JPH0625742B2 - Thermal conductivity measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thermal conductivity measuring device suitable for use in 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 with temperature. The higher the temperature, the higher the thermal conductivity. That is, heat tends to be easily transmitted. 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 it up to the use temperature.

A device shown in FIG. 4 is known as a device 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 this thermal conductivity measuring device, a sample S whose thermal conductivity is to be measured is arranged at a central position in a protective cylinder a, and standard electric heating plates s ₁ and s ₂ whose thermal conductivity is known are arranged above and below the sample S. , A main heater b and an auxiliary heater c create a thermal equilibrium state inside the protective cylinder a as shown by a broken line A in the figure, and a temperature gradient like a broken line B is formed on the sample S and the standard heat transfer plates s ₁ and s _2. It is what makes me. Then, the average internal temperature of the sample S is kept at a temperature to be measured, and the temperatures at the upper surface and the lower surface of the sample S are measured by the thermometers e and e in the steady state, and the temperature difference between them and the heat flow measurement plate d The heat conductivity of the sample S at that temperature is calculated from the heat quantity of the steady heat flow measured by the above, that is, the heat transmission flow rate that has passed through the sample S.

That is, the heat transmission flow rate is Q (Kcal / h), the thermal conductivity of the sample S is λ (Kcal / m · h · deg), the thickness dimension of the sample S is t (m), and the effective area of the sample S is A ( m ² ), the upper surface temperature and the lower surface temperature of the sample S are θ ₁ and θ ₂ (° C.), respectively, the relationship of Q = (λ / t) · A (θ ₁ −θ ₂ ) is established. , Λ is obtained as λ = Q · t / A (θ ₁ −θ ₂ ) ... (1).

The standard heat transfer plates s ₁ and s ₂ have heat insulating properties, hold the temperature of the sample S at a high temperature, and hold the heat flow measurement plate at a low temperature. By measuring the surface temperature with a thermometer f ..., the values of the thermal conductivity obtained from the surface temperature and the above-mentioned heat transmission flow rate Q are compared with the known values of the thermal conductivity to obtain the measured values. It is for verification and correction if necessary.

[Problems to be Solved by the Invention] In the conventional thermal conductivity measuring device described above, in order to obtain sufficient measurement accuracy, the value of the heat transmission flow rate Q passing through the sample S is accurately measured. Needless to say, therefore, the heat flow passing through the inside of the sample does not flow laterally inside the sample, and the steady heat flow inside the protective cylinder a goes to the outside through the peripheral surface of the protective cylinder a. It is important to ensure that the heat is not dissipated, that is, the heat flow only flows from top to bottom and not sideways.

Therefore, in the above-mentioned conventional apparatus, a large number of heaters g for wall surface temperature compensation are provided on the outer surface of the protective cylinder a, and the heaters g are individually controlled to control the inner surface temperature of the protective cylinder a. By conforming to the temperature gradient inside the a, heat transfer between the protective cylinder a and its internal space is eliminated to prevent the internal heat flow from radiating from the peripheral surface of the cylinder a.

However, the above conventional thermal conductivity measuring device is provided with a large number of wall surface temperature compensating heaters g ... And a control device and a wall surface temperature sensor for accurately controlling the large number of heaters g ... As such, etc. are required, it has to be large, complicated, and expensive.

And, the measurement temperature is 1,000 ° C or higher, especially 1,700
If the temperature exceeds ℃, the amount of heat radiated from the heaters g to the surroundings will increase sharply. Therefore, it is extremely difficult to accurately control the wall temperature of the protective cylinder a. In addition to the above, the emitted heat causes a large increase in the ambient temperature, which requires a large-scale cooling means for cooling the surroundings.
There is also a problem in that the amount of heat loss is enormous, the operating cost is high, and it is not preferable from the viewpoint of energy saving.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a thermal conductivity measuring apparatus suitable for use particularly when measuring thermal conductivity under high temperature.

[Means for Solving the Problem] The present invention provides a measurement chamber whose periphery is covered with a heat insulating material inside a furnace vessel, and generates a steady heat flow from the upper part to the lower part in the measurement chamber and distributes it in the measurement chamber. By holding the sample at a desired set temperature, and measuring the temperature difference between the upper surface temperature and the lower surface temperature of the steady heat flow that has passed through the sample and the sample, the value of the heat transmission flow rate and the value of the temperature difference. From the thermal conductivity measuring device configured to measure the thermal conductivity of the sample at the set temperature, the inner surface of the heat insulating material forming the side wall of the measurement chamber has a heat resistance and It is characterized in that it is covered with a wall temperature compensating plate made of a material having a higher thermal conductivity than the heat insulating material.

