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A very long cylindrical shaped "pin" fin is attached to a wall with a base temperature of Tb=65C. The temperature at location " 1 " is given in the diagram (T1=20C at x1=0.21m). See diagram below for geometry, temperatures, and convective heat iransfer coefficient. a) Using the appropriate fin equations, determine the thermal conductivity, k, of the pin fin in units of W/m - K. b) Determine how long the pin fin actually needs to be for the "infinitely long" fin equation assumption to be valid