Abstract

A measurement technique for determining the directional spectral emittance of blackbody cavities was developed and subsequently applied to several specific cavity geometries. The emittance was deduced from cavity reflectance measurements performed with a laser energy source (10.6 μ) and an integrating hemiellipsoid. It was demonstrated that this technique is capable of providing highly precise emittance values with a resolution of five significant figures for high emittance cavities. The emittances of four specific cavity configurations were measured. One of these, an elongated off-axis cone with an entrance lip, gave emittances greater than 0.99999 when coated with nominally specularly reflecting or nominally diffusely reflecting black paints. The emittances of this cavity were on the order of 0.95 in the absence of a coating, the actual emittances of the cavity surfaces being approximately 0.05. Three other cavities with length-to-diameter ratios of three were also studied. These include a cylinder, cone, and off-axis cone having internal surfaces which were coated with black paints. Although the measured emittances were not so high as those for the 12.45-L/D off-axis cone, the level of blackness that was determined is sufficient for most engineering applications.

© 1970 Optical Society of America

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References

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  1. R. P. Heinisch, F. J. Bradac, D. B. Perlick, Appl. Opt. 9, 483 (1970).
    [Crossref] [PubMed]
  2. J. S. Titus, R. N. Schmidt, “Feasibility Investigation of a Low Temperature Variable Infrared Source,” NASA CR 66614 (1968).
  3. E. M. Sparrow, L. V. Albers, E. R. G. Eckert, Trans. ASME, J. Heat Transfer, 84C (1962).
  4. E. M. Sparrow, V. K. Jonsson, J. Opt. Soc. Amer. 53, 1963.
  5. G. G. Gubareff, J. E. Janssen, R. H. Torberg, Thermal Radiation Properties Survey (Honeywell Research Center, 1960).

1970 (1)

1963 (1)

E. M. Sparrow, V. K. Jonsson, J. Opt. Soc. Amer. 53, 1963.

1962 (1)

E. M. Sparrow, L. V. Albers, E. R. G. Eckert, Trans. ASME, J. Heat Transfer, 84C (1962).

Albers, L. V.

E. M. Sparrow, L. V. Albers, E. R. G. Eckert, Trans. ASME, J. Heat Transfer, 84C (1962).

Bradac, F. J.

Eckert, E. R. G.

E. M. Sparrow, L. V. Albers, E. R. G. Eckert, Trans. ASME, J. Heat Transfer, 84C (1962).

Gubareff, G. G.

G. G. Gubareff, J. E. Janssen, R. H. Torberg, Thermal Radiation Properties Survey (Honeywell Research Center, 1960).

Heinisch, R. P.

Janssen, J. E.

G. G. Gubareff, J. E. Janssen, R. H. Torberg, Thermal Radiation Properties Survey (Honeywell Research Center, 1960).

Jonsson, V. K.

E. M. Sparrow, V. K. Jonsson, J. Opt. Soc. Amer. 53, 1963.

Perlick, D. B.

Schmidt, R. N.

J. S. Titus, R. N. Schmidt, “Feasibility Investigation of a Low Temperature Variable Infrared Source,” NASA CR 66614 (1968).

Sparrow, E. M.

E. M. Sparrow, V. K. Jonsson, J. Opt. Soc. Amer. 53, 1963.

E. M. Sparrow, L. V. Albers, E. R. G. Eckert, Trans. ASME, J. Heat Transfer, 84C (1962).

Titus, J. S.

J. S. Titus, R. N. Schmidt, “Feasibility Investigation of a Low Temperature Variable Infrared Source,” NASA CR 66614 (1968).

Torberg, R. H.

G. G. Gubareff, J. E. Janssen, R. H. Torberg, Thermal Radiation Properties Survey (Honeywell Research Center, 1960).

Appl. Opt. (1)

J. Opt. Soc. Amer. (1)

E. M. Sparrow, V. K. Jonsson, J. Opt. Soc. Amer. 53, 1963.

Trans. ASME, J. Heat Transfer (1)

E. M. Sparrow, L. V. Albers, E. R. G. Eckert, Trans. ASME, J. Heat Transfer, 84C (1962).

Other (2)

G. G. Gubareff, J. E. Janssen, R. H. Torberg, Thermal Radiation Properties Survey (Honeywell Research Center, 1960).

J. S. Titus, R. N. Schmidt, “Feasibility Investigation of a Low Temperature Variable Infrared Source,” NASA CR 66614 (1968).

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Figures (6)

Fig. 1
Fig. 1

Arbitrary blackbody cavity shape.

Fig. 2
Fig. 2

Isometric diagram of experimental apparatus.

Fig. 3
Fig. 3

Laser beam characteristics at 9.5 ft (2.87 m.)

Fig. 4
Fig. 4

Modulator.

Fig. 5
Fig. 5

Blackbody cavities.

Fig. 6
Fig. 6

View of off-axis cone showing the spatial orientation of the directional emittance; (a) schematic elevation view; (b) schematic plan view.

Tables (3)

Tables Icon

Table I Directional Spectral (10.6-μ) Emittance of Cavities Coated with a Specularly Reflecting Paint Having Emittance of 0.95

Tables Icon

Table II Directional Spectral (10.6-μ) Emittance of Cavities Coated with a Diffusely Reflecting Paint Having Emittance of 0.975

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Table III Directional Spectral (10.6-μ) Emittance of 12.45-L/D Off-Axis Conical Cavity with a Polished Copper Surface

Equations (6)

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ρ λ ( θ ) = E r / E i ,
α λ ( θ ) = ( E i E r ) / E i = 1 ρ λ ( θ ) .
λ ( θ ) = α λ ( θ ) .
λ ( θ ) = 1 ρ λ ( θ ) .
Δ λ = Δ ρ λ = ρ λ Δ ρ λ / ρ λ .
= 0.9995 ± 0.0001 ,

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