Vacuum drying of sintered spheres of glass beads

Air drying of sintered spheres of glass beads was investigated under vacuum as well as at atmospheric pressure for comparison. The critical moisture c ontents at pressures of 0.97-26.7 kPa were close to that at atmospheric pre ssure. Nevertheless, their mechanisms were different. The drying rate curve s for the falling rate period were predicted from a receding evaporation fr ont model with either a two-step moisture distribution in the pendular stat e or a flat moisture distribution in the pendular state. The predicted as w ell as the observed drying rate curves for the falling rate period at press ures of 0.97-1.47 kPa decreased either by two stages or monotonically, depe nding on the shape of the respective moisture distributions. At subatmosphe ric pressures such as 13.0 and 26.7 kPa, it was, however, difficult to dete rmine the configuration of the water.