Athermocouple junction, which may be approximated as sphere, is to be used for temperature measurement in a gas stream. the convection coefficient between the junction surface and the gas is h = 400 w/m2 ·k and the junction thermophysical properties are k = 20 w/m·k, c = 400 j/kg·k and rho = 8500 kg/m3 . determine the junction diameter needed for the thermocouple to have a time constant of 2 s. if the junction is at 25 °c and is placed in a gas stream that is at 200 °c, estimate the temperature of the junction after 10 minutes. assumptions: 1. temperature of junction is uniform at any instant 2. radiation exchange with the surroundings is negligible 3. losses by conduction throug