Periodic Fluid Motion Research Articles

Effect of Taylor vortex wavelength on polymorphic crystallization of L-histidine

Axial wavelength is a key characteristic parameter of Taylor vortex flows. Thus, in the current study, the effect of Taylor vortex wavelength on the polymorphic nucleation and phase transformation of L-histidine was examined. The vortex wavelength was altered by altering the gap width between the outer and inner cylinders. Further, the vortex velocity was changed by controlling the inner cylinder rotation speed. Owing to the promotion of stable nucleation by the periodic fluid motion, the primary polymorphic fraction of the stable Form A of L-histidine in Taylor vortex flow [Couette–Taylor (CT) crystallizer] was much greater than that in a turbulent eddy flow [mixing tank (MT) crystallizer]. As the vortex wavelength decreased, stable nucleation was promoted, thus increasing the initial polymorphic fraction of the stable Form A. Moreover, the initial polymorphic fraction of the stable Form A increased as the vortex velocity increased. These experimental results are described based on molecular alignment effect of Taylor vortex on stable nucleation. The phase transformation of L-histidine was also strongly influenced by the vortex wavelength and vortex velocity. Hence, the rate of phase transformation in CT crystallizer was approximately ten-fold better than MT crystallizer.

Unsteady MHD Rear Stagnation-Point Flow of a Hybrid Nanofluid with Heat Generation/Absorption Effect

The study of unsteady flow is essential in various engineering systems, for instance, the periodic fluid motion and start-up process. Therefore, this numerical study focuses on examining the unsteady magnetohydrodynamics (MHD) rear stagnation-point flow in Al2O3-Cu/H2O hybrid nanofluid past a permeable stretching/shrinking surface with the impact of heat generation/absorption. By choosing a suitable similarity transformation, partial differential equations are transformed into a system of nonlinear ordinary differential equations and solved using the bvp4c function in the MATLAB package. The effects of the solution domain’s operating parameters are analysed, and dual solutions are observable as the sheet shrinks. It is found that the addition of the suction parameter escalates the heat transfer efficiency. Eventually, the existence of the unsteadiness parameter and the heat generation/absorption effect significantly encourage heat transfer deterioration.

Spherical agglomeration of nickel-manganese-cobalt hydroxide in turbulent Batchelor vortex flow

In this study, turbulent Batchelor vortex flow, due to its periodic fluid motion, was used to produce highly dense and spherical Ni-Mn-Co (NMC) hydroxide agglomerates (microparticles) in a rotation disk crystallizer. A high shear stress (1500 rpm) in the turbulent Batchelor vortex regime, and the presence of ammonia at a pH of 12, help form spherical shaped agglomerates with a high tap density (2.1 g/m3) from irregular shaped agglomerates. The coefficient of variation (0.38) of the agglomerates also narrowed while using this approach. When sufficient ammonia was supplied to form a complex ([M(NH3)n]2+) with all M2+, the reaction rate with OH– slowed and the agglomeration process was affected by the high shear stress in a sufficient amount of time. On the contrary, when ammonia is not present in the reaction solution, free M2+ ions rapidly react with OH– ion, resulting in irregular shaped agglomerates. The pH was related to the OH– concentration and all of the [M(NH3)n]2+ complex was consumed during the agglomeration process when the OH– concentration reached a mol ratio of 1:2 ([M(NH3)n]2+:OH–). When the ammonia feeding rate was higher than 1.2 mL/min, highly dense agglomerate was obtained. However, the [M(NH3)n]2+ complex could not be generated when the pH exceeded a value of 12, according to the mass and equilibrium calculations. In addition, the residence time was significantly shorter (30 min) in the turbulent Batchelor vortex flow regime compared to previous studies (~12 to 50 h). This study suggests that the high shear stress in the turbulent Batchelor vortex flow regime can be effectively used for making highly dense and spherical NMC hydroxide, with high tap density, in a short amount of time.

Influence of Fluid Motions on Polymorphic Crystallization of l-Histidine: Taylor Vortex Flow and Turbulent Eddy Flow

The mechanistic influence of fluid motions, such as a Taylor vortex flow and turbulent eddy flow, on the polymorphic crystallization of l-histidine was investigated. Couette–Taylor (CT) and mixing tank (MT) crystallizers were used for the Taylor vortex flow and turbulent eddy flow, respectively. Due to its periodic fluid motion, the Taylor vortex flow was found to be more favorable than the turbulent eddy flow for polymorphic nucleation of the stable phase. Thus, the polymorphic fraction of the stable phase at the induction point (called the “initial stable polymorphic fraction”) in the CT crystallizer was always much higher than that in the MT crystallizer for all variations of the crystallization conditions, including the rotation/agitation speed, ethanol fraction in the mixture solvent, and cooling rate. When increasing the rotation speed of the inner cylinder in the CT crystallizer, the initial stable polymorphic fraction was significantly increased and reached 100% at a rotation speed above 700 rpm. ...

