We examined in this work the drying characteristics of wastewater sludge. The drying flux of the constant-rate period for sludge cake could be up to 40% higher than that from a sand bed. Owing to the considerable volume shrinkage of cake, cracks would form and develop on the crack surface, which yielded three-dimensional but rather than the one-dimensional cake structure assumed in conventional drying theories. The crack length was fully developed in the first 30 min of drying, while the width of crack increased linearly with time. Using these data the drying flux from the cracks was estimated. Enhanced drying flux was noticeable which depended on the crack shape and the crossflow velocity.

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