Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

340 Chapter 11 Temperature and Temperature-Related Parameters

3.

4.

Problem 11.13

Resistance

Items (hft

2

F/Btu)

1. Inside attic film resistance 0.68


2. Insulation batt (6 in.) 19.0


3. Gypsum wallboard (1/2 in.) 0.45


4. Inside film resistance (winter) 0.68

Resistance

Items (hft

2

F/Btu)

1. Outside film resistance
   (winter, 15 mph wind) 0.17


2. Face brick (4 in.) 0.44


3. Cement mortar (1/2 in.) 0.1


4. Cinder block (8 in.) 1.72


5. Air space (3/4 in.) 1.28


6. Gypsum wallboard (1/2 in.) 0.45


7. Inside film resistance (winter) 0.68

11.12. In order to increase the thermal resistance of a typi-

cal exterior frame wall, such as the one shown in

Example 11.11, it is customary to use 26 studs

instead of 24 studs to allow for placement of more

insulation within the wall cavity. A typical exterior

(26) frame wall of a house consists of the materi-

als shown in the accompanying figure. Assume an

inside room temperature of 68F and an outside air

temperature of 20F with an exposed area of 150 ft

2

.

Determine the heat loss through this wall.

Resistance

Items (hft

2

F/Btu)

1. 
   

   Outside film resistance
   (winter, 15 mph wind) 0.17

   
   


2. 
   

   Siding, wood (1/28 lapped) 0.81

   
   


3. 
   

   Sheathing (1/2 in. regular) 1.32

   
   


4. 
   

   Insulation batt (5 1/2 in.) 19.0

   
   


5. 
   

   Gypsum wallboard (1/2 in.) 0.45

   
   


6. 
   

   Inside film resistance (winter) 0.68

   
   


7. 
   


8. 
   
   
   
   3. 
      
      
      
      4. 
         
         
         
         5. 
            
            
            
            6. 
               
            
            
            
            
         
         
         
         
      
      
      
      
   
   
   
   

Problem 11.12

11.13. A typical ceiling of a house consists of items shown in

the accompanying table. Assume an inside room tem-

perature of 70F and an attic air temperature of 15F,

with an exposed area of 1000 ft

2

. Calculate the heat
loss through the ceiling.

11.14. Estimate the change in the length of a power trans-

mission line in your state when the temperature

changes by 50F. Write a brief memo to your instruc-

tor discussing your findings.

11.15. Calculate the change in 5-m-long copper wire when its

temperature changes by 130F.

11.16. Determine the temperature rise that would occur when

2 kg of the following materials are exposed to

a heating element putting out 500 J. Discuss your

assumptions.

a. The material is copper.

b. The material is aluminum.

c. The material is concrete.

11.17. The thermal conductivity of a solid material can be

determined using a setup similar to the one shown in

the accompanying figure. The thermocouples are

placed at 2.5-cm intervals in the known material

(copper alloy, K = 52 ) and the unknown sample,

w

m#k

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