JP2019120531A - Thermophysical property measuring apparatus and thermophysical property measuring method - Google Patents

Abstract

To provide a thermophysical property measuring apparatus and thermophysical property measuring method capable of conveniently obtaining a thermophysical property value such as accurate thermoelectric power and thermal conductivity regardless of the nature of a sample to be measured.SOLUTION: A thermophysical property measuring apparatus 50 includes current applying means for selectively applying a DC current of positive or negative polarity or an AC current with the same effective value of the DC current to an object to be measured with no temperature difference at both ends contained in the measuring unit 55, and temperature measuring means disposed at a measurement point on a central position or shifted by any distance from the central position of the object to be measured for measuring the temperature of the object to be measured, and a calculation unit 54 for calculating the Thomson coefficient of the object to be measured by calculating the ratio of a first temperature change at the measurement point shifted by any distance from the central portion measured when applying a different DC current of polarity at both ends by the current applying means, and a second temperature change in the central portion measured when the AC current is applied by the current applying means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for measuring thermophysical properties such as thermopower and thermal conductivity.

  Generally, in order to obtain the Thomson coefficient, absolute Seebeck coefficient (thermopower) and thermal conductivity of a sample, current is supplied to the sample to which a temperature gradient is applied, as also shown in Patent Document 1. A method is taken to measure the amount of heat generated above.

WO 2015/025586

  However, in the case of the above measurement, in order to apply a temperature gradient to the sample, it is necessary to install two heaters for heating both ends of the sample and a thermometer for measuring the temperature of each heater. There is a problem that it takes time to prepare for measurement.

  Moreover, in the sample which said temperature gradient does not produce easily, there also exists a problem that the precision in the said measurement worsens.

  The present invention has been made to solve the above problems, and can easily obtain accurate thermophysical properties such as thermopower and thermal conductivity regardless of the properties of the sample to be measured. An object of the present invention is to provide a thermophysical property measuring device and a thermophysical property measuring method.

  In order to solve the above problem, a current applying means for selectively applying an alternating current whose positive or negative direct current or effective value is the magnitude of the direct current to a measurement object having no temperature difference at both ends; A direct current with different polarity is applied to the both ends by the temperature measuring means for measuring the temperature of the object to be measured, which is disposed at the measurement point at an arbitrary distance from the central portion and the central portion of the object to be measured The first temperature change at a measurement point shifted by an arbitrary distance from the central portion measured by the temperature measuring means when applied and the AC current measured by the current applying means are measured by the temperature measuring means Thermophysical property measuring apparatus comprising arithmetic means for calculating the Thomson coefficient of the object to be measured by calculating the ratio to the second temperature change in the central portion To provide.

  Further, in order to solve the above problem, DC current of different polarity is applied to the both ends of the measurement object having no temperature difference at both ends, and the first at the measurement point deviated from the center of the measurement object by an arbitrary distance A second step of measuring a second temperature change at the central portion by applying an alternating current whose effective value is the magnitude of the direct current across the two ends. Calculating a ratio of the first temperature change measured in the first step to the second temperature change measured in the second step to calculate a Thomson coefficient of the measurement object The thermal physical property measuring method which has three steps is provided.

  According to the present invention, it is possible to simply and accurately obtain thermophysical properties such as thermopower and thermal conductivity regardless of the properties of the sample to be measured.

It is a block diagram which shows the structure of the thermophysical property measuring apparatus 50 which concerns on embodiment of this invention. It is a figure which shows the structure of the measurement part 55 shown by FIG. It is a flowchart which shows the thermal physical-property measurement method implement | achieved using the thermal physical-property measurement apparatus 50 shown by FIG. It is the graph which showed the temperature distribution of the sample 4 shown by FIG.

  Hereinafter, a thermophysical property measurement device and a thermophysical property measurement method according to an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or equivalent parts.

  FIG. 1 is a block diagram showing the configuration of a thermophysical property measurement apparatus 50 according to the embodiment of the present invention. As shown in FIG. 1, the thermal property measuring apparatus 50 includes a user interface 51, a storage unit 53, an arithmetic unit 54, a measuring unit 55, and a bus 52 connecting these components to one another.

