12 research outputs found
The High Temperature Annular Shear Cell: A modified ring shear tester to measure the flow properties of powders at high temperature
No full textAlthough changes of cohesive behaviour of powders is observed at high temperature in several industrial process units, conventional testers and procedures are still not suited for testing powder flow properties at high temperature. In this work a High Temperature Annular Shear Cell was designed, built and set-up in order to directly measure the flow properties of powders up to 500°C. A temperature control system was also developed to establish a uniform temperature inside the powder sample. Yield loci at room temperature and 500°C were measured for samples of fluid catalytic cracking catalyst (FCC powder), fly ashes, natural corundum, synthetic porous alumina and glass beads. Experimental evidences did not reveal a univocal effect of temperature in the tested range. Finally, shear tests on glass beads mixed to with some high-density polyethylene (HDPE) (1% of the total weight) confirmed that a significant increase of the cohesive behaviour occurs at high temperature when liquid bridges form due to the melting of one of the solid phases
Correlation of powder flow properties to interparticle interactions at ambient and high temperatures
No full textA combination of a continuum approach and a particle-particle approach to describe the multi-scale nature of the mechanical properties of bulk solids may be beneficial to scientific and engineering applications. In this paper, a procedure is proposed to estimate the interparticle forces beginning with the bulk flow properties as measured with standardized techniques. In particular, the relationship between interparticle forces and bulk solid tensile strength is adopted based on the microscale approaches of Rumpf (1970) and Molerus (1975). The flow properties of fluid cracking catalyst (FCC), corundum and glass bead powders were all characterized with a modified Schulze ring shear cell capable of operating at temperatures up to 500°C. The powder test conditions were selected such that the van der Waals forces were the most significant particle-particle interactions. The model equations describe two cases, in which either elastic or plastic deformation of the contact points is assumed. The results indicate that the model provides the correct order of magnitude for the values of the tensile strength when proper values for the mean curvature radius at the contact points are taken into account. A sensitivity analysis for the main parameters in the model was performed. This analysis indicated that the assumption of plastic deformation at contact surfaces coupled with a decrease in porosity justified an increase of the tensile strength with consolidation stress. Furthermore, the effect of temperature on the measured flow behavior can be explained as a change in the strength of the material
Flow properties of powders at high temperature
No full textProc. of Bulk Solids Europe 2010, International Conference on Storing, Handling and Transporting Bulk, Glasgow (UK) September 9-10, 2010. Poster 3
The Effect of the Elastic and Plastic Behaviour at the Particle Contact Points on the Flow Properties of Powders
No full textA continuum mechanics approach is used by engineering practices to characterize the powder flow properties and to design equipment for the handling and storage of granular materials. However, many studies have highlighted the relevant role of the type and magnitude of the interactions acting between particles on the powder flowability. Therefore, the correlation of a particle-particle approach and a continuum approach may be beneficial to describe the multiscale nature of the mechanical properties of bulk solids for scientific and engineering applications.
In this work, the effect of the elastic and plastic behaviour at the contact surface of the particles on the flow behaviour was analysed starting from the powder flow properties measured by a standardized technique. At this purpose, a relationship between interparticle forces and bulk solid tensile strength was derived according to the microscale approaches of Rumpf (1970) and Molerus (1975). The flow properties of Fluid Cracking Catalyst (FCC) samples, corundum and glass bead powders, which were all characterised with a modified Schulze ring shear cell capable of operating at temperatures up to 500°C, were studied. The testing powder conditions were selected so that the van der Waals forces were the most significant particle-particle interactions. The value the mean curvature radius at the contact points which better estimates the measured data was assumed as proper value, according to the SEM images of the material samples.
