Volume 20, Issue 4 - Special Issue: Multiphase Flows in Process Engineering: Recent Experimental, Theoretical and Numerical Developments; Guest Editors: Shuli Shu, Xizhong Chen, Zhenghong Luo and Jamal Chaouki

Supersonic steam injection from underwater vehicles into surrounding bulk water exhibits the formation of coherent structures due to the interfacial interaction between the steam and water. The mixing between the two is a function of the rate of growth of shear layer. In present work, experimental study is conducted with minor contribution from the CFD, to highlight the phenomena associated to the high-pressure steam injection into a pool of water under the influence of periodic cavitation which occurs near the steam's nozzle exit with its opening being at right angle to the opening of the exit nozzle. PIV setup along with piezoelectric acoustic emission sensors as well as LM35 temperature sensors and pitot tubes were applied to characterize the growth of the shear layer as a function of periodic cavitation with a range of steam's operating pressure. Based on the normalized shear growth rate as well as the Strouhal number and the normalized pitot thickness, the effect of rising in the cavitation on the variations of the thickness of the shear layer was studied. It was observed that higher area under the influence of the shear layer was due to the domination of the coherent flow structures, which influenced improved mixing between the steam and water. Comparison of our data with the available shear growth rate in literature shows good agreement when compared as a function of Mach number.

Numerical Simulations are performed, using Eulerian two fluid model (TFM) to investigate the effects of solid volume fraction and no-slip side walls on the settling particles. It is found that average settling velocity decreases with increasing volume fraction for both gas-solid (GS) and liquid-solid (LS) systems, in good agreement with the Richardson-Zaki 1 − ϕ n ${\left(1-\phi \right)}^{n}$ law. It was also noted that average velocity is independent of the boundary condition for both gas-solid (GS) and liquid-solid (LS) systems. The root mean square value of the solid volume fraction shows the increasing trend with volume fraction, caused by the many particle interactions. Furthermore, no-slip sidewalls were found to damp the velocity fluctuations quantitively, while following the well-known ϕ 1 / 2 ${\phi }^{1/2}$ scaling with volume fraction. Side walls were found to act as kinetic trap for the particles, damping the fluctuation near the walls and plateauing in the mid plane. These simulations showed that the GS system shows the higher solid fraction fluctuations that the LS system at the same Reynolds number, mainly because of the higher collision frequency (higher Stokes number) among the particles.

Inspired by several implementations (metal mining, turbine disc, spinning disk, mechanical engineering and drawing of plastic film) of nanoliquid flow between rotating disks, we have reported a theoretical analysis on magnetohydrodynamic flow of kerosene base liquid containing three different nanoparticles namely manganese-zinc ferrite, cobalt ferrite and nickel-zinc ferrite between two parallel rotating-disks. Thermal radiation and convection thermal-conditions are considered. Furthermore, the significant properties of induced magnetic field are accounted to control the flow and thermal transport phenomenon. Furthermore, the temperature distribution is improved by employing Cattaneo-Christov heat flux. This communication is critical in the engineering sector due to different implementations including power technology, cooling reactors, fuel cells etc. The system of nonlinear higher order dimensionless equations is found by applying appropriate similarities-transformations. The exact solution of such strong nonlinear equations is not possible therefore we construct the numerical solution by employing bvp4c (shooting approach) in the MATLAB. Physical trends of velocities, pressure and thermal fields are discussed in detail. The outcomes indicate that stretching parameter of lower disk causes improvement in axial and radial fluid velocity. Fluid radial velocity near the lower disk is improved for growing Reynolds number. Moreover, the thermal field is enhanced for growing thermal Biot parameter at lower disk.

The goal of this research is to investigate the mathematical framework for the MHD flow of hybrid nanoliquids with CNTs and nonlinear thermally radiation over a moving sheet. This model is used for blood-based nanoliquids for two related nanomaterials. To see temperature fluctuations, the nonlinear and linear thermal radiations were used to differentiate the objective of this model. The main governing equations are converted from PDEs to ODEs using similarities transformations. The shooting approach is used to obtain the graphical and numerical results by employing a bvp4c solver in computational software MATLAB. The results of this research may be used to determine the influence of certain important design factors on heat transfer and, as a result, to optimize energy sources. For increasing the volume fraction of nanomaterials, the velocity field is enhanced. The thermal profile increases as the heat source-sink parameter enlarges. The thermal field has been improved to account for the changes in Eckert number and the temperature ratio parameter. For larger estimations of the Brinkman constant, the entropy field is enhanced. For larger estimations of the volume fraction of nanoparticles, the entropy field is enhanced.

