JPH0231147A - Apparatus and probe for measuring heat conductivity - Google Patents

Abstract

PURPOSE:To measure the heat conductivity of a high temp. conductive liquid by preventing the generation of a Marangoni convection under minute gravity environment. CONSTITUTION:A probe 1 for measuring heat conductivity consists of a semi- columnar measuring part 2, a flange part 3 and a columnar rod part 4, and a liquid 19 to be measured is sealed in a container 13 in a state pressed to a spring through a piston 20. The container 13 and the probe 1 are connected by a cap 16 through a gasket 15 and a current is supplied to a fine wire part 6 through metal lead wires 11 to heat the same and the voltage change between both terminals of the fine wire part is measured by a voltage measuring lead 7 to calculate the temp. rise ratio of the fine wire part 6 and the heat conductivity of the liquid 9. By this method, in such a state that both of a heat convection and a Maragoni convection being the main causes of a measuring error are not present, heat conductivity can be measured with high accuracy while a state having no free surface is held to the liquid to be measured under minute gravity environment.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a technology for measuring thermophysical properties of liquids. More specifically, it relates to a technique for measuring the thermal conductivity of a melt of a substance that is solid at room temperature using an unsteady thin wire method.

(Prior Art) Until now, the thermal conductivity of electrically conductive liquids, especially semiconductor melts, has been evaluated by
[Liquid Semiconductors' Plenum, Press, New York, 1969] conducted measurements by a steady method using a concentric cylinder method. When measuring thermal conductivity in liquids, by using a long plate and a long height,
Journal of Physics E, Volume 14, 143
As reported on page 5, 1981, measurement by the unsteady thin wire method is recommended as it guarantees excellent measurement accuracy.

In order to measure the thermal conductivity of electrically conductive liquids by applying the principle of this unsteady thin wire method, the present inventor has developed a structure in which a conductor is printed on a ceramic substrate and further coated to form a probe. have applied.

This method uses a probe having the structure shown in FIG. That is, in this probe, a thin wire portion 37 and a thin wire lead portion 38 for generating heat using a metal such as platinum are formed on a ceramic substrate 36 made of an oxide such as alumina or a nitride such as aluminum nitride. Current terminals 31 and 33 for flowing current are provided at both ends thereof. Further, in order to measure the change in electrical resistance of the thin wire portion 37, voltage measurement leads 39 are taken out from both ends of the thin wire portion 37 and led to voltage measurement terminals 32 and 34. These four terminals 31.3
2.33.34 and the lead portions 38.39 are made of metal as well as the thin wires. Further, ceramic is coated thereon as an insulating coating film 35 for insulation. A method of measuring the thermal conductivity of an electrically conductive liquid using this probe will be explained with reference to the drawings.

FIG. 6 is an explanatory diagram of the basic configuration showing the principle of measuring the thermal conductivity of a liquid by the unsteady thin wire method using the probe of FIG. 5. In the figure, numeral 41 is the probe shown in FIG. 5, which is immersed in a liquid to be measured 43 contained in a container . A power source 44 is connected to the current terminals 31 and 32,
The thin wire portion 37 is heated with electricity. The Joule heat generated in the thin wire portion 37 increases the temperature of the thin wire portion and escapes toward the liquid to be measured 43 by heat conduction. In this case, the temperature change in the thin wire portion with respect to logarithmic time immediately after energization exhibits the behavior shown in FIG. 7, and the thermal conductivity of the liquid to be measured can be determined from the slope of the straight line portion.

That is, the temperature rise amount Δ of the thin line shown by the straight line part in FIG.
T is expressed by equation (1) using the thermal conductivity λ1 of the liquid to be measured 43, the thermal conductivity λ2 of the ceramic substrate 36, the electric power q input to the thin wire, the electric power input time t, and the constant A.

