Accession Number : AD0257466

Title :   RADIATION TRANSFER BY CLOSELY SPACED SHIELDS

Corporate Author : LITTLE (ARTHUR D) INC CAMBRIDGE MASS

Personal Author(s) : EMSLIE,A.G.

Report Date : MAY 1961

Pagination or Media Count : 1

Abstract : The effects are investigated which occur when radiation shields are placed too close to each other. The anticipated effect is that the radiation transfer rate will increase many times. Such effect would be serious in the storage of cryogenic fuels for long periods in space. Effective protection of such fuels from solar radiation requires total shielding consisting of about 100 layers of metal foil. If the shielding is to be of reasonable over-all thickness, the spacing between the individual foils may be about 0.1 mm. Now at a temperature of 20 K the peak of the Planck radiation distribution corresponds to a wavelength of 0.15 mm. Thus the wavelength of the radiation is of the same order of magnitude as the separation of the foils. Under these conditions two effects causing increase in radiation transfer begin to set in. One of these is the effect of constructive interference when the wave emitted by a foil is reflected back and forth in the small gap between two foils. This results in a very considerable increase in transmission of energy across the gap when the spacing is small compared with the wavelength of the radiation. The other effect can be called radiation tunneling and has to do with the escape of trapped radiation that is undergoing total internal reflection inside one of the metal foils. (Author)

Descriptors :   *SHIELDING, *THERMAL INSULATION, *THERMAL RADIATION, CRYOGENICS, FOILS(MATERIALS), HEAT TRANSFER, LIQUEFIED GASES, LIQUID ROCKET PROPELLANTS, SOLAR RADIATION, THERMODYNAMICS

Distribution Statement : APPROVED FOR PUBLIC RELEASE