Investigating drying mechanisms and model fitting for cold-rolled sludge during hot-air dehydration

The low-temperature hot-air drying behavior of cold-rolled sludge was investigated at 75, 85, and 95 °C, initial thicknesses of 6, 8, and 10 mm, and an air velocity of 0.5 m/s. Each condition was tested three times, and the drying curves represent mean results. Moisture removal was accompanied by shrinkage, cracking, and fragmentation. Four empirical functions were refitted to the retained 6 mm moisture-ratio records using the recorded experimental times and unweighted least squares. The Logarithmic function gave the lowest RMSE at 75 and 95 °C but predicted negative moisture ratios near the recorded endpoints. Modified Page gave the lowest RMSE at 85 °C and remained nonnegative at all three temperatures. A conditional equilibrium-moisture sensitivity analysis gave maximum changes of approximately 1.26% in k and 1.15% in n relative to the Modified Page baseline fits. Conditional diffusivity and Arrhenius calculations illustrated greater sensitivity to the stated assumptions. The results provide an experimental basis for further investigations of low-temperature sludge drying.