Compression Of Packings Research Articles

Simulation of the dynamic packing behavior of preparative chromatography columns via discrete particle modeling.

Preparative packed-bed chromatography using polymer-based, compressible, porous resins is a powerful method for purification of macromolecular bioproducts. During operation, a complex, hysteretic, thus, history-dependent packed bed behavior is often observed but theoretical understanding of the causes is limited. Therefore, a rigorous modeling approach of the chromatography column on the particle scale has been made which takes into account interparticle micromechanics and fluid-particle interactions for the first time. A three-dimensional deterministic model was created by applying Computational Fluid Dynamics (CFD) coupled with the Discrete Element Method (DEM). The column packing behavior during either flow or mechanical compression was investigated in-silico and in laboratory experiments. A pronounced axial compression-relaxation profile was identified that differed for both compression strategies. Void spaces were clearly visible in the packed bed after compression. It was assumed that the observed bed inhomogeneity was because of a force-chain network at the particle scale. The simulation satisfactorily reproduced the measured behavior regarding packing compression as well as pressure-flow dependency. Furthermore, the particle Young's modulus and particle-wall friction as well as interparticle friction were identified as crucial parameters affecting packing dynamics. It was concluded that compaction of the chromatographic bed is rather because of particle rearrangement than particle deformation. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 32:363-371, 2016.

Study of lime hemp composite precasting by compaction of fresh mix — An instrumented die to measure friction and stress state

This paper deals with the processing of lime hemp composite blocks by compaction. A rigid compression die has been developed to reach relatively high compression pressure. This has been fitted with force and strain transducers to measure the stress state during compaction. It provides some means of understanding the effect of mix design and stress level on the compressibility and homogeneity of hardened composites. It is shown that moisture globally increases both friction and packing compressibility. Proper moisture content and paste-to-shiv mass ratio (P/S) can be chosen to reduce the heterogeneity. The combination of friction at wall level and stress transmission is the most detrimental for a moisture content of 20% and a P/S=1.

Constitutive relations for the isotropic deformation of frictionless packings of polydisperse spheres

The isotropic compression of polydisperse packings of frictionless spheres is modeled with the Discrete Element Method (DEM). The evolution of coordination number, fraction of rattlers, isotropic fabric, and pressure (isotropic stress) is reported as function of volume fraction for different system parameters. The power law relationship, with power ≈ 1 / 2 , between coordination number and volume fraction is confirmed in the jammed state for a broad range of volume fractions and for different (moderate) polydispersities. The polydispersity in the packing causes a shift of the critical volume fraction, i.e., more heterogeneous packings jam at higher volume fractions. Close to jamming, the coordination number and the jamming volume fraction itself depend on both history and rate. At larger densities, neither the deformation history nor the loading rate have a significant effect on the evolution of the coordination number. Concerning the fabric tensor, comparing our DEM results to theoretical predictions, good agreement for different polydispersities is observed. An analytical expression for the pressure as function of isotropic (volumetric) strain is proposed for polydisperse packings, based on the assumption of uniform deformation. We note that, besides the implicit proportionality to contact number density (or fabric), no single power-law is evidenced in the relation between pressure and isotropic strain. However, starting from zero pressure at the jamming point, a linear term with a quadratic correction describes the stress evolution rather well for a broad range of densities and for various polydispersities. Finally, an incremental evolution equation is proposed for both fabric and stress, as function of isotropic strain, and involving the coordination number and the fraction of rattlers, as starting point for further studies involving anisotropic deformations.

