ABSTRACT
Analytical results are presented for radiation interchange in cavities having nonisothermal walls in order to implement experimental methods for determining the emittance of solids. The cavity may be visualized as a hole that is machined into the exposed face of a solid whose emittance is to be determined, with the solid being heated uniformly from behind. The results were obtained by solving the coupled problems of radiant transport in the cavity and two-dimensional heat conduction in the solid that bounds the cavity. From the solutions, results for the radiant flux leaving the base surface of the cavity are presented as a function of the emittance, of the depth-radius ratio of the cavity, and of a temperature gradient parameter. This information can be used in conjunction with measurements of the radiances of the base surface and the exposed face of the solid to determine the emittance. A method is also described for simultaneously determining both the emittance of the material and the temperature of the exposed face.
ABSTRACT
Experimental results, obtained using photometry, are obtained to assess the attenuating capability of three baffle geometries. The data obtained include the effect of sensor location in the baffle aperture as well as the type of coating on baffle surfaces. The baffles attenuate best at large viewing angles with surfaces coated with black paint.
ABSTRACT
Diffraction has been numerically modeled using a Monte Carlo statistical analysis. The Heisenberg uncertainty principle has been applied to attain this goal. Example solutions have been studied and are presented to illustrate the utility and accuracy of the technique.
ABSTRACT
This report describes the fabrication of an integrating hemiellipsoid and the associated analytical and empirical evaluation of it. The focusing properties of the instrument are seen to be of high quality, and quantitative information is presented regarding the selection of the size of a detector to be used.
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 micro) and an integrating hemi-ellipsoid. 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.
ABSTRACT
Analytical results, applicable both monochromatically and totally, are obtained for the normal emittance of diffusely emitting and reflecting cylindrical cavities. The analysis takes account of the size and location of the receiver which senses the radiant energy streaming from the cavity opening as well as of the cavity geometrical and surface emittance parameters. It is found that the distance of the receiver from the cavity can have an important effect on the normal emittance results, but that the size of the receiver is of secondary importance. The normal emittance exceeds the hemispherical emittance for cavities having a depth-to-radius ratio greater than unity.