The Tungsten Wire Temperature Sensor

Abstract

Tungsten wire ≤1 mil diameter, when used in a parachute-borne temperature sensor, is in free molecule flow for most of its flight. The heat transfer coefficient for free molecule flow may be found from theory and is directly proportional to the ambient air density. The wire has a time constant <1 sec below 64 km and will therefore quickly arrive at equilibrium temperature. In the absence of solar radiation it differs from recovery temperature by less than 0.5C below 70 km. Solar radiation plays an important part in the equation of heat flow and the difference between wire temperature and ambient temperature depends strongly on the value for the coefficient of absorptivity in the visible range. A comparison of the effects of various factors that contribute to the heat flow is presented.