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It is very important to clarify the mechanism of hardening of a powder layer under humid conditions in order to avoid the potential trouble caused by the layer hardening. This phenomenon is believed to be closely related to the formation of liquid bridge at the contact point of two particles which leads to an increase in adhesion force.In this paper, the applicability of impedance of an electrical equivalent circuit for a particle-contact point system has been examined for the evaluation of adhesion force at different humidity. An electrical equivalent circuit was designed to express the condition of contacting particles in powder layer and the impedance of conductive and non-conductive particles was calculated at different humidity.Adhesion force and impedance of a single contact point of particle with liquid bridge has been measured directly by a modified AFM. Based on the measurements, the applicability of impedance for the investigation of the change in adhesion force acting between contacting particles with liquid bridge was discussed.

The dust cleaning mechanism of a pulse jet-type bag filter was experimentally investigated using various types of plane fabric filters. The time change of pressures up and downstream of the filter, and the displacements of the filter and dust surface were measured in order to relate their characteristics to the dust cleaning. Using a high speed video camera, the dust cleaning process was observed.As a result, the rapid inversion of pressures up and downstream of the filter and its inflation are found to be essential to enhance the dust removal as well as the dust detachability of the filter surface. The instance at which the dust layer separates from the filter surface was related to the difference between the displacements of the filter and the dust surface. It is revealed that the cracking of the dust cake takes place after the separation. The size of separated dust fragments seems to be larger for higher dust detachability, and a schematic model for the dust cleaning process is proposed based on these results.

Chain-like clustering of 3μm Sio2 particles was investigated by Monte Carlo simulation along with the experiment. The magnetic force was applied in parallel to the particle layer suspended in a thin film of magnetic fluid. The size distribution of chain-like clusters was measured in relationship to the coverage c or the bulk-mean area fraction of particles: k=90c1.38 The agreement between the computer simulation and the experiment was fairly good. Particle movement from the initial to final equilibrium positions was also measured for all particles. Monte Carlo simulation was foud to underestimate the particle movement in the region of high particle concentration.

The capillary rising phenomenon is controlled by the complicated intersticial structure in the packed bed. In order to investigate the correlation between the capillary rise and the intersticial structure of a packed bed, the capillary rising velocity is measured for a packed bed of equal sphere size.The experimental results show that the effective suction head for capillary rise depends on the intersticial structure of the bed. The liquid rises through the remaining air cavities in the packed bed. The relationship between the retained air volume and the particle volume fraction is explained from the pervious theory of the pore size distribution in the packed bed.