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2 months ago

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An overhead 25m-long, uninsulated industrial steam pipe of 100-mm diameter, is routed through a building whose walls and air are

at25C. pressurized steam matains a pipe surface temperature of 150C and the coeff of nature convection h = 10W/m^2K. the surface emissivity e= 0.8
1. what is the rate of heat loss from the steam line?
2.if the steam is gernerated in a gas-fired boiler operating at efficenty of 0.9, and natural gas is priced at C=0.02 per MJ, what is the annual cost of heat loss from line?

1 answer:

Viktor [391]2 months ago

8 0

Answer:

1) q=18414.93 W

2) C=12920$

Explanation:

Provided information:

Length of the pipe L=25m

Diameter of the pipe D=100mm =0.1 m

Temperature of air $T_{s1}$ = $T_{\infty1} }$ =25°C.....= 298.15k

Surface temperature of the pipe $T_{s2}$ =150°C.....=423.15k

Emissivity of the surface e= 0.8

Efficiency of the boiler η=0.90

Price of natural gas Cg=$0.02 per MJ

1) Combined total heat loss and radiative heat loss

q= $q_{conv} +q_{rad}$

q= $A[h(T_{s2}-T_{s1})+e$ б( $T_{s2}$ ^4- $T_{s1}$ ^4)]....... (1)

б=5.67×10^-8 W/m^2K^4 (Boltzmann constant)

Area A =L·D·π=25·0.1·π=7.85 m^2

By substituting these values in equation (1)

q=18414.93 W

2) If the boiler runs continuously, the yearly energy loss will be

E=q·t

=18414.93·3600·24·365

=5.81×10^11 J

To calculate the energy consumption of the furnace

Ef =E/η

=6.46×10^5 MJ

Annual expenses

C=Cg·Ef

=12920$

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Provided data includes:

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