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Understanding the behavior of viscoelastic (VE) fluids in confined geometries is crucial for applications in biologic systems, heat transfer devices, enhanced oil recovery, and many others. Here, we perform a systematic steady-state simulation of a VE fluid at low Reynolds numbers through a channel with successive smooth contractions and expansions. We analyze the hydrodynamic performance of the fluid with particular attention to vortex patterns that develop downstream of the contractions. We show that elastic vortices form at higher contraction ratios and that there are critical Weissenberg numbers (Wic) unique to each contraction ratio where the flow shifts from non-vortical to vortical. This Wic increases with an increasing contraction length. The coexistence of elongational-, shear-, and rotational-flow is essential for vortex development and evolution. We also analyzed the effect of the Deborah number (De) on the vortex pattern in a multiple contraction system and observed that the vortex area significantly depends on the distance between the contractions. We show that there are three distinctly different regions in De, in which the flow characteristics change in successive contractions. For high De, the flow in the downstream contraction is significantly affected by the upstream contraction. Our results have implications for the use of VE fluids with various VE properties in different types of porous media. [ABSTRACT FROM AUTHOR]

A theoretical investigation on heat transfer of nanofluid transport in a ciliated channel is presented. A mathematical model for cilia oriented nanofluid transport through the human male reproductive tract is exhibited. Considering the structure of tubules, the Reynolds number is considered very small. The concept of a long wavelength approximation is incorporated to model the nanofluid flow problem. The exact analytical expressions for the x-component of velocity, temperature, nanoparticle concentration, stream function, volume flow rate, and pressure gradient are calculated. The solution for the transverse component of velocity, pressure rise per wavelength, and friction force on the wall of the channel is explored numerically, while variations in crucial flow parameters are examined graphically. [ABSTRACT FROM AUTHOR]

Mixed convective peristaltic flow of incompressible viscoplastic fluid is investigated in a two-dimensional symmetric channel. The rheology of viscoplastic material is characterized by the constitutive equation for Bingham plastic model. The coupling between momentum and energy equations is achieved through Boussinesq approximation. The coupled nonlinear partial differential equations are transformed in wave frame using Galilean transformation and then simplified under realistic assumptions of long wavelength and low Reynolds number. Approximate solution is obtained using regular perturbation method which is restricted to the smaller values of Grashof and Bingham numbers. The validity of approximate solution is established by comparing it with the numerical solution obtained via Matlab built-in routine bvp4c. Based on the numerical solution an extensive analysis is performed in order to analyze the effects of various parameters of interest on flow characteristics, pumping and trapping phenomena. It is found that velocity decreases at the center by increasing Bingham number showing a boundary layer character for large values. However, it increases by increasing Brinkman and Grashof numbers. Moreover, pressure rise per wavelength increases with Bingham number, Brinkman number and Grashof number, in the pumping region. The result further indicate that larger values of Bingham number circumvent bolus growth. [ABSTRACT FROM AUTHOR]

A novel theoretical model for unsteady, non-isothermal flow with temperature variant viscosity for the Newtonian fluid in the presence of transverse magnetic field is studied in the ductus efferentes of human male reproductive tract. Importance of cilia for the fluid transport through ductus efferente is elaborated in this study. To investigate the flow, we considered a channel and constant temperature difference is imposed between the wall of channel. A mathematical model is developed and analytical solution is achieved with the help of Adomian decomposition method (ADM) for MHD heat and fluid flow with temperature dependent viscosity. Flow is modeled by considering assumptions that Reynolds number is small, so that inertial forces are insignificant and wavelength to diameter ratio is maximum, so that pressure can be assumed uniform in the channel. Solutions are presented for the exponential dependent viscosity on temperature. Effect of different flow parameters on the axial and transverse component of velocity are analyzed graphically. Pumping characteristic due to ciliary beat from one row of cilia to another are investigated. Lastly variation of different flow parameters on the trapped bolus and pressure are examined graphically. [ABSTRACT FROM AUTHOR]

