19 research outputs found
Use of time-harmonic FE analysis to compute rotor eddy-current losses in synchronous machines subject to distorted stator currents
No full textThermal Field-Flow Fractionation of Charged Submicrometer Particles in Aqueous Media
No full textThermal field-flow fractionation (ThFFF) of various types of submicrometer silica particles in aqueous media is experimentally investigated under an extended range of medium ionic strengths with and without the presence of surfactant. The experiments were designed to examine the applicability to submicrometer particles of the theory of charged nanoparticles thermodiffusion recently proposed by Parola and Piazza (Parola, A.; Piazza, R. Eur. Phys. J. E. 2004, 15, 255-263). In particular, the expression for the calibration function in terms of particle radius and channel temperature is derived and experimentally verified. Moreover, retention is expected to be dependent on particle surface potential and charge, and on ionic strength. These dependences are experimentally investigated and the pertinent relationships and correlations derived. The effect of heavy metal adsorption on the silica surface was investigated, and significant ThFFF retention changes were measured. Independent measurements of the zeta potential (-potential) indicated that a decrease in the surface charge of a silica particle is a consequence of heavy metal adsorption, which is, in turn, correlated to the observed decrease in ThFFF retention
Use of time-harmonic finite-element analysis to compute stator winding eddy-current losses due to rotor motion in surface permanent-magnet machines
No full textIt is known from the literature that in electric machines with open stator slots, the air-gap flux partly enters the slot openings and induces eddy currents in the conductors placed closest to the air gap, possibly causing local overheating issues. For the study of such phenomenon, time-stepping finite-element analysis
(TSFEA) is employed by many authors. This paper presents an alternative approach based on a set of time-harmonic finiteelement analysis (THFEA) simulations. The proposed method can be applied to surface permanent-magnet machines and offers the advantage of a shorter computation time with respect to THFEA. It is also more suitable for being integrated into automatic design optimization programs. The accuracy of the approach is assessed
by comparing stator eddy-current losses independently computed by THFEA and TSFEA for different machine geometries and operating
conditions. Results obtained in the two ways are shown to be in good accordance
A high-performance 640-kW 10.000-rpm Halbach-array PM slotless motor with active magnetic bearings. Part II: Manufacturing and testing
No full textThe ongoing gas industry expansion calls for quick and strong advances in turbomachinery-coupled highspeed electric motors. Very high efficiency, dynamic performance and reliability are among the main requirements to be met at competitive costs by electric machine suppliers. This paper reports on an industrial R&D project aimed at finding the best compromise between performance targets and production cost reduction through the realization of a 640-kW 10.000-rpm PM motor prototype. The preliminary and optimization design of the motor have been covered in a companion paper (Part I). Here the manufacturing and testing of the prototype are covered. The main technology challenges encountered throughout the manufacturing process are addressed. Furthermore, the paper reports on the testing campaign conducted on the motor under converter supply and in different load and speed conditions. The prototype testing was successful and proved the possibility to reach and exceed a 98% motor efficiency target with affordable costs and available technologies
A high-performance 640-kW 10.000-rpm Halbach-array PM slotless motor with active magnetic bearings. Part I: Preliminary and detailed design
No full textThe ongoing gas industry expansion calls for quick and strong advances in turbomachinery-coupled highspeed electric motors. Very high efficiency, dynamic performance and reliability are among the main requirements to be met at competitive costs by electric machine suppliers. This paper reports on an industrial R&D project aimed at finding the best compromise between performance targets and production cost reduction. The development of a 640-kW 10.000-rpm PM motor prototype with slotless stator and Halbach-array magnetically-levitated PM rotor is discussed, including in particular the basic technology selection and design optimization processes. In a companion paper (Part II), prototype manufacturing and testing will be reported to assess the technology and design solutions adopted
Investigation into induction motor equivalent circuit parameter dependency on current and frequency variations
No full textInduction motors are presently the most widespread kind of electric machinery used for industrial and general purpose applications. The parameters of their equivalent circuit model can be determined with a combination of magneto-static and time-harmonic Finite Element Analysis (FEA) simulations. This paper investigates how equivalent circuit parameters depend on current and frequency variations. Calculation results obtained from FEA combined with analytical formulas are experimentally assessed by measurements on a small sample motor used for household appliances
Low Temperature Scanning Tunneling Microscope and Its Application to Material Characterization
No full textA low temperature and high vacuum compatible fiber optic interferometer was designed and constructed to debug a malfunctioning low temperature scanning tunneling microscope (LT-STM). With its help, the temperature dependent behavior of a Pan-style piezoelectric actuator was studied. The scanning tunneling microscope (STM) was modified accordingly and worked reliably below 10 K.
Other properties of the STM were also improved. The electronic noise was reduced from hundreds of picoamps to approximately 10 picoamps by improving the shielding and avoiding ground loops. An eddy current damper was implemented to reduce the vibrational noise. A new mechanical sample stage was introduced to allow manipulation of the sample during experiments. As a result, beautiful atomic resolution images of graphite and self-assembled dodecanethiol monolayer on gold were obtained.
Scanning tunneling spectroscopy (STS) measurements were carried out on flux-grown HfNiSn single crystals. Instead of a semiconductor gap, a square root zero bias anomaly (ZBA) which typically presents in disordered systems was observed. Both the temperature dependent resistivity and the magnetoresistance of HfNiSn show characteristic features of disordered systems as well. Below 200 K, the resistivity saturates or obeys a 3 dimensional variable-range hopping (VRH) behavior. The magnetoresistance can be well explained by the Fukuyama-Hoshino (F-H) model for 3D weak anti-localization (WAL). These results indicate that the intrinsic anti-site disorder in HfNiSn may cause Anderson localization. In addition, theories developed and refined in the 1980's for the electron-electron interaction in disordered systems can be used to understand the physical properties and to guide the modifications of half Heusler materials
Kosterlitz-Thouless Transition in Helium Films
No full textJournals published by the American Physical Society can be found at http://journals.aps.org
A nuclear magnetic resonance probe of Fe-Al and Al20V2Eu intermetallics
No full textAl-rich Fe-Al systems (FeAl2, Fe2 Al5 and Fe4Al13) and Al20V2Eu have complicated
structures with quasicrystal-like features making these materials potentially of
interest for magnetic behavior. However, there is not much work on these materials.
To study the variety of magnetic properties, we use NMR, magnetic susceptibility,
specific heat and other methods in this work.
The microscopic electronic and magnetic properties of the Al-rich Fe-Al system
and Al20V2Eu have been studied via 27Al NMR at temperatures between 4 and 500 K.
The results of spin lattice relaxation rates reveal a pseudogap in Fe4Al13 and Fe2Al5
around the Fermi-level in the density of states. Besides, a square well gap with a width
of 2 meV and center at Fermi energy was detected by specific heat measurements in
Fe2Al5. Both Fe4 Al13 and Fe2Al5 are non-magnetic systems with dilute magnetic defects,
while FeAl2 is a concentrated local magnetic moment system. In Al20V2Eu, a
crossover was observed in NMR, magnetization and transport measurements. Above
40 K, Eu(2+) local magnetic moments dominate; below 40 K, a transition to a Kondo
regime is observed, where the Kondo effect leads to the reduction of localized moments
due to the formation of a spin-compensated Kondo cloud. With increasing
magnetic field, f electrons participate more and more in excitations near the Fermi
level and a heavy-Fermion state was observed through specific heat measurements at
high magnetic field
