Abstract
Globe thermometers of various designs have been evaluated in a heated-wall wind funnel that provided a 98% complete radiation enclosure and a wide range of conditions of wind velocity and air temperature to represent extreme heat stress environments. Results showed that a good design for minimum time lag (the time required for the instrument to reach equilibrium) was a 6-inch diameter sphere having a 0.015-inch thick aluminum shell and either a miniature thermistor or a thermocouple as a sensor. Its time lag would be at the most, 10 minutes, whereas a globe thermometer using a liquid-in-glass thermometer would require 21 minutes. Convective heat transfer coefficients on 4-inch and 6-inch diameter spheres obtained by recent reseachers at wind velocities between 30 and 1000 fpm were used in the derivation of a straightforward expression for mean radiant temperature. This was employed to verify globe thermometer readings during tests over the full range of velocities and at radiant source temperatures (of the tunnel walls) ranging from ambient air temperature to 275°F above it. Globe thermometer temperatures were found to be valid over the full range of test conditions, which represent all conditions that are likely to be encountered in practice.