JPS608457B2 - Thermal conductivity measurement method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring thermal conductivity called the so-called unsteady hot wire method, and an apparatus for automatically measuring thermal conductivity based on this method.

To explain the conventional unsteady hot wire method in detail, for example, a heating wire is placed on the central axis of a cylindrical sample, a constant electric power is supplied to this heating wire, and the temperature change of the heating wire at this time is measured by a side heating element. The thermal conductivity of the sample is calculated based on this temperature change.

That is, when power is supplied to the heating wire, heat is generated from the heating wire, and this heat diffuses within the sample and escapes to the outside. Therefore, if the thermal conductivity of the sample is high, the heat generated by the heating wire will easily diffuse, and the temperature of the heating wire will therefore rise slowly, but if the thermal conductivity of the sample is low, the heat generated by the heating wire will diffuse easily. Because of this, the temperature of the heating wire rises at a steep gradient. (Note that this phenomenon does not apply immediately after the start of power supply, but is a phenomenon observed in time width B (shown in FIGS. 1 and 2) after a certain period of time has elapsed from the start of power supply, as will be described later). Focusing on such a phenomenon, thermal conductivity can be measured by measuring the temperature change of the heating wire. Further detailed description will be given based on FIGS. 1 and 2. After setting the sample to the temperature to be measured T'o, constant power is supplied to the heating wire. If this power supply start point is defined as zero point, the temperature of the heating wire increases as shown by curve A in FIG. This curve A becomes a logarithmic curve with a constant time width B that is a predetermined time elapsed from the zero point. Therefore, as shown in FIG. 2, if the logarithm ln of time is plotted on the axis and temperature T is plotted on the vertical axis, a straight line C is formed in the above-mentioned constant time width B. Thermal conductivity is then determined from a theoretical analysis in which the reciprocal of the slope of this straight line C is proportional to the thermal conductivity of the sample. In addition,
In Figure 2, the sample deviates from the straight line C after a certain time width B because it has a finite length and diameter, and heat dissipates from the air surrounding the sample (which has extremely low thermal conductivity compared to the sample). ), and if the sample has infinite length and infinite diameter, the linear state will be maintained even after the above time has elapsed. The thermal conductivity can be calculated from theoretical analysis using the following formula. = 8MZ-- ~・} 4 lights △T Enter here: Thermal conductivity of the sample (W/(m.

C)) g: Heat flow per unit length of heating wire (W/m) 7,
, D2: Is it the elapsed time within the above-determined time range? , <↑2T,, T2: heating wire temperature △T at each elapsed time ↑,, ↑2: temperature difference T2-T, equation {1} is an approximate equation obtained by omitting higher-order terms from the theoretical equation. When the condition is good;<o-17, the results match within 1%.

Here, r: distance between the heating line and the overflow point. Q: Thermal diffusivity of sample (renoh) ↑: Elapsed time (h) It is.

However, in the conventional measurement method described above, it is possible to accurately measure thermal conductivity on the condition that the sample temperature is maintained at a constant temperature, that is, the temperature to be measured T'o.

In other words, the sample temperature and the heating wire temperature (hereinafter referred to as base temperature) are required to be constant even after power supply starts, assuming that no power is supplied to the heating wire. If the base temperature is rising as shown by straight line D in Figure 1, the heating wire temperature will change as shown by curve D' and the measured temperature difference between time points 7 and 2 will be △To. , is larger than the true temperature difference ΔT caused only by the diffusion phenomenon of heat generated when power is supplied to the heating wire, and if the base temperature is decreasing as shown by straight line E in Figure 1, then The heating wire temperature changes as shown by curve E' and reaches a point in time. , 72 is ΔT8, which is smaller than the true temperature difference ΔT. Therefore, the thermal conductivity M obtained by substituting the above ΔTD and ATE into the equation {1} is not an accurate value. Therefore, if the ambient temperature of the sample changes due to changes in temperature in the morning and evening, for example, there is a drawback that accurate thermal conductivity cannot be measured. Also, the temperature to be measured T'. If the temperature is higher or lower than room temperature, the sample must be heated in a heating furnace or cooled in a cooling furnace.
Since it is necessary to set the sample at a constant temperature T'o, there is a drawback that the time required for heating or cooling is extremely long. That is, the measured temperature T'. Taking as an example the case where T'o is higher than room temperature, the sample is heated so that the sample temperature rises as shown by curve F in Fig. 3 and gradually reaches the measurement temperature T'o. Since it must be kept stable at the measured temperature T'o, what is the heating time? It takes F hours and becomes extremely long. The present invention was made based on the above circumstances, and its purpose is to measure the heating wire temperature at least at two points in time before the zero point when power is started to be supplied to the heating wire, and to measure the heating wire temperature based on the measurement results. Assuming fluctuations in the base temperature, on the other hand, the temperature at two points after the zero point, , 72, is measured, and the temperature measured at 71, 2nd is corrected for the fluctuation in the base temperature as described above. It is possible to determine the true temperature change, which is corrected only by the diffusion phenomenon of the generated heat, and thereby determine the accurate thermal conductivity, and it is also possible to measure the thermal conductivity even in the process of increasing or decreasing the sample temperature. The present invention aims to provide a method for measuring thermal conductivity that can shorten the time required to heat and cool a sample until it reaches a temperature to be measured, and also to provide a measuring device that can automatically measure the thermal conductivity.

