@article{36983, abstract = {{AbstractThe use of structured measuring systems to prevent wall slip is a common approach to obtain absolute rheological values. Typically, only the minimum distance between the measuring surfaces is used for further calculation, implying that no flow occurs between the structural elements. But this assumption is misleading, and a gap correction is necessary. To determine the radius correction $$\Delta r$$ Δ r for specific geometries, we conducted investigations on three Newtonian fluids (two silicon oils and one suspension considered to be Newtonian in the relevant shear rate range). The results show that $$\Delta r$$ Δ r is not only shear- and material-independent, but geometry-dependent, providing a Newtonian flow behaviour in a similar viscosity range. Therefore, a correction value can be determined with only minute deviations in different Newtonian fluids. As the conducted laboratory measurements are very time-consuming and expensive, a CFD-approach with only very small deviations was additionally developed and compared for validation purposes. Therefore, simulation is an effective and resource-efficient alternative to the presented laboratory measurements to determine $$\Delta r$$ Δ r for the correction of structured coaxial geometries even for non-Newtonian fluids in the future.}}, author = {{Josch, Sebastian and Jesinghausen, Steffen and Dechert, Christopher and Schmid, Hans-Joachim}}, issn = {{0035-4511}}, journal = {{Rheologica Acta}}, keywords = {{rheology, rheometry, suspension, coaxial, correction}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Experimental and simulative determination and correction of the effective gap extension in structured coaxial measuring systems}}}, doi = {{10.1007/s00397-023-01383-2}}, year = {{2023}}, } @article{31035, abstract = {{AbstractFurther innovation in the field of selective laser sintering (SLS) is strongly connected to the availability of new materials since the market is dominated by polyamide 12 (>90%). The aim of this publication is to develop a descriptive model for the droplet formation process in a Filament Extension Atomizer to predict the applicability to exploit further polymers for the SLS process. The feasibility was tested, investigated and characterized using a “Dripping out of a nozzle” setup for uniaxial extension. The droplet formation process was then observed via high-speed camera imaging and classified for certain parameters. The experiments were carried out using semi-diluted polyethylene oxide (600–4000 kg/mol), glycerol and water solutions as model fluids. Driven by the Plateau-Rayleigh instability, different types of spherical droplets were observed and various droplet formation mechanisms demonstrated and analyzed. Based on the experimental results, a predictive model is derived to describe various essential parameters.}}, author = {{Neukötter, Moritz and Jesinghausen, Steffen and Schmid, Hans-Joachim}}, issn = {{0035-4511}}, journal = {{Rheologica Acta}}, keywords = {{Rheology, SLS, Lasersintering, exensional rheology}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Model droplet formation in extensional filament stretching within a Filament Extension Atomizer}}}, doi = {{10.1007/s00397-022-01339-y}}, year = {{2022}}, } @inproceedings{43238, author = {{Rüther, Torben and Jesinghausen, Steffen and Schmid, Hans-Joachim}}, keywords = {{Couette, Rheology, Correction}}, location = {{Sevilla}}, title = {{{A novel correction method for the shear rate in a couette rheometer (Vortrag)}}}, year = {{2022}}, } @article{21949, abstract = {{This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries. The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.}}, author = {{Haist, Michael and Link, Julian and Nicia, David and Leinitz, Sarah and Baumert, Christian and von Bronk, Tabea and Cotardo, Dario and Eslami Pirharati, Mahmoud and Fataei, Shirin and Garrecht, Harald and Gehlen, Christoph and Hauschildt, Inga and Ivanova, Irina and Jesinghausen, Steffen and Klein, Christopher and Krauss, Hans-W. and Lohaus, Ludger and Lowke, Dirk and Mazanec, Oliver and Pawelczyk, Sebastian and Pott, Ursula and Radebe, Nonkululeko W. and Riedmiller, Joachim Jürgen and Schmid, Hans-Joachim and Schmidt, Wolfram and Secrieru, Egor and Stephan, Dietmar and Thiedeitz, Mareike and Wilhelm, Manfred and Mechtcherine, Viktor}}, issn = {{1359-5997}}, journal = {{Materials and Structures}}, keywords = {{Rheology, Wall Slip, Slip, apparent slip, suspension, cement, concrete}}, title = {{{Interlaboratory study on rheological properties of cement pastes and reference substances: comparability of measurements performed with different rheometers and measurement geometries}}}, doi = {{10.1617/s11527-020-01477-w}}, year = {{2020}}, } @article{21947, abstract = {{Wall slip is a long-known phenomenon in the field of rheology. Nevertheless, the origin and the evolution are not completely clear yet. Regarding suspensions, the effect becomes even more complicated, because different mechanisms like pure slip or slip due to particle migration have to be taken into account. Furthermore, suspensions themselves show many flow anomalies and the isolation of slip is complicated. In order to develop working physical models, further insight is necessary. In this work, we measured experimentally the wall slip velocities of different highly filled suspensions in a rectangular slit die directly with respect to the particle concentration and the particle size. The slip velocities were obtained using a particle image velocimetry (PIV) system. The suspensions consisting of a castor oil–cinnamon oil blend and PMMA particles were matched in terms of refractive indexes to appear transparent. Hereby, possible optical path lengths larger than 15 mm were achieved. The slip velocities were found to be in a quadratic relation to the wall shear stress. Furthermore, the overall flow rate as well as the particle concentration has a direct influence on the slip. Concerning the shear stress, there seem to be two regions of slip with different physical characteristics. Furthermore, we estimated the slip layer thickness directly from the velocity profiles and propose a new interpretation. The PIV technique is used to investigate the viscosity and implicit the concentration profile in the slit die. It is shown that the particle migration process is quite fast.}}, author = {{Jesinghausen, Steffen and Weiffen, Rene and Schmid, Hans-Joachim}}, issn = {{0723-4864}}, journal = {{Experiments in Fluids}}, keywords = {{Rheology, Wall Slip, Slip, apparent slip, suspension}}, title = {{{Direct measurement of wall slip and slip layer thickness of non-Brownian hard-sphere suspensions in rectangular channel flows}}}, doi = {{10.1007/s00348-016-2241-6}}, year = {{2016}}, }