  Here, the user interface 51 has a function of receiving an operation command to the thermal property measuring apparatus 50 of the user and displaying the generated data so that the user can visually recognize. Further, the storage unit 53 stores the program executed by the calculation unit 54 and stores data supplied via the bus 52. Arithmetic unit 54 performs a predetermined arithmetic operation on the supplied data by executing the program stored in advance in storage unit 53. The specific contents of the calculation will be described in detail later. The measurement unit 55 also measures the thermoelectric characteristics of the sample to be measured.

  FIG. 2 is a diagram showing the configuration of the measurement unit 55 shown in FIG. As shown in FIG. 2, the measurement unit 55 includes a chamber 1, metal blocks 2 and 3, thermocouples 5 and 10, and a current application unit 100. Here, the current application unit 100 includes a positive polarity DC power supply 6 for generating a DC current, a negative polarity DC power supply 7 for generating a DC current having the same magnitude and polarity as the DC current, and the DC current having an effective value And an AC power supply 8 for generating an AC current having a magnitude of and a switch 9.

The measurement unit 55 is designed to be able to sufficiently satisfy the thermal boundary conditions in thermal analysis. Specifically, the inside of the chamber 1 is evacuated to suppress the convective transfer of heat, and the metal blocks 2 and 3 of the temperature T ₁ are connected to both ends of the sample 4. These metal blocks 2 and 3 have a function as a heat bath.

  In addition, a thermocouple 10 is attached to the central part of the sample 4, but in order to actively utilize the self-joule heat generation of the sample 4 generated simultaneously with Thomson heat, only a given distance x from the central part of the sample 4 The thermocouple 5 is attached to the shifted position (hereinafter referred to as "shift measurement point"). The thermocouples 5 and 10 preferably have a sufficiently small thermal conductance to reduce the heat flow.

  Further, between the ends of the sample 4 is connected a current applying unit 100 capable of generating a direct current having different polarity and an alternating current having an effective value equal to that as described above. Here, the waveform of the alternating current generated by the alternating current power supply 8 may be periodic, and, for example, a sine wave or a rectangular wave can be considered.

  Furthermore, the switch 9 is turned on in the order of the AC power supply 8, the positive polarity DC power supply 6, the negative polarity DC power supply 7, and the AC power supply 8 by the control signal Ct. This operation will be described in detail later.

  FIG. 3 is a flow chart showing a thermal property measuring method realized by the thermal property measuring apparatus 50 shown in FIG. In the following, the thermal physical property measurement method will be described in detail with reference to FIG.

Installing the metal block 2 and 3 of the temperature T ₁ of the opposite ends of the sample 4 in a first step S1. Then, in step S2, the thermocouple 10 is attached to the central portion of the sample 4 and the thermocouple 5 is attached to a shift measuring point which is shifted by an arbitrary distance such as 1/4 of the length of the sample 4 from the central portion. Incidentally, as shown in FIG. 2, x coordinates of both ends of the sample 4, the origin position of the displacement measuring point, respectively the coordinates (-l _1), are the coordinates l _2.

  Here, the reason for attaching the thermocouple 5 to the displacement measurement point as described above will be described. FIG. 4 is a graph showing the temperature distribution of the sample 4 when the horizontal axis represents the position x with the center of the sample 4 as the origin and the vertical axis represents the temperature T of the sample 4.

  As shown in FIG. 4, the temperature distribution due to Joule heating is parabolic as shown by a broken line graph g1. Therefore, the temperature gradient I2 is zero in the central portion of the sample 4, and the Thomson effect due to the temperature gradient caused by the Joule effect does not occur. On the other hand, at positions other than the central portion of the sample 4, since there are finite temperature gradients I1 and I3 as shown in FIG. 4, Thomson heat due to Joule heat is generated. Then, due to such a Thomson effect, the temperature distribution is asymmetrical with respect to the origin, as shown by the graph g2. Therefore, by shifting the measurement position of the temperature from the central portion, it is possible to measure the temperature change due to the Thomson effect due to the temperature gradient generated by the self Joule heating.

