JPH03225268A - Direct heating type calorimetric instrument - Google Patents

Abstract

PURPOSE:To accurately measure heat capacity by surrounding a sample by plural heat insulating shields consisting of the same material as the sample and supplying heating power proportional to the volume of the sample and the shields. CONSTITUTION:The cylindrical sample 1 is surrounded by the double cylindrical heat insulating shields 7a, 7b consisting of the same material as the sample and heated by supplying current from a DC power supply 8 through a variable resistor 8 and the shields 7a, 7b are directly heated by supplying current from a DC power supply 11. Power proportional to respective volume of the sample 1 and the shields 7a, 7b is supplied so that electric energy per unit volume of the sample 1 coincides with that of the shields 7a, 7b and the internal temperatures of the sample 1 and the inner shield 7b are measured through measuring holes 6, 15, 16 at the same period. consequently, the temperature difference between the sample 1 and the external can be reached to zero as close as possible and the heat capacity of the sample 1 can be accurately measured.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a direct heating type calorimeter, and is particularly useful in the steel industry, metal industry, chemical industry, atomic crab industry, aerospace industry, etc. This invention relates to an improvement in a direct heating type calorimeter suitable for measuring the heat capacity of metal and alloy samples.

<Conventional technology and the problems it attempts to solve> In recent years,
There is a great deal of interest in technology for accurately measuring the thermal constant of a sample over a wide temperature range, and various calorimetry methods have been proposed in the fields of electronics and optics.

There are mainly three types of high-temperature calorimeters: an adiabatic type, a laser flash method, and a direct heating type. These 3
A common source of error in conventional calorimeters is that the amount of heat exchanged between the sample and the outside world increases significantly with temperature.

Let's use an example of an adiabatic calorimeter to estimate how much this amount is. Heat transfer is carried out by conduction, convection, and radiation, but for now we will ignore the contribution of convection (it is a function of gas pressure, and roughly speaking, we can multiply the contribution of gas conduction by one or more factors). Considering, the overall heat transfer coefficient is K = Kr, 1K s 1Kll
------(Given by D. Here, K6, Kg, K
, l are the heat transfer coefficients due to gas conduction, solid conduction, and radiation, respectively. These coefficients are determined by the dimensions, shape, surface emissivity of the sample container and heat insulating shield, the size and number of Petery 1' lines, etc., but by making certain appropriate assumptions, the contribution of each can be expressed as Rth γ. , as shown in Figure 2. That is, below 600 K, the contribution of KG is the largest, but above 600 K, the contribution of 1 (8) becomes the largest and increases in proportion to 'I゛3, and above +0001, other contributions become It becomes almost negligible.

Next, when trying to measure the heat capacity of Sample 11 with an accuracy of 1% using this calorimeter, the sample container and the heat insulating sole 1'
(-for boat fishing, the average temperature difference between the test t't and the outside world) Δ'F, try multiplying it by 90γ to find out how much it is.

In addition to the amount of heat used for the temperature T1 (=Δ'F) in Trial 11,
Assume that it is consumed as heat leak Q°.

Q=CΔTl−Q′−(21
Here, C is the heat capacity of the sample. Regarding the heat riff Q', the following (3) and (3) hold true. Here, Δ゛1゛ is the time average of Δ′F, and ΔL is the time required for measurement.

So, from equations (2) and (3), the relative error δ is CΔ′r
It becomes T to C.

The heat capacity of test t1 is 5 J K-', Δ1゛/ΔL, is I
Assuming KmIn -', in order for δ to be 0.01 or less, Δ1゛ becomes 0.04 at 50OK, and 100O
It must be less than 0.01 at K and 0.002 at 2000; considering that the best limit of adiabatic control is about 0.002, this number is quite severe at high temperatures. I understand. At high temperatures, equation (4) is close to (
Therefore, it is expressed as CΔ′■゛. Here, ε is the emissivity of the sample or sample container, and S is its surface area.

In order to reduce δ, 1. Select a FIS instrument with low emissivity and keep the surface of the sample container small.

■ Precisely control the insulation so that the average temperature difference T between the sample container and the insulation shield is small.

