JPH0625741B2 - Thermal conductivity measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention is suitable for measuring the thermal conductivity of various materials such as heat insulating materials and heat insulating materials especially at high temperatures. It is about.

“Prior Art” Generally, the values of thermal conductivity of various materials used as heat insulating materials and heat insulating materials are not always constant but change depending on temperature conditions, and as shown in FIG. 5, the temperature is high. The higher the thermal conductivity, the easier it is to transfer heat. Therefore, especially for a material whose thermal conductivity at high temperature is a problem, such as a heat insulating material or a heat insulating material used under a temperature condition exceeding 1,000 ° C., the thermal conductivity cannot be measured. It is necessary to actually heat the sample to the working temperature.

An apparatus shown in FIG. 6 is known as an apparatus for measuring such thermal conductivity. In this conventional thermal conductivity measuring device, a main heater b and an auxiliary heater c are arranged in an upper portion and a lower portion of a protective cylinder a having a heat insulating property to generate a steady downward heat flow inside the protective cylinder a. In addition, a heat flow measuring plate d for measuring the heat flow rate of the steady heat flow is provided above the auxiliary heater c.

In order to perform the measurement with this thermal conductivity measuring device, a sample S whose thermal conductivity is to be measured is arranged at the center position in the protective cylinder a, and standard heat transfer plates whose thermal conductivity is known are arranged above and below the sample S.
By disposing s ₁ and s ₂ and controlling the main heater b and the auxiliary heater c, a thermal equilibrium state shown by a broken line A in the figure is created inside the protective cylinder a, and the sample S and the standard heat transfer plate s ₁ , A temperature gradient such as a polygonal line B is formed on s ₂ and the average internal temperature of the sample S is maintained at a temperature T ° C. at which the thermal conductivity should be measured.

Then, in the steady state, the accurate temperatures of the upper surface and the lower surface of the sample S are measured by the thermometers e, e, and the temperature difference between them and the heat flow of the steady heat flow measured by the heat flow measurement plate d, that is, the sample S are transmitted. The thermal conductivity of the sample S at the temperature T ° C. (average internal temperature of the sample S) is calculated from the heat transmission flow rate.

That is, it is assumed that the measured heat transmission flow rate is Q (Kcal / h), the upper surface temperature and the lower surface temperature of the sample S are θ ₁ and θ ₂ (° C.), respectively, and the thickness dimension of the sample S is δ (m), Assuming that the effective area of the sample S is A (m ² ), the thermal conductivity λ (Kcal / m · h · deg) of the sample S at the temperature T ° C. is Q = (λ / δ) · A (θ ₁ Since the relation of −θ ₂ ) is established, it can be obtained from this formula as λ = Q · δ / A (θ ₁ −θ ₂ ) ... (1).

The standard heat transfer plate in the conventional thermal conductivity measuring device
s ₁ and s ₂ are for keeping the temperature of the sample S at a high temperature, and by measuring their surface temperature with a thermometer f ... This is for verifying the measured value by comparing the value of the thermal conductivity obtained from the above with the known value of the thermal conductivity, and for correcting it if necessary.

Further, reference characters g ... Are wall surface temperature compensating heaters, and these heaters g ... Control the surface temperature of the protective cylinder a so that the temperature gradient inside the protective inner cylinder a is in the state of A. This prevents heat transfer between the protective cylinder a and the internal space thereof and prevents the heat flow from radiating from the peripheral surface of the protective cylinder a.

[Problems to be Solved by the Invention] By the way, when the measurement is performed using the thermal conductivity measuring device as described above, the upper surface and the lower surface of the sample S are standard heat transfer plates
Since it is in contact with s ₁ and s ₂ , it is not easy to measure the surface temperature accurately when the temperature becomes high, and the measurement range is restricted by it.

Therefore, it may be possible to omit the standard heat transfer plates s ₁ and s ₂ , but it is possible to omit the standard heat transfer plate s ₁ on the upper surface side, but it is possible to omit the standard heat transfer plate s ₂ on the lower surface side. However, when the measurement temperature is particularly high, the heat flow measurement plate d needs to be kept at a low temperature, and therefore cannot be omitted.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a measuring method capable of easily and accurately measuring the thermal conductivity of a sample, especially at high temperatures.

"Means for Solving the Problem" In the present invention, when measuring the thermal conductivity λs of a sample at a predetermined measurement temperature T, first, the lower surface temperature t ₀ of the standard heat transfer plate is measured.
While the temperature is kept constant and the upper surface temperature t ₁ is changed stepwise, the thermal conductivity λ of the standard heat transfer plate at each temperature is increased.
₁ is obtained, and then the sample is superposed on the upper surface of the standard heat transfer plate, and the lower surface temperature of the standard heat transfer plate is maintained as it is at the above temperature t _0, and the upper surface temperature of the sample is maintained at the measurement temperature T, Obtain the total thermal conductivity λt of the standard heat transfer plate and the sample in this state, and measure the sample based on the value of the total conductivity λt and the thermal conductivity λ ₁ at each temperature of the standard heat transfer plate. It is characterized in that the thermal conductivity λs at the temperature T is calculated.

