Lock-on characteristics behind two side-by-side cylinders of diameter ratio two at small gap ratio

The lock-on characteristics, the detailed interactions and downstream evolutions of the wakes behind side-by-side cylinders of unequal diameter (D/d?=?2), spaced by a gap ratio 0.75 (G/D?=?0.75), are investigated at Reynolds number 600 by the dye flow visualization, laser Doppler anemometry (LDA) and particle image velocimeter (PIV) velocity measurements. The lock-on frequency bands are studied by LDA and PIV at Reynolds number 2,000. The D, d and G are the diameters of the large, the small cylinders and the net gap between two cylinders, respectively. Periodic excitations, in form of rotary oscillation about the cylinder center, are applied to the large cylinder with the same amplitude. It is found that while the large cylinder is excited, two lock-on frequency bands of the wake behind the large cylinder are detected. These two lock-on frequency bands correspond to the primary and the one-third sub-harmonic lock-on of the wake behind large cylinder, respectively. These two lock-on frequency bands distribute symmetrically about the fundamental and the third superharmonic of the natural shedding frequency behind a single cylinder at the same Reynolds number. The left-shifted frequency band (1.8?≤?f _e /f _os ?≤?2.0) is not considered as a locked-on frequency band because the phase difference between two excitation frequencies across f _e /f _os ?=?2.0 vary significantly. While the wake behind the large cylinder is locked-on at f _e /3 (or f _os ), the gap flow becomes unbiased and the frequency of the wake behind small cylinder remains around the natural shedding frequency. Thus, the frequency band of 3.0?≤?f _e /f _os ?≤?3.22 is also not locked-on because the phase difference in the narrow wake excited at f _e /f _os ?=?2.93 and 3.07 changes significantly. Note f _e and f _os denote the excitation frequency and the natural shedding frequency behind a single large cylinder, respectively.     

An experimental investigation of swirl atomizer sprays

In our previous studies (Chu et al. in Heat Mass Transf 43(11):1213–1224, 2007), a theoretical model of swirl atomizers was successfully established. From the analysis, the equations for the droplet size, velocity components, the boundary layer thickness and the spray cone angle were deduced based on the fundamental governing equations. The purpose of this study is to further compare the experimental result with the theoretical one already gained by a satisfactory embodiment of series of experiments. The aim is to corroborate the analytical results of the influence of atomizer construction and controlled pressure difference on typical swirl chambers. The results provide the droplet diameter as a function of pressure difference, swirl atomizer geometry, flow rate, spray cone angle. The experimental outputs also show a good confirmation of theoretical results and can also be used for further optimization on existing swirl chambers. Based on the results obtained, an optimization methodology on characteristics of swirl atomizers is proposed with the adjustment of individual design parameter and the matching flow number.     

A theory for grain-size reduction in granular flows of spheres

Summary We derive a kinetic theory for homogeneous granular shear flows of identical spheres in which collisions between particles result in small fractures on their peripheries and, over time, effectively reduce their average diameter. In obtaining statistically averaged constitutive relations for the rates of energy dissipation and mass loss, we employ the integral expression derived by Jenkins and Savage [1983] for the collisional source of a particle property. However, in calculating the stress, we modify their expression for the collisional flux in order to ensure that the stress is symmetric when the particles interact through central forces. The constitutive relations are employed in the balance equations for mass, momentum, and energy in order to predict, for a fixed shear rate and particle number density, the manner in which the solid fraction, granular temperature, and induced stresses vary with time.

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Zusammenfassung Wir entwickeln eine kinetische Theorie für die homogene Scherströmung von identischen Kugeln, in welcher die Zusammenstösse der Teilchen kleine Risse in ihrer Oberfläche verursachen und sich dadurch ihr mittlerer Durchmesser mit der Zeit verringert. Um die statistisch gemittelten konstitutiven Beziehungen für die Energiedissipations- und Massenverlustraten zu erhalten, verwenden wir den von Jenkins und Savage [1983] hergeleiteten Integralausdruck für die von den Kollisionen verursachte Quellenstärke einer Teilchenzustandsgrösse. Bei der Berechnung der Spannung verwenden wir jedoch einen abgeänderten Ausdruck für den Fluss durch Kollision; dadurch wird sichergestellt, dass der Spannungstensor symmetrisch ist, wenn die Kontaktkraft zwischen den Teilchen normal zur Kontaktebene wirkt. Die konstitutiven Beziehungen werden in die Gleichungen für die Erhaltung von Masse, Impuls und Energie eingesetzt, um zu berechnen, wie sich der Festkörperanteil, die Granulartemperatur und die induzierten Spannungen als Funktion der Zeit verändern; der Geschwindigkeitsgradient und die Anzahl Teilchen pro Volumen sind dabei konstant.

     

The effect of F substitution on the magnetic properties of Nd−Fe−B based compounds

Various efforts are currently undertaken to raise the relatively low Curie temperature of the otherwise promising Nd?Fe?B type permanent magnet material. The substitution of Fe by several elements was found to increaseT _c, which, on the other hand, can be accompanied by a reduction of the magnetocrystalline anistropy. In the present paper a systematic Mössbauer study was carried out, using Co, Ni, Al, Si and Ga as substituents. The specific influence of each element upon the magnetic properties is attributed to its preference for entering a certain Fe lattice site. Simple atomic size considerations are proved to be insufficient for explaining the preferred occupation observed experimentally. Obviously the local electronic structure has to be studied more carefully. Finally, the interplay between magnetism and metallurgy (particularly the formation of precipitations), is found to be of some importance.     

Improved Synthesis of 9- and 10-Methylbenz[a] Anthracenes

The synthesis of 9- and 10-methylbenz[a]anthracenes by improved methods are described. These new procedures are simple and convenient, and provide the title compounds in good yields and high purity.     

Induction of differentiation of human leukemia cells by various combinations of cytokines and low-molecular-weight inducers

To explore agents for differentiation therapy of leukemias, various combinations of cytokines and low-molecular-weight inducers were examined for differentiation-inducing activity toward three kinds of human leukemia-derived cell lines. The strongest differentiation inducing activity on promyelocytic HL60 cells and histiocytic U937 cells was obtained by combining recombinant tumor necrosis factor (rTNF), interferon-gamma (IFN-gamma), retinoic acid (RA), and 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3). For myeloblastic ML1 cells, the combination of rTNF, IFN-gamma, and RA had the strongest differentiation-inducing activity.