Problem 2. An immersion heater element, made of tungsten, is in the shape of an 8 mm diameter

sphere.

a) The heater element is immersed in atmospheric-pressure water at 20 °C. Assuming that the water

surrounding the element is stagnant and isothermal, calculate the maximum heating power if the

element surface temperature must not exceed water's saturation temperature.

b) The heating element can be exposed to air under accident conditions. Calculate the element's

surface temperatures for the aforementioned condition in part (a) if the element is exposed to

stagnant and atmospheric air at 20 °C, assuming that the electric power continues at the same rate

as in part (a).

c) Suppose as a safety measure, a fan is designed to blow air across the element when it is exposed

to air. Calculate and plot the element's steady-state surface temperature for air velocities varying

in the 0.05 to 2 m/s. For simplicity neglect the contribution of radiation everywhere.