Variable Thermal Conductivity Research Articles

Swirling flow analysis of Eyring–Powell fluid between coaxial disks with variable property

Abstract The main objective of this study is to examine an unsteady swirling flow of a non-Newtonian Eyring–Powell fluid between two coaxial disks. The lower and upper disks are considered to rotate with different angular velocities. The three-dimensional axisymmetric flow phenomenon and heat transfer mechanism are observed with the consequences of the magnetic field and variable thermal conductivity of the fluid. The variable thermal conductivity is taken to be dependent on the fluid temperature. The implementation of the Von Karman similarity transformations on the constituting equations of the flow phenomenon yields the dimensionless system of the non-linear equations. An optimal homotopy analysis technique is adopted to obtain analytical solutions for highly non-linear equations. In view of the same and opposite directions of disks rotation, the various aspects of the flow system corresponding to the pertinent parameters are discussed with physical significance. The obtained results indicate that both radial and axial fields are the escalating functions of the Eyring–Powell fluid parameter. Moreover, the heat transfer rate enhances with the improving variable thermal conductivity parameter.

Early-Hydration heat and influencing factor analysis of Large-Volume concrete box girder based on equivalent age

Large-volume concrete box girders are vulnerable to early cracking because of the hydration reaction at early ages. The excessive temperature difference between the core and external surface is the main reason for early cracking. Controlling the temperature field of concrete can reduce the risk of early cracking. Therefore, numerical simulations and tracking tests of a 50-m box girder were conducted. The early-age temperature field was simulated using ABAQUS and the secondary development of the subroutine. Meanwhile, the influences of different construction and curing method parameters were analyzed. The subroutine UMATHT considers the variations of hydration degree, thermal conductivity, and specific heat with equivalent age. The results indicate that the early-age hydration temperature of the box girder follows a general trend of “increasing temperature — continuous high temperature — cooling.” The measured results verify the accuracy of the numerical simulation method. The temperature peak and temperature difference between the core and surface increased with the increase in concrete section size, pouring temperature, and cement dosage. The effects of pouring temperature and cement dosage on the temperature rise and cooling rate were reversed. For every 5 °C decrease in the pouring temperature, the temperature peak of the web also decreased by approximately 5 °C, while the temperature difference between the core and surface of the web decreased by approximately 2 °C. When thermal insulation measures were taken for the box girder's outer formwork, the concrete temperature peak increased slightly, but the temperature difference between the core and surface decreased significantly. When the thickness of the polystyrene foam board reached 1 cm, the temperature difference between the core and web surface could be controlled within 6.1 °C.

Influence of MHD mixed convection flow for maxwell nanofluid through a vertical cone with porous material in the existence of variable heat conductivity and diffusion

The primary objective of this paper is to investigate the magnetohydrodynamic (MHD) mixed convection flow for Maxwell nanofluid, which is debated in the context of a vertical cone containing porous material. In addition, variable thermal conductivity and Dufour's effects are considered. Utilizing similarly transformable variables allows the modeled equations to be converted into a set of non-linear ODEs. After that, these equations are solved numerically by employing the shooting method, followed by the fourth-order Runge–Kutta integration process. The effects of certain prominent physical factors, such as the diffusion coefficient, the Prandtl number, the thermophoresis parameter, and the magnetic parameter, are explored numerically on the velocity, temperature, and concentration profiles. The most important takeaways from this work are that an increase in Maxwell parameters and magnetic parameters leads to a reduction in velocity. The temperature rises as the parameters for radiation and thermophoresis increase, but the values for the Prandtl number and the Brownian motion parameters fall as the values increase. The following table shows the importance of the skin-friction coefficient, the Nusselt number coefficient, and the Sherwood number coefficient. A comparison is made with the data that was reported in the past, and it is found that there is a remarkable degree of agreement.

Thermal conductivity of metallic nanoparticle using surface effect and kapitza resistance

To estimate the size dependence of thermal conductivity of metallic nanoparticles, different theoretical models and experimental techniques have been used by different groups of researchers. But it still requires an accurate model that supports the experimental results at low dimensions. A model is proposed to predict the change in thermal conductivity of metallic nanoparticles with size by extending the bond-energy model assuming core shell structure. In present work, we have taken metallic nanoparticles as samples for the verification of proposed model. It is observed that the coefficient of thermal conductivity of nanoparticles decreases by lowering the size of nanoparticles. The variation in thermal conductivity of metallic nanoparticles with their shape and size can be successfully explained by introducing the theory including the surface effect and kapitza resistance. It is found that the computed value has a deviation of maximum ±5% with experimental results which is in the permissible range of experimental measurement.