[Embodiment] An embodiment of the method of the present invention will be described below with reference to the drawings.

First, with reference to FIG. 1, a thermal conductivity measuring apparatus suitable for carrying out the method of the present invention will be described.
FIG. 1 is a vertical cross-sectional view showing a schematic configuration of the device,
Reference numeral 1 in the drawing is a furnace vessel. The furnace vessel 1 includes a main body 2 and a main body 2 each having a water cooling jacket and a hinge 3 attached to the main body 2.
It is composed of the lid body 4 connected by.

Inside the furnace vessel 1, a disk-shaped lower heat insulating material 5,
By the upper heat insulating material 6 and the cylindrical side heat insulating material 7,
A measurement chamber 8 in which the sample S is arranged is formed. A main heater 9 for keeping the inside of the measuring chamber 8 at a predetermined temperature is attached to the upper space of the measuring chamber 8, and the inner surface temperature of the lower insulating member 5 is heated by the heat flow in the lower insulating member 5. Compensation heaters 10 for keeping the same as the temperature of the measurement chamber plate 15 (described later) are embedded. The main heater 9 and the compensation heaters 10 penetrate the lid 4 of the furnace container 1 and the main body 2. The electrodes 11 and 12 are connected. Reference numeral 13 is a radiation thermometer for measuring the temperature in the measurement chamber 8.

The inner surface of the side heat insulating material 7 forming the side wall of the measuring chamber 8 is made of a material having sufficient heat resistance and excellent thermal conductivity, for example, graphite, heat-resistant steel, molybdenum, or the like. It is covered with a wall surface temperature compensating plate 14 formed in a tubular shape. This compensating plate 14 carries heat from the upper part to the lower part of the measuring chamber 8 due to its excellent thermal conductivity, so that the inner surface temperature of the side cross-section member 7 is adjusted to the sample S or the standard heat transfer plate 24 (described later). It is for keeping the same temperature. Therefore, in this device,
It is not necessary to provide heaters g for wall surface temperature compensation in the conventional device, and the device is simplified and downsized.

Further, a disc-shaped heat flow measuring plate 15 is arranged in the central portion of the upper surface of the lower heat insulating material 5, and an annular compensating cooling plate 16 is provided around the heat flow measuring plate 15.
Are arranged. The heat flow measuring plate 15 has a flow passage for the temperature measuring gas for measuring the heat transmission flow formed in a spiral shape, and the temperature measuring gas is circulated in the flow passage as indicated by an arrow in the figure. A gas inlet pipe 17 and a gas outlet pipe 18 are connected to each other. Also, the compensating cooling plate 1
6, a flow passage for circulating the cooling gas is formed in a spiral shape, and a cooling gas introduction pipe 19 and a cooling gas derivation pipe 20 for circulating the cooling gas as shown by arrows in the drawing are provided. Each is connected. The above temperature measuring gas,
The cooling gas is introduced into the heat flow measuring plate 15 and the compensating cooling plate 16 after being brought to a predetermined temperature by the gas preheaters 21 and 22 embedded in the lower heat insulating material 5. Although not shown, thermometers for measuring the inlet temperature and the outlet temperature of the temperature measuring gas and the inlet temperature and the outlet temperature of the cooling gas are respectively provided.

The heat flow measuring plate 15 measures the temperatures at the inlet and the outlet of the temperature measuring gas, and from the temperature difference and the gas flow rate, the heat receiving amount of the temperature measuring gas, that is, the heat transmission flow rate passing through the sample S. Is for measuring. Further, the compensating cooling plate 16 arranged around it is for holding heat exchange between them by being kept at the same temperature as the heat flow measuring plate 15.

A lower temperature measuring plate 23 is arranged on the upper surfaces of the heat flow measuring plate 15 and the compensating cooling plate 16, and a standard heat transfer plate 24 having heat insulating property is arranged on the upper surface thereof, and a sample whose upper surface thermal conductivity is to be measured. S is arranged, and the upper temperature measuring plate 25 is further arranged on the upper surface thereof. A thermocouple thermometer (not shown) is inserted in each of the lower temperature measuring plate 23 and the upper temperature measuring plate 25, and the lower surface temperature of the standard heat transfer plate 24 and the thermocouple thermometer or the radiation thermometer 13 are inserted. The upper surface temperature of the sample S can be measured.

