A cartridge electrical heater is shaped as a cylinder of length
L = 200 mm and outer diameter D = 20 mm. Under normal operating
conditions, the heater dissipates 2 kW while submerged in a
water flow that is at 20°C and provides a convection heat
transfer coefficient of h = 5000 W/m^2K. Consider the area of
the ends to be small compared to the overall surface area,
determine the surface temperature Ts of the cylinder. If the
water flow is inadvertently terminated while the heater
continues to operate, the heater surface is exposed to air that
is also at 20°C but for which h = 50 W/m^2K. What is the
corresponding surface temperature of the cylinder?