Thermodynamics HW Solutions 253

Thermodynamics HW Solutions 253 - Chapter 3 Steady Heat...

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Chapter 3 Steady Heat Conduction 3-140 The change in the R -value of a wood frame wall due to replacing fiberwood sheathing in the wall by rigid foam sheathing is to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat transfer through the wall is one-dimensional. 3 Thermal properties of the wall and the heat transfer coefficients are constant. Properties The R-values of different materials are given in Table 3-6. Analysis The schematic of the wall as well as the different elements used in its construction are shown below. Heat transfer through the insulation and through the studs will meet different resistances, and thus we need to analyze the thermal resistance for each path separately. Once the unit thermal resistances and the U -factors for the insulation and stud sections are available, the overall average thermal resistance for the entire wall can be determined from R overall = 1/ U overall where U overall = ( Uf area ) insulation + ( Uf area ) stud and the value of the area fraction f
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