Agglomeration of Ni-rich hydroxide crystals in Taylor vortex flow

The agglomeration of Ni-rich hydroxide crystals (Ni0.9Co0.05Mn0.05)(OH)2 was studied in a continuous Couette-Taylor (CT) crystallizer. Due to the excellent mixing and periodic fluid motion of the Taylor vortex flow in the CT crystallizer, the formation of spherical and uniform agglomerate particles of Ni-rich crystals was promoted as the rotation speed and the mean residence time increased. Thus, for a rotation speed of 1500rpm and mean residence time of 60min, with a high feed concentration of 3.0mol/L produced a high tap-density of agglomerate particles of 2.13g/cm3, which is higher than any previously reported values. These results were due to the excellent micromixing effects of Taylor vortex in the CT crystallizer. In addition, the long mean residence time contributed to the formation of spherical particles due to the extended exposure of the agglomerates to the fluid shear. Furthermore, the formation of spherical particles was optimized at a pH of 12.0 and required a high concentration of ammonia due to the high composition of Ni ions in the Ni-rich hydroxide crystals and the short mean residence time in the continuous CT crystallizer. Moreover, when comparing the crystallization in a continuous MSMPR crystallizer, which required a long mean residence time of 12h for a high tap-density of above 2.0g/cm3, the continuous CT crystallizer was clearly much more effective for the formation of uniform spherical particles due to the more efficient hydrodynamic fluid motion of the Taylor vortex in the CT crystallizer in contrast to the random turbulent eddy motion in the MSMPR crystallizer.

The pressure–velocity correlation in oscillatory turbulent flow between a pair of bluff bodies

Turbulent flow measurements were conducted between two bluff bodies set in uniform flow in tandem arrangement. The velocity field obtained with PIV was averaged with respect to either time or phase of periodic pressure oscillation induced by vortex shedding from the bluff body, i.e., Reynolds decomposition or three-level decomposition. The Reynolds stresses caused by periodic fluid motion was found excessively large compared with those related to turbulent fluctuations in the entire flow field in observation. The PIV data were used to solve the discrete Poisson equation of instantaneous pressure. The effect of organized vortex motion caused strong correlations between velocity and pressure gradient when observed from the framework of the Reynolds averaging.

Fluid and Particle Laser Doppler Velocity Measurements and Mass Transfer Predictions for the Usp Paddle Method Dissolution Apparatus

AbstractThis research was motivated by the lack of experimental data concerning the complex flow fields produced by the USP Paddle Method Dissolution Test Apparatus, which influence the reproducibility and sensitivity of the resulting dissolution data.A one-component He-Ne fiber optics laser Doppler anemometer and a conditional sampling computer data acquisition provided unique three-dimensional fluid velocity measurements in most regions of the fluid inside the vessel. Tangential velocities which are predominant in magnitude decrease as a function of distance from the paddle to the liquid surface. Low magnitude circulation patterns in the axial direction exist with little Interaction between the fluid above and below the paddle. The radial velocity component also exhibits a low magnitude. In the vicinity of the paddle, a periodic fluid motion produced by the wake formed behind the paddle exists. Close to the bottom of the vessel, tangential fluid velocities were approximately equal to solid body rotation...

A comparison of stability and accuracy of some numerical models of two‐dimensional circulation

AbstractThe purpose of the paper is two‐fold: Firstly, we develop stream function‐‐vorticity and primitive variable finite element models of two‐dimensional barotropic equations that satisfy the conservation of mean vorticity, mean squared vorticity (or enstrophy) and mean kinetic energy, and scondly, we present a comparative study of a number of numerical schemes for their accuracy in phase speed as well as in amplitude calculations for a two‐dimensional, time‐dependent, stream function‐‐vorticity equation for periodic fluid motion in a channel. A circular vortex is placed in a uniform channel flow of a constant velocity (U) as an initial condition. An analytic solution exists for the problem such that the vortex moves with a constant speed U conserving the shape of the vortex: where U, ψ0 a are constants. This example makes it easier to identify the cause of phase speed error, either due to linear or non‐linear processes, and furthermore, to find a satisfactory scheme for time integration. The numerical schemes compared include: Arakawa Jacobian,1 Arakawa–Matsuno scheme, Galerkin finite element, Lax–Wendroff, leap‐frog, and Crank–Nicholson. The effect of a variational adjustment (see Sasaki16) is also studied. Computational time, RMS errors in stream function and vorticity, and the conservation of the mean kinetic energy and enstrophy are compared at the end of 120 (one period) and 240 (two periods) time steps. The study indicates that the numerical scheme that employs finite elements in space (same as Arakawa Jacobian) and Crank–Nicholson in time is the most accurate among the schemes studied.

