Explicit finite difference simulations for accelerating cross diffusion flow over a perpendicular shield with parabolic motion

The heat transfer phenomenon subject to thermos-diffusion effects convey important applications in the heating processes, extrusion systems, chemical processes and various engineering systems. The objective of current work is to observe the contribution of Soret and Dufour effects in oscillating shield for cross diffusion flow. The perpendicular shield with oscillating motion induced the flow. The magnitude of oscillations is assumed to be small so that laminar flow due to oscillating shield has been resulted. The motivations for addressing the thermos-diffusion phenomenon due to oscillating of shield are due to applications in oscillatory pumps, moving surface, metal detectors, power systems etc. The dimensionless problem is obtained via introducing the appropriate set of variables. The numerical outcomes are suggested by using the most interesting explicit finite difference scheme. The physical illustration for flow parameters is presented. Moreover, the aspect of physical quantities involving the flow are graphically reported.     

Variable chemical species and thermo-diffusion Darcy–Forchheimer squeezed flow of Jeffrey nanofluid in horizontal channel with viscous dissipation effects

This research communicates the applications of thermos-diffusion effect associated to the squeezing flow of Jeffrey nanofluid due to horizontal channel. The problem presents the applications of inertial effects by following the Darcy–Forchheimer flow. Moreover, the effects of viscous dissipation and activation energy phenomenon has been discussed. The dimensionless attention of problem is retained. The shooting technique is implemented to present the numerical computations. The numerical validation of results is reported. The essential assessment of physical flow parameters is studied. The numerical outcomes are presented for heat and mass transfer phenomenon. It is observed that presence of inertial forces control to velocity flow in the regime. The enhancing contribution of thermal and concentration rate is noted for inertial constant.     

Numerical treatment of Casson nanofluid Bioconvectional flow with heat transfer due to stretching cylinder/plate: Variable physical properties

PurposeThe purpose of the current framework is to scrutinize the two-dimensional flow and heat transfer of Casson nanofluid over cylinder/plate along with impacts of thermophoresis and Brownian motion effects. Also, the effects of exponential thermal sink/source, bioconvection, and motile microorganisms are taken.Methodology/ApproachThe resulting non-linear equations (PDEs) are reformed into nonlinear ODEs by using appropriate similarity variables. The resultant non-linear (ODEs) were numerically evaluated by the use of the Bvp4c package in the mathematical solver MATLAB.FindingsThe numerical and graphical illustration regarding outcomes represents the performance of flow-involved physical parameters on velocity, temperature, concentration, and microorganism profiles. Additionally, the skin friction coefficient, local Nusselt number, local Sherwood number, and local microorganism density number are computed numerically for the current presented system. We noted that the velocity profile diminishes for the rising estimations of magnetic and mixed convection parameters. The Prandtl number corresponds with the declining performance of the temperature profile observed. The enhancement in the values of the Solutal Biot number and Brownian motion parameter increased in the concentration profile.OriginalityIn specific, this framework focuses on the rising heat transfer of Casson nanofluid with bioconvection by using a shooting mathematical model. The novel approach of the presented study is the use of motile microorganisms with exponential thermal sink/source in a Casson nano-fluid through a cylinder/plate. A presented study performed first time in the author’s opinion. Understanding the flow characteristics and behaviors of these nanofluids is crucial for the scientific community in the developing subject of nanofluids.     

A lubricated stagnation point flow of nanofluid with heat and mass transfer phenomenon: Significance to hydraulic systems

The improved thermal association of heat transfer is considerably observed due to interaction of nanoparticles in recent days. The lubrication phenomenon with heat and mass transfer effects plays a key role in the hydraulic systems. In current research, the thermal impact of nanofluid over a lubricated stretching surfaces near a stagnation point analytical has been studied. A thin layer of lubricating fluid with a variable thickness provides lubrication. The inspection of thermophoresis and Brownian motion phenomenon is illustrated via Boungrino model. The analytical finding of refurbished boundary layer ordinary differential equations is obtained by a reliable and proficient technique namely variational iteration method (VIM). The Lagrange Multiplier is a potent tool in proposed technique to reduce the computational work. In addition, a numerical comparison is presented to show the effectiveness of this study. The range of flow parameters is based on theoretical flow assumptions. Physical inspection of involved parameters on velocities, temperatures, concentrations, and other quantities of interest when lubrication is presented. The current results present applications in polymer process, manufacturing systems, heat transfer and hydraulic systems.     