"Operation" In the thermal conductivity measuring apparatus of the present invention, the inner surface of the heat insulating material forming the side wall of the measuring chamber is covered with the wall temperature compensating plate made of a highly conductive material, so that the wall temperature compensating plate is not affected by the heat inside the measuring chamber. The temperature inside the measurement chamber becomes the same as the temperature inside the measurement chamber due to its own heat transfer action, and as the distance increases, the temperature decreases due to heat dissipation to the heat insulating material, and is almost the same as the sample temperature. It is naturally held in the chamber, the heat transfer in the radial direction is stopped, and the steady heat flow is prevented from being radiated through the side wall, so that sufficient measurement accuracy can be obtained.

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

FIG. 1 is an elevational sectional view showing a schematic configuration of a thermal conductivity measuring apparatus according to an embodiment of the present invention, and FIG. 2 is an enlarged view of a main part thereof, in which reference numeral 1 is a furnace vessel. The furnace vessel 1 is composed of the present invention 2 each having a water cooling jacket, and a lid body 4 connected to a main body 2 by a hinge 3.

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 inside.
A main heater 9 for keeping the inside of the measurement chamber 8 at a predetermined temperature is attached to the upper space of the measurement chamber 8, and the inner surface temperature of the lower heat insulating material 5 is set in the lower heat insulating material 5. A compensating heater 10 for keeping the temperature equal to that of a heat flow measuring plate 15 (described later) is embedded, and the main heater 9 and the compensating heater 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 (hereinafter, simply referred to as compensating plate) 14 formed in a cylindrical shape. Although details will be described later, this compensating plate 14 transfers the heat in the measurement chamber 8 to the lower portion of the inner surface of the side heat insulating material 7 due to its excellent thermal conductivity, and thus the sample S and the standard heat transfer plate 24 (described later). ) To prevent heat radiation in the peripheral direction.

Further, a cylindrical 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 measurement plate 15 has a measurement gas flow passage for measuring the heat transmission flow rate formed in a spiral shape, and allows the measurement gas to flow through the flow passage as indicated by an arrow in the figure. The gas inlet pipe 17 and the 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-mentioned measuring gas and cooling gas are brought to a predetermined temperature by the gas preheaters 21 and 22 embedded in the lower heat insulating material 5, and then the heat flow meter side plate 15 and the compensating cooling plate 1 respectively.
It will be introduced in 6. Although not shown, thermometers for measuring the inlet temperature and outlet temperature of the measuring gas and the inlet temperature and outlet temperature of the cooling gas are respectively provided.

The heat flow measuring plate 15 measures the temperature at the inlet and outlet of the measuring gas to determine the amount of heat received by the measuring gas, that is, the heat transmission flow rate through the sample S, from the temperature difference and the gas flow rate. It is for measuring. Further, the compensating cooling plate 16 arranged around it is controlled such that the temperature of the cooling gas becomes equal to the temperature of the temperature measuring gas, so that the surface temperature of the compensating cooling plate 16 is the surface of the heat flow measuring plate 15. The temperature is maintained at the same level, which prevents heat exchange between them, eliminates the measurement error of the heat transmission flow rate, and prevents the temperature of the lower surface of the sample from being different between the central part and the peripheral part. This is to prevent the amount of heat from flowing laterally.

A 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 disc-shaped standard heat transfer plate 24 made of a material having a known thermal conductivity is arranged on the upper surfaces thereof. .
This standard heat transfer plate 24 holds the temperature of the sample S at a high temperature, like the standard heat transfer plates s ₁ and s ₂ in the above-described conventional apparatus.
In addition to keeping the surface temperature of the heat flow measurement plate 15 at a low temperature, the temperatures of the upper and lower surfaces of the heat flow measurement plate 15 are measured by a thermometer (not shown) inserted in the temperature measurement plate 23 and a lower temperature measurement described later. By measuring with a thermocouple thermometer 27 inserted in the hot plate 25, the measured value is verified and corrected from the temperature difference between them and the known thermal conductivity.

