The heat transfer from the CPU of a personal computer may be increased by attaching an aluminium block (k = 220 W/mK) with 8 rectangular fins attached to its upper surface. The CPU chip measures 40 x 40 mm and the block is sized so that just covers the chip. There is no thermal contact resistance between the chip and the block. The block is 5 mm thick, the fins are 12 mm long and 2 mm thick. The surrounding air is at a temperature of 20C and there is a uniform convection heat transfer coefficient of h = 20 W/m2K. i) Calculate the rate of heat transfer from the CPU if its temperature is 90°C. ii) Determine the overall surface efficiency.

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