Siegfried Ripperger

Effect of membrane length, membrane resistance, and filtration conditions on the fractionation of milk proteins by microfiltration

We investigated the fractionation of casein micelles and the whey protein β-lactoglobulin (β-LG) of skim milk by crossflow microfiltration (0.1 μm) for the first time by a novel approach as a function of membrane length and membrane resistance. A special module was constructed with 4 sections and used to assess the effects of membrane length by measuring flux and β-LG permeation (or transmission) as a function of transmembrane pressure and membrane length. Depending on the position, the membranes were partly controlled by a deposit layer. A maximum for β-LG mass flow through the various membrane sections was found, depending on the position along the membrane. To study the effect of convective flow toward the membrane, membranes with 4 different intrinsic permeation resistances were assessed in terms of the permeation and fouling effects along the flow channel. From these findings, we derived a ratio between transmembrane pressure and membrane resistance, which was useful in reducing the effect of deposit formation and, thus, to optimize the protein permeation. In addition, the fouling effect was investigated in terms of reversible and irreversible fouling and, in addition, by differentiation between pressure-induced fouling and adsorption-induced (pressure-independent) fouling, again as a function of membrane length.

Polydisperse particle size characterization by ultrasonic attenuation spectroscopy for systems of diverse acoustic contrast in the large particle limit

Ultrasonic attenuation spectroscopy offers advantages over other spectrometric methods for the determination of suspension and emulsion size distributions. One advantage is the possibility of conducting measurements in highly concentrated or optically opaque dispersions. Models useable for the inversion of measured attenuation spectra to calculate particle size distributions are available and widely used, but their applied forms only allow for the characterization of particles smaller than 10μm. In this paper, a methodology using the Faran model for elastic scatterers is examined in the region of micrometer-sized particles with respect to its suitability for the prediction of measured attenuation spectra and size distributions of various material combinations. All selected particle fractions and fluid materials were characterized independently from ultrasonic attenuation spectroscopy with respect to their material properties, size distributions, and shape. A comparison of measured and calculated attenuation spectra shows an acceptable agreement. The chosen methodology for particle sizing applications is further confirmed if a fit of the model to the measurement data is performed. In this approach, the solids volume fraction is treated as the only fit parameter. The findings indicate that the methodology is suitable for polydisperse particle size characterization for a wide range of acoustic contrast.Ultrasonic attenuation spectroscopy offers advantages over other spectrometric methods for the determination of suspension and emulsion size distributions. One advantage is the possibility of conducting measurements in highly concentrated or optically opaque dispersions. Models useable for the inversion of measured attenuation spectra to calculate particle size distributions are available and widely used, but their applied forms only allow for the characterization of particles smaller than 10μm. In this paper, a methodology using the Faran model for elastic scatterers is examined in the region of micrometer-sized particles with respect to its suitability for the prediction of measured attenuation spectra and size distributions of various material combinations. All selected particle fractions and fluid materials were characterized independently from ultrasonic attenuation spectroscopy with respect to their material properties, size distributions, and shape. A comparison of measured and calculated attenuati...

MEASUREMENT OF ADHESION FORCES IN AIR WITH THE VIBRATION METHOD

The vibration method represents a practical method for the measurement of adhesion forces and adhesion force distributions. This method causes sinusoidally alternating stresses and yields detachment and contact forces between particles and substrate of the same order of magnitude. Alternating contact forces of the vibration method can cause an adhesion force intensification through flattening of asperities. The measuring principle of the vibration method and the analysis of experimental results are described in the article. Normal adhesion forces (pull-off forces) are measured using the vibration method and the colloidal probe technique. The results of both methods show good agreement for small particle sizes. The influence of the detachment force direction is shown by comparing tangential and normal adhesion forces measured using particle reentrainment in a turbulent air flow and the vibration method, respectively. The surface roughness of the substrate and the relative humidity are shown to significantly influence the measured adhesion forces. For the calculation of the adhesion forces, an approach by Rabinovich was combined with approximations of plastic micro asperity flattening. The Rabinovich approach accounts for roughness effects on the van der Waals force by incorporating the rms roughness of the interacting surfaces. rms-values of the particles and substrates were measured with atomic force microscopy at different scanning areas.

