In a gas-fired boiler, stainless steel tubes of inner and outer diameters $Di=26 mm and $Do=30 mm, respectively, thermal conductivity ks=15 W/m⋅K, and emissivity ϵ=0.30 are submerged in saturated water at a pressure of 1.523 bar. What is the heat rate per unit length from a section of tube whose outer surface temperature is Ts,o=575 K?