The solid-liquid mixing characteristics in a stirred tank with pitched blade impellers, dislocated impellers, and dislocated guide impellers were investigated through using CFD simulation. The effects of impeller speed, impeller type, aperture ratio, aperture length, solid particle diameter and initial solid holdup on the homogeneity degree in the solid-liquid mixing process were investigated. As expected, the solid particle suspension quality was increased with an increase in impeller speed. The dislocated impeller could reduce the accumulation of solid particles and improve the cloud height compared with pitched blade impeller under the same power consumption. The dislocated guide impeller could enhance the solid particles suspension quality on the basis of dislocated impeller, and the optimum aperture ratio and aperture length of dislocated guide impeller were 12.25% and 7 mm, respectively, in the solid-liquid mixing process. Smaller solid particle diameter and lower initial solid holdup led to higher homogeneity degree of solid-liquid mixing system. The dislocated guide impeller could increase solid particle integrated velocity and enhance turbulent intensity of solid-liquid two-phase compared with pitched blade impeller and dislocated impeller under the same power consumption.

The solid-liquid flow field is established in the stirred reactor with baffles and draft tube. Mixing time and suspension quality of the flow field are studied. Based on the Eulerian multiphase flow model and RNG k − ε turbulence model, the CFD model is established for the simulation research. By comparing the experimental data of solid concentration distribution and mixing time with the simulated values, it is proved that the CFD model established can be used to study the flow field in the stirred reactor. The effects of stirring speed, liquid viscosity and solid particle size on mixing time and suspension quality are considered. With the increase of stirring speed, mixing time decreases, mixing uniformity is improved. Mixing time decreases first, then increases slightly with the increase of liquid viscosity, and the suspension quality is improved. When the solid particle size increases, mixing time increases rapidly, but the mixing uniformity becomes worse.

The nanofluid is most advantageous to enhance the heat efficiency of base fluid by submerging solid nanoparticles in it. The metals, oxides, and carbides are helpful to improve the heat transfer rate. In the present analysis, the role of the slip phenomenon in the radiative flow of hybrid nanoliquid containing SiO 2 silicon dioxide and CNTs over in the porous cone is scrutinized. The behavior of the magnetic field, thermal conductivity, and thermal radiation are examined. Here the base fluid ethylene glycol water (C 2 H 6 O 2 −H 2 O) is used. Accepting similarity transformation converts the controlling partial differential equations (PDEs) into ordinary differential equations (ODEs). The numerical solution is obtained by utilizing the Lobatto-IIIa method. The significant physical flow parameters are discussed by utilizing tables and graphs. Final remarks are demonstrating the velocity profile is declined via higher magnetic parameter while boosted up for nanoparticles volume fraction. Furthermore, the thermal profile is enriching via thermal conductivity parameter, radiation parameter, and nanoparticles volume fraction.

This article focuses on the influence of fractal-like tree node (FTN) on the mixing efficiency and pressure drop of the micromixer. The mixing efficiency of FTN micromixers with different branch angle δ  = 30°, 60° and 90° are compared at six kinds of Reynolds (Res). We can get that the micromixer with δ  = 90° has higher mixing efficiency at any Re. The mixing results of the center FTN and the stagger FTN micromixer show that the center FTN has better mixing effect. The angle of FTN and the number of FTN are the key to improve the mixing efficiency. They are also the key to change the pressure drop in the microchannel. The FTN can slow down the pressure drop and maintain the stable pressure drop between two adjacent FTNs. The way to obtain a more stable pressure range is to increase the distance between two adjacent FTN. This provides a reliable reference for maintaining a stable pressure in the microchannel.

The mixing characteristics of floating particle dispersion process in an eccentric stirred tank with dislocated fractal impellers were investigated using computational fluid dynamics (CFD) and experimental analyses. Solid concentration distribution, axial solid concentration profile, cloud height, solid integrated velocity, power consumption and just drawdown speed were investigated. Results showed that dislocated fractal impeller can enhance solid integrated velocity and fluid turbulent fluctuation intensity compared with dislocated pitched blade impeller, and eccentric agitation coupled with dislocated fractal impeller could destroy the typical circulation loops and symmetric flow field and improve the axial circulation efficiency of floating particles on the basis of dislocated fractal impeller. Eccentric agitation coupled with dislocated fractal impeller could further enhance the floating particle dispersion homogeneity ( MI ) and decrease the just drawdown speed ( N jd ) on the basis of dislocated fractal impeller and dislocated pitched blade impeller at the specific power consumption. Meanwhile, eccentric ratio of 0.3 or 0.4 was optimal for the floating particle mixing process in this work.