【発明の詳細な説明】[Detailed description of the invention]
［産業上の利用分野］
この発明は、放射温度計の校正等に用いられる
黒体炉に関するものである。
［従来の技術］
黒体炉の空洞部（凹部）の材質として、アルミ
ニウム等の熱伝導率の良好なものを用いると、材
質の酸化による凹部内壁の黒化は期待できない。
黒体炉のみかけ放射率は、凹部の形状、凹部を
構成する材料の表面放射率、そして凹部の温度分
布で決定される。凹部の表面放射率が高く、温度
分布が均一なほど良質の黒体炉が得られる。
このため、熱伝導率に優れたアルミニウム等の
金属材料で凹部を形成して、温度の均一性を備
え、かつ、内壁に強制的な酸化や塗装を施して表
面放射率を高めることが行われている。
アルミニウムの場合、強制強化による表面放射
率の向上は高々0.6であり、黒体炉として不十分
で、放射率を高める塗装が必要である。
［発明が解決しようとする課題］
ところが、その塗布面の塗装むらにより、黒体
炉の開口に対向する箇所の炉底に温度分布を生
じ、長期的使用により剥離し放射率の変化等の測
定誤差を招く。しかも、第１図、第２図に示すよ
うな円錐空洞や、二重円錐空洞の場合、多重反射
により放射率を高めるため炉底の頂点部に頂角が
形成されているのであるが、この頂角が塗料によ
り塗りつぶされてしまい、炉底の温度分布を生
じ、空洞放射率の低下がおきる。さらに、炉底が
アルミニウム等のような鏡面反射の強い材質の場
合、そのままのほうが多重反射により空洞放射の
効果を高めることができる。（A.Ono、
Calclation of the directional emissivities of
cavities by the Monte Carlo method、J.Opt.
Soc.Am、Vol.70、No.５、（1980）547−554）。
この発明の目的は、以上の点に鑑み、黒体炉の
炉底温度分布を良好にし、空洞放射率を高めるよ
うにした黒体炉を提供することである。
［課題を解決するための手段］
この発明は、一端開口で凹部を有する黒体炉に
おいて、前記開口部に対向する箇所を除いた凹部
内壁を黒色としたことを特徴とする黒体炉であ
る。
［実施例］
第１図、第２図は、円錐円筒空洞、二重円錐円
筒空洞の黒体炉についての、この発明の一実施例
を示す構成説明図である。
図において、１はアルミニウム等の熱伝導率の
良い材料よりなる一端開口で凹部を有する炉体、
２は炉体１を加熱する加熱体（ヒーター）、３は
開口に対向する箇所の炉底を除く凹部内壁に塗布
された黒体（黒色、黒化）塗料である。
つまり、炉体１の内壁のうち、側面部分に黒体
塗料３を塗布して固有放射率を高め、炉底部分に
は黒体塗料３を塗布しないで、材質の鏡面反射成
分を利用して多重反射による空洞効果を高めるこ
とにより、炉底の温度分布が良好で、空洞放射率
の高い黒体炉とすることができる。
次に、第３図の長さＬ、半径ｒの円筒空洞につ
いて実効放射率の計算例を示す。炉底の放射率を
εb、炉底を除く内壁の放射率をεwとすれば次表
のようになる。
[Industrial Application Field] The present invention relates to a blackbody furnace used for calibrating radiation thermometers, etc. [Prior Art] If a material with good thermal conductivity, such as aluminum, is used as the material for the cavity (recess) of a blackbody furnace, blackening of the inner wall of the recess due to oxidation of the material cannot be expected. The apparent emissivity of a blackbody furnace is determined by the shape of the recess, the surface emissivity of the material that makes up the recess, and the temperature distribution of the recess. The higher the surface emissivity of the recesses and the more uniform the temperature distribution, the better the quality of the blackbody furnace. For this reason, the recesses are made of a metal material such as aluminum with excellent thermal conductivity to ensure temperature uniformity, and the inner walls are forcibly oxidized or painted to increase the surface emissivity. ing. In the case of aluminum, the improvement in surface emissivity due to forced strengthening is at most 0.6, which is insufficient for a blackbody furnace, and requires coating to increase the emissivity. [Problem to be solved by the invention] However, due to uneven coating on the coated surface, a temperature distribution occurs at the bottom of the furnace in the area facing the opening of the blackbody furnace, and it peels off after long-term use, making it difficult to measure changes in emissivity, etc. invites errors. Moreover, in the case of conical cavities and double conical cavities as shown in Figures 1 and 2, an apex angle is formed at the apex of the furnace bottom in order to increase the emissivity through multiple reflections. The apex angle is covered with paint, resulting in temperature distribution at the bottom of the furnace and a decrease in cavity emissivity. Furthermore, if the furnace bottom is made of a material with strong specular reflection, such as aluminum, the effect of cavity radiation can be enhanced by multiple reflections if left as is. (A.Ono,
Calculation of the directional emissivities of
cavities by the Monte Carlo method, J.Opt.