Then, on the upper surface of the standard heat transfer plate 24, the lower temperature measuring plate 25
Is arranged, the sample S whose thermal conductivity is to be measured is arranged on the upper surface thereof, and the upper temperature measuring plate 26 is further arranged on the upper surface thereof. Thermocouple thermometers 27 and 28 are inserted in the lower temperature measuring plate 25 and the upper temperature plate 26, respectively, and the upper surface of the sample S is
The temperature of the lower surface can be measured.

In order to measure the thermal conductivity λ of the sample S at a high temperature with the apparatus having the above configuration, first, the sample S is placed in the measurement chamber 8, the upper measurement plate 26 is placed on the upper surface, and the upper measurement is performed. A thermocouple thermometer 28 is inserted in the plate 26. Then, the measurement chamber 8 is sealed by the upper heat insulating material 6 and the furnace container 1
The lid 4 is closed, the main heater 9 and the compensating heater 10 heat the inside of the measurement chamber 8 to a predetermined set temperature, and the internal temperature of the sample S is maintained at the temperature T ° C. at which the thermal conductivity should be measured. In addition, the measurement gas and the cooling gas are supplied to the preheaters 21 and 2, respectively.
It is heated to a predetermined temperature by 2 and circulated through the heat flow measuring plate 15 and the compensating cooling plate 16, and the temperatures thereof are kept equal.

When the temperature in the measurement chamber 8 and the internal temperatures of the sample S and the standard sample 24 are in a steady state, that is, when the temperature change is no longer recognized, the temperatures θ ₁ and θ ₂ on the upper and lower surfaces of the sample S are measured with a thermocouple thermometer. The temperature is measured by the sensors 28 and 27, and the temperatures of the inlet and outlet of the measuring gas flowing through the heat flow meter side plate 15 are measured. Then, from the temperature difference of the measuring gas and the flow rate thereof, the amount of heat received, that is, the heat transmission flow rate Q passing through the sample S is obtained,
The thermal conductivity λ at the temperature T of the sample S is calculated from the heat transmission flow rate Q, the temperatures θ ₁ and θ _{2 on} the upper and lower surfaces of the sample S, and the thickness dimension t of the sample S by using the above equation (1). . In this case, the effective area A of the sample S is the area of the heat flow measurement plate 15.

Further, by measuring the temperature difference between the upper and lower surfaces of the standard heat transfer plate 24, the thermal conductivity is obtained from those values and the above-mentioned heat penetration flow rate Q, and the value is compared with the known thermal conductivity value. It suffices to verify the measurement result and correct it if necessary.

The thermal conductivity measuring device described above does not need to be provided with a heater for wall temperature compensation, which was necessary in the conventional device,
The heat transmission flow rate Q passing through the sample S can be accurately measured.

That is, also in this device, it is inevitable that heat is generated from the side heat insulating material 7 due to the temperature difference from the outside like the conventional device. Alternatively, the temperature around the standard heat transfer plate 24 will drop, but in this device, the compensation plate 14 made of a good heat conductive material extending from the inner surface of the measurement chamber 8 is provided to compensate for this. The amount of heat radiated by the heat transfer action of the plate 14 is transferred to the side heat insulating material 7 through the compensating plate 14, so that heat dissipation from the sample S or the standard heat transfer plate 24 to the peripheral direction is effectively prevented. It is a thing. (Note that the main purpose of the compensating plate 14 is to transfer the heat of the measuring chamber 8 to the lower portion of the inner surface of the side heat insulating material 7 as described above, so it is not always necessary to provide it on the entire side surface of the measuring chamber 8. Not).

