Philipp Gittler

Dielectrophoretic particle dynamics in alternating-current electro-osmotic micropumps

This letter deals with the dynamics of dielectric microparticles in alternating-current electro-osmotic micropumps, which is based on the competitive interplay of inertial, dielectrophoretic, and viscous drag forces. The electric field and the electro-osmotic flow are modeled and computed by means of finite elements and particle trajectories are evaluated taking into account the forces above. Thereby, mean traveling height and velocity depend on driving voltage and frequency, which allows for an effective type of particle manipulation and separation. The obtained particle velocities show good agreement with measured velocities of hollow glass beads in a device realized in SU8/glass technology.

A Passive Magnetically and Hydrodynamically Suspended Rotary Blood Pump

A combined hydrodynamic-magnetic bearing allows the design of rotary blood pumps that are not encumbered with mechanical bearings and magnets requiring sensors or electrical power. However, such pumps have so far needed very small and accurately manufactured gaps between rotor and housing to assure effective hydromagnetic bearing behavior. In order to use this concept in disposable pump heads, a design that allows larger rotor-housing gaps, and thus larger manufacturing tolerances, is needed. A pump with passive magnetic bearings and a gap between rotor and housing in the range of 0.5 mm was designed. Numerical simulations were performed to optimize the rotor geometry at low levels of shear stress. An experimental test stand was used to find a range of speeds and gap settings that resulted in low levels of vibration and useful pressure-flow relationships. Three different rotor geometries were tested using a viscosity-adjusted test fluid. Blood damage tests were conducted within the desirable range of speeds and gap settings. In this study stable pump performance was demonstrated at total gap widths between 0.3 and 0.7 mm at flows of 0-10 L/min, with afterloads up to 230 mm Hg. Best performance was achieved with rotors sliding on a fluid pillow between the rotor and the outer housing at a gap distance of 50 to 250 microm. The inner gap distance, between the rotor and the inner housing, could be as great as 500 microm. Hemolysis tests on the prototype within the chosen operating range showed lower values (NIH = 0.0029 +/- 0.0012 g/100 L) than the Biomedicus BP-80 pump (NIH = 0.0033 +/- 0.0011 g/100 L). In conclusion, it is possible to build rotary blood pumps with passive hydromagnetic bearings that have large gaps between their rotors and housings. Rotor behavior is sensitive to the position of the permanent magnetic drive unit. To minimize vibration and blood damage, the fluid gaps and the rotational speed have to be adjusted according to the desired operating point of the pump. Further study is needed to optimize the magnetic drive unit and to ascertain its ability to withstand inertial loads imposed by sudden movements and external shock.

CFD, a design tool for a new hot metal desulfurization technology

AbstractThispaperconsidersCFDmodellingofdesulfurizationcarriedoutinalargevesselcontaininghotmetalcoveredbyathicksyntheticslaglayer.Duringnitrogenstirringsulfurtransferstotheslag.Sulfurionsinthe slag have to be removed by oxidation (O 2 lance) to restore slag desulfurization capability. The mac-roscopic metallurgical reactions occurring during hot metal desulfurization and slag regeneration arestudiedbykineticlawsforpermanentandtransientphasecontact.Mechanicalmetal–slaginteractionsarecalculatedbyshearstressconsiderationsforstratifiedflows.Thepositionofthephaseinterfaceandtheslagsurface is obtained by an adaptive grid algorithm. Flow initiation by rising gas bubbles is simulated bymeansofanalgebraicdriftfluxmodel.Asaresultofthesesimulationsthefullythree-dimensionalflow-andtemperature fields in the slag and metal phase are obtained. Furthermore the variation of the time-dependent concentration fields of the main reactants can be observed. 2002 Elsevier Science Inc. Allrights reserved. Keywords:CFD simulation; Hot metal desulfurization; Slag regeneration; Metallurgical reactions

Numerical optimization and experimental investigations on the principle of the vortex diuser

is optimized with respect to axial thrust within the framework of the lifting-line theory. Finite airfoil performance is accounted for by applying lift and drag coefficients from wind-tunnel data. The so-gained optimal design for the vortex diffuser blades is realized on a small-scale model, and wind-tunnel tests are carried out to investigate drag reduction of the vortex diffuser for comparison with numerical results. Furthermore, the goal is to gain some experience and data for preparation of real flight testing on an unmanned aerial vehicle. As the vortex diffuser can produce forces and moments in all three directions, a pure wing–body configuration with vortex diffusers instead of rudder, elevator, and ailerons would be possible. The wind-tunnel tests also deliver data to investigate basic flight mechanicsofsuchaconfiguration.Inthecaseofasymmetricvortexrollup,thepaperdemonstratesawaytooptimize the vortex diffuser settings online in the wind tunnel. Experiments clearly show that the vortex diffuser is able to reduce drag in high-lift/high-angle-of-attack configurations. Wind-tunnel tests, however, also demonstrate some problems for practical design of the vortex diffuser.

Numerical, Experimental and Analytical Investigation of the Mass Outflow From a Pickling Tank

The process of pickling is an important intermediate step in the production line of steel processing. The strip surface is cleaned from grease and scales before further processing by immersion into an acid bath. Problems arising at higher process speeds with increasing inclination of the free surface are reduced strip immersion length and increased mass outflow. In this paper a differential equation is derived describing the influence of the bath depth on the local surface inclination for a simplified two-dimensional case. Since it can only be solved analytically for trivial boundary conditions a numerical solution has been computed giving an estimation for the order of growth of the bath inclination and mass outflow with the strip velocity. Further, a series of CFD simulations of the complete three-dimensional geometry at different strip velocities have been carried out calibrating the formulas of mass outflow. In the course of the CFD simulations the deformation of the free surface was calculated by a VOF model with explicit reconstruction of the interface. A standard κ–e turbulence model was applied and special considerations have been made regarding the boundary conditions. Finally the resulting formula has been verified making use of data from a small scale model. It was found that the overflow at the far end of the tank is the dominant mass transfer mechanism at process velocities of the current generation of pickling tanks. Still, due to the superior order of growth, mass drag-out via the upper side of the strip becomes important for process velocities of 8 to 10 m/s. The good accordance of the analytical solution, CFD simulation and experiment indicate that the formula derived in the first part of the paper is a good estimation for the mass outflow from the pickling tank, hence making time and resource consuming CFD simulations obsolete for the design layout. Further the validity of geometrically non similar small scale models could be showed.Copyright