Answered

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The brick wall (of thermal conductivity

1.16 W/m ° C) of a building has dimensions

of 5 m by 7 m and is 18 cm thick.

How much heat flows through the wall in

a 17.2 h period when the average inside and

outside temperatures are, respectively, 24°C

and 8°C?

Answer in units of MJ.

Sagot :

Answer:223.46 MJ

Explanation:

Given

The thermal conductivity of brick wall is [tex]k=1.16\ W/m.^{\circ}C[/tex]

Cross-section of Wall [tex]A=5\m \times 7\ m[/tex]

time period [tex]t=17.2\ h=17.2\times 60\times 60=61,920\ s[/tex]

Inside temperature [tex]T_i=24^{\circ}C[/tex]

Outside temperature [tex]T_o=8^{\circ}C[/tex]

Heat transfer through the bricks

[tex]\dot{Q}=kA\dfrac{dT}{dx}[/tex]

[tex]\dot{Q}=1.16\times 35\times \dfrac{16}{0.18}\\\\\dot{Q}=3608.88\ W[/tex]

Heat flow for 17.2 h

[tex]Q=3608.88\times 61,920=223.46\ MJ[/tex]

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