This will be described in detail with reference to FIG. The value of the amount of heat radiation Q ₁ from the side heat insulating material 7 in contact with the sample S via the compensating plate 14 is as follows: average heat conductivity of the side heat insulating material 7 is λ ₁ , its thickness dimension is d ₂ , diameter dimension D, ₁ 1 the height of the sample S, ₁ a top temperature of the sample S theta, ₂ a lower surface temperature of specimen theta, when the external surface temperature of the side heat insulating material 7 and theta _3, approximately follows It is represented by a formula. (Note that the following equation is assumed that the diameter dimension D of the side heat insulating material 7 is sufficiently large and can be approximated by flat plate heat transfer,
Further, the thickness dimension d ₁ of the compensating plate 14 is an extremely small value as compared with D, and is an approximate expression when it can be omitted. ) Q ₁ = (λ ₁ / d ₂ ) ・ π ・ D ・₁₁ × [{(θ ₁ + θ ₂ ) / 2} −
θ ₃ ] On the other hand, the upper part of the compensating plate 14 faces the inside of the measurement chamber 8 and its part has a sufficiently high temperature. When the temperature of the compensating plate 14 decreases due to heat radiation from the side heat insulating material 7, As shown by the arrow in the figure, a heat transfer action occurs from the upper part to the lower part of the compensating plate 14, and the heat is carried from the upper space in the measuring chamber 8 to the side heat insulating material 7 through the compensating plate 14. . The amount Q ₂ of heat transfer is approximately represented by the following equation, where λ ₂ is the average thermal conductivity of the compensating plate 14 and d ₁ is its thickness dimension.

_{Q 2 = {λ 2 / (} 1 1/2)} · π · D · d 1 × {(θ 1 -θ 2) /
2} Therefore, so that Q ₁ = Q ₂ , that is, the heat radiation amount Q ₁ from the side heat insulating material 7 and the compensating plate 1 for the side heat insulating material 7
If the values of the thermal conductivity λ ₂ and the thickness dimension d ₁ of the compensating plate 14 are appropriately set so that the heat transfer amount Q ₂ from 4 is the same, the temperature of the side heat insulating material 7 will not drop. Therefore, the temperature of the compensating plate 14 does not decrease, and the temperature of the compensating plate 14 is naturally kept at the temperature of the sample S. As a result, the heat flow passing through the inside of the sample S is effectively prevented from flowing outside through the compensating plate 14 and the side heat insulating material 7.

Note that the above calculation example shows only the outer peripheral portion of the sample S, but similar heat radiation occurs also in the outer peripheral portion of the standard heat transfer plate 24. Therefore, the actual thickness dimension d ₁ of the compensating plate 14 is the same. It goes without saying that it is determined by calculation over the range.

As described above, according to this apparatus, only by providing the compensating plate 14 made of the material having good thermal conductivity on the inner surface of the side heat insulating material 7, the heat radiation from the sample S to the side can be effectively prevented. Since the steady heat flow only flows downward and the heat transmission flow rate Q that has passed through the sample S can be accurately measured by the heat flow measurement plate 15, sufficient measurement accuracy can be obtained. Further, this device does not require a heater for wall temperature compensation and a control device for them, which were required in the conventional device, and can realize downsizing, simplification, and cost reduction of the device, and significantly simple operation. In addition, it does not cause enormous heat loss, and thus is suitable for use especially in measurement at high temperature.

Next, another embodiment of the present invention will be described with reference to FIG.

In the embodiment described above, the amount of heat released from the side heat insulating material 7 and the amount of heat transferred from the compensating plate 14 to the side heat insulating material 7 are assumed to be uniform in the thickness direction of the sample S. Usually, this is sufficiently effective, but more strictly, since there is a temperature gradient inside the sample S, the heat dissipation amount Q ₁ and the heat transfer amount Q _{2 above} are in the thickness direction of the sample S. Not constant.

Therefore, in this embodiment, the thickness of the compensating plate 14 is gradually reduced from the upper part to the lower part so that the heat transfer amount to each part of the side heat insulating material 7 is changed corresponding to the heat dissipation amount. Therefore, a higher measurement degree can be obtained.

This will be described in detail with reference to FIG. As shown in FIG. 3, considering the heat balance at the position of the distance 1x from the lower surface of the sample S, and letting the heat radiation amount from the side heat insulating material 7 at this position of 1x be Q ₁ ′, this Q ₁ ′ The value of is approximately expressed by Q ₁ ′ = (λ ₁ / d ₂ ) · π · D · 1x × {θ ₂ + (θ ₁ −θ ₂ ) · 1x / 21 ₁ −θ ₃ }.