  Next, in step S3, the inside of the chamber 1 is evacuated.

Next, in step S4, a direct current I _{+ DC} of positive polarity is applied to both ends of the sample 4 and the temperature T _{+ DC} at the displacement measurement point of the sample 4 is measured by the thermocouple 5. In step S5, both ends of the sample 4 A direct current I- _DC of negative polarity is applied thereto, and the temperature T _-DC at the displacement measurement point of the sample 4 is measured by the thermocouple 5.

Then, in step S6, the calculation unit 54 calculates the average difference between the temperature T _{+ DC} measured in step S4 and the temperature T _-DC measured in step S5 using the following equation (10), The above-mentioned temperature change δT _DC is calculated.

  Next, in step S7, an alternating current is applied to both ends of the sample 4 using an alternating current power supply 8, and the temperature at the central portion of the sample is measured by the thermocouple 10.

Next, in step S8, the computing unit 54 executes the program stored in advance in the storage unit 53 to use the temperature change δT _DC obtained in step S6 and the temperature δT _ACm obtained in step S7. Calculate Thomson coefficient μ. Then, the absolute thermopower S is determined using the Thomson coefficient μ according to the following Kelvin equation (1). In the formula (1), T represents a temperature, and T ₀ represents a superconducting transition temperature.

  Then, in step S9, the calculation unit 54 calculates the thermal conductivity of the sample using the Thomson coefficient μ calculated in step S8, and a specific calculation method will be described later.

  In the thermal property measurement method shown in FIG. 3, the order of step S1 and step S2 may be reversed. Further, either measurement using a direct current consisting of step S4 and step S5 or measurement using an alternating current in step S7 may be performed first. In addition, the calculation of the thermal conductivity in step S9 may not necessarily be performed after the absolute thermopower is determined.

  Hereinafter, the method of calculating the Thomson coefficient μ will be described in detail.

  First, heat conduction analysis based on Fourier's law is performed to derive a theoretical expression of Thomson coefficient at an arbitrary temperature measurement point x.

As shown in FIG. 2, both ends of the sample 4 are kept at a constant temperature T ₁ , and at the same time, a direct current or an alternating current is applied to the sample 4. The heat flow generated in the sample 4 flows into the heat bath having a constant temperature (in this case, room temperature) via the sample and the thermocouple 5 attached to the sample.

The position coordinates of the thermocouple 5, as shown in FIG. 2, the origin shift measuring point, both ends of the sample 4 respectively coordinates (-l _1), a one-dimensional coordinate x such that coordinates l ₂ Indicated. Here, assuming that the total length of the sample 4 is a length l, the length l is equal to the sum of the absolute value of the coordinate (−l ₁ ) and the coordinate l ₂ .

When a direct current I is applied to a sample having the above thermal boundary conditions, the heat conduction equation in the steady state of the sample can be expressed as the following equation (2). In equation (2) and below, a is the cross-sectional area of the sample, κ is the thermal conductivity of the sample, T is the temperature of the sample, ρ is the electrical resistivity of the sample, p is the perimeter of the sample, σ is Stefan-Boltzmann The constant, ε, represents the emissivity of the sample, and T ₀ represents the zero point temperature of the thermocouple 5.

  In the above equation (2), the first term on the left side indicates heat conduction in the sample, the second term indicates heat generation and heat absorption by the Thomson effect, the third term indicates Joule heat, and the fourth term indicates radiant heat. And in the steady state, the right side of the above equation (2) becomes zero. Here, the following equation (3) can be obtained by dividing both sides of the equation (2) by ak.

  The heat loss due to radiation shown in the fourth term on the left side of the equation (3) can be ignored here because it is 1/100 or less of Joule heat in the vicinity of room temperature. In addition, although it can not disregard at high temperature, it becomes a good approximation in the temperature area | region 200 degreeC-400 degreeC. In addition, the temperature distribution in the sample is assumed to be sufficiently small, and physical property values such as the Thomson coefficient, the electrical conductivity, and the thermal conductivity are also treated as constants. Under these assumptions, equation (3) is simplified as in equation (4).