ΔT=[(q/4n(λ1+λz)][1n(t)+A
] (1) Since the thermal conductivity λ2 of the ceramic substrate 36 and the electric power q input to the thin wire are known, the seventh
If the slope q/4n (λ1+λ2) of the straight line in the figure is found, the thermal conductivity λ1 of the liquid to be measured 43 can be found.

Here, since the resistivity of the material constituting the thin wire section changes depending on the temperature, when the voltage change at both ends of the thin wire section 37 which is heated with a constant current is measured by the voltage measuring device 45, the resistivity of the thin wire section 37 changes with the temperature. The amount of temperature rise ΔT can be measured as a change in resistance of the thin wire portion, that is, a change in voltage across both ends of the thin wire portion, and a time change in the amount of temperature rise ΔT of the thin wire portion 37 as shown in FIG. 7 can be obtained.

(Problem to be solved by the invention) By the way, the first region that deviates from the straight line in Fig. 7 is due to a transient error, and the latter region M is due to the influence of convection in the fluid to be measured. It is something. Thermal conductivity measurement basically involves applying a temperature difference and measuring the flow of heat, so under gravity, the occurrence of convection is unavoidable. Therefore, measurements are taken within a short period of time until convection occurs, but the time until convection occurs, that is, the area M
The time L1 until the start of is generally short, from several seconds to about 10 seconds, and depending on the values of the specific gravity, viscosity, heat capacity, thermal conductivity, etc. of the liquid being measured, it overlaps with the transient error area and a straight line portion may be obtained. There may be cases where this is not possible. In this case, it is impossible to measure thermal conductivity on the ground, and it is necessary to measure it in an environment where no convection occurs.

Even if there is a temperature difference, an environment without convection cannot be achieved unless the influence of gravity is eliminated. Therefore, it is necessary to perform measurements in a so-called microgravity environment. A microgravity environment can be achieved not only in space, but also through suborbital flights by aircraft, suborbital flights by rockets, etc. In recent years, various measurements and experiments using microgravity environments have been progressing. .

By the way, in a microgravity environment, instead of the thermal convection caused by the density distribution of the liquid disappearing, Marangoni convection caused by the surface tension distribution occurs, stirring the inside of the liquid. Marangoni convection is a flow that occurs when there is a free surface of a liquid due to the difference in surface tension caused by the temperature distribution of the free surface.In the gravitational environment on the ground, it is hidden behind thermal convection and is not noticeable. In places where it is not present, it becomes a noticeable flow and even stirs the liquid. The most effective way to avoid this is to eliminate the free surface.

The first object of the present invention is to suppress the occurrence of Marangoni convection even in a microgravity environment by using a thermal conductivity measuring probe having a thin metal wire part on a ceramic substrate, and to measure the thermal conductivity of liquids, especially at high temperatures. The present invention provides a thermal conductivity measuring device capable of measuring the thermal conductivity of a conductive liquid.

Next, other problems to be solved by the present invention will be described. In conventional unsteady fine-wire thermal conductivity measurements, the atmosphere of the liquid to be measured in a container is not vacuumed, and the liquid to be measured may react with surrounding gas, such as when measuring thermal conductivity at high temperatures. , the material may change. That is,
A second object of the present invention is to provide a thermal conductivity measuring device in which a liquid to be measured is vacuum-sealed.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a container for holding a liquid to be measured, and a thermal conductivity measurement device having a ceramic substrate inserted into the container and a thin metal wire portion. probe for
The cap is tightened with force across the gasket,
The liquid to be measured, which is solid at room temperature, is sealed, and the liquid to be measured turns into a molten liquid.In order to maintain the liquid to be measured in a state in which there is no free surface in close contact with the measurement surface of the probe, the piston is pushed by a spring to remove the liquid to be measured. The structure is such that the measurement liquid is applied to the probe measurement surface and the container wall.