■ Maintain good thermal contact between the heater and the sample and increase the temperature increase rate to reduce the measurement time Δ.

Possible methods include: However, - lastly, ■ and ■ often contradict each other. The adiabatic type emphasizes ■ at the expense of ■, and the flash method, direct heating method, etc. emphasize ■ at the expense of ■.

However, in reality, the adiabatic method cannot be used at high temperatures of 2000 K or higher. In addition, in the flash method, since the temperature is measured on the back surface of a thin sample, it takes time for the temperature to diffuse, and there is a problem that the measurement time ΔL is short.

On the other hand, in a direct heating calorimeter, energy is applied by directly applying electricity to the conductive sample, and the temperature rises by 1
In this case, if the sample is uniform, the temperature of the sample will rise uniformly and instantaneously, so if electrical energy can be input in a short time, can be very small.

In fact, a calorimeter (lligh Temperature 5) developed by Cezairlyan of NBS Company in the United States
science Vol, 13 (1980) I', 11
3), a temperature T of 1000 K is applied to the metal sample.
It is reported that it takes only about 0.1-1.0 degrees to obtain 1.

As shown in FIG. 3, this amount of heat 51 is
When the sample L is heated by directly passing current through a pair of electrodes 2.2 to both ends of the sample, the voltage applied to the sample L is taken out by a voltage probe 4.4 held by an insulating material 3.3, and
It is configured to measure the temperature with a thermocouple 5.5 embedded in the sample 1, and to measure the emitted light from the measurement hole 6 made in the center of the sample 1 with a radiation thermometer (not shown). A major feature of this calorimeter is that the measurement time ΔL can be made extremely small. In addition, since the measurement hole 6 is equipped with so-called horse body conditions, it is possible to measure the temperature closer to the true temperature.

However, even with this heat value old, the t1 temperature for two people was 3000
Since the ambient temperature is close to room temperature even in cases where the temperature is about
Since the average temperature difference T in the above-mentioned equation (5) becomes very large, there is a drawback that it becomes a major cause of measurement error.

The present invention was made to solve the problems of the prior art as described above, and an object of the present invention is to provide a direct heating type calorimeter with high measurement accuracy.

<Means for Solving the Problems> The present invention is a direct heating type calorimeter that measures the amount of heat by directly applying electric power to a conductive sample, and includes a cylindrical sample and a tube surrounding the sample. A cylindrical heat-insulating seal made of the same material as the SIE material, and this heat-insulating shield I.
A is characterized by comprising a heating means for inputting electric power in the same proportion as the amount of electric power per unit volume inputted to the sample, and a temperature measuring means for measuring the temperature of the sample and the heat insulating shield material, respectively. This is a direct heating type calorimeter.

<Function> In the case of the heat quantity of the configuration as shown in Figure 3, when the sample becomes high temperature, the heat will leak from the sample to the outer wall of the heat chamber 31 by direct radiation. Cezair mentioned above
LYAN considers this heat loss to be a necessary evil and attempts to estimate and correct the amount of heat loss from the natural heat radiation curve from the product temperature. However, even with this method, if the ambient temperature is the same as the test tl temperature, it is thought that the temperature will be higher when the temperature is lowered, and the heat leakage ■ will be smaller. There is no guarantee that the amount of heat will be the same, and it is inevitable that there will be considerable measurement error.

Therefore, in the present invention, as shown in FIG. 4, a cylindrical heat insulating shield material 7 is provided to reduce the amount of heat leakage itself.
The purpose is to reduce measurement errors by reducing Δ′■゛. Here, as can be seen from equation (5) above, in order to reduce the error due to heat leakage, it is desirable to use a metal material with a low emissivity as the material of the heat insulating shield material 7. As a high melting point metal material with low emissivity, 7a
, W, r't, Nb.

Mo or an alloy containing them is desirable.

Such a heat insulating shield does not need to be a heavy cylinder, and if permitted by the arrangement of the device, it is preferable to have double or triple layers. In the method of preventing heat leakage from freezing, it is possible to reduce 8T, but it is not possible to reduce it to zero.

