MidTerm1_Questions_F09

MidTerm1_Questions_F09 - Midterm Progress Assessment ECH...

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Midterm Progress Assessment ECH 3223, Fall 2009 Monday, October 19 Directions: Two hours. Open book. No notes. Calculator needed. Start each problem on a new page. Maximize your score by showing all work. Good luck to you!! Problem #1: Tube wall, non-constant conductivity (25 points) Consider a tube wall of inner and outer radii R i and R o , whose temperature are main- tained at T i and T o , respectively. The thermal conductivity of the cylinder is temperature dependent and may be represented by an expression of the form k = k 0 (1 + βT ). Obtain an expression for the heat transfer per unit length of the tube. Problem #2: Array of fins (25 points) Circular copper rods of diameter D = 1 mm and length L = 25 mm are used to enhance heat transfer from a surface that is maintained at T s 1 = 100 o C. One end of the rod is attached to this surface (at x = 0) while the other end ( x = 25 mm) is joined to a second surface, which is maintained at T s 2 = 0 o C. Air flowing between the surfaces (and over the rods)

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