Thermodynamic study of radiative chemically reactive flow of induced MHD sutterby nanofluid over a nonlinear stretching cylinder

Incompressible two dimensional steady flow of Sutterby fluid over a nonlinear stretching cylinder. The fluid properties are variable under the Buongiorno model of nanofluid. The effect of induced magnetic field applied on the sutterby fluid using the heat generation and chemical reaction. The nonlinear radiative with thermal and concentration slip have been studied. Under the above expectations, the mathematical model established using the governing equations. These equations are become partial differential equations by means of boundary layer approximation. The partial differential equations reduced in the form of ordinary differential equations by implementing the transformations. The dimensionless system solved through numerical approach. The impression of governing physical parameters are reported in graphically as well as tabular form. The temperature of fluid boosted up due to larger values of variable thermal conductivity. As the thermal conductivity of liquid enhanced due to thermal conductivity increasing which increased the fluid temperature. The fluid temperature enlarged due to increment of Brownian motion. Physically, the fluid temperature boosted for different values of Brownian motion because increment of Brownian motion means increment in kinematic energy which improved the fluid temperature.

Motor Yağı Bazlı Nanoakışkanlar ile Farklı Tipteki Nanoparçacıkların Absorpsiyon ve Termal Analizinin Deneysel Olarak İncelenmesi

Nanofluids are fluid suspensions of nanoparticles that exhibit notable properties enhancement even at low nanoparticle concentrations. This work compares the measured and calculated thermophysical parameters of nanofluidic motor oil. Thermophysical parameters of motor oils include thermal conductivity, viscosity, and Absorbance. The nanofluidic engine oil was prepared by dispersing multi-walled carbon nanotube (MWCNTs) and copper oxide (CuO) at different particle concentrations (0.03-0.12) %. The oil characteristics were measured at wide range of temperature. The viscosity data were found to be comparable to the numbers reported in literature. We found that the thermal conductivity increased up to five times with minor variance in some cases. The variation in thermal conductivity can be related to several reasons such as oil specifications and nanofluid preparation conditions. The measured Absorbance of the nanofluid is comparable to literature and has direct proportion relation with the volume fraction of nanoparticles.

Variable thermal conductivity in micropolar thermoelastic medium without energy dissipation possessing cubic symmetry

This investigation deals with the effect of variable thermal conductivity in a micropolar thermoelastic medium without energy dissipation with cubic symmetry. The normal mode technique is employed for obtaining components of physical quantities such as displacement, stress, temperature distribution and microrotation.

A comparative thermal case study on thermophysical aspects in thermally magnetized flow regime with variable thermal conductivity

It is well consensus among researchers affiliated with the field of thermal engineering that the thermophysical characteristics of heat transfer in fluid science own abundant applications like thermal distillation systems, heat exchangers, steam-electric power generation, electronic cooling, solar collectors, refrigeration systems and spacecraft thermal protection are to mention just a few. Considering such importance we offer a thermal case study on thermophysical aspects in a thermally magnetized non-Newtonian fluid along with a first-order chemical reaction effect. The flow field is carried with the following thermophysical effects namely, mixed convection, heat generation, viscous dissipation, thermal radiations, and temperature-dependent variable thermal conductivity. We have offered comparative analysis for temperature and Nusselt number by considering thermally radiative and non-radiative thermal flow fields. The thermal outcomes on temperature and Nusselt number are also reported for both the absence and presence of the heat generation effect. For both radiative and non-radiative Casson flow, the temperature shows an inciting nature towards Casson and variable thermal conductivity parameters. The magnitude of the Nusselt number towards Eckert, Prandt numbers, curvature, heat generation, and Casson fluid parameters is higher for the presence of thermal radiations while the opposite is the case for positive variation in the thermal conductivity parameter.

