Secondary Velocity Research Articles

Prevalence of secondary flow due to hall currents on radiative squeezing flow of a CuO-water nanofluid in a rotating channel: numerical prediction

The current study describes three-dimensional incompressible mixed convection flow with convective heat and mass transport on squeezing nanofluid from a rotating channel under impact of Hall current, heat source and Soret number. The current flow model is formulated to consider water based nanofluids with nanoparticle CuO (Copper Oxide). Effectively a nanoscale formulation with the Tiwari-Das model deployed to study material properties. The basic flow equations rendered to non-dimensional form via similarity transformation for which numerical simulations utilizing the fourth-fifth order Runge-Kutta-Fehlberg scheme with the help of Maple, it is a simple iteration scheme that does not require any evaluation of perturbation and linearization for solving non-linear system of equations. Graphical results for primary velocity, secondary velocity, temperature and nanoparticle concentration distributions are presented for different controlled parameters. Furthermore, computed numerical results for skin friction, Nusselt number and Sherwood number for different emerging parameters are tabulated and discussed in detail. The results are verified for limiting cases by comparing with various investigators and found to be in excellent agreement. Outcomes reveal that decrease in secondary flow to a rising channel rotating term and Hall current term. Squeezing term improved the flow rate motion, but reduces nanoparticle conductivity and species diffusion. Thermo-diffusion term stimulated the CuO nanofluid reaction. The authors have hope that the results obtained in the present study not only provide useful information for applications, it also serves as a complement to the previous studies.

Analysis and validation of mathematical models of secondary velocities along vertical and transverse directions in wide open-channel turbulent flows

Cellular secondary flows are inevitably present in turbulent flows through ducts, natural or artificial channels, and compound channels. Secondary currents significantly modify the characteristics of turbulent quantities, the pattern of primary flow velocity by causing dip-phenomenon. To understand the detailed mechanism and hidden cause, modelling of secondary flow velocities is crucial. In this study, proper mathematical models of secondary flow velocities along vertical and transverse directions are proposed for steady and uniform turbulent flow through wide open channels with equal smooth and rough bed strips. Starting from the continuity and the Reynolds averaged Navier–Stokes equations, governing equation for secondary velocity is derived first and then using appropriate boundary conditions (no-slip boundary conditions at channel bottom and free surface, and maximum vertical velocity in magnitude at the interface of two cellular secondary cells and at mid-depth of the channel. All these conditions are consistent with several experimental observations). A new model of the streamwise Reynolds shear stress is proposed for the entire cross-sectional plane and using it, the analytical solutions are obtained. Proposed models include the effects of viscosity of the fluid and the eddy viscosity model of turbulence. All suggested models are validated with existing experimental data in rectangular open-channel flows, compound open channel flows, and duct flows, and satisfactory results are obtained. Furthermore, models are also compared with existing empirical models from literature to show the effectiveness and superiority of proposed models. Apart from these, the obtained results from this study are used to investigate the effects of vertical and transverse secondary flow velocities on the settling velocity vector in a cross-sectional plane. Effective alternative models for the settling velocity vector are suggested. The model of settling velocity vector is also compared with the existing model. Finally, all results are justified from physical viewpoints.

Analytical models of mean secondary velocities and stream functions under different bed-roughness configurations in wide open-channel turbulent flows

Analytical models of mean secondary velocities and stream functions under different bed-roughness configurations in wide open-channel turbulent flows

Boger nanofluid: significance of Coriolis and Lorentz forces on dynamics of rotating fluid subject to suction/injection via finite element simulation

