Fakultät 10 / Institut Allgemeiner Maschinenbau
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The article presents results of an analytical and numerical modeling of electron fluid motion and heat generation in a rectangular conductor at an alternating electric potential. The analytical solution is based on the series expansion solution (Fourier method) and double series solution (method of eigenfunction decomposition). The numerical solution is based on the lattice Boltzmann method (LBM). An analytical solution for the electric current was obtained. This enables estimating the heat generation in the conductor and determining the influence of the parameters characterizing the conductor dimensions, the parameter M (phenomenological transport time describing momentum-nonconserving collisions), the Knudsen number (mean free path for momentum-nonconserving) and the Sh number (frequency) on the heat generation rate as an electron flow passes through a conductor.
In a supersonic flow, disturbances of different parameters arise. These perturbations can have a significant impact on the interaction of the flow with the surface. When gas flow passes through a shock wave, perturbations are transformed depending on the initial parameters of the flow. Therefore, it is important to be able to correctly assess the intensity of these transformations. In this work, for the first time, a method has been proposed that allows us to estimate the dynamics of variation of disturbances of flow parameters when passing through an oblique shock wave. The influence of the shock wave inclination angle β, Mach number, intensity of disturbances of velocity, density, temperature, and pressure in front of the shock wave on perturbations of the flow parameters behind the shock wave was investigated. The Mach numbers ranged from 1.2 to 10 and the shock wave inclination angle varied from 15° to 90°. It was shown that the interaction of a supersonic gas flow with an oblique shock wave has a significant effect on the transformation of the perturbations of the flow parameters. The perturbations of temperature and pressure behind the shock wave increase significantly with the increasing angle β and Mach number in front of the shock wave. With the increasing Mach number, the velocity perturbations behind the shock wave first increase, then decrease, passing through a maximum, and afterwards the flow becomes more stable.
Symmetry transformation methods are widely used in fluid flow problems. One such method is renormalization group analysis. Renormalization group methods are used to develop a macroscopic turbulence model for non-Newtonian fluids (Oldroyd-B type). This model accounts for the large-distance and large-time behavior of velocity correlations generated by the momentum equation for a randomly stirred, incompressible flow and does not account for empirical constants. The aim of this mathematical study was to develop a k -ε RNG turbulence model for non-Newtonian fluids (Oldroyd-B type). For the first time, using the renormalization procedure, the transport equations for the large-scale modes and expressions for effective transport coefficients are obtained. Expressions for the renormalized turbulent viscosity are also derived. This model explains the phenomenon of the abrupt growth of the irregularity of velocity at low values of the Reynolds number.
Laser welding has become well established for joining Ni-Ti-based shape memory alloys and extends the manufacturability of highly functional components with complex geometries. Published studies on the effect of laser welding on alterations to microstructure and properties of these alloys, however, mainly deal with conventional component dimensions and linear laser beam movement. In view of the increasing importance of microtechnology, research into joining of thin-walled Ni-Ti components is therefore of interest. At the same time, studies comparing oscillating and linear beam movement on other materials and the authors’ own work on Ni-Ti materials suggest that oscillating beam movement has a more favorable effect on alterations in material properties and microstructure. Therefore, laser welding of foils made of Ni55/Ti45 with 125 µm thickness was systematically analyzed using a fiber laser and circular oscillation. Amplitude A and frequency f were varied from 0 to 200 µm and 0 to 2000 Hz, respectively. Microstructural analysis showed that by increasing the frequency, grain refinement could be achieved up to a certain value of f . An increasing amplitude led to decreasing hardness values of the weld seam, while the influence of f was less pronounced. The analysis of the weld material using chip calorimetry (Flash DSC) revealed that the beam oscillation had fewer effects on the change in transformation points compared to a linear beam movement.
This article theoretically investigates the interaction of a normal shock wave in a flow with chemical reactions under high-temperature conditions. The main novelty of the work is that the thermal effect of chemical reactions is modeled as a function of the temperature. A modified Rankine–Hugoniot model for a shock wave in a flow with chemical reactions has been developed. It is shown that for an exothermic reaction the pressure jump increases with increasing Arrhenius numbers. This is due to the additional energy introduced into the flow as heat is released during the chemical reaction. For endothermic reactions, the opposite trend is observed. The change in the speed of the adiabatic gas flow as it passes through a normal shock wave depending on the type of chemical reaction is clarified. The study provides comparisons between the results of the analytical and numerical solutions of the modified Hugoniot adiabatic equations.