In this paper, the researchers explore heat transfer and magneto-hydrodynamic flow of hybrid nanofluid in a rotating system among two surfaces. The upper and lower plates of the system are assumed penetrable and stretchable, respectively. The thermal radiation and Joule heating impacts are considered. A similarity technic is applied to alter governing energy and momentum equations into non-linear ordinary differential ones that contain the convenient boundary conditions and used the Duan-Rach Approach (DRA) to solve them. Influences of assorted parameters including rotation parameter, suction/blowing parameter, radiation parameter, Reynolds number, hybrid nanofluid volume fraction, and magnetic parameter on temperature and velocity profiles are examined. Also, a correlation for the Nusselt number has been developed in terms of the acting parameters of the present study. The outcomes indicate that Nusselt number acts as an ascending function of injection and radiation parameters, as well as volume fraction of nanofluid. [ABSTRACT FROM AUTHOR]

The paper deals with the study of heat and mass transfer in an unsteady viscous incompressible water-based nanofluid (containing Titanium dioxide nanoparticles) between two orthogonally moving porous coaxial disks with suction. A combination of iterative (successive over relaxation) and a direct method is employed for solving the sparse systems of linear algebraic equations arising from the FD discretization of the linearized self similar ODEs. It has been noticed that the rate of mass transfer at the disks decreases with the permeability Reynolds number whether the disks are approaching or receding. The findings of the present investigation may be beneficial for the electronic industry in maintaining the electronic components under effective and safe operational conditions. [ABSTRACT FROM AUTHOR]

In the current research, the effect of thermophoretic motion combined with temperature-dependent thermal conductivity on natural convection flow around the surface of a sphere at several circumferential locations has been presented. The modeled nonlinear governing partial differential has been transformed into a dimensionless form with the help of appropriate non-dimensional variables. Later, the finite difference method is applied to solve the proposed model. The effect of controlling parameters, such as thermal conductivity variation parameter γ , Prandtl number Pr, Schmidt number Sc, thermophoretic coefficient k , and thermophoresis parameter N t on the velocity field, temperature distribution, mass concentration, skin friction, rate of heat transfer, and rate of mass transfer has been highlighted. The estimations of the emerging parameters on the physical properties are displayed in graphical and in tabular forms. It has been predicted that the rise in γ , N t , S c , Pr, and k increases the velocity distribution, but the reverse behavior has been seen in the temperature field. The enhancement in N t , S c , Pr, and k boosts up the curves of mass concentration, and the rise in γ suppresses the concentration function. It has been observed that an increase in γ reduces the skin friction and the rate of mass transfer but opposite behavior of the rate of heat transfer occurs. Furthermore, increasing values of Sc cause the skin friction to lose the dominance in the rate of heat and mass transfer. It has been also noticed that increasing values of N t strengthen the skin friction and rate of heat transfer, and attenuation occurs in the case of the rate of mass transfer. [ABSTRACT FROM AUTHOR]

The main theme of the present communication is to analyze the flow of micropolar Casson fluid with the influence of dissipation effects and inclined magnetic field upon a stretching surface by incorporating the Lobatto IIIA based numerical solver. In the presented study, the Navier–Stokes theory is exploited to model the governing fluidic system and similarity variables are used to reduce the system of governing partial differential equations into the equivalent ordinary differential equation-based model. A graphical and tabular illustration of the result of the system using the Lobatto IIIA method for the study of influential effects of various sundry parameters against the velocity profile, temperature, and microrotation are presented with brief interpretations. Results show that the increment of the inclination angle diminishes the velocity and upsurges the temperature, while, the Eckert number reduces the rate of heat transfer and shear stress, however, on the other hand, enhances the temperature and velocity profiles. [ABSTRACT FROM AUTHOR]

This article addresses the phenomenon of boundary layer flow and heat transfer in respect of the motion of second grade viscous fluid over an unsteady stretchable surface. Optimal variational iteration method (OVIM) is employed to solve the governing differential equation. OVIM is the modified version of variational iteration method (VIM). The convergence of the obtained solution as well as the effect of pertinent parameters on the velocity components are discussed, tabulated, and graphed. Behaviour of coefficient of skin-friction is also tabulated and explained for different parameters. Comparison of residual errors sought via use of VIM and OVIM is also presented. [ABSTRACT FROM AUTHOR]

