Numerical simulation techniques for the efficient and accurate treatment of local fluidic transport processes together with chemical reactions

This work describes a numerical framework developed for the efficient and accurate simulation of microfluidic applications related to two leading ex-periments of the DFG SPP 1740 research initiative, namely the ‘Superfocus Mi-cromixer’ and the ‘Taylor bubble flow’. Both of these basic experiments are con-sidered in a reactive framework using the SPP 1740 specific chemical reaction systems. A description of the utilized numerical components related to special meshing techniques, discretization methods and decoupling solver strategies is provided and its particular implementation is performed in the open-source CFD package FeatFlow [19]. A demonstration of the developed simulation tool is based on already defined validation cases and on suitable examples being re-sponsible for the determination of the related convergence properties (in the range of targeted process parameter values) of the developed numerical frame-work. The subsequent studies give an insight into a parameter estimation method with the aim of determination of unknown reaction-kinetic parameter values by the help of experimentally measured data

Mathematical Modeling of Coolant Flow in Drilling Processes with Temperature Coupling

The paper presents a mathematical modeling approach for a novel drilling strategy with coolant flow. Numerical tools for efficient simulations of such drilling applications are explained. We model the fluid flow with the Navier-Stokes equation in a rotational frame of reference and the solid domain is treated with the Fictitious Boundary Method (FBM). This enables us to utilize a unified mesh for the solid and fluid part of the domain and heat transfer between these is treated in an implicit way

Benchmarking and validation of a combined CFD-optics solver for micro-scale problems

In this work, we present a new approach for coupled CFD-optics problems that consists of a combination of a finite element method (FEM) based flow solver with a ray tracing based tool for optic forces that are induced by a laser. We combined the open-source computational fluid dynamics (CFD) package FEATFLOW with the ray tracing software of the LAT-RUB to simulate optical trap configurations. We benchmark and analyze the solver first based on a configuration with a single spherical particle that is subjected to the laser forces of an optical trap. The setup is based on an experiment that is then compared to the results of our combined CFD-optics solver. As an extension of the standard procedure, we present a method with a time-stepping scheme that contains a macro step approach. The results show that this macro time-stepping scheme provides a significant acceleration while still maintaining good accuracy. A second configuration is analyzed that involves non-spherical geometries such as micro rotors. We proceed to compare simulation results of the final angular velocity of the micro rotor with experimental measurements

Mathematical modeling of coolant flow in discontinuous drilling processes with temperature coupling

Nickel-based alloys, like Inconel 718, are widely used in industrial applications due to their high-temperature strength and high toughness. However, machining such alloys is a challenging task because of high thermal loads at the cutting edge and thus extensive tool wear is expected. Consequently, the development of new process strategies is needed. We will consider the discontinuous drilling process with coolant. The main idea is to interrupt the drilling process in order to let the coolant to flow around the cutting edge and to reduce thermal loads. Since measurements inside the borehole are (nearly) impossible, simulations are a key tool to analyze and understand the proposed process. In this paper, a 3D fluid flow simulation model with Q2P1 Finite Elements in combination with the Fictitious Boundary Method is presented to simulate the coolant flow around the drill inside the borehole. The underlying equations are transformed into a rotational frame of reference overcoming the challenges of mesh design for high rotational domains inside the fluid domain. Special treatment of Coriolis forces is developed, that modifies the ‘Pressure Poisson’ Problem in the projection step improving the solver for high angular velocities. To further take high velocities into account, a two-scale artificial diffusion technique is introduced to stabilize the simulation. Finally, Q1 Finite Elements are used to simulate the heating and cooling processes in both the tool and the coolant during the complete discontinuous drilling process. The simulation is split into a ‘contact’ and a ‘no contact’ phase and a coupling strategy between these phases is developed. FBM is utilized to switch between the two configurations, thus only one unified grid for both configurations is needed. The results are used to gain insight into the discontinuous drilling process and to optimize the process design

Reactive Flow Simulation of Micromixers Based On Grid Deformation Techniques

Process intensification of engineering applications in the framework of reacting flows in micromixer devices attracts the attention of engineers and scientists from various fields. With the steadily increasing available computational resources the traditional experimentally supported investigations may be extended by computational ones. For this purpose, a simulation framework based on state of the art numerical techniques extended with special grid deformation techniques has been developed. Its validation in terms of comparison with computational and experimental results in reacting, as well as in non-reacting frameworks has been performed on the basis of the T-mixer, and SuperFocus mixer, respectively. The computational efficiency of the developed tool is shown to be applicable for optimization tasks, such as reverse engineering purposes

Arduino-based slider setup for gas–liquid mass transfer investigations

The implementation of traditional sensors is a drawback when investigating mass transfer phenomena within microstructured devices, since they disturb the flow and reactor characteristics. An Arduino based slider setup is developed, which is equipped with a computer-vision system to track gas–liquid slug flow. This setup is combined with an optical analytical method allowing to compare experimental results against CFD simulations and investigate the entire lifetime of a single liquid slug with high spatial and temporal resolution. Volumetric mass transfer coefficients are measured and compared with data from literature and the mass transfer contribution of the liquid film is discussed

Swimming by reciprocal motion at low Reynolds number

Biological microorganisms swim with flagella and cilia that execute nonreciprocal motions for low Reynolds number (Re) propulsion in viscous fluids. This symmetry requirement is a consequence of Purcell's scallop theorem, which complicates the actuation scheme needed by microswimmers. However, most biomedically important fluids are non-Newtonian where the scallop theorem no longer holds. It should therefore be possible to realize a microswimmer that moves with reciprocal periodic body-shape changes in non-Newtonian fluids. Here we report a symmetric 'micro-scallop', a single-hinge microswimmer that can propel in shear thickening and shear thinning (non-Newtonian) fluids by reciprocal motion at low Re. Excellent agreement between our measurements and both numerical and analytical theoretical predictions indicates that the net propulsion is caused by modulation of the fluid viscosity upon varying the shear rate. This reciprocal swimming mechanism opens new possibilities in designing biomedical microdevices that can propel by a simple actuation scheme in non-Newtonian biological fluids

Hydrodynamika vertikalneho toku suspenzii tuhe castice - plyn

Available from Slovak Centre of Scientific and Technical Information, under shelf-number: A582772 / Slovenska Technicka Univerzita v BratislaveSIGLESKSlovak Republi

Improvement of part load efficiency of a combined cycle power plant provisioning ancillary services

According to the type of ancillary service provisioned, operation mode of a power plant may change to part load operation. In this contribution, part load operation is understood as delivering a lower power output than possible at given ambient temperature because of gas turbine power output control. If it is economically justified, a power plant may operate in the part load mode for longer time. Part load performance of a newly built 80 MW combined cycle in Slovakia was studied in order to assess the possibilities for fuel savings. Based on online monitoring data three possibilities were identified: condensate preheating by activation of the currently idle hot water section; change in steam condensing pressure regulation strategy; and the most important gas turbine inlet air preheating. It may seem to be in contradiction with the well proven concept of gas turbine inlet air cooling, which has however been developed for boosting the gas turbine cycles in full load operation. On the contrary, in a combined cycle in the part load operation mode, elevated inlet air temperature does not affect the part load operation of gas turbines but it causes more high pressure steam to be raised in HRSG, which leads to higher steam turbine power output. As a result, less fuel needs to be combusted in gas turbines in order to achieve the requested combined cycle's power output. By simultaneous application of all three proposals, more than a 2% decrease in the power plant's natural gas consumption can be achieved with only minor capital expenses needed.Combined cycle Part load performance Ancillary services Electric efficiency Fuel savings