Heat Transfer from Extended Surfaces Part 1 CH EN 3453 – Heat Transfer Reminders… • Homework #3 due Friday • Help session this afternoon, 4:30 pm in MEB 2325 • Exam #1 in three weeks – Covers all assigned reading material in Chapters 1, 2, 3, 4, 5Extended Surfaces (fins) Figure 3.12 Use of fins to enhance heat transfer from a plane wall. (a) Bare surface. (b) Finned surface. Types of FinsA Fin Energy Equation for Extended Surface Eq. 3.66 Page 158 General Form: Eq. 3.67 Page 158 For a straight fin of constant cross-sectional area: …where P is the perimeter (meters) of the pin …where Ac is the cross-sectional area of the pin As is the external surface area on the sides of the pin ( )01122=−⎟⎟⎠⎞⎜⎜⎝⎛−⎟⎟⎠⎞⎜⎜⎝⎛+∞TTdxdAkhAdxdTdxdAAdxTdscccFour Scenarios for Treating Pin Tips Example – Book Problem 3.116 Turbine blade mounted on proposed air-cooled rotating disc (Tb = 300°C) in a gas turbine with gas stream at T∞ = 1200°C. (a) If max allowable blade temperature is 1050°C and blade tip is assumed to be adiabatic, will the air cooling approach work? (b) What is the rate of heat transfer from blade to coolant? h = 250 W/m2·K = 50 mm k = 20 W/m·K Ac = 6x10–4 m2 P = 110 mm 300°C 1200°CGas Turbine Blade