This study briefings the roles of Coriolis, and Lorentz forces on the dynamics of rotating nanofluids flow toward a continuously stretching sheet. The nanoparticles are incorporated because of their unusual qualities like upgrade the thermal transportation, which are very important in heat exchangers, modern nanotechnology, electronics, and material sciences. The primary goal of this study is to improve heat transportation. Appropriate similarity transformations are applied for the principal PDEs to transform into nonlinear dimensionless PDEs. A widely recognized Numerical scheme known as the Finite Element Method is employed to solve the resultant convective boundary layer balances. Higher input in the solvent fraction parameter has a rising effect on the primary velocity and secondary velocity magnitude, and decreasing impact on the distributions of temperature. It is seen that growing contributions of the Coriolis, and Lorentz forces cause to moderate the primary and secondary velocities, but the temperature and concentration functions show opposite trend. The concentration, temperature, and velocities distributions for suction case is prominently than that of injection case, but inverse trend is observed for local Nusselt and Sherwood numbers. These examinations are relevant to the field of plastic films, crystal growing, paper production, heat exchanger, and bio-medicine.

Biofilm streamer growth dynamics in various microfluidic channels.

Biofilms are microbial colonies that are encapsulated in extracellular polymers secreted by cells through their proliferation and differentiation. Biofilms exist on solid surfaces, liquid surfaces, or in liquid media, where the growth of the bacterial biofilm is closely related to the velocity of the secondary flow, main flow, and geometry of the channel, which are difficult to measure in a natural fluid environment, making the study of the biofilm streamer growth process difficult. In this study, we used microfluidic channels made of polydimethylsiloxane to study the growth dynamics of Bacillus subtilis biofilm streamers. We observed that the biofilm streamer growth undergoes three stages with different growth characteristics. First, we found that the initial growth of the streamer is located at the position with the maximum value of P = secondary flow velocity × main flow velocity. Second, the biofilm underwent floating growth around the microcolumn obstacle. After the transition stage, the last growth stage includes two types because of the different attachment strengths and mechanical properties of the biofilm. Our research provides new insights into the formation and shedding of biofilm streamers in natural and industrial environments and helps us to better understand biofilm growth in fluid flow.

Rotatory flow of MHD (MoS2-SiO2)/H2O hybrid nanofluid in a vertical channel owing to velocity slip and thermal periodic conditions

BackgroundThe present article is a mathematical study on oscillatory pressure-driven MHD flow of a hybrid nanofluid in a vertical rotating channel. Hall current effect along with velocity slip and thermal periodic boundaries are the main focus of the present mathematical analysis. In the present investigation Molybdenum disulfide and silicon dioxide, nano-scaled particles are suspended in water. MethodologyMathematical modeling is carried out by considering rotating frame in the rectangular coordinate system and suitable non-dimensional variables are incorporated for simplification and non-dimensionalization of the problem. The hybrid nanofluid velocity and temperature distributions are derived in closed form with the aid of mathematics software MATHEMATICA. The prominent parameters’ effect on flow and heat transfer is investigated and studied through graphs. Significant findingsIt is concluded that hybrid nanofluid transport is highly influenced by surface roughness within the channel. Mixed convection and rotation parameters contribute to decelerating primary velocity and accelerating secondary velocity for both silicon dioxide as well as MoS2−SiO2 nano and hybrid nanofluids, respectively.

Numerical investigation on combustion and NOx formation characteristics under deep-staging conditions within a cyclone barrel

Numerical investigation on combustion and NOx distribution characteristics of coal within a cyclone barrel under deep-staging conditions was conducted. Char conversion model and NOx formation model with refined NO heterogeneous reduction mechanism and oxidation rate of HCN suitable for cyclone barrel were implemented and validated with experimental data. The maximum deviations between the predicted and experimental values of NO and CO concentrations are 12.1% and 18.6% respectively under various stoichiometric ratios. Based on the refined models, the NO distribution in cyclone barrel under deep-staging condition is obtained. In the cyclone barrel, the concentration of NOx is higher in the primary-air-controlled and near-wall zones, which hinders further NOx reduction. The appropriately delayed secondary air supply can avoid the centralized supply of O2 and form a reducing atmosphere region in the primary-air-controlled zone, which greatly reduces the initial formation of NOx. In addition, the central zone of the cyclone barrel is the core region for NOx reduction. The area of the central zone with a strong reducing atmosphere can be significantly enlarged by increasing the velocity of secondary air. The NOx formation in cyclone barrel drops by 26.5% under deep-staging condition when the secondary air velocity increases from 20 m/s to 50 m/s. Finally, the oxygen-enriched and deep-staging technology is applied to the cyclone barrel. An ultra-low NOx formation in cyclone barrel is achieved. When the O2 concentration of secondary air increases from 0.21 to 0.40, the NOx formation drops by 64.1% under deep-staging condition. Moreover, the elevated flue gas temperature with O2 enriched in cyclone barrel makes it more suitable for the safe operation of slag tapping cyclone barrel.

