
Concept explainers
Calculate the reduction in heat transfer rate.

Answer to Problem 28P
The reduction in heat transfer rate is
Explanation of Solution
Given data:
Area of the concrete wall,
Thickness of the concrete wall,
Thickness of the insulation batt,
Inside temperature of concrete wall,
Outside temperature of concrete wall,
From Table 11.3 in the textbook, the thermal conductivity of the concrete wall is,
The thermal conductivity of the insulation batt is,
Formula used:
The formula for the heat transfer is,
Here,
Calculation:
Convert the unit of area of cross section into meter.
Convert the unit of thickness into meter for
Convert the unit of thickness into meter for
Substitute
From the truth the temperature difference in
Substitute
Change the unit of thermal conductivity for insulation batt,
For the temperature difference
Rearrange equation (1), we get
Here,
From equation (3), the expression for the heat transfer rate of the concrete wall with insulation batt is,
Substitute
Hence the reduction in heat transfer is,
Substitute
Therefore, the reduction in heat transfer rate is
Conclusion:
Hence, the reduction in heat transfer rate is
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Chapter 11 Solutions
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