JP7016141B2 - Thermophysical property measuring device and thermophysical property measuring method - Google Patents

Description

The present invention relates to an apparatus and a method for measuring thermophysical characteristics such as thermoelectricity and thermal conductivity of a solid.

The absolute value of the thermoelectric power of a metal material such as lead or platinum is an indispensable physical property value in a relative measurement method of thermoelectric power widely used in the field of physical property measurement. Absolute thermoelectric power is derived by comparative measurement using a superconductor as a reference material, utilizing the state where the thermoelectric power of a metal material becomes zero. Since this method limits the measurable temperature range to a temperature lower than the superconducting transition temperature, in order to expand the measurable temperature range, the absolute thermoelectricity is used from the measurable Thomson coefficient using the Kelvin relational expression. It is necessary to guide the ability.

Here, in the following Patent Document 1, the Thomson coefficient is not used in the thermal conductivity, dimensions, and heat loss value from the thermometer in a sample such as metal, which is required by the conventional direct current method (DC method). The technique of the alternating current method (AC method) for measuring the temperature is disclosed.

WO / 2015/025586

However, in the above AC method described in Patent Document 1, even the heat loss generated on the surface of the sample to be measured is not taken into consideration. Therefore, an ideal measurement environment is required, but there is a problem that a large cost is incurred in order to perform measurement in such an environment.

The present invention has been made to solve the above-mentioned problems, and provides a thermophysical property measuring device and a thermophysical property measuring method capable of easily obtaining highly accurate absolute thermoelectricity and thermal conductivity at a lower cost. The purpose is to provide.

In order to solve the above problems, the present invention applies an AC voltage or an AC current to a metal to which a temperature gradient is applied, measures the first temperature change in the central portion of the metal, and applies an AC voltage to the metal. A positive DC voltage equal to the value or a positive DC current equal to the effective value of the AC current is applied, the second temperature change in the central portion is measured, and a negative DC voltage equal to the effective value of the AC voltage is measured. A measuring means for measuring a third temperature change in the central portion by applying a negative DC current equal to the effective value of a voltage or an alternating current, and a difference between the second temperature change and the third temperature change. The Thomson coefficient in an ideal environment based on the ratio to the first temperature change depends on (PγL) / K (P is the circumferential length in the cross section of the metal, L is the length of the metal, and K is the thermal conductance of the metal). Provided is a thermophysical property measuring device provided with a calculation means for calculating a Thomson coefficient of a metal by correcting with a correction term . Note that γ includes the term 4εσT ₀ ³ (ε is the radiance rate, σ is the Stefan-Boltzmann constant, and T ₀ is the ambient temperature of the metal).

Further, in order to solve the above problems, the present invention applies an AC voltage or an AC current to a metal to which a temperature gradient is applied, measures the first temperature change in the central portion of the metal, and applies an AC voltage to the metal. A positive DC voltage equal to the effective value of the AC voltage or a positive DC current equal to the effective value of the AC current is applied to measure the second temperature change in the central portion, and the negative voltage equal to the effective value of the AC voltage. The difference between the step of measuring the third temperature change in the central portion by applying a negative DC current equal to the effective value of the DC voltage or AC current of the above, and the difference between the second temperature change and the third temperature change. The Thomson coefficient in an ideal environment based on the ratio of to the first temperature change is (PγL) / K (P is the circumferential length in the cross section of the metal, L is the length of the metal, K is the thermal conductance of the metal). Provided is a thermophysical property measuring method including a step of calculating a Thomson coefficient of a metal by correcting with a corresponding correction term . Note that γ includes the term 4εσT ₀ ³ (ε is the radiance rate, σ is the Stefan-Boltzmann constant, and T ₀ is the ambient temperature of the metal).

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a thermophysical property measuring device and a thermophysical characteristic measuring method capable of easily obtaining highly accurate absolute thermoelectricity and thermal conductivity at a lower cost.

