current for comparison and fitting.

[0073] The judgment unit judges whether the fitting degree of the theoretical thermal response current and the experimental thermal response current meets the pre-set convergence condition.

[0074] Further, there is no air residue between the measured liquid and the medium film and the metal thin layer, the laser spot diameter of the laser pulse applied to the metal thin layer is 1-2 orders of magnitude higher than the thickness of the measured liquid, the thickness of the measured liquid is 50-100 microns, and the thickness of the metal thin layer is 1-10 microns.

[0075] Further, the calculation formula of the theoretical thermal response current is:

[0076]

[0077]

[0078] where I sim is the theoretical thermal response current, x is the spatial position along the thickness direction of the metal thin layer-measured liquid-medium film structure, t is the time, ΔT3(x, t) is the temperature change inside the medium film, χ is the coefficient of the medium film, A and d are the laser irradiation area and the thickness of the medium detector, respectively, E(x) is the electric field distribution, ε0 and ε r are the vacuum dielectric constant and the relative dielectric coefficient of the sample, respectively, α ε and α x are the temperature coefficient of the relative dielectric coefficient and the thermal expansion coefficient of the sample, respectively.

[0079] Further, the established simulation model is:

[0080] Heat conduction equation:

[0081]

[0082] Boundary condition:

[0083]

[0084]

[0085] T i (x, t) = T i+1 (x, t)(x = x i+1 )(i = 1, 2) (5)

[0086]

[0087] Initial conditions:

[0088] T i (x, t = 1) = T rm (x i ≤ x ≤ x i+1 )(i = 1, 2, 3) (7)

[0089] where x is the spatial position along the thickness direction of the metal thin layer - measured liquid - medium thin film structure, t is time, x = x1, x2, x3, x4 respectively correspond to the surface of the metal thin layer receiving the laser pulse, the surface of the metal thin layer contacting the measured liquid, the surface of the medium thin film contacting the measured liquid and the surface of the medium thin film not contacting the measured liquid, i = 1, 2, 3 respectively represent the metal thin layer, the measured liquid, the medium thin film, T i (x, t) represents the temperature distribution of the i-th layer, D i represents the thermal diffusivity of the i-th layer, k i represents the thermal conductivity of the i-th layer, f(t) is the heat source boundary of the laser pulse, and T rm is the ambient temperature.

[0090] Further, the corresponding temperature distribution change in the medium thin film is calculated by the simulation model as:

[0091] I. Assuming f(t) = 0, the homogeneous solution of the equation is solved by separation of variables method;

[0092] (1) Separate T i (x, t) into a product of a time function and a spatial function as follows:

[0093] T i (x, t) = X i (x)Γ i (t) (8)

[0094] where X i (x) is the spatial function of the i-th layer, and Γ i (t) is the time function of the i-th layer;

[0095] (2) Substitute the above equation (8) into the heat conduction equation (2) and the boundary conditions (3)-(6) to obtain:

[0096]

[0097] - k1X1' = 0, (x = x1) (10)

[0098] - k i X i ' = -k i X i+1 ' (x = x i+1 ) (9) i+1 (x = x i+1 ) (i = 1, 2) (11)

[0099] X i ' = X i ' (x = x i+1 ) (10) i+1 (x = x i+1 ) (i = 1, 2) (12)

[0100] - k3X3' = 0, (x = x4) (13)

[0101] According to equations (11)-(12), the time function of the ith layer is:

[0102]

[0103] (3) Since the time functions of each layer are equal, equations (10)-(14) are an eigenvalue problem about the space function, and the eigenfunction of the space function is:

[0104] X(β m , x) = X i (β m , x) (15)

[0105] where β = β m is the eigenvalue of the eigenfunction;

[0106] where the orthogonal relationship of the eigenfunction is:

[0107]

[0108] where N(β m ) is:

[0109]

[0110] The superposition coefficient c m is obtained from the initial condition (7) and the orthogonal relationship (16):

[0111]

[0112] The solution of the temperature distribution is:

[0113]

[0114] c m Substitute equation (19) into equation (18), and simplify to obtain:

[0115]

[0116] The general solution of eigenfunction X i (β,x) is:

[0117]

[0118]

[0119]

[0120] Substitute equations (21)-(23) into boundary conditions (10)-(13) to obtain the coefficient matrix of the eigenfunction:

[0121]

[0122] Wherein, A1,A2,A 3, ,B1,B2,B3 are the coefficients of the eigenfunction equation.

