[en] Convective flow phenomena (draft flow, Hele-Show flow) in a variety of slender vertical gaps heated from below subject to specified lateral boundary conditions are investigated. Temperature fields in the fluids are visualized by holographic interferometry. Power density spectra of time dependent thermocoupole signals are calculated. Flows in porous materials are simulated with the aid of the experiment. (orig./HP)

[en] Some common experimental techniques to determine local velocities and to visualize temperature fields in natural convection research are discussed. First the physics and practice of anemometers are discussed with emphasis put on optical anemometers. In the second and third case the physics and practice of the most developed interferometers are discussed; namely differential interferometry for visualization of temperature gradient fields and holographic interferometry for visualization of temperature fields. At the Institut fuer Reaktorbauelemente these three measuring techniques are applied for convection and pipe flow studies. (orig.)

[en] This paper studies the time dependent convective flows in Hele-Shaw slots which are heated from below. In this experimental study, the evolution of oscillatory phenomena is traced through the time dependent regime which is bounded on either side by regions of steady flow. The history of thermal events is recorded by thermocouples which protrude into the test fluid (silicon oil, Pr ≅ 37) at the four corners of the cavity. Flow patterns are visualized by holographic interferometry and temperature signals are analyzed using Fourier transforms and correlation functions. The results of this investigation show that the richness of the dynamic behavior of time dependent convective flows in high Prandtl number fluids is determined by the interaction of individual, spatially distributed instability events. Additionally, this behavior is dependent on the symmetry of the flow pattern which governs phase-locking properties of thermal plumes developing at different locations. (orig.)

[en] Segregation in compound electronic materials and advanced structural alloys is one of the prime foci in materials research. A radioscopic technique was developed to visualize density fields in opaque metallic melts. Beginning with pure element melts, the technique was refined to study alloys. With the pure monocomponent gallium every experiment delivered results that are in line with current theories. When alloying the gallium with indium, the experiments showed under specific conditions serious discrepancies with theory, such as a threshold for onset of convection in natural convection situations. This threshold is linked to an observation of a substantial gravitational segregation of indium in the melt which is, for currently unknown reasons, more than predicted by thermodynamic theory. Further, thermosolutal convection, which is also expected in the alloyed melts, does not develop according to predictions in salt solutions. In conclusion, the experiments have revealed several deficiencies in current theoretical treatments of liquid metal convection with solidification which emphasize the crucial need for experiments to validate analytical and numerical models

[en] Holographic interferometry is well suited for visualizing temperature, density, pressure and concentration fields in transparent fluids. The holographic real-time interferometer allows a continuous observation of stationary and instationary flow processes. After the explanation of the measuring technique, the problems arising during the interferometer set-up as well as the necessary adjusting operations are described. For heat transfer problems new possibilities for the application of holographic interferometry are revealed. Convection in boxes, temperature fields around heated or cooled bodies, concentration and diffusion processes in two phase-flows, mixtures and solutions as well as melting and freezing processes may be investigated. On the basis of particular examples some applications are presented. (orig.)

[en] The evolution of convective flow in a finite Hele-Shaw cell is presented. Two new results were found. First, at the same Rayleigh number there coexist three different flow states in separated regions of the fluid layer, the center region having a steady flow and the two end regions exhibiting time-dependent flow. Second, the flow oscillations in the two end regions are monoperiodic and are never correlated. There is no transition to a more complicated oscillation observed. The time-dependent flow is bound at low and high Rayleigh number by transitions to steady state flow. (orig.)

[en] The phase diagram for a gallium-indium alloy shows that the eutectic is formed at a temperature of 15.3 C and has a eutectic composition of 14.2 at. pct In (21.4 wt pct In). A eutectic melt is expected to solidify completely when the eutectic temperature is reached. This requires that no gravitational segregation occurs in the melt. A survey of the available literature on eutectic Ga-In revealed no prior experiments on the in situ visualization of solidification. The goal of this experimental work was to observe the isothermal solidification of a vertical layer of molten eutectic Ga-In in real-time using X-ray radioscopy