It is a block diagram which shows the structure of the thermophysical characteristic measuring apparatus 1 which concerns on embodiment of this invention. It is a figure which shows the structure of the measuring part 3 shown in FIG. It is a flowchart which shows the thermophysical characteristic measurement method which concerns on embodiment of this invention. It is a block diagram which shows the structure of the thermophysical characteristic measuring apparatus 10 which concerns on other embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the figure, the same reference numerals indicate the same or corresponding parts.

FIG. 1 is a block diagram showing a configuration of a thermophysical characteristic measuring device 1 according to an embodiment of the present invention. As shown in FIG. 1, the thermophysical characteristic measuring device 1 includes a bus 2, a measuring unit 3, a calculation unit 4, a storage unit 5, a display unit 6, and an operation unit 7, which are connected to the bus 2, respectively.

Here, the measuring unit 3 measures the thermoelectric characteristics of the thin metal wire (hereinafter referred to as “metal sample”) or the like, as will be described in detail later. Further, the operation unit 7 receives an operation command for the user's thermophysical characteristic measuring device 1, and the calculation unit 4 calculates the Thomson coefficient, and by extension, the absolute thermoelectricity and thermal conductivity in response to the operation command. Further, the storage unit 5 stores the data measured by the measurement unit 3 and the calculation result by the calculation unit 4, and the display unit 6 visually displays the data stored in the storage unit 5 in response to the operation command. Display for recognition.

FIG. 2 is a diagram showing the configuration of the measuring unit 3 shown in FIG. As shown in FIG. 2, the measuring unit 3 includes a chamber 31, metal blocks 32, 33, thermocouples 35, 61, 62, heating heaters 63, 64, a temperature controller 65, and a voltage application unit 30. The voltage application unit 30 includes a positive DC power supply 36, a negative DC power supply 37, an AC power supply 38, and a switch 39. Here, as the AC power source 38, for example, a quantized AC voltage generator whose effective value can be easily calculated is used, but another AC power source may be used.

Further, the measurement points of the thermocouple 61 for measuring the temperature of the metal block 32 and the thermocouple 62 for measuring the temperature of the metal block 33 are the portions where the metal sample 34 and the metal blocks 32 and 33 are connected, respectively. Placed in.

Then, the temperature controller 65 supplies the heater control signals Hc corresponding to the temperatures measured by the thermocouples 61 and 62 to the heating heaters 63 and 64, so that the temperatures of the metal blocks 32 and 33 are set to the temperatures T1 and ₁ , respectively. The heating heaters 63 and 64 are controlled so as to supply a heat amount such that T ₂ . Specifically, the temperature controller 65 can realize accurate temperature control by using a Pelche element or the like while monitoring the temperature with the thermocouples 61 and 62.

Then, for example, a metal sample 34 is installed as a measurement target in the measurement unit 3 having such a configuration. A thermocouple 35 is attached to the central portion of the metal sample 34 in order to measure heat absorption and heat generation due to the Thomson effect, and further heat generation due to the Joule effect when an AC voltage is applied. At this time, in order to reduce the outflow of heat from the thermocouple 35, a thermocouple having a sufficiently small thermal conductance is attached.

Further, a DC / AC voltage generator 30 capable of generating a DC voltage having a different polarity and an AC voltage having the same effective value as the DC voltage having different polarities is connected between both ends of the metal sample 34. Here, the waveforms of the AC voltage and the AC current generated by the AC power supply 38 may be periodic, and for example, a sine wave or a square wave can be considered.

Then, the switch 39 included in the DC / AC voltage generator 30 selectively conducts (turns on) the positive DC power supply 36, the negative electrode DC power supply 37, and the AC power supply 38 by the control signal Ct.

FIG. 3 is a flowchart showing a thermophysical characteristic measuring method according to an embodiment of the present invention. Hereinafter, the method for measuring thermophysical properties according to the embodiment of the present invention will be described with reference to FIG. In the following, the case where this method is realized by using the thermophysical property measuring device 1 shown in FIGS. 1 and 2 will be described, but it goes without saying that this method is not limited to the thermophysical characteristic measuring device 1 and can be widely applied. stomach.