[0123] II. Assuming that f(t) is a function of laser pulse, according to the homogeneous solution of temperature distribution, the temperature distribution of the sample under the action of thermal pulse is solved by Green function;

[0124] Assume that the Green function is:

[0125]

[0126] The solution of the temperature distribution is obtained as:

[0127]

[0128] Substitute equation (25) into the calculation formula of the theoretical thermal response current to obtain the theoretical thermal response current.

[0129] Compared with the prior art, the present application has the following beneficial effects:

[0130] (1) The present application provides a simple and effective means for high-precision measurement of liquid with high thermal conductivity coefficient, which belongs to transient measurement method, post detector, and thermal pulse passes through metal target layer, liquid, and then reaches medium detector film, when the thickness of the liquid and the laser pulse are constant, the greater the thermal conductivity coefficient of the measured liquid, the higher the energy absorbed by the medium detector, and the more obvious the temperature change of the detector, so that the present application can effectively measure the thermal conductivity coefficient of the liquid, especially for liquid samples with high thermal conductivity coefficient, and has good measurement precision.

[0131] (2) The present application is convenient to operate, fast in measuring speed, and has no excessive requirement on the physical property of the measured sample. The measured sample can be a pure substance or a mixture sample, an insulator or a conductor, a high-purity or a low-purity, and the volume of the liquid sample only needs several microliters, so the present application has a wide application range. BRIEF DESCRIPTION OF DRAWINGS

[0132] Figure 1 is a structural schematic diagram of a sample;

[0133] Figure 2 is a theoretical thermal response current curve of a structure of 5 μm aluminum @ 100 μm measured liquid @ 3.8 μm medium detector under the setting of different liquid thermal conductivities;

[0134] The figure marks are as follows: 1, metal thin layer; 2, measured liquid; and 3, medium thin film. DETAILED DESCRIPTION

[0135] The present application will be described in detail below in combination with the drawings and specific embodiments. The embodiments are implemented on the premise of the technical scheme of the present application, and detailed implementation manners and specific operation processes are given. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. The protection scope of the present application is not limited to the following embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the present application.

[0136] In the drawings, the same components have the same reference numerals, and components with similar structures or functions have similar reference numerals. The size and thickness of each component shown in the drawings are arbitrarily shown, and the present application does not limit the size and thickness of each component. In order to make the drawing clearer and show the cooperation relationship between the components, the components are appropriately scaled and the distance between the components is appropriately increased or decreased in some places of the drawings.

[0137] In the description of the embodiments of the present application, it should be understood that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly understood by those skilled in the art, and are only used to facilitate the description of the present application and simplify the description, and are not intended to indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0138] 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.

[0139] Example 1:

[0140] This invention provides a method for measuring the thermal conductivity of a high thermal conductivity trace liquid, comprising the following steps:

[0141] A dielectric thin film with known parameters is subjected to double-sided metallization, and the liquid to be tested is placed between the dielectric thin film and a metal thin layer with known parameters.

[0142] An external circuit is connected to the dielectric thin film to create a uniformly distributed electric field inside the dielectric thin film, which serves as a dielectric detector. A metal thin layer is used as an absorption target. A laser pulse is applied to the metal thin layer, and the thermal response current generated by the metal thin layer, the liquid under test, and the dielectric thin film under the action of the laser pulse is collected and recorded as the experimental thermal response current.

[0143] By combining the parameters of the dielectric thin film and the metal thin film, a heat transfer simulation model of the metal thin film-liquid under test-dielectric thin film is established. The simulation model is used to calculate the temperature distribution change within the dielectric thin film.

[0144] The thermal conductivity of the liquid under test is taken as an unknown variable. The thermal conductivity of the liquid under test in the simulation model is adjusted to calculate the corresponding temperature distribution change in the medium film. The theoretical thermal response current is calculated based on the temperature distribution change. The characteristics of the theoretical thermal response current and the experimental thermal response current are extracted and compared for fitting. If the fitting degree of the two meets the preset convergence condition, the thermal conductivity of the liquid in the 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.