IgG adsorption on a new protein A adsorbent based on macroporous hydrophilic polymers: II. Pressure–flow curves and optimization for capture

Pressure–flow curves are obtained for a new protein A adsorbent matrix based on macroporous hydrophilic polymer beads with average diameter of 57 μm and a narrow particle size distribution. Experimental data are obtained in a 1 cm diameter laboratory column and in preparative scale columns with diameters of 20, 30, and 45 cm. The results are consistent with a model that assumes a linear relationship between bed compression and relative flow velocity. Surprisingly, the packing compressibility is essentially independent of column diameter for the preparative columns. As a result, after accounting for the variation in extraparticle porosity caused by compression, the column pressure drop is accurately predictable using the Carman–Kozeny equation. A model is also developed to predict productivity for IgG capture as a function of operating conditions based on dynamic binding capacity data presented in Part I of this work. For typical conditions, the model predicts maximum productivity at low residence times, between 1 and 1.5 min, when the dynamic binding capacity is at about 70–80% of the maximum. Combining the two models for column pressure and for dynamic binding capacity allows the design of preparative scale columns that maximize productivity while meeting specified pressure constraints.

Slurry pump gland seal wear

Gland sealing research since the 1950s by BHRA and others has aimed at improving seal (leakage) performance. The principal focus has been on uniform packing compression to more closely match the packing pressure distribution with the fluid (medium) pressure thereby reducing leakage over time. Published research on shaft sleeve/packing wear and seal reliability has typically focussed on a slurry free environment. Should a gland seal process environment deviate from ideal then the system must be more robust to tolerate the ingress of slurry particles. It is postulated that non uniform packing compression is not the sole contributor to gland seal life cycle cost and reliability. An improved scientific understanding of the tribological wear process is required for existing designs. This will lead to lower life cycle cost and improved reliability for end users. In slurry service particle size distribution, shape, and relative hardness with the shaft sleeve are expected to influence the useful life of the shaft sleeve and packing. In this work findings from experimental testing are discussed and a new wear model is proposed.

Effect of diathermy on pain and healing in tonsillectomy, compared with other methods of haemostasis: a randomised study

To compare three methods of haemostasis used for 'cold steel' tonsillectomy, in terms of pain scores and morbidity. Prospective, randomised, single-blinded, controlled clinical study. Three haemostasis methods were compared: compression of the tonsillar fossae with gauze packs; bipolar diathermy; and local anaesthesia then pack compression. The outcome measures were pain scores (derived from a visual analogue scale), peri-operative bleeding, and post-operative episodes of blood-stained saliva, consultation rate, tonsillar bed healing and days before return to regular diet. One hundred and five patients were included. Peri-operative bleeding was significantly reduced in the local anaesthesia group compared with the other two groups. Delayed post-operative tonsillar bed healing was noted in the diathermy group. No other significant differences were found between the three haemostasis groups, for any other outcome measures. The presence of blood-stained saliva was associated with higher pain scores. Diathermy and compression were associated with similar post-tonsillectomy morbidity.

Effect of particle size distribution and packing compression on fluid permeability as predicted by lattice-Boltzmann simulations

Massive parallel lattice-Boltzmann method simulations of flow through highly polydispersed spherical particle packings formed using Monte-Carlo methods were performed. The computed fluid permeabilities were compared to experimental data obtained from blocks made of three natural ground calcium carbonate powders compressed at different levels. The agreement with experimental measurements is excellent considering the approximations made. A series of flow simulations was also performed for packings of spherical particles compressed at different levels with increasing polydispersity modeled with both lognormal and Weibull size distributions. The predicted permeabilities were found to follow reasonably well the Carman–Kozeny correlation although an increasing deviation towards lower predicted permeabilities with increasing polydispersity was observed. Finally, following a careful analysis of the inherent numerical errors, an expression relating the Kozeny “constant” to the size distribution and compression level was derived from the simulation results, which led to a modified correlation.