In step S1, an AC voltage or an AC current is applied to the metal sample 34 to which the temperature gradient is applied by turning on the AC power supply 38, and the first temperature change in the central portion of the metal sample 34 is measured by the thermocouple 35. do.

Next, in step S2, by turning on the positive DC power supply 36 or the negative DC power supply 37, the polarity of the metal sample 34 is different, and the DC voltage equal to the effective value of the AC voltage or the effective value of the AC current. A second temperature change in the central portion of the metal sample 34 is measured by the thermocouple 35 by applying a direct current equal to.

Next, in step S3, the Thomson coefficient is calculated from the ratio of the second temperature change to the first temperature change, which will be described in detail later.

Then, in step S4, at least one of the absolute thermoelectric power and the thermal conductivity of the metal sample 34 is calculated using the Thomson coefficient calculated in step S3.

Hereinafter, a specific example of the thermophysical characteristic measurement method according to the embodiment of the present invention shown in FIG. 3 will be described in detail.

In order to derive the Thomson coefficient that takes into account the heat loss that occurs on the surface of the metal to be measured, consider the following thermal analysis model. As shown in FIG. 2, a temperature difference is applied to both ends of the metal sample, and a current is applied to the metal sample. At this time, the heat flow generated in the metal sample diffuses in the metal sample and flows to both ends of the metal sample. Further, a heat loss flow is generated from the surface of the metal sample according to the temperature difference between the metal sample and the ambient temperature.

When the current I flows through a thin metal wire satisfying the thermal boundary condition in such a thermal analysis model, the heat conduction equation in the steady state of the heater can be expressed as the following equation (1).

In equation (1), the first term on the left side represents solid heat conduction, the second term represents heat generation and endothermic due to the Thomson effect, the third term represents Joule heat generation, and the fourth term represents heat loss from the metal surface due to natural convection and radiation. ing. Here, the variable T is the temperature, and the variable x is the position coordinates of the metal sample. The other parameters are constants, where a is the cross-sectional area, κ is the thermal conductivity, μ is the Thomson coefficient, I is the current, ρ is the electrical resistance, h is the heat transfer coefficient, and P is the outer circumference length in the cross section of the metal sample. , T ₀ is the ambient temperature of the metal sample, ε is the radiation coefficient, and σ is the Stefan-Boltzmann constant.

Here, assuming that the temperature difference is small, the heat loss due to radiation is linearized and analyzed. The boundary condition when a constant temperature difference ΔT is given to both ends of the metal sample, that is, the temperature T (0) at one end is the temperature T _c on the low temperature side, and the temperature T (L) at the other end is the temperature T on the high temperature side. When it is _h , an analytical solution of the temperature distribution as shown in the following equation (2) can be obtained as the solution of the equation (1).

In formula (2), K represents the thermal conductance of the metal sample and is defined as (κ · A) / L using the thermal conductivity κ, cross-sectional area A, and length L of the metal sample. Further, R is the electric resistance of the metal sample and is represented by (ρ · A) / L. The dimensionless parameters κ ₁ and κ ₂ included in equation (2) are solutions to the quadratic equation of equation (3).

Ξ in the equation (3) is a dimensionless constant representing the ratio of the Thomson heat to the thermal conductance of the metal sample. The parameters κ ₁ and κ ₂ are functions of the Thomson coefficient μ and the heat transfer coefficient h, and if the heat transfer coefficient h is zero, the solution of Eq. (3) is the Thomson coefficient.

Since the temperature required in the formula (2) is the temperature in the central portion of the metal sample, L / 2 is substituted for x in the formula (2). Furthermore, since the parameters κ ₁ and κ ₂ are constants related to the Thomson effect and are sufficiently smaller than 1, equation (2) can be expanded to a power series around the parameters κ ₁ and κ ₂ . That is, if T ₀ is ( T _c + _Th ) / 2 and the terms of the third order or higher are ignored, the equation (2) can be expressed as the following equation (4).

