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 = 2.0 mm, electrical resistivity rho_e = 10^6 ohm middot m, thermal conductivity k = 25 w/m middot k, and emissivity epsilon = 0.2. the heater is designed to deliver air at a temperature of t_infinity = 70.5 degree c under flow conditions that provide a convection coefficient of h = 261 w/m^2 middot k for the wire. the temperature of the housing that encloses the wire and through which the air flows is t_sur = 70.5 degree c.
(a) if the maximum allowable temperature of the wire is t_max = 1200 degree c, what is the maximum allowable electric current i? if the maximum available voltage is delta e = 193 v, what is
(b) the corresponding length l of wire that may be used in the heater and
(c) the power rating of the heater?
(a) i_max = a
(b) l = m
(c) p_elec = kw