Engineering Fundamentals: An Introduction to Engineering (MindTap Course List)
Engineering Fundamentals: An Introduction to Engineering (MindTap Course List)
5th Edition
ISBN: 9781305084766
Author: Saeed Moaveni
Publisher: Cengage Learning
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Chapter 11, Problem 9P

Calculate the R-value for the following materials:

a. 4 in. thick brick

b. 10 cm thick brick

c. 12 in. thick concrete slab

d. 20 cm thick concrete slab

e. 1 cm thick human fat layer

(a)

Expert Solution
Check Mark
To determine

Find the R-value for 4in thick brick.

Answer to Problem 9P

The R-value for 4in thick brick is 0.10m2KW.

Explanation of Solution

Given data:

The thickness of the brick, L=4in.

From table 11.3 in the textbook, the thermal conductivity of the brick, k=1.0Wmk.

Formula used:

The formula to find R-value is,

R=Lk (1)

Here,

L is the thickness of the material, and

k is the thermal conductivity of the material.

Calculation:

Substitute 4in for L, and 1.0Wmk for k in equation (1) to find R,

R=4in1.0Wmk[1in=0.0254m]=(4in)(0.0254m1in)1.0Wmk=(4×0.0254)m1.0WmkR=0.10m2KW

Therefore, R-value for 4in thick brick is 0.10m2KW.

Conclusion:

Hence, the R-value for 4in thick brick is 0.10m2KW.

(b)

Expert Solution
Check Mark
To determine

Find the R-value for 10cm thick brick.

Answer to Problem 9P

The R-value for 10cm thick brick is 0.10m2KW.

Explanation of Solution

Given data:

The thickness of the brick, L=10cm.

Calculation:

Substitute 10cm for L, and 1.0Wmk for k in equation (1) to find R,

R=10cm1.0Wmk[1m=100cm]=(10cm)(1m100cm)1.0Wmk=0.1m1.0WmkR=0.10m2KW

Therefore, R-value for 10cm thick brick is 0.10m2KW.

Conclusion:

Hence, the R-value for 10cm thick brick is 0.10m2KW.

(c)

Expert Solution
Check Mark
To determine

Find the R-value for 12in thick concrete slab.

Answer to Problem 9P

The R-value for 12in thick concrete slab is 0.22m2KW.

Explanation of Solution

Given data:

The thickness of the concrete slab, L=12in.

From Table 11.3 in the textbook, the thermal conductivity of the concrete slab, k=1.4Wmk.

Calculation:

Substitute 12in for L, and 1.4Wmk for k in equation (1) to find R,

R=12in1.4Wmk[1in=0.0254m]=(12in)(0.0254m1in)1.4Wmk=(12×0.0254)m1.4WmkR=0.22m2KW

Therefore, R-value for 12in thick concrete slab is 0.22m2KW.

Conclusion:

Hence, the R-value for 12in thick concrete slab is 0.22m2KW.

(d)

Expert Solution
Check Mark
To determine

Find the R-value for 20cm thick concrete slab.

Answer to Problem 9P

The R-value for 20cm thick concrete slab is 0.14m2KW.

Explanation of Solution

Given data:

The thickness of the concrete slab, L=20cm.

Calculation:

Substitute 20cm for L, and 1.4Wmk for k in equation (1) to find R,

R=20cm1.4Wmk[1m=100cm]=20cm×1m100cm1.4Wmk=0.2m1.4WmkR=0.14m2KW

Therefore, R-value for 20cm thick concrete slab is 0.14m2KW.

Conclusion:

Hence, the R-value for 20cm thick concrete slab is 0.14m2KW.

(e)

Expert Solution
Check Mark
To determine

Find the R-value for 1cm thick human fat layer.

Answer to Problem 9P

The R-value for 1cm thick human fat layer is 0.05m2KW.

Explanation of Solution

Given data:

The thickness of the human fat layer, L=1cm.

From table 11.3 in the textbook, the thermal conductivity of the human fat layer, k=0.2Wmk.

Calculation:

Substitute 1cm for L, and 0.2Wmk for k in equation (1) to find R,

R=1cm0.2Wmk[1m=100cm]=(1cm)(1m100cm)0.2Wmk=0.01m0.2WmkR=0.05m2KW

Therefore, R-value for 1cm thick human fat layer is 0.05m2KW.

Conclusion:

Hence, the R-value for 1cm thick human fat layer is 0.05m2KW.

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Chapter 11 Solutions

Engineering Fundamentals: An Introduction to Engineering (MindTap Course List)

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