A Study of Particle Packing Compression under Fluid Drag Force by DEM Simulations

AbstractMany chemical engineering processes, such as chromatography, filtration and drying, amongst others, involve particles in packed beds which undergo some deformation, caused by their own weight or by an external force, for instance, fluid drag force. In some cases, this deformation is of significant importance with regard to resistance to flow, heat and mass transfer. This paper examines the effect of fluid drag force upon a packed bed using the discrete element method (DEM) to simulate a process in which air blows through a packing of 14,000 soft spherical particles. The particles rearrange their locations and deform against one another due to the fluid drag force, which is derived from the Ergun equation. Changes throughout the bed in the voidage distributions, available inter‐phase contact area, pressure drops, and fluid flow field are presented. The influences of fluid superficial velocity, particle rigidness, and initial packing status upon the properties of the compressed particle bed are examined.

Toward a robust model of packing and scale-up for chromatographic beds. 1. Mechanical compression.

The packing of compressible biochromatographic resins at large scale suffers from a poor understanding of how column packing method, resin properties, and column geometry impact column performance. To improve understanding, we develop and evaluate a one-dimensional, continuum mechanics model of column packing by mechanical compression. We show that the model can quantitatively predict the change in bed height, applied stress, and internal axial porosity profile without adjustable parameters when the modulus and wall friction coefficients are determined independently. The model possesses theoretical relationships for wall support and resin rigidity that should enable it to describe the mechanical compression of any biochromatographic resin for any column diameter. Moreover, this framework could provide a path to analogous models for flow packing and dynamic axial compression.

Size exclusion chromatography on soft and semi-rigid packing materials in the dynamic axial compression mode

The effect of dynamic axial compression within a range of up to 5 bar upon the structure of the bed packed with soft and semi-rigid packing materials (Sephadex G-25, Bio-Gel P2 and Toyopearl HW-40) and the associated chromatographic parameters were studied for size exclusion chromatography. Continuous packing compression is accomplished by use of a special column with controlled external pressure applied to the packing. Compression has been shown to favor an overall increase in the resolution with pressure optima observed in some cases.

Calcium Oxalate Monohydrate Precipitation at Phosphatidylglycerol Langmuir Monolayers

Calcium oxalate monohydrate (COM) has been crystallized beneath Langmuir monolayers of four different phosphatidylglycerol lipids, allowing investigation of the influence of the density of headgroup packing and monolayer compressibility on heterogeneous precipitation. The COM crystals were nucleated from metastable solutions at Langmuir monolayers of the phospholipids dipalmitoylphosphatidylglycerol (DPPG), dioleoyphosphatidylglycerol (DOPG), palmitoyloleoylphosphatidylglycerol (POPG), and dimyristoylphosphatidylglycerol (DMPG). Crystal formation was monitored at the air/water interface using Brewster angle microscopy, and in transferred films with scanning electron microscopy. For each Langmuir monolayer it was observed that precipitation is heterogeneous and is selective with respect to the orientation and morphology of the precipitated crystals, with a majority of crystals having the (101̄) face oriented toward the monolayer interface. When the phospholipid monolayers are held at the same pressure, more crystals are observed under DPPG, which is the film with the smallest area per molecule. However, in apparent contrast, nucleation rates increase when the films are expanded. Also, when the four monolayers are held at the same area, nucleation occurs preferentially beneath films at lower surface pressures. The results suggest that the compressibility of the monolayer and the potential of the monolayer to achieve a small area per molecule are more important characteristics that lead to heterogeneous crystallization of COM than is providing a prearranged template. We also observe some evidence that domain boundaries between different monolayer phases can act as nucleation sites.

The COLUMBUS Standard Integral File Structure: A proposed interchange format

AbstractThe integral file structure used in the COLUMBUS Program System is described. This file structure is proposed for use as an interchange format for the exchange of information between various electronic structure codes. Access to the integral and density matrix arrays stored in the file structure is simplified by a supporting subroutine library. This library is portable across various computers and is readily available to programmers from the COLUMBUS distribution files. This library provides for the efficient processing of individual records, including the use of asynchronous I/O and the vectorized processing of packed orbital labels. The individual arrays are identified in a self‐defining and extensible manner, allowing for the addition of new integral types as demanded by the application. The format of the individual records is also self‐defining, allowing for the use of various packing and data compression methods within each record without burdening the calling program with unnecessary complications.

Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data

In this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone (MIZ). The derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression. In the MIZ, the flexure effect is important for short waves. For a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant. In turn, the exponential wave attenuation rate shows a rollover at short wave periods, whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease. The Labrador Ice Margin Experiment (LIMEX), conducted on the MIZ off the east coast of Newfoundland, Canada, in March 1987, provides us with aircraft synthetic aperture radar (SAR) imagery, wave buoy, and ice property data. On the basis of the wave number spectrum from the SAR data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during LIMEX '87, the dispersion relation has been estimated and compared with a model. Wave energy attenuation rates are estimated from SAR data and the ice motion package data which were deployed at the ice edge and into the ice pack, and compared with the model. The model‐data comparisons are reasonably good for the ice conditions observed during LIMEX '87. Some previously reported data of wave attenuation in the MIZ are revisited for model comparison.

Compression of two-dimensional packings of cylinders made of rubber and plexiglas

The stress—strain relationship for the compression of packings of cylinders can be expressed as a power law and it is found that the exponent is different from the microscopic exponent for the compression of two individual cylinders. Experiments with equal size Plexiglas cylinders with detection of stress paths by photoelasticity show that this discrepancy is due to variations in the number of active contacts in the packing as the load is varied. The effects of a mixture of materials with a strong contrast in properties is examined on the basis of percolation theory and it is shown that there are two thresholds: one for continuity and one for rigidity.

Unavoidable flow-rate errors in high-performance liquid chromatography

Two different types (low-pressure mixing and high-pressure mixing) of high-performance liquid chromatographic (HPLC) solvent delivery systems were evaluated for their flow-rate accuracy using three common hydro-organic mobile phases: methanol-water, acetonitrile-water and tetrahydrofuran-water. Both systems delivered flow-rates 2–12% lower than the desired (set) values, depending on the mobile phase composition. Further investigations revealed that these errors in flow-rate were due in part to non-ideal mobile phase behavior (non-zero volumes of mixing, non-zero compressibilities, pressure dependent viscosities, and deviations from Darcy's law) and non-ideal stationary phase behavior (column expansivity and packing compression). An approach to correct for the systematic errors in flow-rate is described for binary solvent mixtures. The approach utilizes correction factors based on non-ideal mobile and stationary phase behavior and has been experimentally confirmed for the mobile phases and columns we examined. Although approximate in nature, our approach reduces the systematic errors in flow-rate about ten-fold, and provides a means for estimating the instrumental contribution to flow-rate error as well. This leaves only an instrumental bias which can be measured and then factored out for all further experiments with that instrument. The resulting improvements in flow-rate accuracy provided by our approach will be extremely useful to researchers who need very accurate retention data for physicochemical measurements as well as to HPLC manufacturers and users for quality control and troubleshooting of these solvent delivery systems.

Wave Propagation in a Solid Ice Pack

The analysis presented in this paper was inspired by the report that the R/V Polarstern has encountered surface waves of large amplitude hundreds of kilometers inside the ice pack in the Weddell Sea. This paper presents analysis of processes that affect waves in an ice pack, namely the refraction of waves at the pack edge, the effects of pack compression on wave propagation, wave train stability and buckling stability in the ice pack. Sources of pack compression and interaction between wave momentum and pack compression are discussed. Viscous damping of propagating waves are also studied. Significant results include the conditions for total reflection of waves at the pack edge, the strong effect of pack compressive stress on wave group speed, with the concomitant possibility of extreme local concentration of wave energy. The result that compressive stress in the pack leads to very rapid development of wave packets, through changes in the parameters for weakly nonlinear modulational instability of the wave field is also notable. The analysis suggests an explanation for the change in wave dispersion observed from the ship between the time of first arrival of the waves and after the pack was partially broken up by the first waves.