The configuration of the thermal conductivity measuring device has been described above. Next, a measuring method using the device will be described. The measuring method described below measures the thermal conductivity λ ₁ of the standard heat transfer plate 24 without directly measuring the lower surface temperature of the sample S when measuring the thermal conductivity λs of the sample S at T ° C. do it,
It is calculated indirectly based on the value.

That is, first, the standard heat transfer plate 2
4 and the upper measuring plate 25 is directly arranged without arranging the sample S on the upper surface thereof, and the measuring chamber 8 is arranged by the upper heat insulating material 6.
And the lid 4 of the furnace container 1 are closed, and the thermal conductivity of this standard heat transfer material 24 is measured. To this end, similar to the conventional device, the main heater 9 and the compensating heater 10 are controlled to generate a steady heat flow in the measuring chamber 8, and the temperature measuring gas and the cooling gas are brought to predetermined temperatures by the preheaters 21 and 22, respectively. The temperatures of the heat flow measuring plate 15 and the compensating cooling plate 16 are maintained at the same level by heating and flowing to the heat flow measuring plate 15 and the compensating cooling plate 16. The temperature is measured, the amount of heat received, that is, the heat transmission flow rate that has passed through the standard heat transfer plate 24 is obtained from the temperature difference of the temperature measurement gas and its flow rate, and the value of the heat transmission flow rate and the upper and lower surfaces of the standard heat transfer plate 24 are both obtained. From the temperature and the thickness dimension, the following (2)
The thermal conductivity of the standard heat transfer plate 24 in this state is calculated by the equation.

In this case, as shown schematically in FIG. 2, the standard heat transfer plate 2
4 is Q ₁ , the lower surface temperature is t ₀ , the upper surface temperature is t ₁ , the thickness dimension of the standard heat transfer plate 24 is δ ₁ , and the thermal conductivity of the standard heat transfer plate in this state is λ ₁ . Then, since Q ₁ = (λ ₁ / δ ₁ ) A (t ₁ −t ₀ ) ... (2), λ ₁ is obtained from this. In this case, the effective area A of the standard heat transfer plate 24 is the area of the heat flow measurement plate 15.

Subsequently, the lower surface temperature t ₀ of the standard heat transfer plate 24 is kept constant, and the upper surface temperature t ₁ is gradually increased by a predetermined temperature until it becomes higher than the measurement temperature T ° C. In the step, measurement is performed in the same manner as above to obtain the thermal conductivity at each temperature, and a graph showing the relationship between the thermal conductivity λ _{1 and} the upper surface temperature t ₁ as shown in FIG. 3 is prepared. Since λ ₁ is a function of t ₁ , it is expressed as λ ₁ = Φ (t ₁ ) ... (3). The function Φ can be approximately calculated by processing a large amount of data using a computer. Of course, this function Φ varies depending on the material of the standard heat transfer plate 24 and the like.

After the thermal conductivity λ ₁ at each temperature of the standard heat transfer plate 24 is obtained as described above, next, the sample S is superposed on the upper surface of the standard heat transfer plate 24, and the upper temperature measuring plate 25 is arranged on the upper surface thereof. To do. Then, as schematically shown in FIG. 4, the lower surface temperature of the standard heat transfer plate 24 is maintained at the same temperature t ₀ as described above, and the upper surface temperature of the sample S is maintained at the measurement temperature T, so that the steady state is achieved. The heat transmission flow rate Qt in that state is measured.
In this case, if the thickness dimension of the sample is δs and the total thermal conductivity of the sample S and the standard heat transfer plate 24 is λt, the following relationship holds.

_{Qt = {λt / (δ 1} + δs)} A (T-t 0) ...... (4) Thus, the value of the overall thermal conductivity .lamda.t between the sample S and the standard heat transfer plate 24 is determined.

The state shown in FIG.
The thermal conductivity of the sample S is λs, the lower surface temperature of the sample S (= upper surface temperature of the standard heat transfer plate 24) is t ₁ ′, the thermal conductivity λ of the standard heat transfer plate 24 in this state. Assuming ₁ ′, the heat transmission flow rate passing through the sample S and the heat transmission flow rate passing through the standard heat transfer plate 24 are both equal to the heat transmission flow rate Qt passing through the whole in the steady state. Expression (4) can be expanded as follows.

Qt = {λt / (δ ₁ + δs)} A (T−t ₀ ) ... (4) = (λ ₁ ′ / δ ₁ ) A (t ₁ ′ −t ₀ ) …… (4) ′ = (λs / Δs) A (T−t ₁ ′) (4) ″ Therefore, if the equation (4) ′ = (4) ″ is given, (λ ₁ ′ / δ ₁ ) A (t ₁ ′ −t ₀ ). = (Λs / δs) A (T−t ₁ ′) (4) On the other hand, the total thermal resistivity Rt between the sample S and the standard heat transfer plate 24 in this state is the thermal resistivity of the standard heat transfer plate 24. It is represented by the sum of R ₁ and the thermal resistivity Rs of the sample S. That is, Rt = (δ ₁ + δs) / λt R ₁ = δ ₁ / λ ₁ ′ Rs = δs / λs, and Rt = R ₁ + Rs, therefore (δ ₁ + δs) / λt = (δ ₁ / Λ ₁ ′) + (δs / λs) (5).

