MT 518 HW 2 Prob. Solutions

# MT 518 HW 2 Prob. Solutions - Page 1 of 4 MT 518 Homework...

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Page 1 of 4 MT 518 Homework Problem Solutions – Lecture #2 2.1 A solid wall is made up of face brick 4 in. thick, cement mortar ½ in. thick, and 1-2-4 mix stone concrete 8 in. thick. If the temperature of the exposed surface of the concrete is 70 F and the temperature of the exposed surface of the face brick is 31 F, find (a) the heat transfer in Btu/hr-ft 2 and (b) the temperature difference across the mortar. (a) R T = R 1 + R 2 + R 3

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Page 2 of 4 From Lect. #2, Slide #6: K brick masonry = 0.38 Btu/hr-ft 2 -°F/ft K cement mortar = 0.42 Btu/hr-ft 2 -°F/ft K concrete = 0.54 Btu/hr-ft 2 -°F/ft R 1 = L 1 /k 1 A = 0 . 1 38 . 0 12 0 . 4 x = 0.877 ºF-hr/Btu R 2 = L 2 /k 2 A = 0 . 1 42 . 0 12 5 . 0 x = 0.099 ºF-hr/Btu R 3 = L 3 /k 3 A = 0 . 1 54 . 0 12 0 . 8 x = 1.23 ºF-hr/Btu R T = 0.877 + 0.099 + 1.23 = 2.21 ºF-hr/Btu Q = (1/2.21)(70 – 31) = 17.6 Btu/hr-ft 2 (b) Q = Δt/R 2 17.6 = Δt /0.099 Δt = 1.74 F
Page 3 of 4 2.2 Air at a 70 F temperature is heated by an 8- by 10-ft horizontal plate

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MT 518 HW 2 Prob. Solutions - Page 1 of 4 MT 518 Homework...

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