[0145] Experimental measurement of sample structure, such as Figure 1 As shown, the overall structure mainly consists of a thin metal layer 1, a liquid layer 2 to be measured, and a dielectric detector 3. The liquid layer 2 to be measured is located between the thin metal layer 1 and the dielectric detector 3, and its thickness is effectively controlled. The thin metal layer 1 serves as an absorptive target for absorbing pulsed laser light. The dielectric film 3, after being metallized on both sides, is connected to an external circuit to create a uniformly distributed electric field within it, thus functioning as a dielectric detector. When the dielectric detector 3 senses a temperature change, a measurable thermal response current is induced across the external measuring current.

[0146] Theoretically, the formula for calculating the thermal response current is:

[0147]

[0148]

[0149] Among them, I sim Let $\frac{x}{t}$ be the theoretical thermal response current, $x$ be the spatial position along the thickness direction of the metal thin film-tested liquid-dielectric thin film structure, $t$ be time, $ΔT3(x,t)$ be the internal temperature change of the dielectric thin film, $χ$ be the coefficient of the dielectric thin film, $A$ and $d$ be the laser irradiated area and the dielectric detector thickness, respectively, $E(x)$ be the electric field distribution, and $ε0$ and $ε$ be the coefficients of the dielectric thin film. r The vacuum permittivity and the relative permittivity of the sample, α ε α x These are the temperature coefficient of the relative permittivity and the coefficient of thermal expansion of the sample, respectively.

[0150] Specifically, after the laser pulse acts on the thin metal layer, some of the energy is absorbed and propagates and diffuses in the form of a thermal pulse. This energy attenuates through the measured liquid to the dielectric detector, eventually reaching thermal equilibrium at room temperature. From formula (1), it can be seen that the thermal response current characteristics generated by the dielectric detector mainly depend on the temperature change within the detector. Assuming the thin metal layer and the dielectric detector remain constant, setting different thermal conductivity values ​​for the measured liquid will directly affect the temperature distribution of the dielectric detector, resulting in thermal response currents with different characteristics on the external circuit. Therefore, based on the characteristics of the current, the thermal conductivity of the liquid can be determined using a fitting method.

[0151] The measurement steps of this invention are as follows:

[0152] 1) Equipment layout and data acquisition

[0153] A dielectric detector with known parameters is fixed to the experimental measurement apparatus. The detector is connected to an external DC voltage circuit and a measuring current, and a uniform electric field distribution exists inside the detector. The liquid to be measured is fixed between the dielectric detector and a thin metal layer with known parameters. During the measurement, it is ensured that there is no air residue between the interface between the liquid and the dielectric film and the metal layer. One free surface of the metal layer is heated by a continuous pulsed laser. After the thermal pulse passes through the metal layer and the liquid to be measured, it is responded to on the dielectric detector, forming a thermal response current in the external circuit. The current is amplified by a preamplifier, and the current data is recorded using an oscilloscope.

[0154] 2) Current fitting method for measuring the thermal conductivity of liquids

[0155] ① Collect the thermal response current generated by the dielectric detector under the action of thermal pulse in the above experimental structure, i.e., the experimental thermal response current. ② Perform a fast Fourier transform on the experimental thermal response current and then normalize it. At this time, the signal characteristics of the current will depend entirely on the internal temperature change of the dielectric detector. ③ Establish a simulation model based on the metal thin layer-liquid-dielectric thin film structure built in the experiment. Given the thermal conductivity of the liquid being tested, calculate the temperature change inside the dielectric detector through the simulation model, and then calculate the simulation signal of the thermal response current according to formula (1), i.e., obtain the theoretical thermal response current. ④ Perform a Fourier transform and normalize on the theoretical thermal response current and compare and fit it with the experimental thermal response current. Repeatedly adjust the given value of the thermal conductivity of the liquid being tested in the simulation model. When the simulation current curve and the actual current curve reach the best fit, the liquid thermal conductivity set in the simulation model is the measured value.

