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Question
A steel frame (K = 45 W m−1°C−1) of total length 60 cm and cross sectional area 0.20 cm2, forms three sides of a square. The free ends are maintained at 20°C and 40°C. Find the rate of heat flow through a cross section of the frame.
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Solution
Thermal conductivity, K = 45 W m–1 °C–1
Length, l = 60 cm = 0.6 m
Area of cross section, A = 0.2 cm2 = 0.2 × 10−4 m2
Initial temperature, T1 = 40°C
Final temperature, T2 = 20°C
Rate of flow of heat = `"Tempreature diffrences"/ "thermal resistance"`
`(DeltaQ)/(Deltat) = (KA ( T_1 - T_2 ))/ ( l )`}
`(DeltaQ)/(Deltat) = (45 xx 0.2 xx 10^-4 ( 40 - 20))/(0.6)`
`= 0.03 W`
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