On the evolution of the viscoelastic properties and its microstructural/chemical origin in filled NBR subjected to coupled thermal and mechanical loads

This study deals with the effect of coupled thermal and cyclic mechanical loadings on the viscoelastic response of carbon black filled nitrile rubber. For this purpose, cyclic loading tests were performed at different temperatures by means of Dynamic Mechanical and Thermal Analysis (DMTA). The type and level of the thermomechanical loadings applied were chosen in order to determine the relative contribution of each of the mechanical and thermal loadings (and their coupling) to the viscoelastic response during the cyclic tests. X-ray Photoelectron Spectroscopy (XPS) and Fourier Transformed Infrared spectroscopy (FTIR) analyses were also carried out to track the change in the chemical structure corresponding to the evolution in the viscoelastic response. First, results obtained show that due to the crosslink increase, the storage modulus increases with the number of cycles. It is also observed that temperature amplifies this phenomenon. Second, the cyclic mechanical loading is found to significantly amplify the effect of temperature.     

A study of heat and mass transfer of Non-Newtonian fluid with surface chemical reaction

Considering the significance of non-Newtonian fluid usage in manufacturing such as molten plastics, polymeric materials, pulps, and so on, significant efforts have been made to investigate the phenomenon of non-Newtonian fluids. In this article the influences of heat and mass transfer on non-Newtonian Walter's B fluid flow over uppermost catalytic surface of a paraboloid is encountered. An elasticity of the fluid layer is considered in the freestream together with heat source/sink and has the tendency to cause heat flow in the fluid saturated domain. The flow problem of two-dimensional Walter's B fluid is represented using Law of conservation of mass, momentum, heat, and concentration along with thermal and solutal chemical reactive boundary conditions. The governing equations are non-linear partial differential equation and are non-dimensionalized by employing stream function and similarity transformation. The final dimensionless equations yielded are coupled non-linear ordinary differential equations. Furthermore, shooting technique along with RK-4th order method is used to get the numerical results. Graphs and tables are modeled by using MATLAB software to check the effects of Walter's B parameter, Chemical reaction parameter and Thickness parameter on temperature, velocity, and concentration profiles. Tabular analysis shows the results of some physical parameters like skin friction coefficient, Nusselt number and Sherwood number due to the variation of Walter's B parameter, thickness parameter and chemical reactive parameter.     

Numerical study of nonlinear mixed convection inside stagnation-point flow over surface-reactive cylinder embedded in porous media

Nonlinear mixed convection of heat and mass in a stagnation-point flow of an impinging jet over a solid cylinder embedded in a porous medium is investigated by applying a similarity technique. The problem involves a heterogenous chemical reaction on the surface of the cylinder and nonlinear heat generation in the porous solid. The conducted analysis considers combined heat and mass transfer through inclusions of Soret and Dufour effects and predicts the velocity, temperature and concentration fields as well as the average Nusselt and Sherwood number. It is found that intensification of the nonlinear convection results in development of higher axial velocities over the cylinder and reduces the thickness of thermal and concentration boundary layers. Hence, consideration of nonlinear convection can lead to prediction of higher Nusselt and Sherwood numbers. Further, the investigation reveals that the porous system deviates from local thermal equilibrium at higher Reynolds numbers and mixed convection parameter.

