In an experiment, the temperature of a hot gas stream is to be measured by a thermocouple with a spherical junc-tion. Due to the nature of this experiment, the response time of the thermocouple to register 99 percent of the initial tem-perature difference must be within 5 s. The properties of the thermocouple junction are k = 35 W/m⋅K, rho = 8500 kg/ m 3 , and c p = 320J/kg⋅K. If the heat transfer coefficient between the thermocouple junction and the gas is 250 W/ m 2 ⋅K, deter-mine the diameter of the junction.