0.2 kg/s of superheated steam at a pressure 0.1 MPa flow through a non-insulated steel pipe of inner diameter 25 mm and 5 m length. The steam enters the pipe at a temperature of ϑ i = 150 ◦C and is...

0.2 kg/s of superheated steam at a pressure 0.1 MPa flow through a non-insulated steel pipe of inner diameter 25 mm and 5 m length. The steam enters the pipe at a temperature of ϑ_i
= 150 ◦C and is cooled to ϑ_e
= 120 ◦C by the time it reaches the outlet. The pipe is surrounded by cold air at a temperature of ϑ₀
= 0 ◦C; the mean heat transfer coefficient from the pipe surface to the air is α_e
= 15W/m²K. Calculate the heat lost to the surroundings and the surface temperature of the pipe at the outlet. The thermal resistances are negligible.

The following properties for steam are given: Prandtl number P r(135 ◦C) = 0.986, specific heat capacity c_p(135 ◦C) = 1.995 kJ/kgK, thermal conductivity λ(135 ◦C) = 0.0276W/Km, dynamic viscosity η(135 ◦C) = 13.62 · 10⁻⁶
kg/sm.