Uniaxial compression of 2d and 3d packings : electrical conductivity measurements

We measured the conductivity of 2nd and 3d packings of conducting grains under a uniaxial vertical pressure. The conductance as a function of stress is a power law with an exponent which is different from the microscopic Hertz exponent. We propose a simple theoretical explanation Mesure de la conductivite d'empilements bi- et tridimensionnels de grains conducteurs soumis a une pression uniaxiale verticale. La conductance en fonction de la contrainte suit une loi de puissance dont l'exposant est different de l'exposant microscopique prevu par la loi de Hertz. On propose une explication theorique simple

Molecular packing and area compressibility of lipid bilayers.

Knowledge of the molecular packing of lipids and water in lipid bilayers is important for understanding bilayer mechanics and thermodynamics. Information on packing is most often obtained from x-ray or neutron diffraction measurements. Given the d spacing, composition, and partial specific volumes of the lipid and water, it is a simple matter to calculate the area per lipid molecule, bilayer thickness, and bilayer mass density. The partial specific volumes are commonly assumed to be those of bulk water and of lipid in excess water regardless of the degree of bilayer hydration. We present evidence here that these assumptions should be seriously questioned. At low hydrations, we find the head groups of egg and dioleoyl lecithin to be much less tightly packed than previously thought and the partial specific volume of water to be considerably smaller than 1 ml/g. Because the molecular packing affects the mechanical properties of bilayers, we use the results to reevaluate published experiments concerning the elastic area compressibility modulus of egg lecithin bilayers and the repulsive hydration force between bilayers.

Distribution of geometric structure parameters over the thickness of porous gauze metals

It has been established that the distribution of the clearance, specific surface, and hydraulic diameter of pores over the thickness of S200 gauze and PGM are essentially similar, which shows that these gauzes and PGM fabricated from them are structural analogs at small degrees of pack compression. It is therefore permissible to employ Eqs. (4)–(6) for calculating the parameters of PGM produced at degrees of compression ɛ⩽0.2. In view of the analogy between PGM and the starting gauze, it is possible to predict the properties of PGM from the geometric structure of the gauze and the conditions of the process by which the material is produced. Increasing the degree of compression of a gauze pack in rolling to 0.3 and more decreases the range of variation of the parameters Φ, dp.h, and Ssp in the direction perpendicular to the PGM surface compared with that in the starting gauze.

Prospective evaluation of hemostatic techniques for liver injuries.

The methods of hemostasis used for liver injuries were evaluated prospectively in 637 patients treated at Detroit General Hospital during a 5-year period. Variables evaluated included severity of injury, presence or absence of bleeding, and methods of hemostasis, The liver injury was either not bleeding or was controlled by temporary pack compression during laparotomy in 325 patients: none of these patients, including the 284 in whom no hemostatic procedure was used, rebled postoperatively. Active bleeding at laparotomy was directly related to the severity of liver injury, and required some hemostatic procedure in 312 patients. The methods of hemostasis were liver sutures (244 patients), nonanatomic resection (30 patients), anatomic resection (21 patients), hepatic artery ligation (nine patients), hepatotomy with intraparenchymal vascular control (five patients), and temporary internal pack with later re-operation (three patients). Rebleeding occurred in eight of the 243 patients who survived (seven after liver sutures and one after nonanatomic resection) and four required re-operation for control of bleeding. Sixty-nine patients with active bleeding died. Death on the table in 38 patients was related primarily to uncontrolled bleeding from liver and major vessel injury. Postoperative rebleeding from the liver occurred in 14 of 31 patients who died after surgery: following initial control by liver sutures (seven patients); anatomic resection (four patients); and hepatic artery ligation (three patients). There was no apparent relationship between any hemostatic procedure and the subsequent appearance of the hepatic ischemia or parahepatic abscess. Based on this experience, the merits and detriments of individual hemostatic procedures are presented.