During the past ten years, lots of new data-driven products and services for tools, machinery and equipment have been developed. While several new players from other industries gained a certain market share, plant and machinery producers also started to enhance their portfolio to take on new data-driven products and services because of the technological changes in Industry 4.0. As a first part of the research, an extensive market study was carried out to analyze how many German companies already offer data-based products and services in addition to their core machines and understand what kind of offerings they make. To classify these offerings, a scheme based on established Industry 4.0 maturity models was developed. In brief, the market for data-driven products and services is still developing, with few technology leaders and fast movers taking the largest share. While the market study gave an overview of what was on offer, the second part of this contribution analyzes how the fast movers with a high level of Industry 4.0 maturity conducted their data-driven services and products. Thus, these few companies were analyzed in more detail, based on public material as well as subsequent expert interviews. Most fast movers in this study relied on the same patterns and approaches, especially when looking at organizational issues such as customer-driven innovation, agile organization of operations, mixed teams, partnering and portfolio enhancement.
The present study investigates the entropy generation of chemically reactive micropolar hybrid nanoparticle motion with mass transfer. Magnetic oxide (Fe3O4) and copper oxide (CuO) nanoparticles were mixed in water to form a hybrid nanofluid. The governing equations for velocity, concentration, and temperature are transformed into ordinary differential equations along with the boundary conditions. In the fluid region, the heat balance is kept conservative with a source/sink that relies on the temperature. In the case of radiation, there is a differential equation along with several characteristic coefficients that transform hypergeometric and Kummer’s differential equations by a new variable. Furthermore, the results of the current problem can be discussed by implementing a graphical representation with different factors, namely the Brinkman number, porosity parameter, magnetic field, micropolar parameter, thermal radiation, Schmidt number, heat source/sink parameter, and mass transpiration. The results of this study are presented through graphical representations that depict various factors influencing the flow profiles and physical characteristics. The results reveal that an increase in the magnetic field leads to a reduction in velocity and entropy production. Furthermore, temperature and entropy generation rise with a stronger radiation parameter, whereas the Nusselt number experiences a decline. This study has several industrial applications in technology and manufacturing processes, including paper production, polymer extrusion, and the development of specialized materials.
Tire wear is a main contributor to microplastics. As we cannot fully avoid tire wear, otherwise we could not brake and stop, new solutions are needed to address this problem. Not only on roads tire wear is released to the environment, even more can be found at airports. The advantage there is that the Tire Wear Airstrip Particles are gathered while cleaning the pavement. This collection is an opportunity to recycle and add new value to it. Whereas rubber powder is a common way to recycle and reuse end-of-life-tires as raw material in rubber compounds, the question is if TWAP is reusable in the same or similar way. In this study TWAP and rubber powder from truck tire treads are analyzed and compared with regard to their morphology, particle size distribution and composition. The particle size distribution of TWAP is broader than rubber powder containing also much smaller particles. The mineral content of TWAP is about 60%. These minerals can be residues of the pavement, brake wear but also rubber ingredients. In comparison to rubber powder, the impurities of TWAP are expected to have an impact with regard to potential applications and should be better separated.
Pyrolysis is becoming increasingly important in the context of recycling and the volume of end-of-life tires worldwide. Sustainable carbon black (sCB), which is produced from pyrolysis oil instead of crude oil, and recovered carbon black (rCB), which is the remaining solid from pyrolysis, are promising secondary raw materials for rubber compounds as a substitute for industrial carbon black produced from fossil resources. This study investigates the possibility of substituting carbon black N550 partially or fully in an EPDM (Ethylene Propylene Diene Monomer) sealing compound. rCB contains impurities that affect the properties of the compound. Aging at higher temperatures, in the presence of oxygen is studied. The properties of the compounds are evaluated after heat treatment in air at different temperatures for up to 6 weeks. The results show that sCB is very close to N550 as a raw material and in terms of its in-rubber properties. Due to the impurities, rCB alters the cross-linking density and structure of the polymer-sulfur network (shift to polysulfidic structure). Lower reinforcement is also observed, which is related to weaker polymer-filler (decrease of I3/1 for sCB by 3% and rCB by 43% related to vCB) and filler-filler interactions. Aging effects are also more pronounced in the compounds containing rCB.
Rupture discs, also known as bursting discs, are indispensable components in fluid-operated systems providing effective protection against hazardous over-pressure or partial vacuum. They belong to a special class of safety devices and are found in a variety of technical applications including pressure vessels, piping systems, reactors and boilers. In all application scenarios, rupture discs act as sacrificial parts that have to fail precisely at a predetermined differential pressure, opening a relief flow path for the working fluid. The membrane employed within rupture discs is usually made out of specific metal alloys or different material layers depending on the particular application. However, for many manufacturers of rupture discs, the production process is characterized by a lack of systematic procedures, relying instead on trial and error as well as empirical values. By means of thorough finite-element-based modeling and simulation of the bulge-forming process of rupture discs, including an elastic–plastic material law, large deformation, as well as contact mechanics, it is possible to accurately predict the resulting stress–strain behavior. All simulation results are rigorously validated through corresponding experiments conducted during the bulge-forming process. Therefore, this contribution provides a reliable basis for the parameter set-up during the manufacturing process of rupture discs.