Unsteady Heat and Mass Transfer MHD Flow of Nano-Fluids with Buoyancy and Variable Thermal Conductivity

Unsteady Heat and Mass Transfer MHD Flow of Nano-Fluids with Buoyancy and Variable Thermal Conductivity

Mathematical modeling and simulation of peristaltic activity in Ree-Eyring fluid flow through non-uniform complaint channel: Different varying conditions

The current study incorporates variable viscosity and thermal conductivity on modeling Ree-Eyring fluid flow inside a peristaltic non-uniform complaint channel. The small Reynolds number and long-wavelength approximations are employed for resolve the governing nonlinear differential equations. Temperature expression is obtained with the help of series solution method. The graphs are drawn on relevant parameters to investigate its effect on velocity, temperature, concentration, and streamlines through MATLAB 2020b. The results confer more velocity in the Newtonian fluid in comparison with non-Newtonian fluid. Also, the model discloses that the size of the bolus can be varied by varying the viscosity parameter. This result helps in understanding the thrombus formation in blood vessels.

Rapid detection of the vacuum failure of logging tools based on the variation in equivalent thermal conductivity

The logging tool is the key downhole facility used for oil and gas exploration. A vacuum flask is indispensable for protecting the inside electronics of the logging tool from extreme working environments. During transport, assembly, or working processes, vacuum flask failure can lead to the destruction of the logging tool. The existing test methods are unable to detect vacuum failure quickly and accurately. To solve this problem, a rapid test method based on the variation in equivalent thermal conductivity before and after vacuum failure was proposed. First, the principle of this method was illustrated in detail, and a simplified 1D heat transfer model was calculated by the finite difference method. We found that the temperature rise ratio between the insulator and heat source (defined as P) can be used as the testing indicator with a 1 h testing time. Subsequently, a rapid test device was designed, and numerical simulations were performed to determine the critical values of the testing indicator for actual vacuum flasks. The simulated results showed that independent of the heating power and initial temperature, the P values for vacuum flasks in normal and abnormal states are 0.391 and 0.299, respectively, with a critical value of 0.351. Finally, experimental tests were conducted to test the effectiveness of the rapid test method and testing indicator. The experimental results showed that the measured P values of normal and abnormal vacuum flasks were above or below the critical value (Pe) under different test conditions, respectively, indicating that the proposed rapid test method can quickly and accurately detect vacuum failure. The maximum error between the simulated and experimental results was only 8.7%.

Modified Finite Element Study for Heat and Mass Transfer of Electrical MHD Non-Newtonian Boundary Layer Nanofluid Flow

Research into the effects of different parameters on flow phenomena is necessary due to the wide range of potential applications of non-Newtonian boundary layer nanofluid flow, including but not limited to production industries, polymer processing, compression, power generation, lubrication systems, food manufacturing, and air conditioning. Because of this impetus, we investigated non-Newtonian fluid flow regimes from the perspectives of both heat and mass transfer aspects. In this study, heat transfer of electrical MHD non-Newtonian flow of Casson nanofluid over the flat plate is investigated under the effects of variable thermal conductivity and mass diffusivity. Emerging problems occur as nonlinear partial differential equations (NPDEs) in opposition to the conservation laws of mass, momentum, heat, and species transportation. The shown problem can be recast as a set of ordinary differential equations by making the necessary changes. A modified finite element method is adopted to solve the obtained set of ODEs. The numerical method is based on Galerkin weighted residual approach, and Gauss–Legendre numerical integration is adopted in the modified finite element method application procedure. To clarify the obtained results, another numerical technique is employed to solve the reduced ODEs. With the help of error tables and the flowing behavior of complicated physical parameters on estimated solutions, this study graphically and tabulatively explains the convergence of analytic solutions. Comparing some of the obtained results with those given in past research is also done. From the obtained results, it is observed that the velocity profile escalates by improving the electric parameter. Our intention is for this paper to serve as a guide for academics in the future who will be tasked with addressing pressing issues in the field of industrial and engineering enclosures.

Electrothermal analysis for reactive Powell Eyring nanofluid flow regulated by peristaltic pumping with mass transfer

The proposed work presents an optimized thermal frame for electroosmosis optimized peristaltic transportation of reactive Powell-Eyring magneto-nanofluid with mass transfer. The peristaltic phenomenon with the applications of electro-kinetic pumping develops the effectiveness of smart pumps in nanotechnologies and medical uses. The thermal and mass characteristics of a nanofluid is obtained by evaluating the well-known Buongiorno model, which allows us to identify appealing aspects of thermophoretic diffusion and Brownian motion. The non-Newtonian nanofluid flows through a porous space under the influence of variable thermal conductivity, chemical reactions, magnetic field, and mixed convection. Zero mass flux at the channel borders are taken. A biological estimate of the creeping transportation model, long wavelength assumptions, and Debye-Hückel linearization is revealed. The resulting equations are then resolved numerically, and the results obtained are discussed in detail along with their graphical representation. The investigation reports that electroosmotic and Joule heating parameters significantly improve the temperature of Powell Eyring nanofluid. The total entropy (irreversibility rate) of the system can be controlled with the thermal conductivity parameter in the case of auxiliary pumping. A development in concentration profile is seen for greater chemical reaction parameters. Further, nanofluid flow declines with higher values of electroosmotic velocity and the Powell-Eyring fluid parameter.

