A 2 in. diameter pipe supplying steam at 300°F is enclosed in a 1 ft square duct at 70°F. The outside of the duct is perfectly insulated. Assume the emissivity of pipe surface and duct surfaces as 0.79 and 0.276, respectively. Estimate the radiation heat transfer per foot length.

The value of heat transferred watt per foot length Q = 54.78 Watt per foot length.

Explanation:

Diameter of pipe = 2 in = 0.0508 m

Steam temperature = 300 F  = 422.04 K

Duct temperature = 70 F = 294.26 K

Emmisivity of surface 1 = 0.79

Emmisivity of surface 2 = 0.276

Net emmisivity of both surfaces ∈ = 0.25

Stefan volazman constant = 5.67 ×

Heat transfer  per foot length is given by

Q = ∈ A ( ) ------ (1)

Put all the values in equation (1) , we get

Q = 0.25 × 5.67 × × 3.14 × 0.0508 × 1 × ( )

Q = 54.78 Watt per foot.

This is the value of heat transferred watt per foot length.

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