An embodiment of the method of the present invention will be described below.

The probe section 1 used in the method of the present invention is shown in FIG.

That is, the sample 2 whose thermal conductivity is to be measured consists of semi-cylindrical sample structures 2a, 2a, which are formed into a cylindrical shape by polymerizing them. Further, the heating wire 3 is sandwiched between the sample constructs 2a, 2a, and is arranged at the central axis of the sample 2 when these are polymerized. This heating wire 3 is made of a round wire, a band wire, or the like. A side heating element, such as a hot junction 4a of a thermocouple 4, is attached to the center of the heating wire 3 by means such as spot welding. Further, in the figure, reference numeral 5 denotes a U-shaped support frame, and both ends of the heating wire 3 are fixed to terminals 6, 6 at the ends of the support frame 5, so that the heating wire 3 is maintained in a straight line. . Further, both ends of the thermocouple 4 are connected to other terminals 7, 7 at the ends of the support frame 5. First, a method for measuring thermal conductivity in the case where the base temperature T8 can be approximated as changing as a linear function of time as shown in FIG. 5 will be described.

As an example, a case will be described in which thermal conductivity at high temperatures is measured. In this case, the heating wire temperatures T3 and T4 at two points before the start of power supply to the heating wire 3 (zero point), for example, at 1-cho 3 and 1-74 are measured. As a result, the base temperature T8 at time 7 is given by the following equation. TB:t+←
3) (773〉...'31) Therefore, the temperature difference △T8 between the base temperatures TB, TB2 at the time when a predetermined time has passed since the zero point is △TB=TB2-T
B.
(T3 + construction value (T, 173)} 73-1-4 = (t-T3)2 niq...■ 73-1-4 On the other hand, the actual measured temperature T at the time of 7,, 2,... L
The actual temperature change △T^ is △T^2T2-T, ... side.Then, when the true temperature change △TR is calculated from the above equation {4', '5}, △TR=△ T^-△TB =T2-T,1 TB20TB, 2T21T,1 (T4-T3)... } Substituting △T in the formula to find the thermal conductivity, E=O.
．． ．． ．． ．． ．． ．． (7) T2-TI-(T4-T3) is 2-
1 and 3 and 4 The above temperature change 4TR' Well, since it is a true temperature change that occurs only due to the diffusion phenomenon of heat generated in the heating wire 3 when power is supplied to the heating wire 3, the above {7- equation The thermal conductivity input will be accurate.

In addition, the measured temperature T'o corresponding to this thermal conductivity is
It can be approximately determined by the following equation as the average of the measured temperatures To and T2 at the zero point and the second point. r.

=T. 1T2...'8} Also, a method for determining the temperature to be measured more accurately will be explained based on FIG. 7.

In other words, in Figure 7, the horizontal axis represents the diameter of the sample, and the vertical axis represents the temperature, and the curve day represents the temperature distribution inside the sample at the zero point.
What about curve 1? The temperature distribution at two points in time is shown. The measured temperature T'o is determined by the following equation. r. =T
m view 1 Tmm...---■Where, Tmin: Temperature at the center of the sample at zero point Tmin=
T.

Tmax: Temperature at the outermost part of the sample at the time of 72.