Characterization of An Open-Pored Nickel Foam with Respect to Aerosol Filtration Efficiency by Means of Measurement and Simulation

The deposition of micron and submicron particles in metallic, ceramic, or synthetic open-pored foams is a special field of aerosol filtration in porous media. This is due to the more complicated pore structure than, for example, fibrous filter media. Therefore, the measurement as well as the simulation of aerosol filtration in open-pored foams involves certain custom-built techniques. The filter efficiency for micron and submicron particles can be measured by differential electrical mobility analyser systems (DEMAS) or optical particle counters (OPC). Empirical formulas are available in literature for open-pored polyurethane foams to determine their aerosol filtration efficiency and pressure drop. An additional method for characterization is direct numerical simulation (DNS) by means of a three-dimensional (3D) model of the pore structure. These models can be obtained either by tomography or by mathematical generation. In this work, the filter efficiency of an open-pored nickel foam with a cell diameter of 450 μm is determined by the methods previously mentioned. The experimental results are in good agreement with the results of the 3D simulation and a semi-empirical approach for polyurethane foams is adapted for a nickel foam. Copyright 2015 American Association for Aerosol Research

Performance of Single and Double Shaft Disk Separators

Rotating disks separators, mounted on single and double hollow shafts, are investigated experimentally. The shaft and disks were enclosed in stainless steel housing. Many parameters were measured to study their influence on the performance of single and double shaft disk filters at various rotation speeds. These parameters are pressure inside the housing, permeate flux, and electrical power consumption. The average velocity coefficient k ˜ for single and double shaft disk separators was estimated and was found to be a good criterion of module performance as well. The comparison of measured and calculated filtration flow rate at various rotation speeds was in a good agreement. The estimated average shear stress is found to be about twice in double shaft filter disk. The feasibility of double shaft disk separator in treating filtration without filter cake is highly appreciated.

Determination of Bulk Flow Property of tef Flour and Seed and Design of a Silo

The flowability of the bulk materials was determined after development of yield locus, wall yield locus, and effect of time consolidation was measured. Data from the obtained curves were read and important parameters such as unconfined stress, major consolidation stress, angle of internal friction, angle of wall friction, and effective angle of internal friction were for further design of silo calculation made ready. Diagrams and relationships developed by Jenike were used to find important silo discharge opening parameters such as the angle of the conical or wedge shaped opening and critical silo opening diameter and width. The relative difference between tef flour and tef seed was made in which the flour has a characteristics indicator of particle size distribution with lower dimension and the flour is cohesive and less flowable and accordingly needs more generous discharge parameters. The comparison between the flour and the seeds was shown in the measurement of flowability indexes and also reflected clearly on the designed silo discharge opening parameters.

Heterogeneous Condensation of Water Vapor on Nanoparticles in a Membrane-Based High-Flow Process Monitored by a New In Situ Measuring Cell

This article presents a membrane-based process to improve separation efficiency of airborne particles by heterogeneous condensation of water vapor. A plant was set up in laboratory scale to control the supersaturated state of water vapor in air accurately. Droplet growth due to heterogeneous condensation is investigated experimentally and supersaturation is calculated by solving the differential equations for heat and mass transfer in a laminar gas flow. The apparatus is based on a water condensation particle counter (WCPC). It operates with several growth tubes in parallel thereby allowing higher aerosol throughput. The increase of particle size based on heterogeneous condensation is detected by an in situ measuring system. Therefore a new measuring cell was operated with well-defined test aerosols differing in wetting abilities and initial nuclei size. First results of particle activation and condensational droplet growth are presented. Copyright 2015 American Association for Aerosol Research

Controlled Generation of Nanoscale Organic Pigments by Adiabatic Expansion in Laval Nozzles and in Expanding Free Jets

As organic pigments are produced mainly in wet chemical processes, a novel gas to particle process for generating organic nanoscale pigments is introduced. This process is based on the expansion of a nearly saturated gas flow from an overpressure regime to ambient pressure conditions. The expansion is achieved in a Laval nozzle and subsequently continues as an expanding free jet in an expansion chamber. This expansion chamber is equipped with an adjustable cooling system. Copper phthalocyanine and Paliogen Red, two organic pigments, were used as test materials. By controlling the temperature in the expansion chamber, particularly in the free jet, nanoscale pigments with high (needle shape) to low (grainy shape) aspect ratios are generated. Particle size distribution measurements as well as scanning electron microscopy and transmission electron microscopy analyses show that newly generated particles differ significantly in size and shape from the cubic-shaped bulk material. Particles with low aspect ratio are below 100 nm in all dimensions. Hence, specific control of temperatures in the expanding free jet offers a tool to produce nanoscale organic pigments with defined particle sizes.

A New Method for the Classification of Micron and Submicron Particles

A new technique for the separation and reduction of fine particle fractions in the lower micron and submicron range was introduced. Experiments demonstrated high-grade efficiencies down to cut points of 0.5 μm with a very small quantity of misplaced material.

Statistical Extinction Method for the Inline Monitoring of Particle Processes

The object of this study is to develop a particle measurement system on the basis of the Statistical Extinction Method, which provides an inline monitoring of different particle processes. The Statistical Extinction Method determines from the mean value and root mean square deviation of a transmission signal through a particle collective, a mean particle size and a particle concentration. For the determination of particle size distribution, an advanced Statistical Extinction Method is developed and verified. This method requires the measurement of transmission signals of several light beams of different beam cross sections through a particle collective.