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It is not uncommon for fans in existing systems to undergo retroactive performance upgrades after many years of operation. Such demands often arise from the addition of new system components or increased production rates. Since completely replacing the fan unit would involve considerable costs and downtime, operators are seeking solutions that enable performance to be increased without having to completely replace the existing machine. However, this requirement significantly limits the available options. If an increase in speed is not possible, moderate pressure increases can be achieved by replacing the impeller or extending the blades. However, these changes are highly system-dependent and restricted by the geometric limitations of the spiral casing. This paper examines an alternative modification of the impeller by subsequently welding deflections to the blade ends, also known as blade tail wedges. Based on a CFD study with experimental validation for a medium-pressure centrifugal fan with backward curved blades, it is shown that adding blade tail wedges causes a significant
shift in the fan characteristic curve towards higher pressures. The results show that the pressure increase can be attributed to an increase in the swirl component caused by the eflection. The effectiveness depends on the length of the deflection, whereby an increasing loss of efficiency due to increased flow separation can also be observed. For the fan under consideration, pressure increases of 15 – 30% can be achieved with only a slight loss in efficiency of 2 – 3% in the relevant range of the characteristic curve and constant effective impeller diameter. A comparison with the affinity laws shows that, for an equivalent increase in performance, the impeller diameter or rotational speed would have to be increased by about 10 %. Hence, despite the marginal loss of efficiency, blade tail wedges can offer an effective
alternative for enhancing fan performance under restrictive boundary conditions for industrial applications on-site.
This study investigates the influence of domain definition and interface placement on the steady-state CFD prediction of performance curves of centrifugal fans. The focus is on the separation between rotating and stationary flow domains as well as on the effects of the selected interface treatment (Frozen Rotor vs. Mixing Plane). The results show that a physically consistent definition of the rotating domain—comprising the impeller and the surrounding vaneless space while the inlet nozzle and casing remain stationary — is essential for obtaining realistic total pressure predictions. Extending the rotating region into geometrically stationary components such as the inlet nozzle or volute casing introduces artificial shear work and erroneous inertial effects, resulting in increased losses and an underestimation of the pressure rise. A realistic rotor–outlet interface that spans the full axial height of the impeller exit yields markedly better efficiency predictions than an idealised, radially truncated interface that numerically acts as an extension of the impeller end-walls. For the present low-specific-speed fan, a moderate transition region within the vaneless space, corresponding to approximately 3–16 % above the impeller exit radius R₂, allows sufficient flow relaxation and leads to stable and physically consistent results. For steady-state simulations, Frozen Rotor solutions benefit from an interface distance of about 13 % above R₂, whereas Mixing Plane models provide the most robust and accurate performance predictions for interface positions around 6–7 % above R₂ in combination with a realistic interface geometry. Correct specification of wall motion, use of the SST k–ω turbulence model and appropriate near-wall resolution (y⁺ ≈ 1–3) are additional key factors for numerical consistency. Overall, the study demonstrates that careful domain definition, suitable interface placement, and a consistent numerical setup are essential prerequisites for physical fidelity and comparability of CFD-based performance curve simulations of centrifugal fans.
Reflow soldering of printed flexible low-cost electronics continues to pose a challenge, which is hampering the growth of the technology. The specific process parameter requirements severely limit the available soldering technologies. This study focuses on the suitability of a new photonic soldering process based on individually controllable near-infrared light emitting diodes (NIR LEDs) for processing screen-printed silver (Ag) structures and etched copper (Cu) structures on polyethylene terephthalate (PET) with low-temperature solders of the Tin-Bismuth-Silver (SnBiAg) group. The approach enabled various component sizes to be successfully soldered under more favorable conditions. An analysis of the shear strength shows comparable behavior for the copper structures compared to samples that were convectively soldered. A significant improvement in the shear strength of the printed silver structures was achieved using the new NIR process.
This file contains a script for determining band gaps from DRS measurements using a semi-automatic approach to eliminate potential user bias during the fitting procedure. The methods are based on the publications from J. Tauc, Materials Research Bulletin, vol. 3, no. 1, Jan. 1968 and P. Makuła, et al., The Journal of Physical Chemistry Letters, vol. 9, no. 23, Dec. 2018.
Flexible Hybrid Electronics (FHE) is the combination of film substrates with etched or printed conductors and conventional SMT components. A particular focus has been placed on thermoplastics such as polyethylene terephthalate (PET) as a low-cost substrate material. However, the use of these materials in standard reflow soldering processes remains a challenge. In addition to the substrate's limited temperature resistance, the dissolution of printed silver conductors in the molten solder over time presents a further challenge.