In addition, in order to achieve vacuum sealing of the liquid to be measured at high temperatures, a metal cartridge and cylinder are placed over the probe, container, and cap for measuring thermal conductivity, which contain the liquid to be measured that is solid at room temperature, a spring, and a piston. The cartridge, cylinder, and hermetic seal are each hermetically sealed together by electron beam welding, resulting in a completely hermetically sealed structure that maintains a vacuum inside the cartridge.

(Example) Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an embodiment of the thermal conductivity measuring device of the present invention.

FIG. 2 is an external view of the thermal conductivity measurement probe used in the embodiment of FIG. 1.

FIG. 3 is a sectional view showing the structure of another embodiment of the thermal conductivity measuring device of the present invention.

First, the first embodiment shown in FIG. 1 will be described.

The thermal conductivity measuring probe 1 used in the first example is as follows:
As shown in FIG. 2, it consists of a semi-cylindrical measuring part 2, a flange part 3, and a cylindrical rod part 4, and everything except the metal used for the wiring is made of ceramics such as alumina. A flat portion of the measurement section 2 is a measurement surface 5, and a thin wire section 6 and a voltage measurement lead 7 are formed by metal wiring under a thin ceramic protective film 30 on the surface. The lead wire 8 from the thin wire part 6 and the lead wire 9 from the voltage measurement lead 7 pass through the ceramics of the flange part and the rod part, and are led out to the end face 10 of the rod part in a completely gas-tight state. It will be done. These wirings can be manufactured by co-firing with ceramics as metal printed wirings using the ceramic green sheet method.

The aforementioned lead wires 8.9 are led out from the end face 10 of the rod portion by metal lead wires 11 made of platinum or the like.

On the other hand, sealing debris 12 is formed on the flange portion 3.

In the first embodiment shown in FIG. 1, the sealing surface 14 of a cylindrical container 13 with one side closed and the sealing layer 12 of the flange portion of the thermal conductivity measuring probe 1 are connected by a cap 16 with a gasket 15 in between. The inside of the container is sealed by tightening the container 13 and the probe 1. Tightening by the cap 16 is performed by engaging the male screw of the cap with the female screw 17 provided at the opening of the container 13.

On the other hand, the liquid to be measured 19 is solid at room temperature, but is heated and melted to a predetermined temperature T when the thermal conductivity of the melt is measured at a predetermined temperature T. This molten liquid to be measured 1
9 is pressed by a spring 21 via a piston 20, and the entire periphery of the liquid to be measured 19 is in contact with the solid;
The probe is sealed in a container in close contact with the measurement surface 5 of the probe and with no free surface. In this case, since the pressing force of the spring 21 is effective, in a microgravity environment, no matter what posture this embodiment is placed in, the liquid to be measured 19 will come into close contact with the measurement surface 5 of the probe, and The fact remains that there is no free surface.

To measure the thermal conductivity of the liquid to be measured 19 using this embodiment, a current is passed through the thin wire portion 6 of the probe through the lead wire protruding from the end surface 10 of the rod portion of the probe. The voltage change at both ends may be measured through a lead wire connected to the voltage measurement lead 7. In other words, if the change in resistance of the thin wire section converted from the voltage change at both ends of the thin wire section is further converted into temperature, and the temperature change of the thin wire section is obtained, as explained in Fig. 7, the temperature rise of the thin wire section with respect to logarithmic time is obtained. The thermal conductivity of the liquid 19 to be measured can be determined from the coefficient (the slope of the straight line portion in FIG. 7).

In addition, when determining the thermal conductivity of the liquid to be measured 19 at a predetermined temperature T, put this example into a heating furnace (not shown), etc., and heat the liquid so that the entire liquid to be measured reaches a uniform temperature T. After heating this example, the thin wire portion 6 may be heated with electricity as described above, and the voltages at both ends of the thin wire portion may be measured.

In other words, by using this example in a microgravity environment, it is possible to maintain a state in which the liquid to be measured has no free surface, and the thermal conductivity of the liquid can be measured without thermal convection or Marangoni convection, which are the main causes of measurement errors. It is possible to obtain highly accurate measurement values.

This example is very effective when measuring the thermal conductivity of a substance that is solid at room temperature as a melt at a high temperature above its melting point. Even for the same substance, the specific gravity of solid and liquid is usually different. That is, when melted, the volume of the melt expands or contracts compared to when it is in the solid phase. While many materials expand in volume when melted, semiconductor materials such as indium antimony contract as they do with ice and water. By using this example, the action of the spring and piston absorbs the volume expansion or contraction when it becomes a melt, making it possible to measure thermal conductivity without damaging the container or creating a free surface. is obvious.

In addition, since the probe used here has the surface of the thin wire part covered with a ceramic insulating film, it can be used not only to measure the thermal conductivity of liquids with poor conductivity, but also when the liquid to be measured has electrical conductivity. It is clear that it is effective.

Next, the materials of the component parts in the embodiment shown in FIG. 1 will be described.

Container 13, cap 16, gasket 15, piston 2
0. The spring 21 may be made of any material as long as it does not react with the liquid to be measured 19 and has the necessary strength. Therefore, room temperature and 1
In the temperature range of about 00°C, the container 13 and cap 16
, the piston 20, and the spring 21 are usually made of commonly used metal materials such as stainless steel. It is desirable that only the gasket 15 be made of an elastic material such as soft metal or rubber.

Furthermore, in the case of samples such as molten salts that corrode metals even at room temperature or in the temperature range of about 100°C, consideration must be given to the material. However, if the container 13, the cap 16, the piston 20, the spring 21, and the gasket 15 are made of a fluorine-based resin such as Teflon, which is resistant to corrosion, there will be no problem. In this case, there is no fear of corrosion in the probe because the surface of the metal wiring portion, such as the thin wire portion, is covered with a ceramic insulating protective film.

On the other hand, when high-temperature heating is required and the liquid to be measured is active and easily reactive, as in the case of measuring the thermal conductivity of a semiconductor melt, it is inappropriate to use metals or fluorine-based resins. For high-temperature melts, it is often convenient to make the container 13, cap 16, gasket 15, piston 20, and spring 21 all from graphite, which has high heat resistance. For example, in the case of indium antimony, which is a compound semiconductor, there is no problem if the container 13, cap 16, gasket 15, piston 20, and spring 21 are all made of graphite. In this case as well, there is no need to worry about corrosion because the surface of the metal wiring parts of the probe, such as the thin wire parts, is covered with a ceramic insulating protective film. Particularly regarding the gasket 15, if GRAFOIL (trade name) manufactured by Union Carbide is used, the gasket can be replaced with a gasket that has high sealing performance and is free of impurities.

By the way, in response to the requirement that the liquid to be measured be sealed in a vacuum atmosphere, if the container is made of metal, it is possible to maintain the inside of the container in a vacuum atmosphere by assembling the first embodiment in a vacuum chamber. can. However, if the container is made of a porous material such as graphite, it may be possible to seal the liquid, but it will not be possible to seal the container airtight against gas. It becomes possible to stop.

Next, a second embodiment will be described with reference to FIG. As shown in FIG. 3, this embodiment replaces the first embodiment 23 shown in FIG.
6 and vacuum sealed.

To realize this, a closed tube-shaped cartridge 24 and a stepped cylindrical cylinder 25 are placed over the first embodiment 23, and the cartridge and cylinder are hermetically joined by electron beam welding or the like. Embodiment 23 is clamped and fixed, and the metal lead wire drawn out from the first embodiment is pulled out from the lead tube 27 of the hermetic seal 26, and the metal lead wire is soldered or silver brazed to the lead tube. After the hermetic seal is sealed, the hermetic seal and the cylinder may be electron beam welded. Since electron beam welding is performed under vacuum, the first embodiment can be sealed while being kept in a vacuum atmosphere.