A finite thin film flow of pseudo-plastic MHD hybrid nanofluid with heat generation and variable thermal conductivity

The primary objective of this article is to get an overview of electrically conductive pseudo-plastic hybrid-nanofluid in a finite thin film over an unsteady, nonlinearly stretching surface. Viscous dissipation, internal heat generation, magnetohydrodynamics, and the temperature-dependent thermal conductivity effects are examined while examining the flow velocity and temperature of the fluid. Different types of hybrid-nanoparticles are assessed, which are the amalgam of , , , and with Carboxy-methyl Cellulose (CMC)-water as base fluid. Further, modified heat conduction of Fourier’s law concerning the power-law model is utilized instead of a classical model. The resolved partial differential equations (PDEs) are transformed into a couple of non-linear ordinary differential equations (ODEs) after using specified transformations. Runge–Kutta technique of order four coupled with shooting method is applied to acquire the numerical solutions. The effects on velocity and temperature profiles due to the behavior of power-law-index, Hartmann number, Prandtl number, and unsteadiness parameter are analyzed and graphically presented. It is observed that and hybrid nanofluid has the most influential impacts on the Nusselt number as compared to the other three combinations. The temperature gets a decline with the increasing power-law index.

Evaporating Rayleigh–Bénard convection: prediction of interface temperature and global heat transfer modulation

We propose an analytical model to estimate the interface temperature $\varTheta _{\varGamma }$ and the Nusselt number $Nu$ for an evaporating two-layer Rayleigh–Bénard configuration in statistically stationary conditions. The model is based on three assumptions: (i) the Oberbeck–Boussinesq approximation can be applied to the liquid phase, while the gas thermophysical properties are generic functions of thermodynamic pressure, local temperature and vapour composition, (ii) the Grossmann–Lohse theory for thermal convection can be applied to the liquid and gas layers separately and (iii) the vapour content in the gas can be taken as the mean value at the gas–liquid interface. We validate this setting using direct numerical simulations in a parameter space composed of the Rayleigh number ( $10^6\leq Ra\leq 10^8$ ) and the temperature differential ( $0.05\leq \varepsilon \leq 0.20$ ), which modulates the variation of state variables in the gas layer. To better disentangle the variable property effects on $\varTheta _\varGamma$ and $Nu$ , simulations are performed in two conditions. First, we consider the case of uniform gas properties except for the gas density and gas–liquid diffusion coefficient. Second, we include the variation of specific heat capacity, dynamic viscosity and thermal conductivity using realistic equations of state. Irrespective of the employed setting, the proposed model agrees very well with the numerical simulations over the entire range of $Ra$ – $\varepsilon$ investigated.

Generalized Thermoelastic Interaction in Orthotropic Media under Variable Thermal Conductivity Using the Finite Element Method

This article addresses a thermoelastic problem under varying thermal conductivity with and without Kirchhoff’s transforms. The temperature increment, displacement, and thermal stresses in an orthotropic material with spherical cavities are studied. The inner surface of the hole is constrained and heated by thermal shock. The numerical solutions are derived using the finite element technique in the setting of the generalized thermoelasticity model with one thermal delay time. The thermal conductivity of the material is supposed to be temperature-dependent without Kirchhoff’s transformation. Due to the difficulty of nonlinear formulations, the finite element approach is used to solve the problem without using Kirchhoff’s transformation. The solution is determined using the Laplace transform and the eigenvalues technique when employing Kirchhoff’s transformation in a linear example. Variable thermal conductivity is addressed and compared with and without Kirchhoff’s transformation. The numerical result for the investigated fields is graphically represented. According to the numerical analysis results, the varying thermal conductivity provides a limited speed for the propagations of both mechanical and thermal waves.

