Jan Skočilas

Determination of pressure drop coefficient by CFD simulation

The article deals with method applied to the verification of the turbulence models. The turbulence models were used in the simulation of the Newtonian fluid turbulent flow in the circular tube. The principle of the method is in the comparison of the pressure drop obtained by the simulation and the analytic solution. The parameters of the fluid flow were varied with the specified Reynolds number range. The pressure drop of inserted element in the pipe is evaluated.

Determination of the rheological properties of thin plate under transient vibration

The article deals with systematic analysis of the transient vibration of rectangular viscoelastic orthotropic thin 2D plate. The analysis is focused on specific deformation models of plate and for specific linear models of rheological properties. The viscoelastic isotropic and anisotropic (orthotropic) materials were investigated. The plate is loaded by general transient impulse. The time and coordinate dependencies of the fundamental quantities - displacements, rotations, stress and deformations in arbitrary points of plate under transient vibration, e. g. the analysis of stress and deformation waves in plates were investigated. The selected models are defined by constitutive equations for stress and deformation dependence. The isotropic and orthotropic model is considered. The analysis results depend on quality of the determined mechanical properties of the materials. The standard methods commonly used are time-consuming and not accurate enough. The new methodology of determining the material parameters directly from investigated plate is proposed and proven.

Squeezing flow of collagen solution – Mathematical model of shear and elastic behavior

This contribution deals with the problem of the squeezing flow of highly concentrated collagen solution (7%). The sample of collagen is compressed between two parallel disks of the texture analyzer instrument TA-XT2i. The bottom disk is fixed and the upper one is approaching at a constant velocity. During experiment the force acting on the moving plate is measured accurately. Total force – deformation dependence data sets were applied for evaluation of parameters of mathematical model having independent parameters for shear and elongation deformation regimes. Because lubricated Teflon foils are attached to the both plates a partial wall slip on plates is considered in the developed mathematical model assuming prevalence of the elongation flow contribution.

Finite Element Transient Dynamic Analysis of Laminated Composite Plates

In recent years, the requirements on the plane and space structures have been growing. The essential aim is to minimize weight and increase the strength and carrying capacity of these structures. One of the possible solutions is application of the layered structure composed from the composite materials. These materials represent the most effective utilization of potential possibilities of mass and energy savings not only from material point of view, but also with respect to structure usage. The article presents the Finite element method (FEM) solution of the displacement, velocity and acceleration distributions in the composite plates. The plate is unidirectional composite consisting of carbon fibers embedded in the epoxy matrix. FEM software ANSYS 11.0 has been used for analysis.

UNSTEADY FLOW OF THIXOTROPIC COLLAGEN SUBSTANCE IN PIPES

Unsteady flow of thixotropic liquid in pipes is solved by 1D and 2D numerical methods using the same constitutive equation — the only difference is in the radial diffusion of the structural parameter. Comparison shows that the neglected diffusion of structural parameter implicates a much stronger effect of thixotropy. The models are applied for analysis of the observed hysteresis of hydraulic characteristic of collagen.

Properties of Starch Based Foams Made by Thermal Pressure Forming

Packaging materials based on expanded polystyrene can be substituted by biodegradable foam, manufactured by direct or indirect electrical heating of a potato starch suspension in a closed mold. This paper deals with an experimental evaluation of selected properties of potato starch and starch foam related to this technology: density, specific heat capacity and specific electrical conductivity of a water suspension of potato starch within the temperature range up to 100 °C, and mass fraction from 5 to 65 %. The electric conductivity and heat capacity changes were observed during direct ohmic heating of a starch suspension between electrodes in a closed cell (feeding voltage 100 V, frequency 50 Hz). Specific electric conductivity increases with temperature, with the exception of the gelatinization region at 60 to 70 °C, and decreases with increasing concentration of starch (the temperature and concentration dependencies were approximated using the Lorentz equation). Direct ohmic heating is restricted by a significant decrease in effective electrical conductivity above a temperature of 100 °C, when evaporated steam worsens the contact with the electrodes. Experiments show that when direct ohmic heating is not combined with indirect contact heating, only 20 % of the water can be evaporated from manufactured samples and the starch foam is not fully formed. This is manifested by only a slight expansion of the heated sample. Only the indirect contact heating from the walls of the mold, with the wall temperature above 180 °C, forms a fixed porous structure (expansion of about 300 %) and a crust, ensuring suitable mechanical and thermal insulation properties of the manufactured product. The effective thermal conductivity of the foamed product (sandwich plates with a porous core and a compact crust) was determined by the heated wire method, while the porosity of the foam and the thickness of the crust were evaluated by image analysis of colored cross sections of manufactured samples. While the porosity is almost constant, the thickness of the crust is approximately proportional to the thickness of the plate.

Flow of bovine collagen in rectangular slit

This contribution deals with the investigation of the bovine collagen flow in the rectangular slit. The slightly compressible collagen liquid (9.5% mass fraction of native bovine collagen in water) was extruded by capillary rheometer of given geometry. A piston pushed the collagen sample from a container to the rectangular capillary. The extrusion rheometer is equipped by pressure sensors mounted at wall of capillary and manually adjusted hydraulic drive enables continuous variation of the piston velocity. The pressure profiles are measured in five places along the capillary simultaneously with increasing shear rate within the range from 1500 to 5000 s−1. It is possible to identify non-elastic shear flow characteristic and the compressibility of collagen matter.

ELECTRICAL AND THERMODYNAMIC PROPERTIES OF A COLLAGEN SOLUTION

This paper focuses on measurements of the electrical properties, the specific heat capacity and the thermal conductivity of a collagen solution (7.19% mass fraction of native bovine collagen in water). The results of our experiments show that specific electrical conductivity of collagen solution is strongly dependent on temperature. The transition region of collagen to gelatin has been observed from the measured temperature dependence of specific electrical conductivity, and has been confirmed by specific heat capacity measurements by a differential scanning calorimetry.

Analysis of hydraulic resistance in conical wye

The fluid flow in the standard pipe element was investigated. Standard CFD tool ANSYS Fluent was applied for fluid flow prediction. The numerical solutions for different turbulence models were compared with experimental data obtained from literature. The integral characteristics (pressure drop) of the pipe element – wye with two inlets and one outlet were used for validation of the numerical results. The air flows in the wye in the turbulent regime. The k-e, k-ω, and Reynolds Stress model and their modifications were applied for turbulence modelling. Two meshes (coarse and fine) of the model were investigated. The models exhibit good agreements with experimental data.

Hydraulic characteristic of collagen.

ally increasing and decreasing flow rates (hysteresis means that the pressure drop curve during increased flow rate is above the pressure drop during decreasing flow rate) was observed. The problem was initiated by industry and by demand for an on-line recording of rheological properties of collagenous material used for extrusion of collagen casings. The Herschel-Bulkley rheological model was capable to describe rheograms in a wide range of deformation rates; however it was not able to describe and explain the hysteresis. As a possible reason thixotropic properties were identified and the hydraulic characteristic was calculated using a thixotropic generalisation of the Herschel-Bulkley model. The developed 1D numerical model can be applied for on-line modelling of transient flows of incompressible thixotropic food materials (startup flow) and at a limited range of flow rates it is also capable to describe the hysteresis of hydraulic characteristics.