Fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios

We present a fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios. Utilizing the high flux of the X-rays generated from the third-generation synchrotron source, we can complete a high- resolution tomography scan within a short period of time, after which the three-dimensional （3D） packing structure can be obtained for the subsequent structural analysis. The image phase-retrieval procedure has been implemented to enhance the image contrast. We systematically investigated the effects of particle shape and aspect ratio on the structural properties including packing density and contact number. It turns out that large aspect ratio rod packings will have wider distributions of free volume fraction and larger mean contact numbers.

Influence of particle packing structure on sound velocity

The anisotropy in the particle systems of different packing structures affects the sound velocity. The acoustic propagation process in four kinds of packing structures（denoted as S45, H60, S90, and D） of two-dimensional granular system is simulated by the discrete element method. The velocity vtof obtained by the time of flight method and the velocity vc obtained from the stiffness tensor of the system are compared. Different sound velocities reflect various packing structures and force distributions within the system. The compression wave velocities of H60 and S90 are nearly the same, and transmit faster than that of D packing structure, while the sound velocity of S45 is the smallest. The shear wave velocities of S45 and H60 are nearly the same, and transmit faster than that of D packing structure. The compression wave velocity is sensitive to the volume fraction of the structure, however, the shear wave velocity is more sensitive to the geometrical structure itself. As the normal stress p is larger than 1 MPa, vtof and vc are almost equal, and the stiffness tensors of various structures explain the difference of sound velocities. When the normal stress is less than 1 MPa, with the coordination number unchanged, the law vtof ∝ p^1/4 still exists. This demonstrates that apart from different power laws between force and deformation as well as the change of the coordination number under different stresses, there are other complicated causes of vtof∝ p^1/4, and an explanation of the deviation from vtof ∝ p^1/6 is given from the perspective of dissipation.

Packing Structures of Thiophene Dimers and Their Effects on Excitation Energies of Thiophene Dimers

The packing structures of thiophene dimers and their effects on excitation energies of thiophene dimers were studied by employing MP2/6-31 ＋ G^＊ and TDDFT calculations. Twelve Optimized dimers with different orientations were obtained by means of MP2/6-31 ＋ G ^＊ optimizations. Among them, five T-shaped and three π-stacked thiophene dimers are local minima in energy. The result shows that the preferable conformation of thiophene dimers is the T- shaped packing, which is in agreement with the results in references. All the excitation energies of both T-shaped dimers（5. 34-5. 48 eV） and π-stacked dimers（5. 15-5. 18 eV） are lower than that of the isolated thiophene（5.68 eV）, indicating that inter-ring interactions decrease the excitation energies.

A STUDY OF PACKING STRUCTURE OF POLY(P-PHENYLENE BENZOBISTHIAZOLE)BY MOLECULAR SIMULATION

Molecular simulation technique was used in an examination of the possibilities of chain packing in the crystalline state for poly(ρ-phenylene benzobisthiazole).It has been found that one reason of hardly forming very ordered crystal of the polymer is the existence of so many stable positions of interchain interaction along chain axis.

Pressure drop of structured packing in pilot column and comparison to common correlations

Packed columns are widely used in the chemical industry such as absorption,stripping,distillation,and extraction in the production of e.g.organic chemicals,and pharmaceuticals.Pressure loss and pressure drop correlations are of special interest when it comes to the hydrodynamic properties of a column.The pressure loss across the column is of interest in the design phase when the size of the blower to drive the gas stream through the column has to be decided.The loading point and flooding point are also influenced by the pressure loss and the area of operation is determined from these points.This work examines four different correlations on pressure drop.The correlations are(i)Ergun’s equation(1952),(ii)an improved version of Ergun’s equation by Stichlmair,Bravo,and Fair(1989),(iii)an equation developed by Billet and Schultes(1999),and(iv)an equation by Rocha,Bravo,and Fair(1993).The complexity of the correlations is increasing in the mentioned order,Ergun’s equation being the simplest one.This study investigates if the more complicated correlations give better predictions to pressure drop in packed columns.This is determined by comparing the correlations to experimental data for pressure drop in a packed column with 8.2 m of structured packing using water as the liquid and atmospheric air as the gas.Seven experiments were carried out for determining the pressure drop in the column with liquid flows varying from 0 to 500 kg·h^(-1).At constant liquid flow,the gas flow was varied from approximately 10 to 70 kg·h^(-1).The pressure drop across the non-wetted column was best described by the correlation by Rocha et al.while the pressure drop for liquid flows from 100 to 500 kg·h^(-1)was,in general,best described by Stichlmair’s equation.For an irrigated column,the highest deviation was a predicted pressure drop 69.6%lower than measured.The best prediction was 0.1%higher than the measured.This study shows,surprisingly,that for a system of water and atmospheric air,complicated correlations on pressure drop determination do not provide better estimates than simple equations.