Applications of carbon nanotubes, single walls carbon nanotubes (SWCNTs) and multiple walls carbon nanotubes (MWCNTs) in thermal engineering have recently attracted significant attention. However, most of the studies on CNTs are either experimental or numerical and the lack of analytical studies limits further developments in CNTs research particularly in channel flows. In thiswork, an analytical investigation is performed on heat transfer analysis of SWCNTs and MWCNTs for mixed convection Poiseuille flow of a Casson fluid along a vertical channel. These CNTs are suspended in three different types of base fluids (Water, Kerosene and engine Oil). Xue [Phys. B Condens. Matter 368, 302–307 (2005)] model has been used for effective thermal conductivity of CNTs. A uniform magnetic field is applied in a transverse direction to the flow as magnetic field induces enhancement in the thermal conductivity of nanofluid. The problem is modelled by using the constitutive equations of Casson fluid in order to characterize the non-Newtonian fluid behavior. Using appropriate non-dimensional variables, the governing equations are transformed into the non-dimensional form, and the perturbation method is utilized to solve the governing equations with some physical conditions.Velocity and temperature solutions are obtained and discussed graphically. Expressions for skin friction and Nusselt number are also evaluated in tabular form. Effects of different parameters such as Casson parameter, radiation parameter and volume fraction are observed on the velocity and temperature profiles. It is found that velocity is reduced under influence of the exterior magnetic field. The temperature of single wall CNTs is found greater than MWCNTs for all the three base fluids. Increase in volume fraction leads to a decrease in velocity of the fluid as the nanofluid become more viscous by adding CNTs. [ABSTRACT FROM AUTHOR]

The paper presents the numerical study of heat and mass transfer analysis in a viscous unsteady MHD nanofluid flow through a channel with porous walls and medium in the presence of metallic nanoparticles. The two cases for effective thermal conductivity are discussed in the analysis through H-C model. The impacts of the governing parameters on the flow, heat and mass transfer aspects of the issue are talked about. Under the patronage of small values of permeable Reynolds number and relaxation/ contraction parameter, we locate that, when wall contraction is together with suction, flow turning is encouraged close to the wall where the boundary layer is shaped. On the other hand, when the wall relaxation is coupled with injection, the flow adjacent to the porous walls decreased. The outcome of the exploration may be beneficial for applications of biotechnology. Numerical solutions for the velocity, heat and mass transfer rate at the boundary are obtained and analyzed. [ABSTRACT FROM AUTHOR]

Flow boiling heat transfer was investigated in stainless steel hypodermic microtubes, whose surfaces were enhanced by gradient crosslinked polyhydroxyethylmethacrylate (pHEMA)/polyperfluorodecylacrylate (pPFDA) coatings thereby offering variations in wettability along the surface as well as high porosity. The initiated chemical vapor deposition (iCVD) method was implemented for coating the inner walls of the microtubes with an inner diameter of 502 μm, and deionized water was used as the working fluid. Experimental results were obtained from the coated microtubes, where one end corresponded to the pHEMA (hydrophilic) coated part and the other end was the most hydrophobic location with the pPFDA (hydrophobic) coating so that wettability varied along the length of the microtube. The results of both the hydrophobic and hydrophilic inlet cases were compared to their plain surface counterparts at the mass flux of 9500 kg/m²s. The experimental results showed a remarkable increase in boiling heat transfer with the coatings. The highest heat transfer coefficients were attained for the pHEMA coated (hydrophobic inlet and hydrophilic outlet) outlet case with a maximum heat transfer enhancement ratio of ~64%. The reason for the enhanced heat transfer with the coated microtubes can be attributed to the increased nucleation site density and bubble release as well as enhanced convection and bubble motion near the surface due to the variation in wettability along the length. The results proved that gradient pHEMA/pPFDA coatings can be utilized as a viable surface enhancement method in microscale cooling applications. [ABSTRACT FROM AUTHOR]

This article focuses on the exact solution regarding convective heat transfer of a magnetohydrodynamic (MHD) Jeffrey fluid over a stretching sheet. The effects of joule and viscous dissipation, internal heat source/sink and thermal radiation on the heat transfer characteristics are taken in account in the presence of a transverse magnetic field for two types of boundary heating process namely prescribed power law surface temperature (PST) and prescribed heat flux (PHF). Similarity transformations are used to reduce the governing non-linear momentum and thermal boundary layer equations into a set of ordinary differential equations. The exact solutions of the reduced ordinary differential equations are developed in the form of confluent hypergeometric function. The influence of the pertinent parameters on the temperature profile is examined. In addition the results for the wall temperature gradient are also discussed in detail. [ABSTRACT FROM AUTHOR]