Publikationen

Lorentz force velocimetry (LFV) is a contactless flow measurement technique for electrically conducting liquids. LFV is based on measuring the flow-induced force acting on an externally arranged permanent magnet (or a magnet system) and being proportional to the velocity (or mass flux) of the flow. This force is equal in magnitude to the braking Lorentz forces induced in the moving conductor. In case of flow rate measurement, the magnetic field lines of the used permanent magnet (or magnet system) penetrate the entire crosssection of the flow. In contrast, in local Lorentz force velocimetry (LLFV), tiny permanent magnets are used of which the penetration depth of its field lines is much smaller than the dimension of the flow. The present study aims to extend LLFV to liquid metal two-phase flow measurement. Such flows are of interest in high-temperature metallurgic processes, such as continuous casting of steel, where injection of argon bubbles into the melt is applied to prevent clogging, to mix the melt and to remove inclusions. In a first test, we investigate the transient response of Lorentz force to a simple arrangement of bubble/particle injected into liquid melt GaInSn at rest. The results show that the recorded Lorentz forces vary significantly and their maximum values are different for each rising bubble/particle. The shapes of Lorentz force signals depend on local liquid flow structures and non-conducting volume effects, both of which are dominated by bubble/particle positions.

Rayleigh-Bénard convection and Taylor-Couette flow are two canonical flows that have many properties in common. We here compare the two flows in detail for parameter values where the Nusselt numbers, i.e. the thermal transport and the angular momentum transport normalized by the corresponding laminar values, coincide. We study turbulent Rayleigh-Bénard convection in air at Rayleigh number Ra=107 and Taylor-Couette flow at shear Reynolds number ReS=2x104 for two different mean rotation rates but the same Nusselt numbers. For individual pairwise related fields and convective currents, we compare the probability density functions normalized by the corresponding root mean square values and taken at different distances from the wall. We find one rotation number for which there is very good agreement between the mean profiles of the two corresponding quantities temperature and angular momentum. Similarly, there is good agreement between the fluctuations in temperature and velocity components. For the heat and angular momentum currents, there are differences in the fluctuations outside the boundary layers that increase with overall rotation and can be related to differences in the flow structures in the boundary layer and in the bulk. The study extends the similarities between the two flows from global quantities to local quantities and reveals the effects of rotation on the transport. This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.

In this article, the transient modelling for a new construction of the Adsorption cold production was investigated. This system, named in this work the combined Adsorption Ice Production system (com-AIP system), was filled by both silica gel (SG) and activated carbon (AC) together in one adsorption reactor as the adsorbent and methanol as the adsorbate and refrigerant. A fined-tube heat exchanger was designed (named combined adsorption reactor) in order to contain two different adsorbents in the adsorption reactor and increase the heat transfer ability between the particles of adsorbents and heat exchanger fins. As a result the input energy required from the external heat source is saved and the coefficient of performance COP of the com-AIP system is improved. The mass flow rate of refrigerant increases and consequently, the refrigeration energy Qe rises too. A cycle simulation computer program of this innovative bed was developed to analyze the refrigeration energy and COP variations by varying heat transfer fluid (hot, cooling and chilled water) inlet temperatures and adsorption/desorption cycle time. The transient behavior of heat and mass transfer fluids has been also studied. Under the standard test conditions of 100 ˚C hot water, 24 ˚C cooling water, and 15 ˚C chilled water inlet temperatures, the simulation results showed that the amount of the ice produced per cycle of 5.34 kg and 0.73 COP can be achieved from the com-AIP system. It was found that the system performance is very much sensitive to the mass flow rate of the refrigerant. The cycle time of the system is not dependent on the amount of the adsorbents but is strongly dependent on driven temperature of heat exchange fluid and the design of the heat exchanger. The com- adsorption reactor allows using the advantages of physical properties of both adsorbents SG and AC. Consequently, this innovative com-AIP system utilizes effectively low-temperature heat sources of temperature between 65 and 100 ˚C, because of the inferior thermodynamic properties of methanol and the low regeneration temperature from silica gel and activated carbon as adsorbents. This strategy (com-AIP system) is completely different from the conventional adsorption reactors, which are filled with one adsorbent in one bed or in two beds.