Model-based condenser fan speed optimization of vapor compression systems. - In: Energies, ISSN 1996-1073, Bd. 13 (2020), 22, 6012, S. 1-26
Vapor compression systems (VCS) cover a wide range of applications and consume large amounts of energy. In this context, previous research identified the optimization of the condenser fans speed as a promising measure to improve the energy efficiency of VCS. The present paper introduces a steady-state modeling approach of an air-cooled VCS to predict the ideal condenser fan speed. The model consists of a hybrid characterization of the main components of a VCS and the optimization problem is formulated as minimizing the total energy consumption by respectively adjusting the condenser fan and compressor speed. In contrast to optimization strategies found in the literature, the proposed model does not relay on algorithms, but provides a single optimization term to predict the ideal fan speed. A detailed experimental validation demonstrates the feasibility of the model approach and further suggests that the ideal condenser fan speed can be calculated with sufficient precision, assuming constant evaporating pressure, compressor efficiency, subcooling, and superheating, respectively. In addition, a control strategy based on the developed model is presented, which is able to drive the VCS to its optimal operation. Therefore, the study provides a crucial input for set-point optimization and steady-state modeling of air-cooled vapor compression systems.
https://doi.org/10.3390/en13226012
Spin-orbit interaction of light in three-dimensional microcavities. - In: Physical review, ISSN 2469-9934, Bd. 102 (2020), 4, 043524
We investigate the spin-orbit coupling of light in three-dimensional cylindrical and tubelike whispering gallery mode resonators. We show that its origin is the transverse confinement of light in the resonator walls, even in the absence of inhomogeneities or anisotropies. The spin-orbit interaction results in elliptical far-field polarization (spin) states and causes spatial separation of polarization handedness in the far field. The ellipticity and spatial separation are enhanced for whispering gallery modes with higher excitation numbers along the resonator height. We analyze the asymmetry of the ellipticity and the tilt of the polarization orientation in the far field of conelike microcavities. Furthermore, we find a direct relationship between the tilt of the polarization orientation in the far field and the local inclination of the resonator wall. Our findings are based on finite-difference time-domain simulations and are supported by three-dimensional diffraction theory.
https://doi.org/10.1103/PhysRevA.102.043524
Fatigue behavior of conventional and stationary shoulder friction stir welded EN AW-5754 aluminum alloy using load increase method. - In: Metals, ISSN 2075-4701, Bd. 10 (2020), 11, 1510, insges. 11 S.
https://doi.org/10.3390/met10111510
Ni3N-coated Ni nanorod arrays for hydrogen and oxygen evolution in electrochemical water splitting. - In: ACS applied nano materials, ISSN 2574-0970, Bd. 3 (2020), 11, S. 10986-10995
Im Titel ist "3" tiefgestellt
Designing high efficiency non-noble metal catalysts for electrochemical hydrogen and oxygen evolution reactions (HER and OER) is a challenging and promising task. In the present work, a large-scale self-supported black nickel sheet composed of nickel nanorod arrays (B-Ni) was successfully fabricated via electroplating with a nanostructured Si template assisted strategy, and Ni3N coating layer was coated on the structured surface followed by a nitrogen plasma treatment with different treatment durations. The black color is due to the immensely enhanced light absorption through the surface nanostructures with high aspect ratio. The samples show promising catalytic performance when used as electrochemical catalysts for both HER and OER in alkaline electrolyte. Benefiting from the nanostructure and the Ni3N coating, B-Ni_N2_10 min exhibits low onset potentials of 1.560 and 0.165 V at a current density of 10 mA/cm2 for OER and HER, respectively. The calculated electrochemical surface area (ECSA) for B-Ni is 10 times higher than the pristine Ni sheet (P-Ni), while after nitrogen plasma treatment, the ECSA for B-Ni_N2_10 min is 21 times higher than that of the P-Ni. In addition, all the catalysts show good electrochemical stabilities. All the improvements for the electrochemical performances suggest that nanostructured nickel nitride could be a promising inexpensive catalyst system for both OER and HER processes.
https://doi.org/10.1021/acsanm.0c02222
Physics-based modeling and parameter identification for lithium ion batteries under high current discharge conditions. - In: Journal of the Electrochemical Society, ISSN 1945-7111, Volume 167 (2020), number 14, 140549
Extreme scenarios of high discharge current must be understood for better battery management system design. Physics-based modeling can give a better insight into the battery response but can be challenging due to the large number of parameters. In this work, an electrochemical pseudo-2D model is developed and used in the parameter identification and validated under high current discharge conditions. Commercial 18650 cells with maximum rated current of 20 A (13.3 C) are characterized with discharge rates up to 40 C under controlled thermal conditions. The proposed three-step parameter identification procedure starts with the open circuit voltage being used to estimate the equilibrium potentials. In a second step, kinetic parameters are identified under high current aided by a parameter sensitivity analysis and parameter optimization with an evolutionary algorithm. The third step is the verification by comparing simulation results with measurements resulting in root main square error under 89 mV for currents until 26.6 C. Limits of the model are explored in the 33.3 C case, where a parameter re-fit shows that polarization effects change for very high current.
