JPH0640026B2 - Emissivity measurement method - Google Patents

Description

The present invention relates to an emissivity measuring method for opaque solid materials such as ceramics and black paints.

[Prior Art and Problems] Conventional emissivity measurement methods include an emissivity method that obtains emissivity by comparing the radiant intensity from a black body cavity whose temperature is strictly measured with the radiant intensity from the sample surface, The reflectance ρ of the sample surface is measured from the ratio of the incident energy to the sample surface and the reflected energy from the sample surface, and in the case of an opaque body, the absorptivity is equal to (1-ρ) The reflectance method that determines the emissivity indirectly from the absorptance and the absorptivity is 1.0
There is a calorimetric method that obtains the hemispherical total emissivity using the Stefan-Boltzmann equation from the relationship between the electrical input supplied by heating a sample in a cavity with a low-temperature surface close to the above and the heat loss due to radiation on the sample surface. However, in the case of the radiation method and the calorimetric method, even if the temperature of the sample surface is measured by using a thin thermocouple, there is a drawback that it is difficult to improve the accuracy because of a heat conduction error through the conducting wire. In addition, in the case of the reflection method, the reflectance of the sample can be obtained fairly accurately in the low temperature region, but when the sample surface temperature rises, the radiant energy from the sample surface itself becomes larger than the reflected energy, which causes a measurement error. Will be increased.

[Object of the Invention] An object of the present invention is to provide a simple emissivity measurement method that does not require accurate temperature measurement of the sample surface, which causes an error, and to correct the temperature rise effect of the sample surface from the cooling curve of the sample surface An object of the present invention is to provide an emissivity measuring method capable of measuring even at high temperature.

[Means and Actions for Solving Problems] The present invention takes the following means in order to eliminate the above-mentioned drawbacks. That is, a hemispherical mirror is installed in front of the ribbon-shaped sample, and reciprocally rotated about a tangential axis passing through the vicinity of the apex of the hemispherical mirror, and a radiometer is installed behind the hemispherical mirror to rotate the hemispherical mirror. The ambient radiance, the radiance of the sample surface, and the apparent radiance due to multiple reflections between the sample surface and the hemispherical mirror are measured instantaneously and continuously depending on the position. Since the emissivity is calculated from the dimensionless ratio of the radiance of the sample alone to the apparent radiance based on the ambient radiance, the measurement method is simple and accurate temperature measurement of the sample surface that causes an error is possible. do not need. Furthermore, since the influence of the temperature rise on the sample surface due to multiple reflection is corrected from the cooling curve of the sample surface, it is possible to measure even at high temperature.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

In FIGS. 1 (a) and 1 (b), the hemispherical mirror 2 installed in front of the sample 1 to be directly energized and heated has a point that the inner surface of the hemispherical mirror and the center line of the measuring hole 3 coincide with each other. A reciprocating rotary motion is performed by the motor 5 and the lever 4 as a rotation center. From the radiometer 6 installed behind the hemispherical mirror 2, when the hemispherical mirror 2 is displaced from the front of the sample 1, only the radiation on the surface of the sample is observed. Due to the multiple reflections between the surface and the hemispherical mirror, an apparent radiation near the black body is observed. Radiometer radiance around observed by 6 L _o, the radiance of the sample surface L, if the radiance of the apparent due to multiple reflections of the sample surface and the semi-spherical surface mirror and L _e, L _o, L, and L _The following relation holds between _e .

ε / ε _e = (L-L _o ) / (L _e -L _o ), (1) where ε: Emissivity of sample surface ε _e : Apparent radiation due to multiple reflection of sample surface and hemispherical mirror Is the rate.

Moreover, if the effective reflectance of the hemispherical mirror is ρ _m when the sample surface is a diffusing surface, the following relation holds.

ε _e = ε / {1- (1-ε) ρ _m } (2) Rewriting equation (2) for ε gives the following.

ε = 1- (1-ε / ε _e ) / ρ _m (3) Since the right side of equation (1) is measured by the thermal imager 7,
The emissivity ε is obtained from the relationship between (1) and Eq. (3).