Hotter liquids generally become more active. For example, compound semiconductors such as indium antimony are extremely sensitive to oxidation, and it is necessary to remove even trace amounts of oxygen from the atmosphere. Therefore, it is very important to keep the liquid to be measured in a vacuum atmosphere to avoid reaction with the atmosphere.

When graphite is used in containers, graphite is porous, so although it can be sealed against liquids, it cannot be made airtight against gases. However, if the structure is as shown in the embodiment shown in Fig. 3, the inside of the cartridge can be evacuated by evacuation during electron beam welding, and the gas inside the container can also be evacuated through the porous graphite of the container. Therefore, the cartridge can be hermetically sealed with the entire inside of the cartridge evacuated, including the inside of the container.

In the second embodiment shown in FIG. 3, a fixing flange 29 having bolt holes 28 for fixing this embodiment to a heating furnace (not shown) or the like is provided in a portion of the cylinder remote from the cartridge. . It is preferable to install such a structure on the low temperature side as much as possible, and to separate it from the liquid part to be measured which requires temperature uniformity.

That is, it is important to install the cylinder in a portion away from the cartridge.

To measure the thermal conductivity of the liquid to be measured 19 using this embodiment, ``Similar to the first embodiment, a current is passed through the metal lead wire drawn out from the hermetic seal to the fine wire portion 6 of the probe. The voltage change at both ends of the thin wire portion at this time may be measured through a metal lead wire connected to the voltage measurement lead 7.

In addition, when determining the thermal conductivity of the liquid to be measured 19 at a predetermined temperature T, heat this example so that the entire liquid to be measured reaches a uniform temperature T, and then Similarly to the first embodiment, it is sufficient to heat the thin wire portion 6 with electricity and measure the voltage at both ends of the thin wire portion.

Note that the materials of the cartridge and cylinder must be considered depending on the temperature to be measured.

When used at temperatures below 100°C, stainless steel is suitable because it can be easily electron beam welded and is readily available.

When heating at temperatures below 1000°C, the cartridge material should be nickel, which has high thermal conductivity, and the cylinder material should be stainless steel, which has low thermal conductivity, in order to improve the temperature uniformity of the liquid to be measured and from the viewpoint of high-temperature strength. It is desirable that the cartridge and mounting facilitate large temperature gradients between the flanges.

When used at temperatures above 1000°C, the cartridge must be made of a heat-resistant material such as tantalum or molybdenum.

Furthermore, as can be seen from the above description, the second embodiment has a completely airtight structure by electron beam welding. Therefore, even if evaporative gas leaks from the liquid to be measured using only the first embodiment, if the second embodiment is used, there is no need to worry about gas leaking to the outside. For example, if the liquid to be measured is a liquid that generates toxic gas, using only the first embodiment may cause damage to the container, poor sealing of the gasket, or the need to use a porous material such as graphite for the container itself. However, in the second embodiment, there is no such concern.

By the way, when measuring the thermal conductivity of the liquid to be measured 19 at a predetermined temperature T, it is possible to check whether the liquid to be measured 19 has reached the predetermined temperature T by using the structure of the embodiment described above. The temperature measured by attaching a thermocouple to the surface of the container 13 or the surface of the cartridge 24 is the temperature of the liquid to be measured 1.
However, the only method available is to set the ambient temperature in the heating furnace in which these examples are heated to the temperature of the liquid to be measured 19.

In such a case, the temperature T of the liquid 19 to be measured is accurate.
cannot be measured. However, if an unsteady lateral line method thermal conductivity measurement probe having a thermocouple 18 embedded therein as shown in FIG. 4 is used, the temperature of the liquid to be measured can be measured almost accurately. That is, in the thermal conductivity measuring probe shown in FIG. If a probe for unsteady lateral line method thermal conductivity measurement is used, which has a structure that is embedded in the rod portion and pulled out from the end surface 10 of the rod portion, the thermocouple 18 is located in the container 13 as well as the liquid 19 to be measured, and the probe is Since it is located close to the measuring liquid 19, the thermocouple 18
The temperature difference between the liquid 19 and the liquid to be measured is extremely small, and the temperature of the liquid to be measured can be accurately measured. Furthermore, since the temperature measuring means for the liquid to be measured is built into the probe, it is possible to measure the temperature of the liquid to be measured very easily.