A sensitivity analysis on the main parameters of the model equations, as the porosity of the assembly and the strength of the particle material, was performed for the two cases in which either elastic or plastic deformation of the contact points were assumed. This analysis indicated that the assumption of plastic deformation at contact surfaces, coupled with the decrease in porosity, justified the increase in the tensile strength with the consolidation stress and better describe the flow behaviour of powders. Furthermore, the effect of temperature on the measured flow behaviour was explained with the change in the strength of the material when plastic deformation occurs at the contact points
A theoretical framework for the interpretation of the effects of temperature on interparticle interactions
No full textA High Temperature Annular Shear Cell was used to directly measure yield loci up to 500°C and to evaluate the effect of temperature on the macroscopic flow properties of powders. A theoretical framework was developed according to the particle-particle approach of Rumpf and Molerus. In particular, the tensile strength of the powder experimentally evaluated for fluid cracking catalyst, corundum and glass beads was related to the van der Waals forces acting between particles assuming alternatively elastic and plastic deformation at contact points. Both the assumptions provide correct order of magnitude results in terms of tensile strength if plausible value of the local curvature at contact points of particles is taken into account. Furthermore, both the increasing cohesive consolidation and the slight increase of the cohesive behaviour with the temperature suggest the occurrence of the plastic deformation of the contact points and, therefore, that the plastic deformation assumption should be adopted to explain the effect of the temperature on the interparticle interactions
The effect of temperature on flow properties of fine powders
No full textChanges of cohesive flow properties of powders at high temperature are observed in many industrial applications, such as fluidized bed reactors, in the filtering of hot gases, granulators and dryers. In this work a modified annular Schulze shear cell was used to measure flow properties of a FCC powder, a corundum powder and fly-ashes between room temperature and 500°C
The measurement of powder flow properties with a mechanically stirred aerated bed
No full textThis paper re-examines a set of experimental data published by Bruni et al. (2007a, 2007b) [Bruni, G., Barletta, D., Poletto, M., Lettieri, P., 2007a. A rheological model for the flowability of aerated fine powders. Chem. Eng. Sci. 62, 397–407; Bruni, G., Lettieri, P., Newton, D., Barletta, D., 2007b. An investigation of the effect of the interparticle forces on the fluidization behaviour of fine powders linked with rheological studies. Chem. Eng. Sci. 62, 387–396] carried out on a mechanically stirred fluid-bed rheometer (msFBR), which was developed to study the rheology of aerated and fluidized powders. The use of aeration below fluidization allowed to carry out experiments with powders at very low consolidation levels. Two mathematical models, based on the Janssen approach to evaluate stresses in powder containers, were developed in order to relate the torque measurements in the Fluidized Bed Rheometer to the flow properties of the powders measured with standard powder flow testers. Results indicate that the models were able to satisfactorily predict the torque measured by the msFBR. The larger complexity of the Walker (1966) [Walker, D.M., 1966. An approximate theory for pressures and arching in hoppers, Chem. Eng. Sci. 21, 975–997] and Walters (1973) [Walters, J.K., 1973. A theoretical analysis of stresses in silos with vertical walls, Chem. Eng. Sci. 28, 13–21] stress analysis adopted in one of the two models did not introduce significant improvements in the evaluation of the stress distribution to justify its use. A procedure for the inverse application of the model was developed and applied to estimate the powder flow properties starting from msFBR data. The application of this procedure provided good results in terms of effective angle of internal friction and is promising for the ability of the system to explore powder flow at very low consolidation states
Sensitivity analysis on a rheological model for the flowability of aerated fine powders
No full textA new model based on dynamic powder flow properties to predict the torque measured in the mechanically stirred fluid-bed rheometer (msFBR) is proposed. A Schulze shear cell was used to measure the powder flow properties. An inverse procedure to evaluate powder flow properties from torque data is proposed and verified with shear cell data
A theoretical framework for the interpretation of the effect of temperature on interparticle interactions
No full textA High Temperature Annular Shear Cell was used to directly measure yield loci up to 500°C and to evaluate the effect of temperature on the macroscopic flow properties of powders. A theoretical framework was developed according to the particle-particle approach of Rumpf and Molerus. In particular, the tensile strength of the powder experimentally evaluated for fluid cracking catalyst, corundum and glass beads was related to the van der Waals forces acting between particles assuming alternatively elastic and plastic deformation at contact points. Both the assumptions provide correct order of magnitude results in terms of tensile strength if plausible value of the local curvature at contact points of particles is taken into account. Furthermore, both the increasing cohesive consolidation and the slight increase of the cohesive behaviour with the temperature suggest the occurrence of the plastic deformation of the contact points and, therefore, that the plastic deformation assumption should be adopted to explain the effect of the temperature on the interparticle interactions
The measurement of powder flow properties with a high temperature shear cell
No full textInvited poster presentation at the IFPRI (International Fine Particle Research Institute) Annual General Meeting, Spa (Belgium), June 27-July 1, 2010
