An air heater may be fabricated by coiling Nichrome wire and passing air in cross flow over the wire. Consider a heater fabricated from wire of diameter D = 1 mm, electrical resistivity p, = 10-m, thermal conductivity k = 25 W/m-K, and emissivity & = 0.2.The heater is designed to deliver air at a temperature of T = 50°C under flow conditions that provide a convection coefficient ofh = 150 W/m2.K for the wire. The temperature of the housing that encloses the wire and through which the air flows is Tur(a) If the maximum allowable temperature of the wire is T max = 1200°C, what is the maximum allowable electric current /? If the maximum available voltage is AE = 110 V, what is (b) the corresponding length Lof wire that may be used in the heater and (c) the power rating of the heater? Hint: In your solution, assume negligible temperature variations within the wire, but after obtaining the desired results, assess the validity of this assumption.= 50°C (a) max (b) L (c) Pelec

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