  Here, the constant C and the constant D are defined as in the following equation (5).

  The above-mentioned constant C is a constant term attributable to the Thomson effect, and the constant D can be regarded as a constant term attributable to Joule heating.

  The boundary conditions of the sample 4 shown in FIG. 2 are given by the following equations (6) and (7).

Note that the second boundary condition represented by the equation (7) indicates the heat loss through the thermocouple 5 attached to the sample 4 and K ₁ is the thermal conductance of the thermocouple 5 in the equation (7) or less Indicates

Here, it is known that an analytic general solution can be obtained in the inhomogeneous boundary value problem consisting of the equation (4) forming an ordinary differential equation and the equations (6) and (7) indicating a boundary condition . Therefore, if series expansion is performed ignoring the second or higher order terms with respect to the position coordinate x, the temperature distribution T _DC in the case of applying a direct current is a coordinate showing the attachment position of the thermocouple 5 as in the following equation (8) It is shown as a function of l ₁ and l ₂ . In the following equation (8), K ₀ represents the thermal conductance of the sample.

  In the equation (8), the first term on the right side represents the initial temperature of the sample 4, and the second term represents the temperature increase due to the Joule heat and the second-order Thomson effect. The coefficient N is a heat loss coefficient through the thermocouple 5 of the sample 4 and is calculated from the ratio of the thermal conductance of the sample 4 to that of the thermocouple 5. The difference δl indicates the difference in length from the thermocouple 5 to both ends of the sample 4.

Here, a constant C by a first-order Thomson coefficient appears in the Joule heat term of the second term on the right side of the equation (8), but this is a Thomson heat term that first appeared in consideration of the temperature gradient of the Joule heat If the difference δl is zero, ie, the thermocouple 5 is attached to the central portion of the sample 4, this term is zero. On the other hand, the temperature distribution T _AC when an alternating current is applied to the sample 4 can be expressed by the following equation (9) obtained by setting the constant C of the equation (8) to zero.

The Thomson coefficient is derived from the analytical equation of the sample temperature obtained so far as follows. As shown in equation (8), the endotherm and heat generation by the first-order Thomson effect depend on the polarity of the current, while the Joule effect and heat generation by the second-order Thomson effect do not depend on the polarity of the current. Therefore, let T _{DC + be} the temperature distribution when the current is applied in the positive direction, and T _{DC− be} the temperature distribution when the current is applied in the negative direction. Here, the average difference ΔT _DC of the temperature at the displacement measurement point of the sample 4 is defined as follows.

Substituting the equation (8) into the equation (10), the average difference δT _DC can be expressed as the following equation (11). That is, since only the odd-order term with respect to the current remains, the average difference δT _DC is expressed by an equation in which the temperature gradient generated by Joule heating is multiplied by the constant term C related to the Thomson coefficient.

Then, if equation (11) is solved for the Thomson coefficient, a Thomson coefficient μ can be obtained as a function of the installation position of the thermocouple as in the following equation (12). Here, it is expressed as μ _{DC in} the sense that a direct current is added.

  Here, when the heat loss from the thermocouple 5 is sufficiently small, the equation (12) can be approximated by the following equation (13).

Here, although the temperature gradient information is not included in the equation (13), parameters relating to various sample information are included, which is complicated. Therefore, equation (13) can be simplified in the same manner as the alternating current direct current method (AC-DC method) by using the temperature change when an alternating current is applied. That is, equation (13) can be transformed as the following equation. In the following formula (14), R represents the electrical resistance of the sample. Further, ΔT _ACm corresponds to the temperature change at the measurement point in the center of the sample, and represents the temperature rise due to Joule heat generated when an alternating current is applied to the sample.

Then, if equation (14) is solved for the Thomson coefficient μ, the following equation (15) is obtained. Here, the Thomson coefficient is expressed as μ _{AC in} the sense that an alternating current is applied.

