Superheated steam at 575ºC is routed from a boiler to the turbine of an electric power plant through steel tubes (k = 35 W/m K) of 300 mm inner diameter and 30 mm wall thickness. To reduce heat loss to the surroundings and to maintain a safe-to-touch outer surface temperature, a layer of calcium silicate insulation (k = 0.10 W/m K) is applied to the tubes, while degradation of the insulation is reduced by degradation of the insulation is reduced by wrapping it in a thin sheet of aluminium having an emissivity of ε= 0.20. The air and wall temperatures of the power plant are 27ºC. Assume that the inner surface temperature of a steel tube corresponds to that of the steam and the convection coefficient outside the aluminium sheet is 6 W/m2 K, (a) What is the minimum insulation thickness needed to ensure that the temperature of the aluminium does not exceed 50ºC? (b) What is the corresponding heat loss per unit meter?
Superheated steam at 575ºC is routed from a boiler to the turbine of an electric power plant through
steel tubes (k = 35 W/m K) of 300 mm inner diameter and 30 mm wall thickness. To reduce heat loss
to the surroundings and to maintain a safe-to-touch outer surface temperature, a layer of calcium
silicate insulation (k = 0.10 W/m K) is applied to the tubes, while degradation of the insulation is
reduced by degradation of the insulation is reduced by wrapping it in a thin sheet of aluminium having
an emissivity of ε= 0.20. The air and wall temperatures of the power plant are 27ºC. Assume that the
inner surface temperature of a steel tube corresponds to that of the steam and the convection coefficient
outside the aluminium sheet is 6 W/m2 K,
(a) What is the minimum insulation thickness needed to ensure that the temperature of the
aluminium does not exceed 50ºC?
(b) What is the corresponding heat loss per unit meter?
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