The metal sample is formed into a ribbon shape and directly heated by electric conduction, and the insulator sample is indirectly heated on a metal ribbon heater to a required temperature by electric conduction of the ribbon heater.

In FIG. 2 (a), when the hemispherical mirror 2 comes in front of the sample 1,
A method of correcting the temperature rise effect of the sample surface due to multiple reflection between the sample surface and the hemispherical mirror is shown. In the time change of the radiance 9 of the sample surface measured by the thermal imager 7,
B is the position just before the radiation on the sample surface begins to return to the sample surface after being reflected by the hemispherical mirror 2, C is the position when the hemispherical mirror 2 covers the front of the sample 1, and C is the position at which the reflected radiation disappears again. A, B, C, D, where the distance from D, B to C is N ₁ , the distance from C to D is N ₂ , the position before B ₁ to N ₁ is A, and the position after D to N ₂ is E. The differences between the radiance at the positions of E and E and the radiance at the periphery are a, b, c, d and e, respectively. F is the point where the extension line connecting A and B and the vertical line of C intersect
(2b-a), the point where the extension line connecting D and E and the vertical line of C intersect is G (2d-e), and the midpoint of F and G is H {(b + d)-(a + e) /
By setting 2} as the radiance of the sample surface alone, the temperature rise effect on the sample surface due to multiple reflections can be accurately corrected.

The data in Fig. 2 (b) is 100 μm thick, 10 mm wide and 100 m long.
Spectral direction (wavelength: 3.5-4.0 μm, direction: 20) of dry graphite film formed on the surface of SUS304 substrate of m
°) It is the result of measuring the ratio of emissivity (ε / ε _e ).
△ and ● are d / c, b / c and correction value {(b + d)-in Fig. 2 (b) respectively.
(a + e) / 2} / c is shown. When the rotation speed of the hemispherical mirror is slow, the effect of increasing the temperature on the sample surface (difference between □ and Δ) is considerably large, but when the rotation speed is 60 or more per minute, it becomes very small within 0.5%. Further, according to the correction method of the present invention (indicated by ●), the reproducibility is 0.5% regardless of the rotation speed of the hemispherical mirror.
Almost constant results within are obtained.

[Effects of the Invention] As described above, the present measuring method instantaneously and continuously measures the ambient radiance, the radiance of the sample alone and the apparent radiance due to multiple reflection depending on the rotation position of the hemispherical mirror, Since the emissivity is calculated from the dimensionless ratio of the radiance of the sample alone and the apparent radiance, which is based on the ambient radiance, the measurement method is simple and accurate temperature measurement on the sample surface is required as an error factor. do not do. Furthermore, since the effect of increasing the temperature of the sample surface due to multiple reflection is corrected, measurement can be performed even at high temperatures.

[Brief description of drawings]

FIG. 1 (a) is a configuration diagram of a measuring apparatus showing an embodiment of the present invention, FIG. 1 (b) is a measurement principle diagram, and FIG. 2 (a) is an explanatory diagram for correcting a temperature rise effect on a sample surface, FIG. 2 (b) is a graph of a measurement example demonstrating the action of the present invention. 1 ... Sample 2 ... Hemispherical mirror 3 ... Measurement hole 4 ... Lever 5 ... Motor 6 ... Radiometer 7 ... Thermal imager 8 ... Chamber 9 ... Radiance of sample surface 10 ... Ambient Radiance of

Claims (2)

[Claims] 1. A hemispherical mirror is installed in front of a sample, and is reciprocally rotated about a tangential axis passing near the apex of the hemispherical mirror as a rotation center. The radiance of the surroundings, the radiance of the sample surface, and the apparent radiance due to multiple reflections between the sample surface and the hemispherical mirror are measured instantaneously and continuously by the rotation position of the An emissivity measuring method characterized by obtaining an emissivity from a dimensionless ratio between a single radiance and an apparent radiance. 2. The effect of increasing the temperature of the sample surface due to absorption due to multiple reflection when the hemispherical mirror covers the sample surface is corrected from the cooling curve of the sample surface. Emissivity measurement method described.