As mentioned above, the temperature to be measured T′o is expressed by the formula '8} or {
9) However, the difference in T'o derived from the two equations is small, and the thermal conductivity^ usually changes slowly with temperature, so which equation should be used in practice? It's okay.

When calculating the above thermal conductivity, the heating of the sample is determined until the sample temperature reaches t'+L as shown by curve G in FIG.
Set it so that it reaches . In this case, when the temperature of the heating wire 3 continues to rise in an unstable state and reaches a temperature near T'o, power can be supplied to the heating wire 3 and the thermal conductivity can be measured. The time to heat the sample is 7G.
The heating time ↑F of the conventional method (shown by curve F in FIG. 3) is significantly shortened. In addition, in the measurement of the thermal conductivity described above, by setting 173 ni 1 cho 2 174 koke 1 72 = 27, the above equation for calculating the thermal conductivity can be replaced by the following equation {7}'.

ln2 entry = rare L-T, ten T3-T4... ...(lo) In this way, the thermal conductivity can be determined using a simpler formula.

Further, in the above embodiment, two points before the zero point, for example, 17
The change in the base temperature TB was determined by measuring the temperature at 3 and 74. In this case, one time point is considered as the zero time point, and the measured temperature To at this zero point and the other time point, for example, -4.
The base temperature may be determined from the measured temperature t. In the above embodiments, the thermocouple 4 was used as the neck temperature element, but a side temperature resistor made of platinum or the like, a thermistor, or the like may be used.

Further, the present invention can also be applied to a device in which a thermocouple as a side temperature element and a neck temperature resistance element also serve as a heating wire. The sample may be rectangular parallelepiped instead of cylindrical. Next, the sixth
As shown in the figure, a method for measuring thermal conductivity in a case where the change in base temperature TB can be approximated as a quadratic function of time 7 will be described.

In this case, the base temperature is expressed by the following equation. TB ni a 20 b 7 nineteen…. ．． ．． 11) Here, To is the measured temperature at zero point.

In addition to the above zero point, there are two points before the zero point.
, 174 and substitute it into the above equation (11), T3=a7 poison-b73 10T.

T4 = a7 taken - b74 10T.

...(12) From now on, the base temperature TB, TB2 at 7, ↑ 2 o'clock after the start of power supply is TBI
= a ding tei + b 71 ten t.

TB2 = a7 wife ten b72 ten T.

...(15) Therefore, to find the change in base temperature △TB, △TB = TB2 - TB, 2a (ne-cho-tei) 10 b x 72 1-tou).・・・． ...(16) Here, a and b are given by equations (13) and (14).

If the actual temperature measured at time points 7, 72 is T,, T2, then the actual temperature change ΔTA is ΔTA=Q-T.
......(17), so the true temperature change △
TR is △TR = △T^ - △TB = T2 - T, - {a (7 robs - C) 10 b (72 - 7 ,)} ・・・・・・(1
8) Substituting this true temperature change △TR into the formula '1} to find the thermal conductivity, g・ln (I2/71)
、． .

(19)^=4 [T2-T. −{a (mi-ot) ten b(
Ding 21 Ding. )} ] However, a and b are equations (13) and (14
) is given by the formula. Here, 173: 1 cho 2 1 cho 4 = -71 cho 2 2 2 cho・ Calculation of thermal conductivity is simplified and becomes as follows.

Enter=Fort 2・{t−T・−俄小h)}−1 ．． ．．・．． ．．・(2o) here a=T30T.

-2r42, Deko b=T33r.

-4T427, so ba=bad wall {T2-T, -3L-T35T4}-1...G
I) 4 In this example, the base temperature was calculated by measuring the heating wire 3 temperatures T3, T4, To at the time of 173, 1, 4, 0. Instead, the temperature T3 at the time of -75 is measured and becomes -73, -74.
The base temperature may be determined by measuring the temperatures T3, T4, and T5 at time points , -75.

In the above two embodiments of the method of the present invention, at the temperature to be measured.

is higher than room temperature, so when the sample is heated and reaches a temperature To near temperature T'o in the heating process, the thermal conductivity ^
Although the method for measuring the temperature T' has been described, the present invention is applicable to the measurement target temperature T'. is lower than room temperature, so it can also be applied to a method in which the sample is cooled and the thermal conductivity is measured during this cooling process, and the formula for determining the thermal conductivity is exactly the same as in the above embodiment. The measured temperature T'o in this case can also be determined by the equation {8), but a more accurate method for determining it will be explained with reference to FIG. That is, like FIG. 7, FIG. 8 shows the temperature distribution inside the sample, and curve J shows the temperature distribution at time zero, and curve K shows the temperature distribution at time 2. , the measured temperature T'o is expressed by the following formula: r.=Tmin1TmaX--- (22) where Tmin is the lower of the temperature at the outermost part of the sample at the zero point or the second point. Temperature Tmax: Temperature of heating wire 3 at time 72 Next, an apparatus for automatically measuring thermal conductivity by implementing the method of the present invention will be described with reference to FIG.

Reference numeral 1 in the figure is the probe section shown in detail in FIG. 4, and the output of the thermocouple 4 of this probe section 1
1. The first input terminal 1 of the analog multiplexer 14 is amplified by the front layer amplifier 12 and the thermometer side amplifier 13.
4a. On the other hand, the temperature of the cold junction of thermocouple 4 is
For example, automatic cold junction compensator 15 with built-in side salt resistor etc.
The output of the compensator 15 is amplified by the cold junction amplifier 16 and then supplied to the second input terminal 14b of the analog multiplexer 14. The respective outputs supplied to the first input terminal 14a and the second input terminal 14b of the analog multiplexer 14 serve as information for calculating o at the temperature to be measured, as will be described later. Further, the output of the thermocouple 4 is amplified by the pre-layer amplifier 12 and subtracted by the pre-cut level by the pre-cut circuit 17, and then supplied to the third input terminal 14c of the analog multiplexer 14. ing. This pre-cut output becomes information for calculating the rate of temperature increase of the heating wire 3 and the thermal conductivity at each point in time, as will be described later. Then, each analog data supplied to the analog multiplexer 14 is sequentially sent to the A/D converter 18 and converted into digital data according to the control signal output to the control input terminal of the analog multiplexer 14. Furthermore, a processing device 20 consisting of a digital input circuit 19, a microcomputer, etc.
The data is stored in the storage device 21 via. This storage device 21
The previous memory is cleared by the IJ set signal from the reset nail 22, and new reading is started. That is, the output digital data supplied to the third input terminal of the analog multiplexer 14 from the input of the IJ set signal is read into the storage device 21 at short intervals, for example, every 2 seconds, under the control of the processing device 20. This data is processed at 72 under the control of the processing device 20.
Only the amount of time is stored, and new data is stored by updating the oldest data. If data is updated and stored in this way, unnecessary data will not be stored and the storage capacity can be reduced. Further, this storage device 21 is configured to stop updating the memory under the control of the processing device 20 which receives a start signal from the start money 023. In addition, this storage device 21
Precut level information is stored in the , and this information is sent to the D/A via the processing device 20 and the digital out circuit 24.
The data is converted into analog data by the converter 25 and output to the pre-cut circuit 17 described above. Further, the processing device 28 connects the thermal conductivity digital display device 26 and the temperature to be measured digital display device 2 through the digital out circuit 24.
7. It is designed to control the semi-Kusunu K lamp 28.
The details will be described later. Further, the output of the thermocouple 4 described above is outputted to a recorder 30 and a moving coil indicator 3 via a pre-layer amplifier 12 and other pre-cut circuits 29. These recorders 30 and moving coil indicator 3
1 is designed to constantly display the heating wire temperature in analog form. Further, the circuit can be directly adjusted by switching the mode switch 11 described above to connect the circuit to the internal reference voltage generator 32. Further, a signal is outputted from the mode switch 11 to the digital input circuit 19 to inform whether the mode is either measurement or measurement mode. Next, a circuit for power supply control will be explained. That is, the input of the alternating current voltage (ACIOOV) is supplied to the power supply circuit 35 via the power switch 33 and the fuse 34. This power supply circuit 35 receives an input AC voltage (A
CIOOV) is rectified and transformed, and a DC voltage of 5 to 15 V is supplied to the power supply circuit 35 for the control circuit described above. Further, this power supply circuit 35 is configured to supply constant power to the heating wire 3 via a DC constant current circuit 36 and a current value controller 37. In addition, 38 constantly analyzes the current flowing through the heating wire 3. It is an ammeter that displays the current value. Further, 39 is a current setting switch, which supplies current value information to the current value controller 37 and also to the storage device 21 via the digital input circuit 19 and the processing device 20. Further, 40 is a heating wire resistance value setting device, and this resistance value information is supplied to a storage device 21 via a digital input circuit 19 and a processing device 20. Further, the start signal from the start plow 23 described above is subjected to timing control to be described later in the processing device 20', and then outputted to the current value controller 37 via the digital out circuit 24, whereby the heating wire Power supply to 3 has started. The operation of the measuring device having the above-mentioned configuration will be explained.

As an example, a case where the temperature to be measured is higher than room temperature will be described. First, the sample 2 is placed in a heating furnace (not shown) and heated. After an appropriate period of time has elapsed after the start of heating, when the power switch 33 is turned on and the reset button 22 is pressed, the output of the thermocouple 3 that is supplied to the third input device 14c of the analog multiplexer 14 as described above is output. (
temperature information) is stored in the storage device 21 under the control of the processing device 20.
The information is stored while being updated sequentially for a width of 72 hours every 2 seconds. Then, the temperature increase rate is calculated in the processing device 20 based on the temperature information stored in the storage device 21, and when the temperature increase rate becomes less than a certain value, for example, IC/min or less (the salt increase rate is It is set so that the temperature to be measured is almost reached when the temperature falls below IC/mjn.)
The preparation OK lamp 28 is turned on under the control of the processing device 20. After confirming this lighting, the operator presses the start button 23. Then, the start signal is sent to digital input circuit 1.
9 to the processing device 201. This processing device 20 holds the start signal until the control signal is outputted to the analog multiplexer 14, and approximately at the same time as the control signal is outputted, the start signal is sent to the current value controller via the digital out circuit 24. 37, and the current value controller 37 receives this and supplies constant power to the heating wire 3. On the other hand, "the storage device 21 is
After storing the temperature information (temperature information input to the third input terminal 14c of the multiplexer 14) at , the updating of the above-mentioned memory is stopped under the control of the processing device 20, and the temperature information at 172, 171, and 0 points is stopped. Temperature information T3, T4,
Other information is erased except for To, and the temperature information T, , T2 of 71, 2 after the zero point is further stored and used as a memory for calculation. Then, in the processing device 201, the thermal conductivity is determined based on the above-mentioned equation for determining the thermal conductivity, for example, equation (21). Input = Home 2 {T2-T・-Koshubei 4}-・Here, g is the resistance value information R of the heating wire from the heating wire resistance value setting device 40 and the current value information 1 from the setting switch 39. From the formula g=R12/1 (1 is the length of the heating wire 3)
It is determined by

In this manner, the determined thermal conductivity value is displayed by the thermal conductivity digital display device 26. In addition, the temperature to be measured To'' and the temperature information To stored in the storage device 21
, L, by shelf-type calculation in the processing device 20. h'=T/ be.

Further, the temperature to be measured L' is displayed on the temperature to be measured digital display device 27 under the control of the processing device 20. Note that the temperature to be measured To' may be calculated by the equation [9} in the processing device 20'. However, in this case, it is necessary to measure the outermost temperature of the sample using another thermocouple (not shown) and supply this temperature information to the processing device 20 and the storage device 21. It should be noted that the method and apparatus of the present invention are not limited to the order of calculations in the above-mentioned embodiments, and can ultimately be applied to any method that measures thermal conductivity based on a true temperature difference. Of course.

As explained above, according to the method of the present invention, the heating wire temperature is measured in advance at at least two points before the zero point when power is started to be supplied to the heating wire, and fluctuations in the base temperature are assumed based on the measurement results. On the other hand, 2 after the zero point
Measure the temperature at time 7,,↑2, and this 7,,72
By adding correction based on the above base temperature to the actual measured temperature at This is what I did.

Therefore, accurate thermal conductivity can be measured without being affected by the ambient temperature of the sample. Furthermore, since the thermal conductivity can be measured even when the sample temperature is rising or falling, the time for heating or cooling the sample can be significantly shortened.
Further, according to the device according to the present invention, in the storage device,
Information on the heating wire temperature before the zero point is stored while being updated sequentially for a predetermined time width at short intervals, and from this stored temperature information, the processing device uses the temperature information at two or more points before the zero point. The base temperature is calculated, the variation due to this base temperature is corrected to find the true temperature change, the thermal conductivity is calculated based on this, and this thermal conductivity is displayed on the display device.