Stability of periodic motion of fluid in a planar channel

The stability of periodic motion of a fluid in a planar channel was investigated experimentally. Two mechanisms of departure from stability of rectilinear motion — at high and low frequencies, respectively — were observed. The critical Reynolds number was found as a function of the pulsation frequency. The results of the quasistationary theoretical approach to the stability of periodic flows [1] agree with the experiment.

Wave Entrainment of Sediment from Rippled Beds

An experimental investigation was conducted with an oscillatory flow water tunnel to elucidate the mechanism of sediment entrainment by periodic fluid motion past rippled beds. The instrumentation used included an optical-type sediment concentration analyzer, a hot-wire anemometer, and an IBM 1801 Data Acquisition and Control System. The signal-averaging technique used to analyze the data permitted decomposition of the concentration and velocity signals into mean, periodic, and random components. The process of sediment entrainment and suspension is explained in terms of flow separation from the ripple crest together with the flow reversal. Simultaneous measurement of temporal and spatial distributions of suspended sediment concentration. Simultaneous measurement of temporal and spatial distributions of suspended sediment relationship and vertical fluid velocity in the region just above the bed showed that the conventional one-dimensional continuity relationship for steady uniform flow is inadequate; the horizontal gradient of streamwise sediment flux is comparable in importance to the vertical gradient of vertical flux of sediment.

Progress in Parametric Pumping

Abstract Parametric pumping is the name given to a novel separation device developed by Richard Wilhelm and co-workers(1,2,3). The principle of operation depends on an immobile phase (e.g. adsorbent) to alternately retard and release selected species. This action coupled with a synchronous periodic fluid flow causes the selectively adsorbed species to be literally pumped from one region to another. In the successful experiments(2,3) a single packed column was used with reservoirs attached to each end. A water jacket surrounding the bed was heated or cooled synchronously with periodic fluid motion. Figure 1 outlines the principle of operation. Essentially, the process operates in a “bucket-brigade” fashion. If one follows the travels of a single solute (see Figure 1) in a non-adsorbable solvent we see that during downflow the column is cooled thus retarding (adsorption step) the solute, allowing the solvent to move unimpeded. When the flow direction changes to an upward motion, the column is heated, releas...

A Mechanical Theory of Spinning Detonation

A review of published experimental data and theoretical discussions of spinning detonation reveals that there does not exist a consistent explanation of all the characteristics of such a phenomenon, particularly the dependence of spinning frequency upon tube diameter. In view of this, it is proposed to treat the problem principally from a hydrodynamic viewpoint by considering a possible periodic fluid motion with a characteristic frequency. It is found that the calculated natural frequencies of vibration of the gaseous products behind a detonation wave agree closely with the measured frequencies of spinning detonation previously published in the literature. An analysis of such vibrations in the light of experimental evidence indicates that the vibratory motion is principally transverse. Of the various possible modes of vibration, the one which is observed depends upon the mixture composition and the tube size. The observed existence of pressure waves in the wake of a spinning detonation wave is probably due to nonuniform combustion at the detonation front. It is shown how the initiation or cessation of combustion in a plane wave gives rise to compression or expansion waves respectively, and how a nonplanar disturbance excites a transverse vibration of characteristic frequency. It is proposed that the uneven combustion of the spinning detonation wave is sustained by the heating and cooling effects of the vibratory pressure waves, which are themselves generated by such irregular combustion; i.e., spinning detonation is a self-excited vibratory phenomenon. Its appearance may thus be-attributed to the susceptibility of the reaction rate to the heating or cooling effects of pressure waves.

LXI. On the stability of steady and of periodic fluid motion (continued from May number).—Maximum and minimum energy in vortex motion

LXI. <i>On the stability of steady and of periodic fluid motion</i> (continued from May number).—<i>Maximum and minimum energy in vortex motion</i>

LII. On the stability of steady and of periodic fluid motion

(1887). LII. On the stability of steady and of periodic fluid motion. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 23, No. 144, pp. 459-464.