Heat transfer from a transistor may be enhanced by inserting it in an aluminum sleeve (k = 200 W/ m. K ) having 12 integrally machined longitudinal fins on its outer surface. The transistor radius and height are r₁ = 2.5 mm and H = 4 mm, respectively, while the fins are of length L = r₃ - r₂ = 8 mm and uniform thickness t = 0.8 mm. The thickness of the sleeve base is r₂ - r₁ = 1 mm, and the contact resistance of the sleeve-transistor interface is R"t.c = 0.6 × 10^-3 m². K/W. Air at T_∞ = 20°C flows over the fin surface, providing an approximately uniform convection coefficient of h = 30 W/m². K

  (a) When the transistor case temperature is 80°C, what is the rate of heat transfer from the sleeve?

  (6) Identify all of the measures that could be taken to improve design and/or operating conditions, such that heat dissipation may be increased while still maintaining a case temperature of 80°C. In words, assess the relative merits of each measure. Choose what you believe to be the three most promising measures, and numerically assess the effect of corresponding changes in design and/or operating conditions on thermal performance.