Therefore, accurate thermal conductivity can be measured automatically.

[Brief explanation of the drawings] Figures 1 and 2 are diagrams showing the change in heating wire temperature with respect to time according to the method of measuring the thermal conductivity of a subordinate column. In Figure 1, the horizontal axis represents time, and In Figure 2, the horizontal axis is the logarithm of time ln
I took 7. Figure 3 shows the sample heating state and measurement temperature TO' in the secondary thermal conductivity measurement method and the measurement method of the present invention.
FIG. Fourth
The figure is a perspective view of the probe part used in the method and apparatus according to the present invention, and FIGS. 5 and 6 are diagrams showing changes in heating wire temperature over time during thermal conductivity measurement by the method of the present invention. FIG. 5 shows a case where the base temperature can be approximated as a linear function with respect to time, and FIG. 6 shows a case where the base temperature can be approximated as a quadratic function. Figures 7 and 8 are diagrams showing temperatures Tmax and Tmin, which are the basis for determining the measured temperature for the measured thermal conductivity. Figure 7 shows the temperature when the sample is heated, and Figure 8 shows the temperature when the sample is heated. The figure shows the case of cooling. FIG. 9 is a block circuit diagram of a measuring device according to the present invention. 1...Probe section, 2...Sample, 3.
... Heating wire, 4 ... Thermocouple, 18 ... A
/D converter, 20...processing device, 21...
Storage device, 26...Thermal conductivity digital display device (display device). Figure 1 Figure 2 Section 3 Figure 4 Figure 5 Figure 6 Section 7 Figure 8 Figure 0

Claims (1)

[Scope of Claims] 1. A heating wire and a temperature measuring element for measuring the temperature of the heating wire are disposed within the sample, and the heating wire is provided at at least two points in time before the zero point at which constant power is started to be supplied to the heating wire. Measure the temperature, and based on this measurement result, calculate the two points τ after zero point.
Base temperature of the heating wire T_B_1, T_B_2 when it is assumed that no power is supplied to the heating wire at _1, τ_2
, and measure the actual heating wire temperatures T_1 and T_2 when power is supplied to the heating wire at the above two points τ_1 and τ_2, and calculate the above T_B_1, T_B_2, T_1, T_2.
Therefore, the true temperature change ΔT_R=T_2−T given only by the heat diffusion phenomenon that occurs when power is supplied to the heating wire
Find _1−T_B_2+T_B_1 and calculate this true temperature change ΔT_R as λ=(g・ln(τ_2/τ_1))/(
4π・ΔT) [Equation (1)] (where λ: thermal conductivity of the sample,
g: heat flow per unit length of heating wire, ΔT=T_2−T_
A method for measuring thermal conductivity, characterized in that the thermal conductivity of the sample is determined by substituting ΔT in 1). 2. A heating wire placed inside the sample and supplied with constant power, a temperature measuring element also placed inside the sample and measuring the temperature of the heating wire, and converting analog data from the temperature measuring element into digital data. A/D converter to convert and this A/D
A storage device that stores digital data from a converter, a processing device that calculates thermal conductivity based on the information stored in this storage device, and a display device that displays thermal conductivity under the control of this processing device. The processing device sequentially updates the heating wire temperature information from the A/D converter in the storage device for a predetermined time width at short intervals before the zero time point when power supply to the heating wire starts. The update of the memory in the storage device is stopped at the zero time point, and from the information on the heating wire temperature at at least two time points before the zero time point, after the zero time point assuming that no power is supplied to the heating wire. Two points in time τ_1, τ_
2 temperatures T_B_1, T_B_2 are calculated, and further, the actual measured temperatures T_1, T_2 at the two time points τ_1, τ_2 stored in the storage device and the above T_B_1, T_B_
2, the true temperature difference ΔT_R=T_2 given only by the heat diffusion phenomenon that occurs when power is supplied to the heating wire
−T_1−T_B_2+T_B_1 is calculated, and this temperature difference ΔT_R is calculated as λ=(g・ln(τ_2/τ_1))/(
4π・ΔT): [Equation (1)] (where λ: thermal conductivity of the sample, g: heat flow per unit length of heating wire, ΔT=T_2−T
A thermal conductivity measuring device characterized in that the thermal conductivity of the sample is calculated and calculated by substituting ΔT in _1), and the thermal conductivity is displayed on a display device.