Athermocouple, with a spherical junction diameterof 0.5 mm, is used for measuring the temperature of hot airflow in a circular duct. the convection heat transfer coefficient of the air flow can be related with the diameter (d) ofthe spherical junction and the average air flow velocity (v)as h 5 2.2(v/d)0.5, where d, h, and v are in m, w/m2? kand m/s, respectively. the properties of the thermocouple junction are k 5 35 w/m? k, r 5 8500 kg/m3, and cp 5320 j/kg? k. determine the minimum air flow velocity thatthe thermocouple can be used, if the maximum responsetime of the thermocouple to register 99 percent of the initial temperature difference is 5 s.