Reliability study of super-ellipsoid DEM in representing the packing structure of blast furnace

In industrial blast furnaces(BFs),the investigations involving the flow behaviors of particles and the resultant burden structure are essential to optimize its operation stability and energy consumption.With the advance of computing capability and mathematical model,the discrete element method(DEM)specialized in characterizing particle behavior has manifested its power in the investigation of BFs.In the framework of DEM,many particle models have been developed,but which model is more suitable for simulating the particle behaviors of BFs remains a question because real particles in BFs have large shape and size dispersity.Among these particle models,the super-ellipsoid model possesses the ability to change shape flexibly.Therefore,the focus of this study is to investigate whether the super-ellipsoid model can meet the requirement of authenticity and accuracy in simulating the behaviors of particles with large shape and size dispersity.To answer this question,a simplified BF charging system composed of a hopper and a storage bin is established.The charging process and the final packing structure are analyzed and compared between experiments and simulations with different shape indexes.The results show that super-ellipsoid particles have prominent advantages over spherical particles in terms of representing the real BF particles,and it can more reasonably reproduce the flow behaviors and packing structure of experimental particles.The computation cost of super-ellipsoid particles is also acceptable for engineering applications.Finally,the micro-scale characteristics of packing structure is analyzed and the single-ring charging process in industry-scale BF using super-ellipsoid particles is conducted.

Liquid-solid mass transfer in a rotating packed bed reactor with structured foam packing

A rotating packed bed(RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid–solid mass transfer in the RPB reactor is a barrier for its design and scale-up. In this work, the liquid–solid mass transfer in a RPB reactor installed with structured foam packing was experimentally studied using copper dissolution by potassium dichromate. Effects of rotational speed, liquid and gas volumetric flow rate on the liquid–solid mass transfer coefficient(kLS) have been investigated. The correlation for predicting kLSwas proposed, and the deviation between the experimental and predicted values was within±12%. The liquid–solid volumetric mass transfer coefficient(kLSaLS) ranged from 0.04–0.14 1^-1, which was approximately 5 times larger than that in the packed bed reactor. This work lays the foundation for modeling of the RPB reactor packed with structured foam packing for heterogeneous catalytic reaction.

Synthesis and Crystal Structure of a New Cu(Ⅱ) Dithiocarbamate Complex CuI(prdtc)(phen)

A new mononuclear Cu（Ⅱ） dithiocarbamate complex CuI（prdtc）（phen） 1 （prdtc = N-pyrrolidinyldithiocarbamate, phen = 1,10-phenanthroline） was synthesized and characterized by elemental analysis, IR spectrum, and single-crystal X-ray diffraction. The crystal belongs to the monoclinic system, space group P21/c with a = 8.7110（9）, b = 14.7143（14）, c = 14.8507（15） A, β = 109.721（6）°, V = 1791.9（3） A3, Z = 4, Dc = 1.916 g/cm3, CI7H16CulN3S2, Mr = 516.89, λ（MoKa） = 0.71073A,μ = 3.178 mm^-1, F（000） = 1012, the final R = 0.0369 and wR = 0.0987. A total of 4082 unique reflections were collected, of which 2916 with I 〉 2σ（I） were observed. The Cu（Ⅱ） atom is five-coordinated in a distorted square-pyramidal geometry by one I atom in the apical position, two S atoms from a prdtc ligand and two N atoms from a phen ligand in the basal plane. There exist face-to-face aromatic π-π stacking interactions between adjacent phen ligands stabilizing the structure and making the complex assemble into a 1D structure along the a axis. It can be concluded that the difference of the dtc flexibility and reaction conditions result in the structural difference between complex 1 and CuI（dmdtc）（phen） （dmdtc = N, N-dimethyldithiocarbamate）.

Effect of number of granulometric fractions on structure and micromechanics of compressed granular packings

The role of number of grain size fractions on structural and mechanical properties of uniaxially com- pressed granular packings with a uniform particle size distribution in terms of number of particles and with various particle size dispersities was studied using the discrete element method. The study addressed packing density, coordination number, contact forces, global stress, and energy dissipation in assemblies composed of frictional spheres. Packing density was found to change with increasing num- ber of granulometric fractions in mixtures with a small ratio of the diameters of the largest to smallest particles. Results indicated a certain value of particle size ratio below which the number of particle size fractions strongly affected packing density. The average coordination number decreased with increasing number of fractions. Detailed analysis of the effect of particle size dispersity on mechanical coordination number, including particles with no less than four contacts, revealed that, contrary to the average coordi- nation number, the mechanical coordination number increased with increasing ratio of the diameters of the largest to smallest particles in the sample. The composition of polydisperse samples strongly affected stress distribution and energy dissipation in granular packings.

Effect of counter current gas phase on liquid film

Liquid film flow is very important in many industrial applications.However,there are few reports about its characteristics on structured packings.Therefore,in this paper,liquid film phenomena were investigated experimentally to exploit new approaches for intensifying the performance of the structured packings.All experi-ments were performed at room temperature.Water and air were the working fluids.The effect of counter current gas phase on the liquid film was taken into consideration.A high speed camera,a non-intrusive measurement techni-que,was used.It is shown that both liquid and gas phases have strong effects on film characteristics.In the present work,liquid film width increased by 57% because of increasing liquid flow rate,while it decreased by 25%resulting from the counter current gas phase.