Fließverhalten granulierter Pulver

An verschiedenen Granulaten aus Karbonyleisen, Zinkmanganferrit, Elektrolytkupfer und Karbonylnickel sowie an Pulvern aus Aluminiumoxyd und Eisen Untersuchung ihrer Fließdauer durch einen Trichter in Abhängigkeit von seinem Düsendurchmesser some Messung des Böschungswinkels des ausgeflossenen Werkstoffes und des Haftwinkels auf Glas und Messing.     

Calculation of SANS intensity for polyethylene: effect of varying fold planes and fold plane roughening

The intensity of the small angle neutron scattering (SANS) for polyethylene crystallized in the lamellar habit from the melt at large supercoolings is calculated for μ = 0.01 to μ = 0.14 [$\text{μ = (}\text{4π}\text{λ}\text{)}\text{sin}\text{(}\text{θ}\text{2}\text{)}$]. Computations are made on models which allow various amounts and types of chain folding and varying degrees of ‘tight’ or ‘regular’ folds. The models that fit the SANS data best have folding along lattice planes in which the stem separation is larger than 0.5 nm (5 Å) or which allow for fold plane roughening on a variety of fold planes. the ‘leapfrog’ type folds mentioned by Sadler were also considered, and a possible cause for their existence suggested. As an example, the variable cluster model gives a good account of the SANS data with the surface roughening suggested by nucleation theory with fold planes [110], [200], and [310], or a mixture. Even though the conditions of crystallization used in preparing the SANS specimens (large supercoolings) were conducive to the maximum surface disorder, the probability of ‘tight’ or ‘regular’ folding, p_tf, was found to be ～0.7 for the best models. This corresponds closely to the theoretical lower bound $\text{p}{}_{\mathrm{tf}}\text{=}\text{2}\text{3}$ which is rigorous for the case of non-tiled stems. The probability of strictly adjacent re-entry in a single specified fold plane, p_ar, was ～0.4 to ～0.7 depending on the particular model chosen. The best models fit not only the SANS data, but also the liquid and crystal density, degree of crystallinity, and characteristic ratio (or radius of gyration). None of the models show the density anomaly inherent in the switchboard or random re-entry models of Yoon and Flory.     

Wireless sensor networks scheduling for full angle coverage

Many current studies in tracking and surveillance assume that a target can be monitored by a single sensor. However, there are situations where a sensor can only monitor a certain portion of the object. Examples include image capturing and coastline monitoring. In our previous work, we develop the Minimum Cost Cover algorithm to identify a set of sensors which preserve 360° coverage of a target with minimum cost, such that when different cost functions for the sensors are used, covers with different optimization objectives can be identified. In this work, we study the scheduling problem to monitor a target continuously with full angle coverage. To increase network lifetime, we develop several algorithms by adopting different cost functions in selecting the sensors. We evaluate the performance of our schemes through extensive simulations. The simulation results show that our proposed Conditional Scheduling metric can help to improve the network lifetime as well as the time to the first node failure.

3D optical coherence tomography as new tool for microscopic investigations of nucleate boiling on heated surfaces

Boiling phenomena are an important aspect in security and efficiency for technical applications with high heat flux like nuclear reactors. This study presents optical coherence tomography (OCT) as a novel modality for three-dimensional and two-dimensional time resolved imaging of nucleate boiling on heated surfaces on a microscopic scale with high spatial (<10 μm) and temporal (>25 frames per second) resolution. Within this study, a borosilicate glass plate coated with an optically transparent and electrically conductive indium tin oxide (ITO) layer with a thickness of approximately 100 nm was used as heating surface. The combination of these two properties allows optical inspection of the nucleate boiling from the backside by OCT focused on the formation, growth and detachment of single bubbles. We demonstrated for the first time that OCT is an excellent tool to acquire two-dimensional and three-dimensional images of the base of vapor bubbles from the backside of the heated surface. The acquired images allow for instance the temporally resolved measurement of the bubble diameter, diameter of the bubble base and the contact angle. Exploiting the phase information of the acquired OCT signal stacks allows imaging the movement of the bubble surrounding fluid. We think that OCT will provide many new insights into the boiling phenomena at the bubble base. The recent enhancement of the acquisition rates of OCT systems will facilitate four-dimensional imaging of single bubble evaporation procedures in the nearer future.     

Profile Scaling of Miniature Centrifugal Fans

This paper addresses issues that relate to downscaling the height of centrifugal fans for application in low profile technologies, such as the cooling of portable power electronics. The parameters studied include flow rate, pressure rise, and power consumption characteristics. The former two of these are measured using a fan characterization rig and the latter by directly measuring the power supplied to the fan. These are studied for fan diameters ranging from 15 to 30 mm with numerous profile heights between 0.3 mm and 15 mm. It is found that all of the phenomena encountered are best described in terms of fan aspect ratio. The results show that the conventional scaling laws cannot be accurately applied when blade profile alone is scaled. Indeed, the only parameter reasonably well predicted was the pressure rise attainable, but that was only accurate for fan aspect ratios greater than 0.17. Below this, the pressure rise generated reduces logarithmically toward zero. The study also reveals that no advantage is gained by using fans of aspect ratio greater than 0.3, as the maximum flow rate attainable decreases slightly above this. Overall, the scaling phenomena reported herein provide invaluable information for the future design of efficient low-profile cooling solutions that are to incorporate such fans.