     

Gel kinetic characteristics and creep behavior of polymer microspheres based on bulk gel

Abstract

Deep profile control technology of polymer microspheres has become a widely used new method in improving oil recovery in heterogeneous reservoirs. The viscoelastic property of polymer microspheres plays an important role in the deformable migration behavior. In this study, a new method of measuring the viscoelastic properties of polymer microspheres based on bulk gel was proposed. Using mechanical rheometer and microrheometer, the effects on the storage modulus and gel performance were systematically researched. The creep-recovery test was applied to characterize the creep behavior of different polymer microsphere bulk gel. The results show that the storage modulus of polymer microspheres could be controlled by adjusting the agent concentration in the synthetic reaction. Moreover, the kinetic equation of gel time of polymer microspheres bulk gel and reaction temperature was established: ln(GT)?=?3289.18(1/T)-9.33. Elastic strain index was put forward as a new parameter to characterize the viscoelasticity of polymer microsphere in creep-recovery test. Finally, relationship between elastic strain index and storage modulus was constructed and a classification criterion of polymer microspheres with different viscoelasticity was proposed based on a large number of creep-recovery results. The research could provide a good theoretical guidance and technical support for the understanding of viscoelasticity of polymer microspheres.     

Unsteady double-diffusive natural convection in a two-sided lid-driven inclined porous enclosure with sinusoidal boundary conditions with Soret and Dufour effects

Unsteady double-diffusive natural convection in an inclined porous enclosure with sinusoidal boundary conditions and Soret and Dufour parameters is studied. The unique aspects of the set-up are that the left vertical and bottom walls are heated and concentrated non-uniformly and uniformly, respectively, while the right vertical wall is well insulated and the top wall is maintained at a constant concentration and cold temperature. A staggered grid finite-difference method is used to solve the system of partial differential equations that model heat and mass transfer inside the enclosure. We demonstrate the effects of the Soret and Dufour parameters and the inclination angle on the unsteady double-diffusive natural convection in the inclined porous enclosure. With all the numerical studies, the least square curve fitting (exponential non-linear curve fitting) of average Nusselt number and average Sherwood number with respect to different Soret and Dufour numbers at the left vertical wall which is non-uniformly heated and concentrated is examined here. Comparison with previously published results shows an excellent agreement.     

Insight into the relationship between the Fourier's law of heat conduction and Fick's law over a Riga device: Fourth grade analysis

Mixed convective flow of fourth grade (Non-Newtonian) fluid model by a Riga stretchable plate is addressed. The aim of the current research work is therefore to explain the role of the fourth grade (Non-Newtonian) fluid model in the field of fluid dynamics. Energy and concentration equations are modeled subject to both Fourier's law of heat conduction and Fick's law. Radiation aspects and heat source/sink phenomenon are also accounted. Entropy analysis is discussed through second thermodynamics law. The (OHAM) approach is used to achieve a meaningful solution. Finally, the emerging variables behavior on the velocity, temperature, concentration and entropy rate are discussed graphically. Here, velocity enhances for increasing range of fourth grade variable. Temperature boosts against rising radiation and thermal relaxation variables, but opposite trend is noted for solutal relaxation parameter on concentration.     

Application of Carbon Fiber-Reinforced Ceramic Composites in Active Thermal Protection of Advanced Propulsion Systems: A Review

Thermal protection is one of the crucial issues for the advanced propulsion systems of Reusable Launch Vehicles. New service requirements for materials, such as high strength, low density, low thermal expansion, high thermal stability, etc., are raised for the thermal structure with the increasing demand of flight Mach numbers and thrust-to-weight ratio. Carbon fiber-reinforced ceramic composites, which generally meet the aforementioned requirements, show great potential for various applications and they have been widely applied in the thermal protection for hypersonic vehicles. This paper gives a comprehensive and systematic review of current research status for carbon fiber-reinforced ceramic composites applied in the thermal structure of advanced propulsion systems. Three aspects are presented and discussed: the ceramic composites fabrication and the property characterization, the thermal performance of composite thermal structure used in practical engines, and the numerical methods for predicting mechanical and thermal properties of composites as well as the physicochemical phenomenon in the cooling channels. Firstly, the main manufacturing processes for the carbon-reinforced ceramic composites are presented and the corresponding advantages and disadvantages are analyzed. The high-temperature oxidation and ablation behaviors of composites are demonstrated and the improvement of oxidation and ablation resistance by introducing the ultra-high-temperature ceramics into C/C composites is discussed in detail. Then, several typical applications of carbon fiber-reinforced ceramic composites (mainly C/SiC), including the work of RCI, JAXA and NASA, have been reviewed and analyzed. After that, the current research status of macroscale equivalent and multiscale numerical methods for predicting the mechanical and thermal properties of composites as well as the complex physicochemical phenomenon occurring in hydrocarbon fuels are sorted out. Finally, several potential prospects are pointed out for the future research on the thermal protection of advanced propulsion systems based on the carbon fiber-reinforced ceramic composites.     