Here, the first term of the formula (4) includes the initial temperature of the metal sample, the second term includes the temperature rise due to Thomson heat including the heat loss from the metal sample surface, and the third term includes the heat loss from the metal sample surface. Joule heat generation, the fourth term corresponds to heat loss from the metal sample.

Next, a known derivation method of the Thomson coefficient will be described based on the equation (4). The endothermic and heat generation due to the first-order Thomson effect depends on the polarity of the current, whereas the Joule effect and natural convection do not depend on the polarity of the current. Therefore, if the temperature change when the current is applied in the positive direction is T _{DC +} and the temperature change when the current is applied in the opposite direction is T _DC- , these temperature changes are as follows using Eq. (4). It can be expressed as equations (5) and (6).

Here, the temperature difference δT at the center of the metal sample obtained by reversing the polarity of the applied current is defined by the following equation (7).

By substituting the equations (5) and (6) into the above equation (7), the temperature difference δT can be expressed as the following equation (8). That is, the effect of the Joule term and the second-order Thomson effect is canceled by the polarity reversal operation of the current, and the temperature difference δT when a direct current is applied can be expressed only by the term of the first-order Thomson effect.

Here, when the equation (8) is solved for the Thomson coefficient μ, the following equation (9) can be obtained in consideration of the heat loss from the surface of the metal sample.

As described above, when there is convection such as natural convection, a correction term corresponding to the ratio of the heat loss due to them and the thermal conductance of the metal sample is added. In this analysis, the temperature around the metal sample is used as the sample average temperature, but the temperature of the metal sample is not uniform because the metal sample has a temperature gradient, Joule heat, and a temperature rise due to the Thomson effect. It can be seen that heat loss due to convection and radiation is inevitable.

Next, a method for deriving the Thomson coefficient by an alternating current (AC) method in which an alternating current is combined with a direct current will be described. When an AC voltage VAC is applied to a thin metal wire that satisfies the same thermal boundary conditions as in the case of direct current and an AC current I (ω) flows, the temperature distribution T in the steady state of the thin metal wire is given by the following equation (10). It is expressed by the heat conduction equation of.

Here, since the endothermic and heat generation effects due to the Thomson effect are proportional to the sinusoidal current, the equation (10) is simplified as in the following equation (11) under the condition that the frequency is sufficiently high to offset the Thomson heat. Be made.

The differential equation of the equation (11) corresponds to the case where the Thomson term is set to zero in the equation (1) in the case of direct current, and the temperature change in the central part of the metal sample can be immediately obtained as in the following equation (12). can.

Equation (12) has a form in which a correction term for heat loss due to convection is added to the temperature rise due to Joule heat generation. That is, under the condition that the frequency is sufficiently high, the Thomson effect is canceled out, and the temperature distribution is such that the Joule effect is superimposed on the initially given temperature gradient.

Here, when the equation (12) is substituted into the equation (8), the equation (8) is transformed into the following equation (13).

Equation (13) includes the ratio of temperature changes (δT / ΔT _AC ) at the center of the metal sample when direct current and alternating current are applied to the same metal sample. Therefore, according to the known direct current (DC) method, the Thomson coefficient is obtained by the alternating current method based on the equation (13), whereas the temperature is directly affected by the heat loss due to natural convection and radiation. In the case, since the ratio of the temperature change is used instead of the temperature as described above, the influence of the heat loss can be reduced. This is because the heat loss related to P ^* (= PγL / K) contained in the equation (8) and the equation (12) is offset by calculating the ratio of the temperature change in the process of deriving the equation (13). be.

Specifically, referring to the equation (9), when the Thomson coefficient is calculated using the equation (13), the influence of heat loss on the Thomson coefficient is reduced to 1/6 of the conventional value. I understand.

The above-mentioned thermophysical property measuring method can also be realized by expressing the algorithm according to this method in a program and causing the thermophysical characteristic measuring device 10 shown in FIG. 4 to execute the algorithm.