Effects of Rotation on Transient Fluid Flow and Heat Transfer Through a Curved Square Duct: The Case of Negative Rotation

The fluid flow and heat transfer through a rotating curved duct has received much attention in recent years because of vast applications in mechanical devices. It is noticed that there occur two different types of rotations in a rotating curved duct such as positive and negative rotation. The positive rotation through the curved duct is widely investigated while the investigation on the negative rotation is rarely available. The paper investigates the influence of negative rotation for a wide range of Taylor number (<i>−10 ≤ Tr ≤ −2500</i>) when the duct itself rotates about the center of curvature. Due to the rotation, three types of forces including Coriolis, centrifugal, and buoyancy forces are generated. The study focuses and explains the combined effect of these forces on the fluid flow in details. First, the linear stability of the steady solution is performed. An unsteady solution is then obtained by time-evolution calculation and flow transition is determined by calculating phase space and power spectrum. When <i>Tr</i> is raised in the negative direction, the flow behavior shows different flow instabilities including steady-state, periodic, multi-periodic, and chaotic oscillations. Furthermore, the pattern variations of axial and secondary flow velocity and isotherms are obtained, and it is found that there is a strong interaction between the flow velocities and the isotherms. Then temperature gradients are calculated which show that the fluid mixing and the acts of secondary flow have a strong influence on heat transfer in the fluid. Diagrams of unsteady flow and vortex structure are further sketched and precisely elucidate the curvature effects on unsteady fluid flow. Finally, a comparison between the numerical and experimental data is discussed which demonstrates that both data coincide with each other.

Physics of coriolis-energy force in bifurcation and flow transition through a tightly twisted square tube

Monitoring the flow characteristics through a twisted tube is an important topic because of its vast applications in several engineering sectors. As a result, highly motivated researchers have focused their efforts on discovering novel properties of fluid flow in a curved tube. A wide range of computational and selective experiments have been conducted to investigate flow characteristics in the square tube. However, a thorough study of the impacts of Coriolis-Energy force is less addressed in literature yet. The goal of this research is to precisely understand the transitional flow pattern and heat transfer in curved square domain. For this, we propose a numerical model for the laminar flow characterization through a twisted square tube. The current study examines the development of Dean vortices, which affect heat generation and thermal flow enhancement under various flow controlling parameters. The flow is driven by a constant pressure gradient parameter, the Dean number (Dn = 1000) over a considerable range of the Taylor number (−2500 ≤ Tr ≤ 2500), while the remaining parameters such as the Grashof number (Gr = 100) and the curvature (δ = 0.02) are kept constant. First, a bifurcation structure of steady solution curves is investigated and linear stability of the solutions is then examined. Time-dependent solution shows several flow instabilities including steady-state, periodic, multi-periodic, and chaotic oscillation. Furthermore, the temperature profiles with contours of axial and secondary flow velocities are exposed, which elucidates the impacts of Coriolis-energy force. The outcomes of the investigation demonstrate that the axial flow is pushed at the tube's inner sidewall for the positive rotation and behaves reversely for the negative rotation. The comprehensive analysis demonstrates that temperature-influenced buoyancy compulsion and centrifugal-Coriolis instability dominate the flow behavior affecting the fluid's characteristic and optimizing heat transmission. The implication of the current study will help researchers to better comprehend the fluid flow and heat transfer in internal heating/cooling/gas turbines, electric generators, biological systems, and some nano-filtration processes.

