1A) (5 points) A metal bar has a cross section of 1 by 2 cm2…

1A) (5 points) A metal bar has a cross section of 1 by 2 cm2 and is made of copper . Thermocouples are inserted at 2 mm and 4 mm below the surface of the bar are reading Ttc1 = 40°C and Ttc2 = 42°C. Estimate the surface temperature of the top of the bar. Assume bar’s sides are insulated.  

Problem 3. (40 points) An air-cooled heat sink with 9 plate…

Problem 3. (40 points) An air-cooled heat sink with 9 plate fins is used to maintain a CPU at 80°C. There is contact resistance of  between the CPU and the base of the sink. Thermal conductivity of the heat sink is 160 W/(m×K). Geometric variables are as follow: fin thickness (tf) = 2 mm, fin length (Lf) = 12 mm, cross-sectional shape of CPU = 2 cm x 2 cm (square), heat sink’s base thickness (tb) = 3 mm. Air temperature is 25°C and convection coefficient is 50 W/(m2K). Ignore internal heat generation and radiation heat transfer. Assume that the fin tips are adiabatic. Draw a thermal resistance circuit that expresses the heat transfer from the CPU’s top surface to air. Below the circuit show the expressions for thermal resistances (e.g., expression for a radiation resistance is 1/hrA). Then, determine the 1) total resistance in K/W (or °C/W) 2) overall fin efficiency and 3) heat rate from CPU to air in W.