An 8-in.-OD horizontal steam pipe carries 220 lbm/h dry saturated steam at 250°F. If ambient air temperature is 70°F, determine the rate of condensate flow at the end of 10 ft of pipe. Use an emissivity of 0.85 for the pipe surface. If it is desired to keep heat losses below 1 percent of the rate of energy transport by the steam, what thickness of fiberglass insulation is required? The rate of energy transport by the steam is the heat of condensation of the steam flow. The heat of vaporization of the steam is 950 Btu/lb.
GIVEN
A horizontal steam pipe in air
Pipe outside diameter (D) = 8 in
Mass flow rate of steam (ms) = 220 lbm/h
Steam temperature (Ts) = 250°F = 710 R
Ambient air temperature (T∞) = 70°F = 530 R
Emissivity of pipe surface (ε) = 0.85
Heat of vaporization (hfg) = 950 Btu/lb
ASSUMPTIONS
Steady state
Air is still
Thermal resistance of the convection in the pipe and of the pipe wall are negligible
The surroundings behave as an enclosure at T∞
Insulation is foil covered, its emissivity ≈ 0.0