Also, considering the heat balance in the compensator 14 at the 1x position, and taking a minute length Δ1 in this portion, the heat transfer amount Q ₂ ′ of heat passing through this Δ1 portion is the average heat of the compensator 14 The conductivity is λ ₂ , and the thickness dimension of the compensating plate 14 at that portion is d ₁ ′.
Then, it is approximately represented by Q ₂ ′ = (λ ₂ / Δ1) · π · D · d ₁ ′ × Δθ. Here, Δθ is a temperature difference between the inner surface temperature θx of the compensating plate 14 at the 1x position and the inner surface temperature of the compensating plate 14 at a position separated by a minute length Δ1 from the 1x position. Is when the temperature gradient of the sample S (that is, the rate of change from the upper surface temperature θ ₁ to the lower surface temperature θ ₂ ) is linear (all the calculation examples so far are examples of such cases). , Δ1 and a constant value.

Therefore, if the value of d ₁ ′ is determined so that Q ₂ ′ = Q ₁ ′ in the above equation, that is, if the value of d ₁ ′ is changed in thickness in proportion to Q ₁ ′, the sample S It is possible to equalize the amount of heat radiated from the side heat insulating material 7 and the amount of heat transfer of the compensating plate 14 at each position in the thickness direction. And for this, 'the value of, d _1' d ₁ alters to satisfy / d ₁ α1x / _{1 1} relationship, that is, the thickness of the compensating plate 14 as shown in FIG. 3 It may be appropriately set so that the thickness gradually decreases from the upper part to the lower part. By doing so, the inner surface of the sample S and the compensating plate 14 in contact therewith are kept at the same temperature over the entire surface, and the heat radiation from the side part of the sample S can be almost completely prevented. As a result, the compensating plate is obtained. The measurement accuracy can be further improved as compared with the case of the above-described embodiment in which the thickness of 14 is constant.

In the above examples, the temperature gradient inside the sample is linear, and the material (heat conductivity) of the heat insulating material and the compensating heat transfer plate is constant, but they may change. In this case, the calculation becomes complicated, and as a result, the dimensional change such as the thickness of the compensating plate does not become linear, but it is possible to obtain essentially the same effect as the case of the above embodiment. There is no end.

Further, although graphite, heat resistant steel, and molybdenum are exemplified as the material of the wall surface temperature compensating plate 14 in the above-mentioned embodiment, the heat resistance which can sufficiently withstand the measurement under high temperature and the thermal conductivity which is sufficiently higher than that of the heat insulating material. Needless to say, other materials may be used as long as they are large materials.

"Effects of the Invention" As described in detail above, the thermal conductivity measuring device of the present invention has an inner surface of a heat insulating material that forms a side wall of a measurement chamber and has a higher heat conductivity than that of the heat insulating material. Since the structure is covered with a wall temperature compensation plate made of a heat-resistant material, the inner surface temperature of the heat insulating material is naturally maintained at the temperature of the sample,
Therefore, the steady heat flow is not radiated to the outside through the side wall, and sufficient measurement accuracy can be obtained. Since the heater for wall temperature compensation, which was required to be provided in the past, is not required, the device can be downsized, simplified, and cost can be reduced, and complicated control is not required, and an enormous amount of heat is required. Since it causes no loss, it is particularly suitable for use in measurements at high temperatures.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a thermal conductivity measuring device of this embodiment, and FIG. 2 is a wall surface temperature in this device. It is a principal part expanded sectional view for demonstrating the heat transfer effect of a compensating plate. FIG. 3 shows another embodiment of the present invention, and is an enlarged sectional view of an essential part for explaining the heat transfer action of the wall temperature compensating plate whose thickness dimension is gradually reduced toward the lower part. FIG. 4 is a vertical sectional view showing a schematic configuration of a conventional thermal conductivity measuring device. S ... Sample, 1 ... Furnace container, 7 ... Side heat insulating material, 8 ...
Measuring room, 14 ... Wall temperature compensator.

Claims (1)

[Claims] 1. A measurement chamber whose periphery is covered with a heat insulating material is provided inside a furnace vessel, and a steady heat flow from the upper part to the lower part is generated in the measurement chamber to place a sample placed in the measurement chamber at a desired set temperature. By holding and measuring the temperature difference between the upper surface temperature and the lower surface temperature of the heat transmission flow rate and the sample of the steady heat flow that has passed through the sample, at the set temperature of the sample from the value of the heat transmission flow rate and the temperature difference. A thermal conductivity measuring device configured to measure thermal conductivity, wherein an inner surface of a heat insulating material forming a side wall of the measurement chamber has a heat resistance and is heat-treated in comparison with the heat insulating material. A thermal conductivity measuring device characterized by being covered with a wall temperature compensating plate made of a material having high conductivity.