  Here, when the heat loss from the thermocouple 5 is sufficiently small, the equation (15) can be approximated by the following equation (16).

  The equation (16) does not include the temperature gradient of the sample, and does not include the thermal conductivity of the sample as in the AC-DC method. That is, it was analytically shown that the Thomson effect can be measured by self-heating without giving a temperature gradient.

  On the other hand, although the physical quantity required additionally is the shift amount of the thermocouple 5, it is not necessary to take a great deal of time in the measurement because it should be measured before the measurement as in the case of placing in the center of the sample 4. it is conceivable that.

  Further, the thermal conductivity of the sample 4 to be measured can be easily calculated using the fact that the equation (13) and the equation (16) become equal values.

  The values of the absolute thermal power and the thermal conductivity calculated by the above method are stored in the storage unit 53 shown in FIG. 1, and the user interface 51 is a predetermined input by the user of the thermal physical property measuring device 50. In response to the operation command, the value is displayed so that the user can visually recognize it.

  As described above, according to the thermophysical property measurement apparatus and the thermophysical property measurement method according to the embodiment of the present invention, the temperature gradient of the sample due to Joule heat generated by the current flowing for measuring the Thomson heat is used. It is not necessary to provide a heater and a thermometer at both ends of the sample in measurement, and even if the sample does not easily generate a temperature gradient, accurate Thomson coefficient, absolute Seebeck coefficient and thermal conductivity can be easily obtained.

5, 10 Thermocouple 6 Positive DC Power Supply 7 Negative DC Power Supply 8 AC Power Supply 9 Switch 50 Thermophysical Property Measurement Device 54 Operation Unit 55 Measurement Unit 100 Current Application Unit

Claims (7)

A current applying means for selectively applying an alternating current whose positive or negative direct current or effective value is the magnitude of the direct current to a measurement object having no temperature difference at both ends;
Temperature measurement means disposed at a central portion of the measurement object and at a measurement point shifted by an arbitrary distance from the central portion, and measuring the temperature of the measurement object;
When a direct current of different polarity is applied to the both ends by the current application means, a first temperature change at a measurement point deviated from the center by an arbitrary distance measured by the temperature measurement means, and the current application means Thermophysical property provided with calculating means for calculating the Thomson coefficient of the object to be measured by calculating the ratio to the second temperature change in the central portion measured by the temperature measuring means when the alternating current is applied measuring device.   The calculation means is configured to measure the temperature of the object to be measured measured at the measurement point when the direct current of positive polarity is applied to the object to be measured, and when applying the negative current of negative polarity to the object to be measured The thermophysical property measuring apparatus according to claim 1, wherein an average difference from the temperature of the measurement object measured at the measurement point is calculated as the first temperature change.   The thermophysical property measuring device according to claim 1, wherein said operation means further calculates at least one of absolute thermopower and thermal conductivity of said measurement object using said Thomson coefficient. A first method of measuring a first temperature change at a measurement point which is shifted by an arbitrary distance from a central portion of the measurement object by applying a DC current of different polarity to the both ends of the measurement object having no temperature difference at both ends. Step and
Applying an alternating current whose effective value is the magnitude of the direct current to the both ends, and measuring a second temperature change in the central portion;
The Thomson coefficient of the object to be measured is calculated by calculating the ratio of the first temperature change measured in the first step to the second temperature change measured in the second step. The thermal physical-property measuring method which has 3rd step. The first step is
A positive current application step of measuring a temperature of the measurement point by applying a positive DC current to the both ends;
A negative current application step of measuring a temperature of the measurement point by applying a negative DC current to the both ends;
The temperature change calculation step according to claim 4, further comprising: calculating an average difference between the temperatures of the measurement points measured in the positive current application step and the negative current application step to obtain the first temperature change. Thermal property measurement method.   The method according to claim 4, wherein the second step is performed before or after the first step. The thermophysical property measuring method according to claim 4, further comprising a fourth step of calculating at least one of absolute thermopower and thermal conductivity of the object to be measured using the Thomson coefficient.

Images