Hall and ion‐slip effects on nanofluid transport from a vertical surface: Buongiorno's model

AbstractThe non‐linear, non‐isothermal, magnetohydrodynamic (MHD) laminar convection flows of Buongiorno's nanofluid past a vertical surface with Darcy‐Forchheimer model is mathematically investigated in the present article. Keller's Box implicit finite difference technique is utilized to solve the dimensionless conservation equations. Graphical and tabulated results are analyzed to study the behavior of primary and secondary velocity, temperature, nanoparticle volume fraction, shear stress rate, heat transfer rate and mass transfer rate for various emerging thermos‐physical parameters. The Hall current and ion‐slip current effects are also considered. Validations of earlier solutions in the literature is also included. The study finds applications in nanomaterial fabrication processing, biomedical, polymer processing, chemical engineering, crude oil purifying, etc.

Non-Coaxially Rotating Motion in Casson Martial along with Temperature and Concentration Gradients via First-Order Chemical Reaction

The effect of non-coaxial rotation on the transport of mass subjected to first-order chemical reaction is studied analytically. The effects of thermal radiation, buoyancy, constructive and destructive chemical reactions along with Casson fluid in rotating frame are discussed. Time evolution of primary and secondary velocities, energy and solute particles are analyzed. The behavior of flow under the variation of intensity of magnetic field is also investigated. Evolutionary behavior of primary velocity is opposite to the evolutionary behavior of secondary velocity. The impact of buoyant force on primary velocity is opposite to the role of buoyant force on the secondary velocity. The evolutionary behavior of temperature is also examined and a remarkable enhancement in temperature is noticed. Thermal radiation causes the fluid to be cooled down as heat energy is escaped by thermal radiation. Evolutionary behavior of concentration is also analyzed and an increasing of concentration versus time is noted. Destructive chemical reaction results a remarkable reduction in the concentration and vice versa for generative chemical reaction.

Modelling Combined Intravenous Thrombolysis and Mechanical Thrombectomy in Acute Ischaemic Stroke: Understanding the Relationship between Stent Retriever Configuration and Clot Lysis Mechanisms.

Background: Combined intravenous thrombolysis and mechanical thrombectomy (IVT-MT) is a common treatment in acute ischaemic stroke, however the interaction between IVT and MT from a physiological standpoint is poorly understood. In this pilot study, we conduct numerical simulations of combined IVT-MT with various idealised stent retriever configurations to evaluate performance in terms of complete recanalisation times and lysis patterns. Methods: A 3D patient-specific geometry of a terminal internal carotid artery with anterior and middle cerebral arteries is reconstructed, and a thrombus is artificially implanted in the MCA branch. Various idealised stent retriever configurations are implemented by varying stent diameter and stent placement, and a configuration without a stent retriever provides a baseline for comparison. A previously validated multi-level model of thrombolysis is used, which incorporates blood flow, drug transport, and fibrinolytic reactions within a fibrin thrombus. Results: Fastest total recanalisation was achieved in the thrombus without a stent retriever, with lysis times increasing with stent retriever diameter. Two mechanisms of clot lysis were established: axial and radial permeation. Axial permeation from the clot front was the primary mechanism of lysis in all configurations, as it facilitated increased protein binding with fibrin fibres. Introducing a stent retriever channel allowed for radial permeation, which occurred at the fluid-thrombus interface, although lysis was much slower in the radial direction because of weaker secondary velocities. Conclusions: Numerical models can be used to better understand the complex physiological relationship between IVT and MT. Two different mechanisms of lysis were established, providing a basis towards improving the efficacy of combined treatments.