[0156] The simulation model is established under the following conditions: (1) The diameter of the laser spot is 1-2 orders of magnitude larger than the sample thickness during measurement, so the heat conduction equation discussed can be approximated as one-dimensional heat transfer; (2) The interfacial thermal resistance between the liquid and the metal thin film and the dielectric detector thin film is very small, and the attenuation of heat flow through the interface can be ignored; (3) During the heating process, the overall temperature change of the sample is small, and the change of physical properties with temperature can be ignored; (4) The thickness of the liquid being measured is 50-100 micrometers, and the thickness of the metal thin film is 1-10 micrometers.

[0157] The established simulation model is as follows:

[0158] Heat conduction equation:

[0159]

[0160] Boundary conditions:

[0161]

[0162]

[0163] T i (x,t)=T i+1 (x,t)(x=x i+1 (i=1,2) (5)

[0164]

[0165] Initial conditions:

[0166] T i (x,t=1)=T rm (x i ≤x≤x i+1 (i = 1, 2, 3) (7)

[0167] Where x represents the spatial position along the thickness direction of the metal thin layer-liquid under test-dielectric thin film structure, t represents time, x = x1, x2, x3, x4 correspond to the surface of the metal thin layer receiving the laser pulse, the surface of the metal thin layer in contact with the liquid under test, the surface of the dielectric thin film in contact with the liquid under test, and the surface of the dielectric thin film not in contact with the liquid under test, respectively, and the i = 1, 2, 3 layers represent the metal thin layer, the liquid under test, and the dielectric thin 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 heat source boundary of the laser pulse, and T be the thermal conductivity of the i-th layer. rm The ambient temperature.

[0168] The temperature distribution change within the dielectric film was calculated using the simulation model as follows:

[0169] I. Assume f(t) = 0, and solve the homogeneous solution of the equation using the method of separation of variables;

[0170] (1) T i (x,t) can be separated into the product of a time function and a space function, as follows:

[0171] T i (x,t)=X i (x)Γ i (t) (8)

[0172] Among them, X i (x) is the spatial function of the i-th layer, Γ i (t) is the time function of the i-th layer;

[0173] (2) Substituting equation (8) into the heat conduction equation (2) and the boundary conditions (3)-(6), we get:

[0174]

[0175] -k1X1′=0,(x=x1) (10)

[0176] -k i X i ′Γ i =-k i+1 X i+1 ′Γ i+1 (x=x i+1 (i = 1, 2) (11)

[0177] X i Γ i =X i+1 Γ i+1 (x=x i+1(i = 1, 2) (12)

[0178] -k3X3′=0,(x=x4) (13)

[0179] Based on equations (11)-(12), the time function of the i-th layer is:

[0180]

[0181] (3) Since the time functions of each layer are equal, equations (10)-(14) are an eigenfunction problem concerning the space function, and the eigenfunctions of the space function are:

[0182] X(β m ,x)=X i (β m ,x) (15)

[0183] Where, β=β m These are the eigenvalues ​​of the eigenfunction;

[0184] The orthogonality relation of the eigenfunctions is as follows:

[0185]

[0186] Where, modulus N(β) m )for:

[0187]

[0188] The superposition coefficient c is obtained from the initial condition (7) and the orthogonality relation (16). m :

[0189]

[0190] The solution for the temperature distribution is:

[0191]

[0192] c m Substituting into equation (19), we can simplify to obtain:

[0193]

[0194] Eigenfunction X i The general solution for (β,x) is:

[0195]

[0196]

[0197]

[0198] Substituting equations (21)-(23) into the boundary conditions (10)-(13), we obtain the coefficient matrix of the eigenfunctions:

[0199]

[0200] in, A1,A2,A 3, B1, B2, and B3 are the coefficients of the eigenfunction equation;

[0201] 2. Let f(t) be a function of the laser pulse. Based on the homogeneous solution of the temperature distribution, the temperature distribution of the sample under the action of the thermal pulse is solved by the Green's function.

[0202] Let the Green's function be:

[0203]

[0204] The solution for the temperature distribution is:

[0205]

[0206] Substituting equation (25) into the calculation formula (1) for the theoretical thermal response current, we can obtain the theoretical thermal response current.

