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MODELING THE INFLUENCE OF INTRINSIC AND EXTRINSIC FACTORS ON INTERPARTICULATE FORCES IN COHESIVE POWDERS
Most of the food, pharmaceutical, and chemical industries rely heavily on the supply of free-flowing powders that finds their application in raw materials, additives, and manufactured products. Improper storage conditions combined with environmental factors affect the free-flowing ability of powders. An undesirable transformation of these free-flowing powders into a coherent mass that resists flow is called caking.
Given the difficulty in quantifying the interparticle forces, both experimentally and numerically, most studies have considered only the humidity effect in powder caking. In this study, the interparticle forces in caked powders were quantified using the simplified Johnson-Kendall-Roberts (JKR) model to account for the material and environmental factors that influence powder caking. The cohesion energy density, which is the ratio of cohesive energy to volume of the particle, was used as the indicator of caking in powders. Simulated force chain network was used to track the relay of interparticle forces under compression. The model was validated experimentally by using caked isomalt powder. The results of the simulations demonstrated that an initial interparticle force of less than 0.01 N did not result in a caked mass. The cohesion energy density was found to be more sensitive to moisture content than consolidation pressure. A 33% increase in moisture at the same consolidation pressure increased the cohesion energy density by 42.45% while a 50% increase in consolidation pressure at the same moisture content increased the cohesion energy density only by 12.23%.
In similar, to understand the progression of caking at the bulk level, the development of tensile strength in isomalt with changes in temperature, relative humidity, and consolidation pressures was modeled and validated using the finite element method. In this model, Darcy's equation and species transport equation was used to model the continuity and momentum transfer in porous media. The heat transfer equation was used to solve the energy and the solid bridging model was used to the tensile strength. This study revealed that storing isomalt above 25 ˚C and 85±0.1% RH could initiate caking or increase in tensile strength. An increase in RH from 85% to 86% increased the tensile strength magnitude by 42.7%. Additionally, the study recommends lowering the consolidation pressures during storage to less than 3 kPa.
To mitigate caking, a powder flow aid device that could transmit vibration energy to powders through direct contact was developed. The device could be controlled remotely using an android application. The portable flow aid device was then tested under static and dynamic conditions and thereby the evolution of stresses during the operation of the device was mathematically analyzed. The decrease in static angle of repose of isomalt using the developed flow aid device for moisture contents of 3.84, 4.84, and 5.92 % was 45, 42.5, and 33 %. The dynamic analysis revealed that the developed device improved the flow rate of isomalt at 3.82% moisture by about 17.64%. On the other hand, a flow obstruction was observed in isomalt at moisture contents of 4.79% and 5.88%. The device was found to aid the flow of isomalt at 4.79% moisture. These observations were mathematically explained using the stress evolution model which predicted a flow obstruction for isomalt at 4.79 and 5.88% moisture contents.
- Doctor of Philosophy
- Agricultural and Biological Engineering
- West Lafayette