Question

Along, square, electrical heating element standing on a corner with one side of the square heating element being 25mm, thermal conductivity k = 240 w/m ? k, density ñ = 2700 kg/m3, and specific heat cp = 900 j/kg ? k is installed in a duct for which air moves in cross flow over the heater at a temperature and velocity of 30°c and 10 m/s, respectively. (a) neglecting radiation, estimate the steady-state surface temperature when, per unit length of the heater, electrical energy is being dissipated at a rate of 1000 w/m. ? (b) if the heater is activated from an initial temperature of 30°c, estimate the time required for the surface temperature to come within 20°c of its steady-state value. ?

Answer 1

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