[0207] The background section mentions Chinese patent CN114264695A, which describes a method and system for measuring the thermal conductivity of a trace liquid. This method uses a pre-detector to measure the thermal conductivity of the liquid. When the heat exchange between the liquid and the dielectric film reaches a critical value, the increase in the thermal conductivity of the liquid will no longer affect the temperature distribution of the dielectric film, resulting in an insignificant change in the thermal response current and ultimately affecting the measurement accuracy.

[0208] The measurement scheme proposed in this invention employs a post-detector method, where the thermal pulse passes sequentially through the metal target layer, the liquid, and then to the dielectric detector film. When the liquid thickness and laser pulse are constant, the higher the thermal conductivity of the measured liquid, the higher the energy absorbed by the dielectric detector, and the more significant the temperature change of the detector. Therefore, this invention is suitable for liquids with relatively high thermal conductivity.

[0209] To demonstrate the effectiveness of this invention, this embodiment verifies the feasibility of the scheme through simulation experiments. The heat source is a pulsed laser with a pulse width of 25 ns and a wavelength of 1064 nm. The parameters of each layer of the sample are shown in Table 1. Assuming the thermal conductivity of the tested liquid is 1 W / (m·K), 10 W / (m·K), and 100 W / (m·K), the theoretical thermal response currents obtained are... Figure 2 The response current curve shown is as follows. Figure 2The theoretical thermal response currents obtained through simulation models for liquid thermal conductivity of 1 W / (m·K), 10 W / (m·K), and 100 W / (m·K) are shown. It can be seen that the characteristics of the response current curve depend on the thermal conductivity of the liquid being measured. For high thermal conductivity liquids with unknown thermal conductivity, this characteristic can be fitted to infer their thermal conductivity. Furthermore, the response currents corresponding to thermally conductive liquids in the range of 1–100 W / (m·K) show a high degree of differentiation, indicating that this method can clearly determine the thermal conductivity of liquids in the range of 1–100 W / (m·K), overcoming the shortcomings of Chinese Patent CN114264695A (a method and system for measuring the thermal conductivity of trace liquids) in terms of low measurement accuracy for trace amounts of highly thermally conductive liquids. Moreover, in practice, the minimum sample volume required for this invention is less than 1 microliter, which also meets the measurement requirements for trace liquids.

[0210] Table 1 Sample Simulation Parameters

[0211]

[0212] The present invention also provides a system for measuring the thermal conductivity of a high thermal conductivity trace liquid, comprising:

[0213] A test stand is provided, on which a dielectric film with known parameters and a metal thin layer with known parameters are placed. The liquid to be tested is placed between the dielectric film and the metal thin layer. The dielectric film is a dielectric film that has undergone double-sided metallization.

[0214] The measuring device includes a voltage unit, a laser unit, and a data acquisition unit. The voltage unit is used to apply a DC voltage to both sides of the dielectric film to create a uniformly distributed electric field inside the dielectric film. The laser unit is used to apply a laser pulse to the metal thin layer. The data acquisition unit is used to acquire the thermal response current generated by the metal thin layer-test liquid-dielectric film under the action of the laser pulse, which is recorded as the experimental thermal response current.

[0215] The simulation model unit is used to combine the parameters of the dielectric thin film and the metal thin film to establish a heat transfer simulation model of the metal thin film-liquid under test-dielectric thin film. The simulation model is used to calculate the temperature distribution change within the dielectric thin film.

[0216] The fitting unit takes the thermal conductivity of the liquid under test as an unknown variable, adjusts the thermal conductivity of the liquid under test in the simulation model, calculates the corresponding temperature distribution change in the medium film, calculates the theoretical thermal response current based on the temperature distribution change, and extracts the features of the theoretical thermal response current and the experimental thermal response current for comparison and fitting.

[0217] The judgment unit determines whether the fit between the theoretical thermal response current and the experimental thermal response current meets the preset convergence conditions.

[0218] 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.

