Ultra low temperature microturbine for magic angle spinning system

We investigate the fluid dynamics of a microturbine system that is applied in a device for chemical and biological analysis—a so-called magic angle spinning (MAS) nuclear magnetic resonance (NMR) probe. The present system is utilized in a wide temperature range from 45K to 293 K. Pressurized air, nitrogen, or helium are used to drive a Pelton type microturbine. This turbine is mounted on a MAS rotor with a diameter between 0.7mm and 3.2 mm. The rotor system is equipped with a pressurized gas bearing that is operated by the same gas species as the turbine. Computational fluid dynamics (CFD) simulations have been performed and compared with fluid dynamics measurements of the MAS system for different diameters, temperatures, and spinning rates between 23 kHz and 120 kHz. To our knowledge, this work is the first comprehensive CFD and experimental study of such a wide temperature range that has been carried out for microturbines with pressurized gas bearings. The results show good agreement between measurements and CFD simulations with appropriate (real) gas models, i.e., the ideal gas model for air at room temperature, Peng–Robinson model for nitrogen at 105 K, and ideal gas model for helium at 45 K

Eccentric Taylor-Couette Flow with orbital motion of the inner cylinder

Abstract: The flow in a Taylor-Couette system is one of the most explored flows today. The behaviour of the flow is characterized by Reynolds number, radii and aspect ratio. By reducing the gap width the TaylorCouette system can be used as a simplified bearing model which has one additional feature. To cover flow effects of a real bearing the rotating inner cylinder moves on an offset track. Thus the system is also characterized by a varying annulus. That changes the eccentricity which is also related to the critical Reynolds number for the system. There is a higher Reynolds number for a higher eccentricity. This is used as a benchmark to validate the code. Depending on the eccentric position of the rotating inner cylinder one can notice either Taylor Vortex flow or Couette Flow. After testing the code the gap width will be adjusted to realistic bearing geometries. This second part refers to bearing simulations where the gap width is adjusted to real bearing conditions. In Fact the present system is a simplified bearing, which covers not all details of a real one. It becomes more complex in later stages of the project, where oil feedings and notches are implemented as well as the occurrence of cavitation. Furthermore the offset tracks will be much more complex. The final goal is to develop a 3D simulation tool for hydrodynamic journal bearings that resolves effects like cross flow from the oil feedings and also cavitation. Known methods based on the Reynolds equations fail to predict important flow characteristics in complex bearing geometries due to their two dimensional nature. If sufficiently low local pressure areas occur, cavitation-related damages may appear. So the pressure distribution of the flow is of interest

Investigation of CO2 Release Pressures in Pipeline Cracks

AbstractThe Carbon Capture and Storage technology can reduce the emissions of carbon dioxide. Within this technology CO2 is segregated from facilities with high pollutant emissions, transported by pipelines and stored in underground geological formations. In this work release pressures in pipeline puncture failures were investigated. In most cases corrosion or obsolescence are the reasons for pipeline damages. CO2 will then escape from the pipeline and disperse. There are some studies of CO2 dispersions but with different assumptions concerning pipeline release pressures. In this work computational fluid dynamics simulations were done to reduce the uncertainties regarding the pressure in pipeline cracks

Numerical simulations of gas-liquid flow in thermal sorption processes

Thermal storage systems, used, e.g., for domestic heating, must be able to compensate the mismatch between supply and demand. The most efficient techniques for thermal storage are based on sorptionstorage processes. Usually in sorption, the adsorption process occurs in combination with a solid stateadsorbent, whereas absorption takes place in a liquid/gas system. During such sorption processes the flow behavior of the carrier medium is crucial for the efficiency of a falling film absorber. In this work the hydrodynamics of the falling liquid film in two geometrical setups, namely on an inclined plane and over two horizontal parallel tubes, is studied. For the simulation the Eulerian-Eulerian model of the software ANSYS CFX and the interFoam application of the open source software OpenFOAM were used. The numerical results of the two geometries were compared with each other and also with existing data from literature to predict the performance of a sorption storage regarding the specific wetted area and the needed height for gravity driven film absorption

Benchmark simulations of flow past rigid bodies using an open-source, sharp interface immersed boundary method

###EgeUn###This study reports benchmark results for a new immersed boundary method based finite-volume solver within the framework of the open-source toolbox foam-extend 3.2. The immersed boundary formulation uses a discrete forcing approach based on a weighted least squares approximation that preserves the sharpness of the boundary. Five test cases with increasing complexity are used. Results are also presented for the flow past a low-aspect-ratio plate that pitches about its leading edge at a Reynolds number of 2000. Force coefficient results are compared with available experimental and computational data. The results show that foam-extend 3.2 appears to be a promising open-source tool for solving flows with steady and unsteady immersed boundaries

Aerodynamic optimization of a microturbine inserted in a magic-angle spinning system

The fluid dynamics of a microturbine system that is applied in a device for chemical and biological analysis – a so-called magic-angle spinning (MAS) probe – is investigated. The drive fluid is pressurized air at ambient temperature provided by nozzles aligned on an intake spiral, driving a Pelton-type microturbine. Computational fluid dynamics (CFD) simulations have been performed and compared with fluid dynamics measurements of the MAS system with 1.3 mm rotor diameter for spinning rates between 23 kHz and 67 kHz. The main optimization criteria of the MAS system are rotor speed and turbine stability and not primarily efficiency, which is standard for turbomachinery applications. In the frame of fabrication tolerances, a sensitivity study has been carried out by varying the nozzles diameter and the nozzle position relative to the rotor. The presented fluid dynamics study of the microturbine system includes the analysis of local fluid flow values such as velocity, temperature, pressure, and Mach number, as well as global quantities like forces and driven torque acting on the turbine. Comparison with the experimental results shows good agreement of the microturbine efficiency. Furthermore, the parameter study of the nozzle diameter reveals optimization potential for this high-speed microturbine system employing a smaller nozzle diameter

Working Report on the Status Quo of Nanomaterials Impact on Health and Environment

Nanotechnology is regarded as one of the key technologies of the future and associated with high expectations by politics, science and economy. Artificially produced nanosized particles and nanoscale system components have new properties which are of importance for the development of new products and applications. Such new properties of materials and substances result from the special properties of surfaces and interfaces and in part, from the geometric shape of the material. In theory nanoparticles (NPs) can be produced from nearly any chemical; however, most NPs that are currently in use today have been made from transition metals, silicon, carbon (single-walled carbon nanotubes; fullerenes), and metal oxides (zinc dioxide and titanium dioxide). Potentially harmful effects of nanotechnology might arise as a result of the nature of the NPs themselves, the characteristics of the products made from them, or aspects of the manufacturing process involved (Borm and Kreyling, 2004). The large surface area, crystalline structure, and reactivity of some NPs may facilitate transport in the environment or lead to harm because of their interactions with cellular material. In the case of nanomaterials, size matters, and could facilitate and exacerbate any harmful effects caused by the composition of the material. The highest risks for humans and the environment are associated with nanomaterials contained in products in the form of free particles. As long as NPs remain firmly embedded in materials, hardly any risk should be expected (Brouwer, 2004). However, it has to be clarified in these cases whether and in which form nanomaterials can be released into the environment during the production process, the use of a product, due to ageing and degradation as well as during disposal and recycling processes. Of course, also in the case of nanomaterials, environmental risk assessment should take into account their entire life cycle