Athermocouple, with a spherical junction diameter of 0.5 mm, is used for measuring the temperature of hot air flow in a circular duct. the convection heat transfer coefficient of the air flow can be related with the diameter (d) of the sphere and the average air flow velocity (v) as h = 2.2(v /d)0.5, where d, h, and v are in m, w/m2•k, and m/s, respectively. the properties of the thermocouple junction are k = 35 w/m•k, rho = 8500 kg/m3, and cp = 320 j/kg•k. the maximum response time of the thermocouple to record 78 percent of the initially applied temperature difference is 5 s. determine the minimum air flow velocity that the thermocouple can be used.