Microwaves in organic synthesis. Thermal and non-thermal microwave effects

Microwave irradiation has been successfully applied in organic chemistry. Spectacular accelerations, higher yields under milder reaction conditions and higher product purities have all been reported. Indeed, a number of authors have described success in reactions that do not occur by conventional heating and even modifications of selectivity (chemo-, regio- and stereoselectivity). The effect of microwave irradiation in organic synthesis is a combination of thermal effects, arising from the heating rate, superheating or "hot spots" and the selective absorption of radiation by polar substances. Such phenomena are not usually accessible by classical heating and the existence of non-thermal effects of highly polarizing radiation--the "specific microwave effect"--is still a controversial topic. An overview of the thermal effects and the current state of non-thermal microwave effects is presented in this critical review along with a view on how these phenomena can be effectively used in organic synthesis.     

Thermal diffusion in solutions containing two or more solute species in equilibrium: The Wagner effect

An exact thermodynamic treatment of the Wagner effect, thermal diffusion in solutions containing two or more species in equilibrium, is given. We consider primarily a solution in which the solute can exist as a monomer A or an n-mer A _n . Both A and A _n are treated as independent solute species. We do not assume that the solution is ideal or dilute.The heat of transport has been derived. It consists of two parts; one due to the intrinsic heat of transport of the species in the system and the other, due to chemical reaction. We found that the heats of transport derived from the Soret and Dufour effects are identical. Accordingly, the reciprocity relation is confirmed for the Onsager phenomenological coefficient for heat-matter coupling.     

Flow,high-elastic (recoverable) deformation,and rupture of uncured high molecular weight linear polymers in uniaxial extension

The behavior of narrow molecular weight distribution polymers has been investigated under uniaxial extension at constant deformation rate and at constant stress. It has been established that up to rupture these polymers behave as linear viscoelastic bodies. A detailed investigation of the rupture phenomenon has shown that the rupture of fluid polymers is due to their transition to the rubbery state at critical deformation rates, with the result that they disintegrate like quasi-cured rubbers. The effect of the temperature and the molecular weight on the critical conditions of rupture has been described in terms of viscoelastic relaxation.     

黏弹性对介观液珠聚并的影响-液珠-细丝-液珠聚并现象及其分析

在四辊流变仪中,黏弹性高分子介观液滴经反复拉伸和松弛形成了有细丝相连的两个黏弹液珠,研究了黏弹液珠的聚并过程,依形状叫做BSB(bead-string-bead,液珠-细丝-液珠)聚并.BSB现象与常见的通过滴间液膜破裂实现的液滴聚并过程大不相同.根据界面上的Laplace力、液珠移动时的黏性阻力和细丝中黏弹应力之间的平衡,推导出一个力学模型来描述BSB现象,理论分析与实验结果相符较好.细丝直径的变化和稳定性由过程参数和物料参数共同决定,尤其是液滴的黏弹性有较大影响.这一效应对多相高分子与复杂流体加工过程的基础理解富有启发.     

