Simulation of the effect of bond strength on the breakage pattern of agglomerates by Distinct Element Method

Chemical, pharmaceutical and food industries amongst many others use agglomerates either as intermediate or manufactured products. The mechanical strength of agglomerates under impact or shear deformation during handling and processing is of great interest to these industries for optimising product specification and functionality. The effect of surface energy on agglomerate behaviour under impact has been investigated using Distinct Element Method (DEM). Four different agglomerates were formed and impacted against a target along the direction of gravity for three different values of the surface energy (0.35, 3.5 and 35.0 J/m²). The agglomerate breakage pattern was influenced by the surface energy and a transition in the mode of failure of agglomerates was observed when the surface energy was varied. Based on the previous work, the surface energy is expressed in terms of Weber Number, We=(V-V0²)ρD/γ. Agglomerates showed extensive deformation under impact at the lowest value of surface energy (0.35 J/m²) and no evidence of fragmentation was found for any value of impact velocity. In this case the agglomerates behaved macroscopically in a ductile mode. At values of surface energy larger than 3.5 J/m² the agglomerates fragmented at the same time as local damage around the impact site occurred. This type of behaviour is typical of semi-brittle material failure. Therefore, the breakage pattern of agglomerates is influenced by the surface energy

Analysis of the flowability of cohesive powders using Distinct Element Method

Computer simulations using Distinct Element Method (DEM) have been carried out to investigate the effect of cohesion on the flowability of polydisperse particulate systems. For this purpose, two assemblies with different values of surface energy and made of 3000 spheres with the mechanical properties of glass beads were considered. The analysis of the flowability of the powders is presented in terms of the unconfined yield stress as a function of strain rate for different pre-consolidation loads. For values of the surface energy of 1.0 J/m2 and strain rates lower than 6 s− 1, the unconfined yield stress does not change significantly indicating a quasi-static behaviour of the particulate assemblies during the compression process. For larger strain rates, the unconfined yield stress varies with the power index of 1.2 of the strain rate. The influence of the pre-consolidating stress on the powder behaviour has also been investigated and a flow factor was obtained from the linear relationship between the unconfined yield stress and pre-consolidation stress. The computer simulations show qualitatively a good agreement with the experimental trends on highly cohesive powder flow behaviour

Receptores tirosina quinasa en cáncer

Máster Universitario en Biología y Clínica del Cáncer: Programa, Objetivos y Metodología.Peer Reviewe

Aguas azoadas, Valladolid : agua, duchas, pulverizaciones, inhalaciones

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

Analysis of the effect of cohesion and gravity on the bulk behaviour of powders using Discrete Element Method

Computer simulations using Distinct Element Method have been carried out to analyse the bulk behaviour of a polydisperse assembly of glass beads. For this purpose an assembly made of 3000 spheres were generated to which the mechanical properties of glass beads were assigned. The system was initially compressed isotropically at a strain rate of 1 s-1 in the absence of gravity and surface energy. Once the assembly reached a packing fraction of about 0.62, the effects of cohesion and gravity on the bulk behaviour were analysed for two different cases. In the first case only gravity was applied, whilst in the second case both gravity and surface energy were acting on the particles. The evolution of the components of the stress tensor for the case in which only gravity was applied indicated that the gravity did not appreciably affect the isotropy of the system. In contrast, the system in which surface energy was introduced became anisotropic. The concept of unconfined yield stress of bulk cohesive powders was used to analyse the effect of surface energy and strain rate. For values of surface energy of 1.0 J/m2 and of strain rate lower than 1 s-1 the unconfined yield strength did not change significantly indicating a quasi-static behaviour for the compression process. However, for values of strain rates larger than 1 s-1 the unconfined yield strength increased with the strain rate, following a power law trend with an index of 1.7

Manifestaciones cutáneas de las enfermedades de tiroides: Revisión

Los trastornos del tiroides son muy prevalentes en la práctica clínica. Un estudio epidemiológico europeo destaca que casi la mitad de los pacientes con enfermedad tiroidea permanecen sin diagnosticar. La prevalencia media de disfunción tiroidea en estudios europeos es aproximadamente un 11%.La enfermedad tiroidea se produce por un nivel anormal de hormona tiroidea (tiroxina) y afecta comúnmente a la piel, tanto en adultos como en niños. Sin embargo también puede dar alteraciones en el pelo y en las uñas. Un aumento o una disminución en los niveles de la hormona tiene repercusión sobre la piel, pelo y uñas. Es importante saber reconocer estos cambios, ya que en varios casos el primer signo de enfermedad tiroidea puede aparecer en la piel, resultando ser útiles y ayudando en el diagnóstico precoz.Grado en Medicin

Mechanistic analysis and computer simulation of impact breakage of agglomerates: Effect of surface energy

Agglomerates are ubiquitous as intermediate or manufactured products in chemical, pharmaceutical and food industries. During handling and processing they may suffer breakage if they are weak. On the other hand, if they are too strong, their dispersion and disintegration could be difficult. The control of their mechanical strength is therefore highly desirable. However, the analysis of agglomerate strength is complex due to the large number of parameters that influence agglomerate behaviour, such as the primary particle size, density and elastic modulus, and the interparticle bond strength. A simple mechanistic model is presented here which relates the number of broken contacts in agglomerate due to impact velocity, interparticle adhesion energy and the particle properties of the particles forming the agglomerate. The model is based on the hypothesis that the energy used to break contacts during impact is proportional to the incident kinetic energy of the agglomerate. The damage ratio defined as the ratio of broken contacts to the initial number of bonds is shown to depend on the dimensionless group, Δ, in the form (ρV2D5/3E2/3)/ Γ5/3, where V is the impact velocity, E the elastic modulus, D the particle diameter, ρ the particle density and Γ the interface energy. This dimensionless group, Δ, incorporates the Weber number, (ρDV2/Γ), which was previously shown to be influential in agglomerate breakage, and may be presented in the form, Δ=WeIe2/3 , where Ie = ED/ Γ. The predicted dependency of the damage ratio on the surface energy has been tested using Distinct Element Method (DEM). Four different agglomerates have been formed and impacted against a target for three different values of the surface energy of the primary particles. The simulation results show that the effect of surface energy is better described by the above mechanistic model than by the Weber number alone, as previously used to characterise the impact strength of agglomerates

Ingesta de gomas elásticas en Garcillas Bueyeras (Bubulcus ibis)

L'anàlisi de nombroses egagròpiles recollides en un dormider d'esplugabous proper a l'abocador de Badajoz i diverses observacions directes d'individus menjant en aquesta zona indiquen que l'espècie ingireix gran quantitat de gomes. Això s'interpreta per la similaritat entre les gomes i els cucs de terra

Aguas azoadas de Valladolid : pasaje de Gutiérrez, Letra C : Privilegio Avilés por 20 años

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201