Soc.Am, Vol.70, No.5, (1980) 547-554). In view of the above points, it is an object of the present invention to provide a blackbody furnace in which the bottom temperature distribution of the blackbody furnace is improved and the cavity emissivity is increased. [Means for Solving the Problems] The present invention is a blackbody furnace having a concave portion with an opening at one end, characterized in that the inner wall of the concave portion except for a portion facing the opening is black. . [Embodiment] FIGS. 1 and 2 are explanatory diagrams showing an embodiment of the present invention regarding a black body furnace having a conical cylindrical cavity and a double conical cylindrical cavity. In the figure, 1 is a furnace body made of a material with good thermal conductivity such as aluminum, which has an opening at one end and a recessed part;
2 is a heating element (heater) that heats the furnace body 1, and 3 is a black body (black, blackened) paint applied to the inner wall of the recess except for the bottom of the furnace at a location opposite to the opening. In other words, the black body paint 3 is applied to the side parts of the inner wall of the furnace body 1 to increase the intrinsic emissivity, and the black body paint 3 is not applied to the bottom part of the furnace body 1, using the specular reflection component of the material. By increasing the cavity effect due to multiple reflections, a blackbody furnace with good temperature distribution at the bottom of the furnace and high cavity emissivity can be achieved. Next, an example of calculating the effective emissivity for a cylindrical cavity of length L and radius r in FIG. 3 will be shown. If the emissivity of the hearth bottom is εb, and the emissivity of the inner wall excluding the hearth bottom is εw, the following table is obtained.
【表】
この計算例で分かるように、炉壁の放射率εw
を0.9としたとき、炉底の放射率εbを0.5として
も、放射率は約0.98で十分大きく実用的に十分で
ある。また、炉底の放射率を0.5としたとき、内
壁の塗料が落ちてその放射率が0.9から0.8に落ち
たとしても、放射率はほとんど変化せず実用上問
題とならない。
また、炉底の温度分布も、炉底に黒体塗料を塗
布した場合は約±0.5Kあつたのに対し、この発
明による炉底に黒体塗料を塗布しない場合では、
温度分布は±0.2Kと大幅に改善され、しかもば
らつきが少ない。
［発明の効果］
以上述べたように、この発明の黒体炉は、一端
開口部に対向する箇所である炉底を除いた凹部
（空洞）内壁を黒体塗料を塗布して黒色としてい
るので、炉底の温度分布は少なく、空洞放射率も
良好で、劣化も少なく、高精度、高信頼性のもの
となる。[Table] As you can see from this calculation example, the emissivity of the furnace wall εw
When is set to 0.9, even if the emissivity εb at the bottom of the furnace is 0.5, the emissivity is approximately 0.98, which is sufficiently large for practical use. Furthermore, assuming that the emissivity of the furnace bottom is 0.5, even if the paint on the inner wall falls and the emissivity drops from 0.9 to 0.8, the emissivity will hardly change and will not pose a practical problem. In addition, the temperature distribution at the hearth bottom was about ±0.5K when black body paint was applied to the hearth bottom, whereas when black body paint was not applied to the hearth bottom according to this invention,
The temperature distribution has been significantly improved to ±0.2K, and there is little variation. [Effects of the Invention] As described above, in the black body furnace of the present invention, the inner wall of the recess (cavity) except for the bottom of the furnace, which is the part facing the opening at one end, is painted black by applying black body paint. , the temperature distribution at the bottom of the furnace is small, the cavity emissivity is good, there is little deterioration, and it is highly accurate and reliable.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図、第２図、第３図は、この発明の一実施
例を示す構成説明図である。
１……炉体、２……加熱体、３……黒体塗料。
FIG. 1, FIG. 2, and FIG. 3 are configuration explanatory diagrams showing one embodiment of the present invention. 1...Furnace body, 2...Heating body, 3...Black body paint.