AnswerKeyXIII

Assumeanenergycontentof20mjkgforperfectlydrywoodand

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Unformatted text preview: a given volume of freshly cut wood with the seasoned one. Assume an energy content of 20 MJ/kg for perfectly dry wood, and 2.3 MJ/kg of energy needed to vaporize water. Also assume that the volume of wood does not change as it dries. Answer In 1 kg of freshly cut firewood, 0.7 kg is water, and 0.3 kg is perfectly dry wood. Perfectly dry wood contributes 0.3 kg × 20 MJ/kg = 6 MJ of heat, out of which 0.7 kg × 2.3 MJ/kg = 1.61 MJ is lost in evaporating water. Thus, 1 kg of freshly cut firewood has a heat content of just 4.39 MJ. In 1 kg of seasoned firewood, 0.2 kg is water, and 0.8 kg is perfectly dry wood. Perfectly dry wood contribut...
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