Therefore, in the present invention, the heat insulating shield material 7 is further actively heated to reduce ΔT to zero, thereby successfully reducing the measurement error significantly. That is, according to the present invention, the heat insulating shield material 7 is made of the same material as the sample 1, and the same amount of power per unit volume as that required to heat the sample l is simultaneously input, so that the sample This makes it possible to bring the temperature difference between l and the outside world as close to zero as possible, making it possible to accurately measure the heat capacity of the sample.

<Example> Below, an example of the present invention will be described with reference to FIG.

As shown in the figure, a cylindrical sample 1 is surrounded by double cylindrical heat insulating shield members 7a and 7b made of the same material as sample 1, and the sample 1 is connected to a DC current T4fA8 through a variable resistor 9. The electrode 4 heats the heat insulating shields 7a and 7b, and the DC power supply 10 directly heats the heat insulating shields 7a and 7b.

The power input to the sample 1 is determined by the voltage value measured by the voltmeter 12 connected to the voltage probe 3 and the current 811.
The current detected by 3 (obtained by direct calculation).

The power supplied to the sample 1 and the heat insulating shield materials 7a and 7b is proportional to their volume ratio, but if it is affected by the circuit resistance of the current-carrying system, etc., It is made adjustable by an electric fA voltage of 10 and a variable resistor 9.

The timing circuit 14 connects the sample 1 and the heat insulating shield material 7a,
7b and 7b at the same time, and the trigger for energization is adjusted to within an error of approximately ±1 μs.

Further, the diameter of the measurement hole 6 provided at the center of the sample l is, for example, 2 mmφ, and a measurement hole 15 having a diameter of, for example, 4 mmφ is penetrated through the heat insulating shield materials 7a and 7b corresponding to this measurement hole 6. radiant temperature n (not shown)
The internal temperature of the sample I is sampled every 0.5+ns, for example.

On the other hand, the temperature of the heat insulating shield materials 7a and 7b can be measured by providing a measurement hole 16 with a diameter of, for example, 2 mm in the outer shield 'tA7a, and measuring the radiation light emitted from the inner heat insulating shield material 7b by different radiation temperatures (Fig. (not shown) at the same period.

Using tantalum as the material for Sample 1 and the heat insulating shield material 7, the specific heat capacity was measured at 2900 K, with the power ratio per unit volume input to both being given as shown in Table 1. The results are shown in Table 1. For comparison, the measurement results for a conventional example without a heat shield are also shown.
As is clear from this table, the reproducibility of the four measurements according to the present invention was within ±0.4% of the average value. Therefore, compared to the comparative example, at least 1
/3 or better.

<Effects of the Invention> As explained above, according to the present invention, a heat insulating shield material made of the same material as the sample is used to surround the sample, and the heating power per unit volume of the sample is proportional to its volume ratio. Since the temperature difference between the sample and the outside world can be brought as close to zero as possible, the heat capacity of the sample can be measured as a positive value.

[Brief explanation of drawings]

Fig. 1 is a measurement bronch diagram showing an embodiment of the present invention including a partial cross section, Fig. 2 is a characteristic diagram showing the relationship between the overall heat transfer coefficient and temperature T, and Fig. 3 is a direct energization diagram. FIG. 4 is a schematic diagram showing a conventional example of a type calorimeter. FIG. 4 is a schematic diagram showing the configuration of a direct current type calorimeter of the present invention. 1... Sample 5, 2... Electrode. 4...Voltage probe 1 6...Measurement hole. 7... Heat insulation shield material 0.11... DC power supply (heating means). 9...Variable resistance! 2... Voltmeter 13... Ammeter, 14... Timing circuit. 15, 16...Measurement holes.

Claims (1)

[Claims] This is a direct heating type calorimetry device that measures the amount of heat by directly applying power to a conductive sample, and includes a cylindrical sample and a cylindrical heat insulating shield made of the same material as the sample surrounding the sample. heating means for inputting electric power into the heat insulating shield material at the same rate as the amount of electric power per unit volume inputted into the sample, and temperature measuring means for measuring the temperature of the sample and the heat insulating shield material, respectively. A direct heating type calorimetry device characterized by comprising: