A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10 cm thickness is 20 W/m2 . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in
IVEN
• Concrete wall
• Thickness (L) = 100 cm = 0.1 m
• Heat loss (q/A) = 20 W/m2
• Surface temperature
? Inner (Ti) = 22°C
? Outer (To) = 6°C FIND
• The thermal conductivity (k) and compare it to the tabulated value
ASSUMPTIONS
• One dimensional heat flow through the wall
• Steady state conditions exist
SKETCH
The rate of heat transfer for steady state, one dimensional conduction,
Solving for the thermal conductivity
This result is very close to the tabulated value in Appendix 2, Table 11 where the thermal
conductivity of concrete is given as 0.128 W/(m K).
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