For the outside walls of a home, two layers are often combined, such as a layer of wood and a layer of sheet rock (plaster). The rate of heat transfer becomes: P = Δ Q/second = A Δ T/ (Rw+Rsr) . What is the advantage of using combined 2-cm layers of wood and plaster versus using just a 4-cm layer of wood for home insulation. Assume a wall area A = 15 x 10 -4 cm2, and an indoor outdoor temperature difference of 15 degrees C.

Question
Asked Nov 12, 2019
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For the outside walls of a home, two layers are often combined, such as a layer of wood and a layer of sheet rock (plaster). The rate of heat transfer becomes: P = Δ Q/second = A Δ T/ (Rw+Rsr) . 

What is the advantage of using combined 2-cm layers of wood and plaster versus using just a 4-cm layer of wood for home insulation. Assume a wall area A = 15 x 10 -4 cm2, and an indoor outdoor temperature difference of 15 degrees C. 

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Expert Answer

Step 1

Given,

Thickness of wood in combined,(, ) =2 cm
Thickness of plaster in combined,t, =2 cm
Thickness of wood alone,(y), -4 cm
Area of wallA =15x10 cm2
Difference of temperature, AT 15 °C
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Thickness of wood in combined,(, ) =2 cm Thickness of plaster in combined,t, =2 cm Thickness of wood alone,(y), -4 cm Area of wallA =15x10 cm2 Difference of temperature, AT 15 °C

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Step 2

Rate of heat transfer when both material wood and plaster wall are used in combination will be more than in using single wood wall combination because resistance in combination of wood and plaster will be more than resistance of wood wall,

AAT
Р-
|(R)
(RRR
where,Thermal resistance to heat conduction, R =
kA
k Thermal Conductivity of material
Universal accepted value,k 4x10 W/m-k
Plakr 3.8x10 w/m-k
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Image Transcriptionclose

AAT Р- |(R) (RRR where,Thermal resistance to heat conduction, R = kA k Thermal Conductivity of material Universal accepted value,k 4x10 W/m-k Plakr 3.8x10 w/m-k

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Step 3

Resistance of wood and pl...

(RTRR
()
Plashr
Wood
2
1
1
(R)
15x104x1043.8x10
(R1333.33(2500+2631.58)
(R1333.33(5131.58)
(R684x10
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(RTRR () Plashr Wood 2 1 1 (R) 15x104x1043.8x10 (R1333.33(2500+2631.58) (R1333.33(5131.58) (R684x10

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