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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 37, Iss. 10 — Oct. 1, 1947
  • pp: 808–808

Power Losses from Heated Objects in Still Air

B. T. BARNES, W. E. FORSYTHE, and E. Q. ADAMS  »View Author Affiliations

JOSA, Vol. 37, Issue 10, pp. 808-808 (1947)

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The various factors affecting conduction and convection are discussed. Ordinarily, the power carried away from a heated body by these processes cannot be calculated accurately. Two ways of measuring it are described: (1) by boiling water in a container and subtracting from the power input the losses due to evaporation and radiation; and (2) by silvering the bulb of a 500-watt tungsten-filament lamp on the outside, and then making the power input such that the average bulb temperature is the same as that of the unsilvered lamp at normal input. A similar test, but with the bulb silvered on the inside, combined with the results of test (2), gave the power radiated by the bulb. Thus, we find 8 percent of the input to a regular 500-watt lamp carried off by conduction and convection, 11 percent by bulb radiation, the rest by direct filament radiation.

Test (1) showed a conduction and convection loss of about 0.05 watt/cm2 at 100°C. This exceeded the radiation loss for every surface tested except a radiator enamel (total emissivity 0.77).

B. T. BARNES, W. E. FORSYTHE, and E. Q. ADAMS, "Power Losses from Heated Objects in Still Air," J. Opt. Soc. Am. 37, 808-808 (1947)

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