Fine cohesive particles (Group C) are extensively used in various processes, particularly in the pharmaceutical industry. However, fluidization and flowability during continuous flow present several challenges. These challenges include non-fluidization, excessive elutriation of particles, slow drying rates, and uneven humidity distribution. Given the insufficient information available regarding Group C particles, this thesis was conducted through experimental methods and modeling to improve the fluidization quality increase drying rates, and prevent the elutriation of wet wheat flour particles with an average diameter of 15 microns (Group C). The study eva‎luated several parameters, including minimum fluidization velocity, particle volume distribution, particle size distribution, the fraction of particles exiting the bed, changes in bed temperature, drying rates, and the final moisture content of the particles. Due to the significance of small adhesive particles (Group C) and their extensive applications across various industries, particularly in the pharmaceutical sector, fluidization under continuous flow presents several challenges. These challenges include non-fluidization, excessive elutriation of particles, slow drying rates, and uneven humidity distribution. Given the limited information available regarding Group C particles, this thesis employs experimental methods and modeling to enhance fluidization quality, increase drying rates, and prevent the elutriation of wet wheat flour particles with an average diameter of 15 microns (Group C). The study eva‎luates several parameters, including minimum fluidization velocity, particle volume distribution, particle size distribution, the fraction of particles leaving the bed, changes in bed temperature, drying speed, and final moisture content of the particles. The reduction in minimum fluidization velocity under pulsed flow, with an increase in frequency from 0.003 Hz to 5 Hz, was 12.4% and 41.5% compared to continuous flow, respectively. This indicates a reduction in agglomerate size. The fluidization quality of fine cohesive particles under continuous flow and pulsed flow at low frequencies is poor but improves with increasing frequency up to 5 Hz due to the overcoming of cohesive forces. The rate of particle elutriation under continuous flow is extremely high. The elutriation of particles is minimal under the optimal frequency range of 0.1 Hz for pulsed flow and 0.003 Hz to 0.1 Hz for mixed flow. The critical frequency is identified at 0.5 Hz. The drying rate of particles under continuous flow and pulsed flow at 0.033 Hz is low due to uneven particle distribution; however, it increases with frequency, reaching up to 5 Hz. In contrast, under mixed flow at a low frequency of 0.033 Hz, the drying rate improves due to enhanced fluidization quality. With the proposed CFD-PBM, along with considerations of van der Waals forces, capillary forces, and electrostatic forces, the movement, particle size distribution, and drying rate are predicted comprehensively. The results indicated that under pulsed flow at a high frequency of 5 Hz and mixed flow at a low frequency of 0.033 Hz, the quality of fluidization was significantly enhanced due to a reduction in agglomerate size and a more uniform particle volume distribution. The agglomerate diameter under mixed flow at 0.033 Hz decreased by approximately 41% compared to continuous flow and by 21% compared to pulsed flow at 0.033 Hz. The drying rate and moisture removal reached 78% under mixed flow at 0.033 Hz, while the minimum rate was about 17% under continuous flow. Additionally, the increase in final particle temperature under mixed flow at 0.033 Hz was minimal due to high mass transfer, which is crucial for sensitive materials.

محسن نصراصفهاني

مسعود حق شناس فرد

احمد محب , صفورا كريمي