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Drying of Wet Antibiotic Crystals in a Vacuum$-$Shelf Dryer Small$-$scale drying tests were performed in a vacuum$-$shelf dryer with wet antibiotic crystals contained in a tray at a solids depth of $2cm.$ Water at $70C$ was circulating through the shelves, and the absolute pressure was maintained at $100mmHg.$ The wet crystals initially had a water content of $70\%.$ The solids reached dryness after $10h$ of drying. It is proposed to dry these crystals in a large$-$scale dryer at a bed depth of $2\mathrm{.}5cm$ and using water circulating through the shelves at $70C.$ The plant dryer can be operated at an absolute pressure no lower than $150mmHg.$ Estimate how long it will take to reach dryness in the large dryer. For changes in what variable is the estimated drying time the most sensitive$?$