Browsing by Subject "Extrusion"

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Macroscopic rheology of non-Brownian suspensions at high shear rates: the influence of solid volume fraction and non-Newtonian behaviour of the liquid phase
(2021) Wilms, Patrick; Hinrichs, Jörg; Kohlus, Reinhard
Modelling the macroscopic rheology of non-Brownian suspensions is complicated by the non-linear behaviour that originates from the interaction between solid particles and the liquid phase. In this contribution, a model is presented that describes suspension rheology as a function of solid volume fraction and shear rate dependency of both the liquid phase, as well as the suspension as a whole. It is experimentally validated using rotational rheometry ( ≤ 0.40) and capillary rheometry (0.55 ≤ ≤ 0.60) at shear rates > 50 s−1. A modified Krieger-Dougherty relation was used to describe the influence of solid volume fraction on the consistency coefficient, , and was fitted to suspensions with a shear thinning liquid phase, i.e. having a flow index, , of 0.50. With the calculated fit parameters, it was possible to predict the consistency coefficients of suspensions with a large variation in the shear rate dependency of the liquid phase ( = 0.20–1.00). With increasing solid volume fraction, the flow indices of the suspensions were found to decrease for Newtonian and mildly shear thinning liquid phases ( ≥0.50), whereas they were found to increase for strongly shear thinning liquid phases ( ≤0.27). It is hypothesized that this is related to interparticle friction and the relative contribution of friction forces to the viscosity of the suspension. The proposed model is a step towards the prediction of the flow curves of concentrated suspensions with non-Newtonian liquid phases at high shear rates.
Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows
(2021) Wilms, Patrick; Wieringa, Jan; Blijdenstein, Theo; van Malssen, Kees; Kohlus, Reinhard
The rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.
Storable cheese curd—effect of milk homogenization as a pre-treatment and freezing and extrusion of cheese curd on production of pasta filata style cheese
(2024) Schmidt, Florian; Graf, Britta; Hinrichs, Jörg; Schmidt, Florian; Institute of Food Science and Biotechnology, Department of Soft Matter Science and Dairy Technology, University of Hohenheim, Garbenstrasse 21, 70599, Stuttgart, Germany; Graf, Britta; Institute of Food Science and Biotechnology, Department of Soft Matter Science and Dairy Technology, University of Hohenheim, Garbenstrasse 21, 70599, Stuttgart, Germany; Hinrichs, Jörg; Institute of Food Science and Biotechnology, Department of Soft Matter Science and Dairy Technology, University of Hohenheim, Garbenstrasse 21, 70599, Stuttgart, Germany
This study investigates the production of pasta filata style cheese from a storable, frozen intermediate material. Homogenization (2–16 MPa, single-staged) of milk (fat/protein = 0.9) was used as a tool to decrease fat globule size and consequently fat losses. Plasticization was achieved by using a single-screw extruder set up with double-jacketed hot water cycle. Non-frozen and frozen cheese curd as well as the extruded pasta filata style cheese pre-treated with different homogenization pressure was analyzed regarding the thermo-rheological properties. Fat and protein gain/loss during extrusion was evaluated by analyzing fat in dry matter (FDM) and protein in dry matter (PDM) before and after extrusion. Homogenization of cheese milk leads to a reduction of tan δ for thereof produced raw cheese curd material as well as the extruded products. Freezing and extrusion counteract the reduction of tan δ . A homogenization pressure of 8 MPa is sufficient to prevent fat losses during extrusion while still maintaining plasticization of the product for fresh and frozen material, respectively. The FDM after extrusion is 0.8% higher for fresh material and 4.9% higher for frozen material, which means that the fat concentrates during extrusion due to water loss. Moreover, there is no loss of PDM for all samples, regardless of the homogenization pressure. A combination of homogenization pressure, freezing, and extrusion leads to a plasticizable product without losses of fat and protein. Hence, frozen cheese curd can be used as a storable intermediate.