Note that the structure shown in FIG. 4 can be realized by using the ceramic green sheet method, and does not interfere with the effect of sealing the liquid to be measured in FIGS. 1 and 3.

(Effects of the Invention) As described above, according to the present invention, the thermal conductivity of a liquid to be measured can be measured in a microgravity environment without providing a free surface to the liquid to be measured. Therefore, according to the present invention, even in liquids whose thermal conductivity cannot be measured under gravity due to the influence of convection,
Accurate thermal conductivity measurements can be made in a microgravity environment without causing Marangoni convection.

In addition, it is possible to completely prevent the leakage of evaporated gas from the liquid being measured to the outside, making it possible to measure the thermal conductivity of melted liquids that generate toxic gases in a sufficiently safe manner. can be kept in a vacuum atmosphere, making it possible to prevent reactions with the atmosphere such as oxidation.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an embodiment of the thermal conductivity measuring device of the present invention, and FIG. 2 is an external view of a probe for measuring thermal conductivity used in the embodiment of FIG. Fig. 3 is a sectional view showing the structure of another embodiment of the thermal conductivity measuring device of the present invention, Fig. 4 is an external view of a thermal conductivity measuring probe with a built-in thermocouple, and Fig. 5 is a cross-sectional view showing the structure of another embodiment of the thermal conductivity measuring device of the present invention. Fig. 6 is an explanatory diagram of the basic configuration showing the principle of thermal conductivity measurement using the unsteady thin wire method, and Fig. 7 is a perspective view showing a conventional example of a probe for measuring thermal conductivity using the unsteady thin wire method. It is a diagram showing the principle. In the figure, 1... Probe for measuring thermal conductivity, 5... Measurement surface, 6
゜37...Thin wire part, 7,39...Voltage measurement lead,
8, 9...Leader line, 11...Metal lead, 13.
42... Container, 15... Gasket, 16... Cap, 18... Thermocouple, 19.43 Liquid to be measured, 2
0...Piston, 21...Spring, 24...
Cartridge, 25-0. cylinder, 26.・Hermetic seal, 36...ceramic substrate.

Claims (1)

[Claims] 1. Consists of a semi-cylindrical measuring part, a flange part, and a cylindrical rod part, and the flat measuring surface of the measuring part has a thin wire part covered with a thin ceramic protective film. A voltage measurement lead part is formed, and the lead wire from the thin wire part and the lead wire from the voltage measurement lead pass through the flange part and the rod part, and are led out to the end face of the rod part in an airtight structure.The flange part has a sealing wire. A probe for measuring thermal conductivity, which has a structure in which a shoulder is formed, the wiring is made of metal, and everything else is made of ceramics. 2. The thermal conductivity measuring probe according to claim 1, wherein a thermocouple is embedded in the ceramic near the measurement surface within the thermal conductivity measuring probe. 3. The measurement part of the thermal conductivity measuring probe according to claim 1 or 2 is inserted into a circular tubular container with one side closed, and the measuring part of the thermal conductivity measuring probe according to claim 2 is sealed at the opening of the container. A thermal conductivity measurement device characterized in that the container includes a piston and a spring for pressing the sample to be measured against the container wall and the probe measurement surface. 4. The thermal conductivity measurement device according to claim 3, wherein the closed tube-shaped cartridge and the stepped cylindrical cylinder formed on the outer periphery of the device are hermetically connected, and the metal drawn out from the thermal conductivity measurement probe is further provided. A device for measuring thermal conductivity, characterized in that the lead wire is hermetically sealed and drawn out of the cylinder, and the container and the probe for measuring thermal conductivity are hermetically isolated from the outside air.