Wyniki wyszukiwania - Biblioteka Nauki

1

Pumping Capacity of Pitched Blade Multi-Stage Impellers

100%

Jirout T.

Chemical and Process Engineering

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2014

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tom 35

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nr 1

47-53

EN

This paper extends knowledge about flow in an agitated batch with pitched blade multi-stage impellers. Effects of various geometrical parameters (blade number, distance between impellers) of pitched blade multi-stage impellers on pumping ability have been investigated. Axial velocity profiles were measured by LDA (Laser Doppler Anemometry). Axial pumping capacities were obtained by integration of measured axial velocity profiles in outflow from impellers. Main attention was focused on the effect of the distance between impellers in multi-stage configurations, on their pumping capacity and flow in the mixing bath in comparison with an independently operating pitched blade impeller with the same geometry. In case of a relatively close distance between impellers H3/d = 0.5 - 0.75, the multi-stage impeller creates only one circulation loop and the impellers itself behave identically as pumps in series. However for relative higher distance of impellers than H3/d = 1.25, the multi-stage impeller creates two separated circulation loops.

2

Effects of a fully submerged boulder within a boulder array on the mean and turbulent flow fields: Implications to bedload transport

86%

Papanicolaou A. , Kramer C. , Tsakiris A. , Stoesser T. , Bomminayuni S. , Chen Z.

Acta Geophysica

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2012

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tom Vol. 60, no. 6

1502-1546

EN

The objective of this coupled experimental and numerical study is to provide insight into the mean and turbulent flow fields within an array of fully submerged, isolated, immobile boulders. Our study showed that the velocity defect law performed well for describing the mean flow around the boulder within the array. A prerequisite, however, was to accurately estimate the spatial variability of u* around the boulder, which was achieved via the boundary characteristics method. The u* exhibited considerable spatial variability within the array and form roughness was shown to be up to 2 times larger than the skin roughness in the boulder near-wake region. Because the boulders bear a significant amount of the flow shear, the available bed shear stress for entrainment of the mobile sediment, τols, near the boulders was roughly 50% lower than the ambient τols. The τols variability induced by the boulders could lead to a threefold overestimation of the sediment transport rate.

3

Energy saving PMSM position control respecting Coulomb friction

72%

Minarech P. , Vittek J. , Szychta E. , Luft M.

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2011

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tom nr 6

EN

The paper describes development of a new energy saving control algorithms for precise position control of permanent magnet synchronous motor. Designed control algorithms limit energy consumption for defined rotor position maneveur, increase efficiency of the drive and contribute to the substantial improvements of environment. Overall position control system consists of three parts. As the first part, the 'minimum energy generator' computes a special acceleration, velocity and position profile, where the magnitude and time of acceleration or deceleration are determined such a way that comply with position demand and prescribed time for position maneuver. The role of 'feed-forward precompensator', as a second part, is to achieve precise tracking of the prescribed reference position with zero dynamic lag. Third part is position controller, which can be based on field oriented control, forced dynamics control or sliding mode control. Developed 'energy saving control algorithms' are easy to implement digitally and can be exploited for position control of existing a.c. drives.

PL

Artykuł opisuje wyznaczenie nowych algorytmów energooszczędnego sterowania do precyzyjnego sterowania położeniem silnika synchronicznego z magnesami trwałymi. Zaprojektowane algorytmy sterowania ograniczają zużycie energii dla określonego manewru położeniem wirnika, zwiększają efektywność napędu i przyczyniają się do istotnej poprawy środowiska. Ogólnie rzecz biorąc, system sterowania położeniem składa się z trzech części. Jako część pierwsza, "generator minimalnej energii" oblicza szczególne profile przyspieszenia, prędkości i położenia, gdzie wielkość i czas przyspieszenia lub deceleracji są wyznaczane w taki sposób, że są zgodne z żądanym położeniem i czasem przewidzianym na manewr zmiany położenia. Rolą "wstępnego kompensatora sprzężenia antycypacyjnego", jako drugiej części, jest osiągnięcie precyzyjnego namierzenia przewidzianego położenia referencyjnego (odniesienia) przy zerowym opóźnieniu dynamicznym. Trzecią częścią jest sterownik położenia, który może bazować zorientowanym sterowaniu, sterowaniu wymuszonym dynamiką lub sterowaniu ślizgowym. Opracowane "algorytmy energooszczędnego sterowania" są łatwe do wdrożenia cyfrowego i mogą być stosowane do sterowania położeniem istniejących napędów prądu zmiennego.

4

Testing air-flow velocity distributions across a section of a duct at a mine-ventilation station

72%

Dziurzyński W. , Krach A.

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2001

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tom Vol. 46, nr 3

227-236

EN

This paper details the construction of air volume flow rate measurement apparatus in mine ventilation ducts using the profile of velocities integration method and describes measurements with the use of this equipment to take measurements the duct in a main, multi-fan ventilation station installed in one of the mines in the Polish copper field. The results of the in-situ measuring procedure were used to calculate the distribution of velocities of air-flow across the duct section for single fans and with various parallel configurations of fans.

PL

W artykule przedstawiono budowę urządzenia do pomiaru strumienia objętości powietrza w kopalnianych kanałach wentylacyjnych metodą całkowania bryły prędkości oraz podano opis wykonania pomiaru z zastosowaniem tego urządzenia w kanale wielowentylatorowej stacji głównego przewietrzania jednej z kopalń zagłębia miedziowego. Wyniki przeprowadzonych pomiarów wykorzystano do wyznaczenia pola prędkości przepływu powietrza w kanale przy pracy pojedynczych wentylatorów i różnych wariantów pracy równoległej.

5

Double-averaged velocity profiles over fixed dune shapes

72%

McLean S. R. , Nikora V. I. , Coleman S. E.

Acta Geophysica

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2008

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tom Vol. 56, no. 3

669-697

EN

Spatially averaged profiles of time averaged velocity, using integrals over thin horizontal slabs (Cartesian double average), are employed in characterizing the flow over fixed dune shapes. For comparison the spatial averaging method of Smith and McLean (1977) that averages along lines at constant distance from the local bed elevation is also investigated. The Cartesian double averaged profiles of the inverse of the velocity shear are nearly constant below the crest elevation, but increase rapidly above the crest level. This results in velocity profiles that increase linearly with distance from the bed below the crest. Above the crest it can be argued that the velocity increases logarithmically, but a power law profile can also be argued. Spatially averaged eddy viscosity profiles are calculated by multiplying the average Reynolds stress by the inverse shear. The resulting profile is more complex than the uniform flow counterpart.

6

Herschel - Bulkley model for two-phase blood flow in narrow vessel

58%

Das S. , Saha G. C.

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2010

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tom Vol. 15, no 1

19-34

EN

A mathematical model for a two-phase blood flow through a circular narrow vessel has been developed by considering blood to be a non-Newtonian liquid of Herschel-Bulkley type and taking into consideration the slip velocity at the wall of the vessel. Analytical expressions for velocities of blood in the peripheral layer and central core layer, flow rate and apparent fluidity of blood have been obtained and their natures are portrayed graphically for different parameters.