https://doi.org/10.1149/1945-7111/abc726
Localized and programmable chemical vapor deposition using an electrically charged and guided molecular flux. - In: ACS nano, ISSN 1936-086X, Bd. 14 (2020), 10, S. 12885-12894
Chemical vapor deposition is a widely used material deposition technique. It commonly provides a uniform material flux to the substrate to cause uniform thin film growth. However, the ability to precisely adjust the local deposition rate would be highly preferable. This communication reports on a chemical vapor deposition method performed in a localized and programmable fashion by introducing an electrically charged and guided molecular flux. This allows for local adjustments of the deposition rate and three-dimensional shape by controlling the electric fields. Specifically, the precursor molecules are charged and then guided by arrays of electrodynamic funnels, which are created by a patterned dielectric layer, to predetermined deposition locations with a minimal spot size of 250 nm. Furthermore, nearest neighbor coupling is reported as a shaping method to cause the deposition of three-dimensional nanostructures. Additionally, the integration of individually addressable domain electrodes offers programmable charge dissipation to achieve an ON/OFF control. The described method is applicable to a wide variety of materials and precursors. Here, the localized and programmable deposition of three-dimensional copper oxide, chromium oxide, zinc oxide, and carbon nanowires is demonstrated.
https://doi.org/10.1021/acsnano.0c03726
Methodology for benchmarking radio-frequency channel sounders through a system model. - In: IEEE transactions on wireless communications, Bd. 19 (2020), 10, S. 6504-6519
Development of a comprehensive channel propagation model for high-fidelity design and deployment of wireless communication networks necessitates an exhaustive measurement campaign in a variety of operating environments and with different configuration settings. As the campaign is time-consuming and expensive, the effort is typically shared by multiple organizations, inevitably with their own channel-sounder architectures and processing methods. Without proper benchmarking, it cannot be discerned whether observed differences in the measurements are actually due to the varying environments or to discrepancies between the channel sounders themselves. The simplest approach for benchmarking is to transport participant channel sounders to a common environment, collect data, and compare results. Because this is rarely feasible, this paper proposes an alternative methodology - which is both practical and reliable - based on a mathematical system model to represent the channel sounder. The model parameters correspond to the hardware features specific to each system, characterized through precision, in situ calibration to ensure accurate representation; to ensure fair comparison, the model is applied to a ground-truth channel response that is identical for all systems. Five worldwide organizations participated in the cross-validation of their systems through the proposed methodology. Channel sounder descriptions, calibration procedures, and processing methods are provided for each organization as well as results and comparisons for 20 ground-truth channel responses.
https://doi.org/10.1109/TWC.2020.3003617
Development of a cantilever calibration device :
Entwicklung einer Cantileverkalibriereinrichtung. - In: Technisches Messen, ISSN 2196-7113, Bd. 87 (2020), 10, S. 622-629
Das Messen kleiner Kräfte ist in vielen wissenschaftlichen Bereichen, wie beispielsweise der Physik oder Biologie, erforderlich. Bei Kräften im Bereich von Nanonewton werden typischerweise AFM-Cantilever als Kraftsensoren genutzt. Die Steifigkeit des Cantilevers muss bekannt sein um von der Durchbiegung auf die Kraft zu schließen. Aufgrund von Fertigungsabweichungen kommt es zu einer großen Streuung der Cantileversteifigkeit. Für eine präzise Kraftmessung muss daher jeder einzelne Cantilever kalibriert werden. Das derzeit genauste Kalibrierverfahren basiert darauf die Kraft-Weg-Kennlinie des Cantilevers statisch zu messen und ihren Anstieg zu bestimmen. In diesem Artikel wird ein neuartiger Prüfstand beschrieben welcher nach diesem Prinzip arbeitet. Ein Interferometer misst die Position und eine neuartige, eingelenkige Wägezelle die Kraft des Cantilevers. Die Wägezelle wurde in zwei unabhängigen Experimenten mit übereinstimmendem Ergebnis kalibriert. Abschließend werden die Messergebnisse einer Cantileverkalibrierung präsentiert.
https://doi.org/10.1515/teme-2020-0064
Recent research progress of anode materials for potassium-ion batteries. - In: Energy & Environmental Materials, ISSN 2575-0356, Bd. 3 (2020), 2, S. 105-120
The next-generation smart grid for the storage and delivery of renewable energy urgently needs to develop a low-cost and rechargeable energy storage technology beyond lithium-ion batteries (LIBs). Owing to the abundance of potassium (K) resources and the similar electrochemical performance to that of LIBs, potassium-ion batteries (PIBs) have been attracted considerable interest in recent years, and significant progress has been achieved concerning the discovery of high-performance electrode materials for PIBs. This review especially summarizes the latest research progress regarding anode materials for PIBs, including carbon materials, organic materials, alloys, metal-based compounds, and other new types of compounds. The reversible K-ion storage principle and the electrochemical performance (i.e., capacity, potential, rate capability, and cyclability) of these developed anode materials are summarized. Furthermore, the challenges and the corresponding effective strategies to enhance the battery performance of the anode materials are highlighted. Finally, prospects of the future development of high-performance anode materials for PIBs are discussed.
https://doi.org/10.1002/eem2.12059
Modeling of single-walled carbon nanotube binding to nitric oxide synthase and guanylate cyclase molecular structures. - In: Neurophysiology, ISSN 1573-9007, Bd. 52 (2020), 2, S. 110-115
Previously, we have demonstrated that water dispersible single-walled carbon nanotubes (SWCNTs) may be used in low therapeutic doses in antihypertensive therapy as promising agents capable of activating constitutive nitric oxide synthase (NOS) in spontaneously hypertensive rats, thus increasing the NO production in central and peripheral elements of the cardiovascular system [1]. Here we confirm this effect by docking and molecular dynamics simulations, clearly showing that SWCNTs may interact with NOS and guanylate cyclase molecular structures.
https://doi.org/10.1007/s11062-020-09859-0