A 2-kW resistance heater wire whose thermal conductivity is k_=10.4 Btu/h · ft · °F has a radius of r0 = 0.06 in and a length of L= 15 in., and is used for space heating. Assuming constant thermal conductivity and one-dimensional heat transfer, express the mathematical formulation (the differential equation and the boundary conditions) of this heat conduction problem during steady operation