[0219] 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 high thermal conductivity trace liquid, characterized in that, Includes the following steps: A dielectric thin film with known parameters is subjected to double-sided metallization, and the liquid to be tested is placed between the dielectric thin film and a metal thin layer with known parameters. An external circuit is connected to the dielectric thin film to create a uniformly distributed electric field inside the dielectric thin film, which serves as a dielectric detector. The metal thin layer is used as an absorption target. A laser pulse is applied to the metal thin layer, and the thermal response current generated by the metal thin layer, the liquid under test, and the dielectric thin film under the action of the laser pulse is collected and recorded as the experimental thermal response current. By combining the parameters of the dielectric thin film and the metal thin film, a heat transfer simulation model of the metal thin film-liquid under test-dielectric thin film is established. The simulation model is used to calculate the temperature distribution change within the dielectric thin film. The thermal conductivity of the liquid under test is taken as an unknown variable. The thermal conductivity of the liquid under test in the simulation model is adjusted to calculate the corresponding temperature distribution change in the medium film. The theoretical thermal response current is calculated based on the temperature distribution change. The characteristics of the theoretical thermal response current and the experimental thermal response current are extracted and compared for fitting. If the fitting degree of the two meets the preset convergence condition, the thermal conductivity of the liquid in the 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 established simulation model is as follows: Heat conduction equation: , Boundary conditions: , Initial conditions: , in, The spatial position along the thickness direction of the metal thin film-liquid-medium thin film structure. For time, These correspond to the surfaces of the metal thin film receiving laser pulses, the metal thin film in contact with the liquid being tested, the dielectric thin film in contact with the liquid being tested, and the dielectric thin film not in contact with the liquid being tested, respectively. The layers represent a thin metal layer, the liquid being tested, and a thin dielectric 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 heat source boundary of the laser pulse. The ambient temperature; The temperature distribution change within the dielectric film was calculated using the simulation model as follows: I. Assumptions The homogeneous solution of the equation is obtained by using the method of separation of variables; (1) The separation variable is the product of a time function and a space function, as follows: , in, For the first The spatial function of the layer, For the first The time function of the layer; (2) Substituting equation (8) into the heat conduction equation (2) and the boundary conditions (3)-(6), we get: , According to equations (11)-(12), the first... The time function of the layer is: , (3) Since the time functions of each layer are equal, equations (10)-(14) are an eigenfunction problem concerning the space function, and the eigenfunctions of the space function are: , in, These are the eigenvalues ​​of the eigenfunction; The orthogonality relation of the eigenfunctions is as follows: , Among them, the model for: , The superposition coefficient is obtained from the initial condition (7) and the orthogonality relation (16). : , The solution for the temperature distribution is: , Will Substituting into equation (19), we can simplify to obtain: , Eigenfunctions The general solution is: , Substituting equations (21)-(23) into the boundary conditions (10)-(13), we obtain the coefficient matrix of the eigenfunctions: , in, , , The coefficients of the eigenfunction equation; II. Setting The temperature distribution of the sample under the action of the thermal pulse is solved by Green's function based on the homogeneous solution of the temperature distribution. Let the Green's function be: , The solution for the temperature distribution is: , Substituting equation (25) into the formula for calculating the theoretical thermal response current yields the theoretical thermal response current.

2. The method for measuring the thermal conductivity of a high thermal conductivity trace liquid according to claim 1, characterized in that, There is no air residue between the liquid being tested, the dielectric film, and the metal thin layer. The laser spot diameter of the laser pulse applied to the metal thin layer is 1-2 orders of magnitude larger than the thickness of the liquid being tested. The thickness of the liquid being tested is 50-100 micrometers, and the thickness of the metal thin layer is 1-10 micrometers.

3. The method for measuring the thermal conductivity of a high thermal conductivity trace liquid according to claim 1, characterized in that, The formula for calculating the theoretical thermal response current is: , , in, This is the theoretical thermal response current. The spatial position along the thickness direction of the metal thin film-liquid-medium thin film structure. For time, For the temperature change inside the dielectric thin film, The coefficient of the dielectric thin film, , These represent the area irradiated by the laser and the thickness of the medium detector, respectively. For electric field distribution, The vacuum permittivity and the relative permittivity of the sample are compared respectively. These are the temperature coefficient of the relative permittivity and the coefficient of thermal expansion of the sample, respectively.