The approach presented in this work uses multiple individually controllable Near Infrared LEDs as an energy source to selectively irradiate and thus locally heat FHE assemblies as required. Irradiation is applied from below through the substrate material, thereby enabling direct heating of the solder joint whilst preventing shading by the component body. The temporal and local controllability of the irradiation allows the placement density and the omission of temperature sensitive areas to be taken into account. This approach enables a more material-friendly and energy-efficient soldering process.
Im ZIM-Kooperationsprojekt „ALUSolder“, gefördert durch das Bundesministerium für Wirtschaft und Klimaschutz im Rahmen des IraSME-Netzwerks mit Partnern aus Deutschland und Österreich, wird der Ersatz von Kupfer durch Aluminium entlang der gesamten Prozesskette der Leiterplattenfertigung untersucht. Der Projektansatz basiert auf der selektiven Beschichtung der Anschlussflächen aus Aluminium mit einer chemisch aufgebrachten Nickel-Phosphor-Schicht. Dieses Metallisierungs-verfahren ist mit den für starre Leiterplatten verwendeten Kunststoffen und Kompositmaterialien kompatibel und ermöglicht lötfähige Oberflächen für den anschließenden einseitigen Reflowlötprozess bei einlagigen Leiterplatten. Im weiteren Verlauf wird untersucht, welche Leiterbahnstrukturen mit der eingesetzten Aluminiumlegierung zuverlässig realisiert werden können. Zudem wird die Haftfestigkeit zwischen Leiterbahn und Epoxidverbundsystem im Vergleich zu herkömmlichen Kupferleiterbahnen analysiert. Zur Bewertung der Zuverlässigkeit und Lebensdauer werden verschiedene Umwelt-simulationstests durchgeführt. Anschließend werden die gealterten Lötverbindungen umfassend hinsichtlich ihrer mechanischen und elektrischen Eigenschaften charakterisiert und den Lötverbindungen konventioneller Kupferleiterplatten gegenübergestellt. Ziel des Projekts ist es, die technologischen Grundlagen für den industriellen Einsatz von Aluminiumleiterstrukturen zu schaffen und somit einen Beitrag zur Elektronikproduktion der Zukunft zu leisten.
Carbon‐doped TiO2 nanoparticles were prepared by a facile carbothermal treatment at different temperatures. The synthesis was conducted in a rotary tube furnace under an acetylene/nitrogen gas flow. A detailed analysis of the morphology of the particles revealed a layered graphene structure surrounding the TiO2core with a temperature‐shell thickness of 1–1.5 nm. The material exhibits a significant shift in the Raman Eg(1) mode toward higher wavenumbers. High carbon contents were determined by X‐ray photoelectron spectroscopy. This led to the conclusion that in addition to the carbon in the shell, carbon is also incorporated into the TiO2 structure. Substitutional doping in favor of titanium or oxygen atoms could be excluded based on XPS measurements due to the absence of Ti–C bonds and the lack of changes in lattice parameters of the unit cell or microstrain. An interstitial incorporation of carbon is therefore most likely. Either the incorporation of carbon or the carbon shell suppressed the phase transition from anatase to the thermodynamically stable rutile which is expected above 600 Celsius. Additionally, the process inhibits the crystallite growth at higher treatment temperatures.
Microwave technology has been established in industry and households for decades; nevertheless, its use in production is still limited to some relatively specific applications. For providing an overview – even for non-specialists – the authors will cover several aspects of microwave technologies: The development of new microwave-oven concepts, simulation of electromagnetic field distributions within microwave systems, measurement of dielectric properties using dielectric spectroscopy, and various applications of microwave technologies. The authors have developed and patented a continuous microwave oven with a maximum sample width of 800 mm, utilizing mono-mode and multi-mode technology at frequencies of 2.45 and 5.7 GHz, with the option of additional heating via infrared irradiation. This device can be used for continuous processing of bulk goods as well as for the continuous microwave treatment of individual items. We demonstrated a combination of horizontal impregnation and coating plant with the continuous microwave oven. To analyze materials including thermosetting resins and composites regarding their complex dielectric function changes depending on frequency, temperature, and changes in composition or degree of curing, dielectric spectroscopy, which ranges from μHz to GHz (10-6 to 3 x 109 Hz), can be used. The dielectric data provides input for subsequent simulations of the influence of different materials on the electromagnetic fields of the microwave ovens. Finally we present exemplary results of different applications of microwave technology, starting with the microwave vulcanization of injection-molded elastomer sealing rings, through experiments on microwave sintering of additive inkjet-manufactured conductor tracks on different substrates, to the mechanical and color modification of European woods for tropical wood substitution in high-priced stringed instruments. In addition the authors demonstrate the applicability of microwave technologies for fast and energy-efficient recycling of polyurethane foams and established a scale-up to up to 90 liters in the microwave oven.
