A wire is to be heated from 70°F to 200°F by blowing hot air past it as shown in Fig. 7.31. If the length of the heating section is 2 ft, determine the wire velocity required in order to accomplish the desired heating. Assume that the air temperature is constant at 400°F and the temperature of the wire is uniform at any cross section (NBi« 1). Neglect axial conduction, and take the air velocity to be 100 ft/sec. The properties of the wire are
