Along, square, electrical heating element standing on a cornerwith one side of the square heating element being 25mm, thermalconductivity k = 240 W/m ? K, density ñ = 2700 kg/m3, andspecific heat cp = 900 J/kg ? K is installed in aduct for which air moves in cross flow over the heater at atemperature and velocity of 30°C and 10 m/s, respectively.
(a) Neglecting radiation, estimate the steady-state surfacetemperature when, per unit length of the heater, electrical energyis being dissipated at a rate of 1000 W/m. ?
(b) If the heater is activated from an initial temperature of30°C, estimate the time required for the surface temperature tocome within 20°C of its steady-state value. ?
