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Question: heating of lumber timbers and pallets is used to kill...

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Heating of lumber, timbers, and pallets is used to kill insects to prevent transfer between countries in international trade. A typical requirement is that the slowest heating point of any wood configuration be held above 56ºC for at least 30 min. Consider hot air (70ºC) heating of boards that are initially at 6ºC. The boards are 3.8 cm thick, 32.0 cm wide, and 8 ft long. The thermal conductivity of the wood is 0.3 W/mK, and the thermal diffusivity of the wood is 9x10-8 m2/s. The hot air blows across the 32.0-cm wide surfaces (both top and bottom) at ~1.3 m/s, to yield a convection coefficient of 10.25 W/m2K. (a) What is the center temperature of the board after 3.5 min of heating? (b) Calculate the total required treatment time (i.e., time to reach 56ºC + 30 min).

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