Aslab of white pine, 4 cm thick, has a moisture content of 20 wt% at the start of the drying process. the equilibrium moisture content is 4 wt% for the humidity conditions in the drying air. the ends and edges are covered with moisture-resistance coating to prevent evaporation. the diffusivity of water through pine is 1.0e-9 m2/s. if the two large surfaces are exposed to the drying air and the resistance to mass transfer outside the pine is negligible, (a) estimate the time required to reduce the moisture content of the slab at the center to 10 wt% and (b) the time to reduce the (average) water content to 10 wt%. if the external mass transfer resistance is equal to the internal mass transfer resistance, (c) estimate the time required to reduce the moisture content of the slab at the center to 10 wt% and (d) the time to reduce the (average) water content to 10 wt%.