Chemically reactive accelerating radiative flow of Eyring Powell nanofluid with microorganisms and buoyancy forces

Recently, the nanofluids report multidisciplinary applications in the various era of engineering like engine cooling, solar energy production, cooling of engineering devices, diesel generator performance etc. Owing to such novel applications, the aim of current communication is to report the significances of bio-convection for unsteady Eyring Powell nanofluid due to bidirectional oscillatory stretching surface. The enrollment of buoyancy forces and magnetic impact are worked out to inspect the stability and thermal on set of nanofluids. Heat transformation features are explored by utilizing thermal radiation. Further, the characteristics of chemical reaction and activation energy have been considered for physical significance. Unlike traditional approach, the governing equations are not altered into ordinary set of equation but only diminish the independent variables. This task makes the non-dimensional equations in highly complicated from which the convergent technique via HAM is successfully implemented. The physical outcomes of dominant variables on profiles of microorganisms, concentration, temperature, velocity and skin frictions are conferred graphically while local motile density, Sherwood and Nusselt numbers are deliberated through different tables. It is noted that the amplitude of bidirectional shear stresses and velocities periodically get increase for higher material parameter. This analysis emphasized that concentration distribution augments for rising values of activation energy variable, whereas conflicting situation occurs for temperature difference parameter. Moreover, motile microorganism's distributions are diminished by improved values of bio-convected Peclet and bio-convected Lewis numbers.     

Bioconvection in oxytactic microorganism-saturated porous square enclosure with thermal radiation impact

This investigation addresses bioconvection of oxytactic microorganisms in a porous square enclosure by thermal radiation impact. The bioconvection flow and heat transfer in porous media are formulated based on Darcy model of Boussinesq approximation. Appropriate transformations lead to the non-dimensionalized governing partial differential equations. Galerkin finite element method for the resulting equations is computed. The role of relevant parameters on the streamlines, isotherms, isoconcentrations of oxygen and microorganisms and average Nusselt number is analysed in the outputs. It is revealed that the flow intensity of bioconvection is pronounced with larger Rayleigh number and reduced with radiation parameter. Furthermore, the temperature distribution is affected significantly with Rayleigh number. Radiation parameter serves to fasten the heat transfer in the enclosure. Oxygen density is enhanced with Rayleigh number and radiation parameter. The profile of motile isoconcentrations is boosted with Rayleigh number. The stability of microorganisms is improved with the radiation parameter.

     

Phase separation and gelation of polymer-dispersed liquid crystals

Polymerization-induced phase separation in polymer-dispersed liquid crystal is studied by computer simulations in two dimensions. The domain morphology resulting from phase separation is investigated by solving the coupled set of equations for the local volume fraction and the nematic order parameter, taking into account the viscoelastic effects and gelation due to polymerization. Comparing the morphology of phase separation by temperature quench, it is shown that the viscoelastic effects and gelation enable the polymer-rich phase to form a stable interconnected domain even when the polymer component is minority. The experimental evidence consistent with this characteristic feature is also given.     

Numerical simulations of viscoelastic particle migration in a microchannel with triangular cross-section

The migration of a spherical particle immersed in a viscoelastic liquid flowing in a microchannel with a triangular cross-section is investigated by direct numerical simulations under inertialess conditions. The viscoelastic fluid is modeled through two constitutive equations to investigate the effect of the second normal stress difference and the resulting secondary flows on the migration phenomenon. The results are presented in terms of trajectories followed by the particles released at different initial positions over the channel cross-section in a wide range of Weissenberg numbers and confinement ratios. Particles suspended in a fluid with a negligible second normal stress difference migrate toward the channel centerline or the closest wall, depending on their initial position. A much more complex dynamics is found for particles suspended in a fluid with a relevant second normal stress difference due to the appearance of secondary flows that compete with the migration phenomenon. Depending on the Weissenberg number and confinement ratio, additional equilibrium positions (points or closed orbits) may appear. In this case, the channel centerline becomes unstable and the particles are driven to the corners or “entrapped” in recirculation regions within the channel cross-section. The inversion of the centerline stability can be exploited to design efficient size-based separation devices.