In the above equations, λs is the thermal conductivity of the sample S to be finally obtained at the temperature T, and λ ₁ ′ and t ₁ ′ are unknowns, but λ ₁ ′ is the upper surface temperature t ₁ ′, And lower surface temperature t
_Since it is the thermal conductivity of the standard heat transfer plate 24 at ₀ , from the above formula (3), λ ₁ ′ = Φ (t ₁ ′) (3) ′. Therefore, the above equations (4), (5),
By solving the simultaneous equations consisting of the three equations (3) ′, all of the above three unknowns λs, λ ₁ ′ and t ₁ ′ can be obtained. It should be noted that this calculation can be performed extremely easily by using a microcomputer. Also, without seeking function Φ representing the relationship between the thermal conductivity lambda ₁ and the upper surface temperature t ₁ of the standard heat transfer plate 24, representing the thermal conductivity lambda ₁ and the relationship of the upper surface temperature t _1, such as Figure 3 It is also possible to read the values of λ ₁ ′ and t ₁ ′ that satisfy the relationships of equations (4) and (5) from the graph.

As described above, according to the above method, the lower surface temperature t ₁ ′ of the sample S which is in contact with the upper surface of the standard heat transfer plate 24 and which has been difficult to perform accurate measurement in the past is directly measured. It is possible to obtain the thermal conductivity λs of the sample S by calculation without performing the measurement, and therefore, it is preferable to adopt it when measuring the thermal conductivity at a particularly high temperature where the standard heat transfer plate 24 cannot be omitted. However, the configuration of the heat input conductivity measuring device can be simplified.

If the same standard heat transfer plate is always used, it is sufficient to measure its thermal conductivity only once at the beginning to create a graph as shown in Fig. 3 and obtain the function Φ. It is not necessary to measure the thermal conductivity of the standard heat transfer plate each time.

"Effects of the Invention" As described in detail above, the thermal conductivity measuring method of the present invention first determines the thermal conductivity of the standard heat transfer plate, and then superimposes the sample on the standard heat transfer plate to obtain the Since the total conductivity is obtained and the thermal conductivity of the sample is calculated based on those values, it has been difficult to measure in the past, and the heat flowing through the measuring device caused the error. The thermal conductivity of the sample can be obtained without directly measuring the lower surface temperature of the sample that is in contact with the standard heat transfer plate. It is suitable for use in the measurement, and the structure of the thermal conductivity measuring device can be simplified.

[Brief description of drawings]

1 to 4 are views for explaining an embodiment of the present invention. FIG. 1 is a vertical sectional view of a thermal conductivity measuring device suitable for carrying out the method of the present invention. FIG. 2 is a schematic diagram for explaining the measurement state of the thermal conductivity of the standard heat transfer plate, FIG. 3 is a diagram showing the relationship between the thermal conductivity of the standard heat transfer plate and the upper surface temperature, and FIG. 4 is the standard. It is a figure for demonstrating the measurement state of the total thermal conductivity in the state which the heat transfer plate and the sample were piled up. FIG. 5 is a diagram showing the relationship between thermal conductivity and temperature, and FIG. 6 is a vertical cross-sectional view showing a conventional thermal conductivity measuring device and its schematic configuration. S ...... sample, 24 ...... standard heat transfer plate, T ...... measured temperature, t ₀ ...... underside temperature of the standard heat transfer plate, t _1, t ₁ '...... top temperature of the standard heat transfer plate, lambda ₁ ... … The thermal conductivity of the standard heat transfer plate, λt …… Total thermal conductivity, λs …… The thermal conductivity of the sample.

Claims (1)

[Claims] 1. When measuring the thermal conductivity λs of a sample at a predetermined measurement temperature T, first, the lower surface temperature t ₀ of a standard heat transfer plate is measured.
While the temperature is kept constant and the upper surface temperature t ₁ is changed stepwise, the thermal conductivity λ _{1 at} each temperature of this standard heat transfer plate is increased.
Then, the sample is superposed on the upper surface of the standard heat transfer plate, and the lower surface temperature of the standard heat transfer plate is maintained at the above temperature t ₀ as it is, and the upper surface temperature of the sample is maintained at the measurement temperature T. Determine the total thermal conductivity λt of the standard heat transfer plate and the sample in the state, the value of the total conductivity λt and the measured temperature of the sample based on the value of the thermal conductivity λ ₁ at each temperature of the standard heat transfer plate A method for measuring thermal conductivity, characterized in that the thermal conductivity λs at T is calculated.