Effect of Particle Orientation on Heat Transfer in Arrays of Prolate Particles

Direct Numerical Simulations have been carried out to study the forced convection heat transfer of flow through fixed prolate particles for a variety of aspect ratios ar={5/4,5/3,5/1}with Reynolds number(Re)up to 100.Three variations of the solid volume fraction c={0.1,0.2,0.3}with four Hermans orientation factors S={−0.5,0,0.5,1}are studied.It has been found that changes in S cause prominent variations in the Nusselt number.In general,Nusselt number increases with the decrease of S.For all three aspect ratios,the Nusselt number remains a linear function of S at different c and Re.Therefore,it is concluded that,for heat transfer from prolate muti-particle system,the effects of orientations cannot be ignored.A new correlation for Nusselt number has been developed for arrays of prolate particles using the simulation data as a function of Re,c,S and ar.

The Versatile Method to Control the Orientation of BN Particles in Thermoset Matrix

A new thermally conductive thermoset composite has been developed. A hybrid organic-inorganic material composed of an epoxy resin crosslinked with a flexible diamine hardener, and a BN, was prepared by incorporating epoxy structure units covalently into a BN via the sol-gel approach. The precursor was obtained by the reaction of DGEBA （diglycidyl ether of bisphenol A） with TEOS （tetraethyl orthosilicate）. The precursor was then hydrolyzed and co-condensated with tetraethyl orthosilicate which is covalently bond with the hydroxyl groups on the BN surface at room temperature to yield epoxy-BN hybrid sol-gel material. FTIR spectroscopy confirmed the formation of organic and inorganic network. The thermal conductivity as measured by thermal conductive analyzer showed an increase up to 0.4048 W/m.K, for a mixture containing 0.4 wt% of BN fillers in the epoxy matrix. Moreover, the optimum conditions for surface modification of BN particle were also investigated.

Study of orientation and morphology of elliptical particles in drum granulation by dynamic simulation

Sphericity is an important indicator of particle flow properties in rotary granulation. Here, a dynamic simulation approach is proposed to study the formation of particle sphericity during agglomeration by investigating both the orbit and attitude of non-spherical particles in a rotary drum. First, geometric crite- ria are presented to substitute a dual-sphere particle model for the commonly encountered ellipsoidal particle model assuming the long radius of the dual-sphere particle is equal to that of the ellipsoidal particle. Next, a discrete element method is applied to calculate the positions and orientations of dual- sphere particles during granulation. The relationship between shape and attitude in the dual-sphere model is then analyzed by comparing the obtained orientation angle-oblateness curves. A conclusion can be drawn that the particle orientation angle decreases with increasing particle oblateness within a certain range.

Statistical variation of characteristics of random packed beds of Raschig rings:The influence of the sample size

Many studies on random packed beds have been dedicated to local porosity(void fraction)or orientation distribution of particles.However,despite the random nature of the considered packings,very little attention has been devoted to examination whether the number of particles used in experiments/simulations is sufficiently large to get reproducible results.The reproducibility of the key packing parameters depends on the size of the population of particles(sample size)and ordering effects induced by the confining walls.This work investigates quantitatively the influence of the sample size on the statistical variation of the packed bed characteristics.Packed beds of Raschig rings were generated with a sequential algorithm and three column diameters were considered.It has been found that in the case of the orientation distribution the results depend strongly on the sample size,especially for slender columns,while the porosity profiles are well-reproducible characteristics even for relatively small packings of rings.Some complementary results for full cylinders are also included.