Numerical investigation of the heat and mass transfer process within a cross-flow indirect evaporative cooling system for hot and humid climates

This paper presents an investigation on the process of heat and mass transfer within an indirect evaporative cooling (IEC) system with a cross-flow arrangement for hot and humid climates. For this purpose, a numerical model based on energy and mass balance within IEC has been developed that predicts condensation from the primary air. The numerical model is validated employing numerical and experimental data from the literature with a perfect agreement. Precise simulations are executed to observe and investigate the condensation cases, including (non, partial, and full condensation) in the dry channel. The performance of the IEC system is evaluated under variable operating conditions, including primary and secondary air velocity, inlet temperature, humidity ratio, and wettability factor. The results noted that the three condensation states in the primary air channel depend on operating conditions such as humidity ratio, inlet temperature, velocity, and wettability factor. Besides, the wettability factor greatly affects the condensation and cooling process; when the factor is reduced to 0.5, condensation is delayed; and the amount was reduced to 0.52 g/kg instead of 1.32 g/kg when the factor is 1. Also, the average temperature at the outlet increased from 20.2 °C to 23.4 °C when the factor was reduced from 1 to 0.5, respectively. Furthermore, increasing the secondary air inlet velocity enhances the condensation process as the state changes from non-condensing to condensing and the humidity ratio decreased from 14.65 g/kg to 13.7 g/kg; besides, the temperature difference and cooling capacity are also improved.

A new benchmark for the secondary fluid flow through curved ducts

Steady flow through curved ducts has numerous applications in the chemical engineering sciences. A recent example is within the field of microfluidics in which curved ducts have cross-section dimensions much smaller than one millimetre. The validation of steady fluid flow through curved microfluidic ducts is a crucial part of verifying any experimental work or numerical modelling in this field. Of particular interest is a measure of the secondary flow which consists of a counter-rotating vortex pair in the cross-sectional plane. We develop a new model for the magnitude of the secondary flow velocity within curved ducts having rectangular cross-sections. Our modelling respects the scaling at asymptotically small flow rates while carefully considering how this is modified for increasing Dean number. Lastly, we discuss why this new model is a more appropriate benchmark of the secondary flow than a power law model commonly found throughout the literature.

Flow velocity behavior programming on open channel bends

Flow velocity on open channel bends generally experiences additional velocity which is called secondary velocity. This paper aims to analyse and calculate the velocity that occurs in an open channel bend in general. The calculation that the writer uses is the calculation with fortran programming, in a case study of a river that bends, where the variables that must be present are given. The results of calculations and measurements of Secondary Speeds that occur at channel bends in this Open Channel will be very useful for river channel improvement or flood prevention in river channels, especially on existing bends. The conclusion is that at the bend of an open channel or river, there will be an increase in flow velocity in the transverse direction. This additional velocity is caused by the additional secondary velocity, namely the transverse velocity.

Numerical investigation on the effect of second throat diameter on two-throat nozzle ejector

The employment of two-phase ejectors in the CO2 refrigeration systems is widely developed recently. Due to the lack reports on the two-throat nozzle ejectors, the performance of CO2 two-throat nozzle ejector varied with different second throat diameter (D t ) was numerically investigated under different primary pressures (P p ). The accuracy of established numerical simulation model was confirmed with the assistance of experimental data summarized in the literature. The simulated results show that the two-throat nozzle ejector performance corresponding to entrainment ratio (Er) is of better stability with relatively bigger D t under different working conditions. Next, the axial static pressure corresponding to bigger D t is lower than that of smaller one at pre-mixing chamber. And the secondary flow velocity of bigger D t is accelerated better as compared to that of smaller one.

High-speed impact of micron-sized diesel drop trains—Splashing dynamics, secondary droplet formation, and effects of pre-existing film thickness

