The Heat Conductivity of Tungsten and the Cooling Effects of Leads upon Filaments at Low Temperatures

Abstract

The theory and the equations governing the temperature distribution, resistance, and heat flow in a tungsten filament as affected by its leads are given for the low temperature range (A low temperature vs. current scale for tungsten is calculated from these equations using measurements of heat conductivity given in this paper and previously obtained data on the radiating properties and resistance of tungsten. It is given in the form of tables and formulas from which, knowing the current, filament dimensions, and lead and bulb temperatures one can find the maximum temperature, $T_1$, of the filament. Methods are described for calculating the effect on $T_1$ of a spring attached to one end of the filament. The heat conductivity of tungsten, $\lambda$, was determined experimentally for this low temperature range. $\lambda$ at 273°K is 1.66 watts ${\mathrm{cm}}^{-1\mathrm{}}$ ${\mathrm{deg}.\mathrm{}}^{-1\mathrm{}}$ and decreases with rising temperature according to the equation $log\lambda \pm 0.9518=0.30logT$ to 1.31 at 600°K.