4. A system for measuring the thermal conductivity of a high thermal conductivity trace liquid, characterized in that, include: A test stand, on which a dielectric film with known parameters and a metal thin layer with known parameters are placed, and the liquid to be tested is placed between the dielectric film and the metal thin layer, wherein the dielectric film is a dielectric film that has undergone double-sided metallization treatment; The measuring device includes a voltage unit, a laser unit, and a data acquisition unit. The voltage unit is used to apply a DC voltage to both sides of the dielectric film to create a uniformly distributed electric field inside the dielectric film. The laser unit is used to apply a laser pulse to the metal thin layer. The data acquisition unit is used to acquire the thermal response current generated by the metal thin layer-test liquid-dielectric film under the action of the laser pulse, which is denoted as the experimental thermal response current. The simulation model unit is used to combine the parameters of the dielectric thin film and the metal thin film to establish a heat transfer simulation model of the metal thin film-liquid under test-dielectric thin film. The simulation model is used to calculate the temperature distribution change within the dielectric thin film. The fitting unit takes the thermal conductivity of the liquid under test as an unknown variable, adjusts the thermal conductivity of the liquid under test in the simulation model, calculates the corresponding temperature distribution change in the medium film, calculates the theoretical thermal response current based on the temperature distribution change, and extracts the features of the theoretical thermal response current and the experimental thermal response current for comparison and fitting. The judgment unit determines whether the fit between the theoretical thermal response current and the experimental thermal response current meets the preset convergence conditions. The established simulation model is as follows: Heat conduction equation: , Boundary conditions: , Initial conditions: , in, The spatial position along the thickness direction of the metal thin film-liquid-medium thin film structure. For time, These correspond to the surfaces of the metal thin film receiving laser pulses, the metal thin film in contact with the liquid being tested, the dielectric thin film in contact with the liquid being tested, and the dielectric thin film not in contact with the liquid being tested, respectively. The layers represent a thin metal layer, the liquid being tested, and a thin dielectric 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 heat source boundary of the laser pulse. The ambient temperature; The temperature distribution change within the dielectric film was calculated using the simulation model as follows: I. Assumptions The homogeneous solution of the equation is obtained by using the method of separation of variables; (1) The separation variable is the product of a time function and a space function, as follows: , in, For the first The spatial function of the layer, For the first The time function of the layer; (2) Substituting equation (8) into the heat conduction equation (2) and the boundary conditions (3)-(6), we get: , According to equations (11)-(12), the first... The time function of the layer is: , (3) Since the time functions of each layer are equal, equations (10)-(14) are an eigenfunction problem concerning the space function, and the eigenfunctions of the space function are: , in, These are the eigenvalues ​​of the eigenfunction; The orthogonality relation of the eigenfunctions is as follows: , Among them, the model for: , The superposition coefficient is obtained from the initial condition (7) and the orthogonality relation (16). : , The solution for the temperature distribution is: , Will Substituting into equation (19), we can simplify to obtain: , Eigenfunctions The general solution is: , Substituting equations (21)-(23) into the boundary conditions (10)-(13), we obtain the coefficient matrix of the eigenfunctions: , in, , , The coefficients of the eigenfunction equation; II. Setting The temperature distribution of the sample under the action of the thermal pulse is solved by Green's function based on the homogeneous solution of the temperature distribution. Let the Green's function be: , The solution for the temperature distribution is: , Substituting equation (25) into the formula for calculating the theoretical thermal response current yields the theoretical thermal response current.

5. The system for measuring the thermal conductivity of a high thermal conductivity trace liquid according to claim 4, characterized in that, There is no air residue between the liquid being tested, the dielectric film, and the metal thin layer. The laser spot diameter of the laser pulse applied to the metal thin layer is 1-2 orders of magnitude larger than the thickness of the liquid being tested. The thickness of the liquid being tested is 50-100 micrometers, and the thickness of the metal thin layer is 1-10 micrometers.

6. The system for measuring the thermal conductivity of a high thermal conductivity trace liquid according to claim 4, characterized in that, The formula for calculating the theoretical thermal response current is: , , in, This is the theoretical thermal response current. The spatial position along the thickness direction of the metal thin film-liquid-medium thin film structure. For time, For the temperature change inside the dielectric thin film, For the coefficient of the dielectric thin film, , These represent the area irradiated by the laser and the thickness of the medium detector, respectively. For electric field distribution, The vacuum permittivity and the relative permittivity of the sample are compared respectively. These are the temperature coefficient of the relative permittivity and the coefficient of thermal expansion of the sample, respectively.

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