This work investigates surface impingement of monodispersed diesel drop trains using computational simulations. The three-dimensional simulations include high-speed impact of micrometer-sized fuel drops onto initially dry and wetted stainless steel substrates. The drop size and impact velocity are representative of fuel injection conditions in internal combustion engines (ICEs). The drop trains serve as a simplified representation of fuel spray. To accurately capture the film that naturally develops on initially dry substrates, a dynamic diesel-stainless steel contact angle model was developed using experiments of single drop impact under ICE representative temperature. Simulations are presented for a highly splashing case and the effects of a pre-existing film on splashing dynamics were investigated, including the temporal evolution of splashed mass and film thickness. It was concluded that for thin films, the effect of pre-existing film thickness is less significant than in single drop impingement. Secondary droplet characterization was performed on simulation results, leading to instantaneous and time-averaged distributions of secondary droplet size, velocity magnitude, and trajectory angle. It was found that for each drop impingement, approximately 58% of the splashed mass is from the impinging drop itself, while the remainder of the splashed mass is composed of film liquid. From a high resolution case, details of secondary droplet formation are observed and three distinct phases of secondary droplet formation are identified. The detailed analysis of drop train impingement under engine-relevant conditions serves as a first step toward a robust understanding of fuel impingement and the development of cleaner and more efficient ICEs.

Numerical study on heat absorbing MHD radiating and reacting flow past an impulsively moving vertical plate with ramped temperature and concentration with Hall current

In this paper, we made elaborate investigation of the Hall current and radiation effects on MHD heat absorbing unsteady natural convection flow of a viscous incompressible electrically conducting fluid past an impulsively moving infinite vertical plate with ramped temperature and concentration in the presence of first order chemical reaction. The constructing coupled PDEs of the model along with initial and boundary conditions are solved numerically by utilizing the robust FEM. The effects of significant parameters on the primary and secondary velocities, temperature and concentration within the boundary layer are examined. The computational assessment of the primary and secondary shear stresses, rate of heat and mass transfer at the plate surface are put in tabular form. The thermal and mass buoyancy effects elevate both primary and secondary velocity components whilst reverse trend takes place when radiation and chemical reaction parameters are increased. Both primary and secondary velocity components decrease with increasing magnetic parameter whilst opposite trend are noticed with increasing Hall parameter. An increase in Prandtl number and radiation parameter results to reduce temperature distribution. The concentration distribution decreases with increase in Schmidt number and chemical reaction parameter. The significant difference between the fluid velocities is noticed due to the ramped and isothermal boundary conditions.

Heat Transfer Analysis and Magnetohydrodynamics Effect on Peristaltic Transport of Ree–Eyring Fluid in Rotating Frame

This paper discusses Ree–Eyring fluid’s peristaltic transport in a rotating frame and examines the impacts of Magnetohydrodynamics (MHD). The results deal with systematically (analytically) applying each of the governing equations of Ree–Eyring fluid, the axial and secondary velocities, flow rate due to auxiliary stream, and bolus. The effects of some distinctive variables, such as Hartman number, heat source/sink, and amplitude ratio, are taken under consideration and illustrated through graphs.

Effect of Hall current on the flow and heat transfer of non-Newtonian power-law nanofluid in the presence of Cattaneo–Christov heat flux and free stream

The nanofluids are a recent challenging task in a nanotechnology field used in heat transfer enhancement for base fluids. The major purpose of this research is to examine the influences of Hall current on the non-Newtonian power-law nanofluid on an exponentially extending surface. Implementation in the Cattaneo–Christov heat flux and the free stream is performed to analyze the thermal relaxation features. Entropy generation evaluation and Bejan number during the convection flow are investigated. The Runge–Kutta–Fehlberg method is employed to resolve the transformed governing nonlinear equations. The impacts of the key physical factors on the profiles of primary and secondary velocities, temperature and entropy generation are discussed across the graphs. The local skin-friction coefficients, Nusselt and Sherwood numbers are demonstrated in a tabular form under the impacts of key physical parameters. Two different types of power-law indicators including pseudoplastic fluid [Formula: see text] and dilatant fluid [Formula: see text] are conducted. The results indicated that the flow speed decreases at dilatant fluid compared to pseudoplastic fluid due to higher viscosity. Increasing Hall current parameter powers the axial and secondary velocity profiles. Thermophoresis parameter powers the profiles of the temperature, nanoparticle volume fraction and local entropy generation. The dilatant fluid [Formula: see text] gives higher values of [Formula: see text] and [Formula: see text] compared to the pseudoplastic fluid [Formula: see text].