Here, the thermophysical characteristic measuring device 10 includes an input / output node 12, a bus 13 connected to the input / output node 12, a central processing unit (CPU) 14 connected to the bus 13, and a memory 15.

In the thermophysical property measuring device 10 having such a configuration, the program is stored in the memory 15, and the CPU 14 reads the program from the memory 15 and executes the program to measure the thermophysical characteristics according to the embodiment of the present invention. The method is realized.

From the above, according to the thermoelectric power measuring method and the thermophysical property measuring device according to the embodiment of the present invention, the Thomson coefficient can be measured even in an air or gas atmosphere. Therefore, in the measurement above room temperature, the vacuum exhaust device or the radiation shield Is no longer needed. Further, even in a low temperature experiment below room temperature for deriving the Seebeck coefficient, vacuum exhaust of the heat exchange gas becomes unnecessary, so that the turnaround time in the measurement can be significantly shortened.

From these, according to the thermoelectric power measuring method and the thermophysical characteristic measuring apparatus according to the embodiment of the present invention, it is possible to easily obtain highly accurate absolute thermoelectric power and thermal conductivity at a lower cost.

1 Thermophysical property measuring device 3 Measuring unit 4 Calculation unit 32, 33 Metal block 34 Metal wire (metal sample)
35, 61, 62 Thermocouple 36 Positive DC power supply 37 Negative DC power supply 38 AC power supply 39 Switch 63, 64 Heating heater 65 Temperature controller 30 DC / AC voltage generator

Claims (5)

An AC voltage or AC current is applied to the metal to which the temperature gradient is applied, the first temperature change in the central portion of the metal is measured , and the positive DC voltage or positive DC voltage equal to the effective value of the AC voltage is applied to the metal. A positive DC current equal to the effective value of the AC current is applied to measure the second temperature change in the central portion, and a negative DC voltage equal to the effective value of the AC voltage or the effective AC current. A measuring means for measuring a third temperature change in the central portion by applying a negative DC current equal to the value ,
The Thomson coefficient in an ideal environment based on the ratio of the difference between the second temperature change and the third temperature change and the first temperature change is (PγL) / K (P is in the cross section of the metal. A calculation means for calculating the Thomson coefficient of the metal by correcting with a correction term according to the circumference length, L is the length of the metal, and K is the thermal conductance of the metal .
Equipped with
The γ includes a term of 4εσT ₀ ³ (ε is the radiance rate, σ is the Stefan-Boltzmann constant, and T0 _is the ambient temperature of the metal).
Thermophysical property measuring device. The thermophysical property measuring device according to claim 1 , wherein the measuring means includes a quantized AC voltage generator that generates the AC voltage when the AC voltage is applied . The thermophysical characteristic measuring device according to claim 1 or 2, wherein the calculation means calculates the absolute thermoelectricity of the metal using the calculated Thomson coefficient. An AC voltage or AC current is applied to the metal to which the temperature gradient is applied, the first temperature change in the central portion of the metal is measured , and the positive DC voltage or positive DC voltage equal to the effective value of the AC voltage is applied to the metal. A positive DC current equal to the effective value of the AC current is applied to measure the second temperature change in the central portion, and a negative DC voltage equal to the effective value of the AC voltage or the effective AC current. A step of measuring a third temperature change in the central portion by applying a negative DC current equal to the value, and
The Thomson coefficient in an ideal environment based on the ratio of the difference between the second temperature change and the third temperature change and the first temperature change is (PγL) / K (P is in the cross section of the metal. The step of calculating the Thomson coefficient of the metal by correcting with the correction term according to the circumference length, L is the length of the metal, and K is the thermal conductance of the metal).
Including
The γ includes a term of 4εσT ₀ ³ (ε is the radiance rate, σ is the Stefan-Boltzmann constant, and T0 _is the ambient temperature of the metal).
Thermophysical characteristic measurement method. The method for measuring thermophysical properties according to claim 4, further comprising a step of calculating the absolute thermoelectricity of the metal using the calculated Thomson coefficient.

Images