example 7-2 - Example 7-2 A composite wall consists of...

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Example 7-2 A composite wall consists of three layers bolted together: 3/8 in. of plain carbon steel, 1 in. of low density particle board, and 1/4 in. of oak. The bolts, which are all made of steel, are 1/2 in. in diameter and are spaced in a rectangular array on 8 in. centers. Calculate the equivalent thermal resistance for a 1 sq. ft. section of wall. View of section A-A Solution: Form a resistance network for a unit cell, 8 in. by 8 in., as shown by the dotted line in the figure.

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1 1 1 steel layer L R kA = 2 2 2 particle board L R = 3 3 3 oak L R = 123 4 2 1 bolt 2 LLL R d k π + + = ⎛⎞ ⎜⎟ ⎝⎠ 5123 R RRR = ++ 45 tot RR R = + This is the resistance for an 8 in. by 8 in. section of the wall, that is () *2 8in. 64in. 0.444ft A == = 2 The area to use in R 1 , R 2 , and R 3 , is 2 * 2 d AA =− ( ) 2 22 0.5 0.444ft ft 0.443ft 21 2 A = 2
() o 1 2 31 f t in 81 2 i n hF 0.00201 Btu Btu 35 0.443ft hf tR R ⎛⎞ ⎜⎟ ⎝⎠ == ⋅⋅ where k 1 is from Table B-2. o 2 2 1ft 1in 12in 4.18 Btu Btu 0.045 0.443ft R where k 2 is from Table B-5. o 3 2 11 f t in 41 2 i n 0.480 Btu Btu 0.098 0.443ft R

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This note was uploaded on 04/06/2009 for the course ENGR 2250 taught by Professor Borca-tasciuc during the Spring '08 term at Rensselaer Polytechnic Institute.

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example 7-2 - Example 7-2 A composite wall consists of...

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