Dual solutions of radiative Ag-MoS_2/water hybrid nanofluid flow with variable viscosity and variable thermal conductivity along an exponentially shrinking permeable Riga surface: Stability and entropy generation analysis

ABSTRACT In this analysis, the Silver-Molybdenum disulfide ()/water hybrid nanofluid flow past a permeable exponentially shrinking Riga surface with thermal radiant energy is considered. The novelty of this work is to find out the effects of variable viscosity, variable thermal conductivity with hybrid nanofluid’s slip velocity, and convective thermal boundary conditions over a shrinking Riga surface on velocity, temperature, skin-friction coefficient, Nusselt number, and entropy generation. The MATLAB programming platform with a fourth-order method to solve boundary value problem (bvp4c) was employed to get a good account of all pertinent flow parameters before solving the controlling partial differential equations numerically. Here of Silver () and of Molybdenum disulfide () nanoparticles in the hybrid model are considered in the base fluid water. The basic achievement of this analysis is to explore the Nusselt number, skin friction coefficient along with entropy formation, and Bejan number. The irreversibility factor is calculated using the thermodynamics second law. The findings also point to the presence of dual-nature solutions in the shrinking sheet region for a given value of a high mass suction parameter, with a stable upper solution branch and unstable lower solution branch. Two solutions are found for the limited range of shrinking parameter when and the solutions terminate at in the shrinking region. Additionally, the first solution generates a positive minimum eigenvalue (), whereas the second solution generates a negative eigenvalue (), indicating the solution’s stability. Nusselt number is enhanced for variable viscosity parameter but diminished by variable thermal conductivity parameter for the stable solution. The entropy generation and the Bejan number both increase significantly with the increment of the thermal radiant-energy parameter, Biot number, and Eckert number. These results are crucial in the long term because they allow us to optimize heat transmission for cooling and heating applications. Hence, this investigation is incredibly significant in the present era, particularly in the automotive industry, home industry, paper plastics, ceramics, food packaging, food colorants, cancer treatment, cosmetics, pharmaceuticals, fabrics, paints, and soaps as well.

Peristaltic flow of a hyperbolic tangent fluid with variable parameters

This article investigates the peristaltic flow of a hyperbolic tangent fluid with variable viscosity and thermal conductivity through a vertical asymmetric channel. Consideration is given to the effects of viscous dissipation, chemical reactions, and convection heat at the channel walls. The relevant mathematical modeling incorporates lubrication approximation. The resulting system of highly non-linear differential equations is converted non-dimensional via suitable quantities. The non-dimensional parameters formed in viscosity or thermal conductivity are treated as variables. This treatment is the fundamental recommendation of the current study to avoid obtaining unrealistic results. Using the built-in package (ParametricNDSolve) in the computing program Mathematica, the analysis is performed numerically, and the results for temperature and concentration profiles in addition to the trapping phenomenon are shown through graphs. The major findings show that an increase in temperature is associated with a decrease in viscosity, whereas the opposite (unrealistic) behavior is maintained when the variable parameters are treated as constants. Results also indicate that the thermal conductivity at relatively low temperatures is enhanced, whereas the opposite trend is noted at higher temperature values. Potential applications for the current work include cooling techniques used in medical and industrial applications, food processing, and blood flow in microvessels.

Thermodynamic analysis for peristaltic flow of Carreau-Yasuda magneto nanofluid through a porous medium

Thermodynamic analysis for mixed convective peristaltic transportation of Carreau–Yasuda (CY) magneto nanofluid is presented. The assumed nanofluid is a mixture of graphene nano-powder and ethylene glycol. The Carreau–Yasuda model is considered to represent the non-Newtonian features of nanofluids. A mathematical model is developed under the effects of a porous medium, variable thermal conductivity, Brownian motion, viscous dissipation, magnetic field, thermophoresis, and Ohmic heating assumptions. Mass and heat transfer aspects are also considered. The flow and heat/mass transfer equations were made using Buongiorno’s model of nanofluids. No-slip and zero mass flux boundary conditions are entertained for velocity, thermal, and concentration profiles. A numerical solution via built-in technique is obtained for a coupled system of equations. Graphical outcomes predict that due to Ohmic heating characteristics temperature profile increases. The heat transfer rate at the wall decreases for higher thermal conductivity parameter. The irreversible rate can be controlled by maintaining Darcy’s number. The concentration of nanomaterials increases when the thermophoresis parameter is improved. Fluid velocity is slowed down by enhancing the Hartman number and it improves by enhancing the thermal Grashof number.

Impact of magnetohydrodynamics in bidirectional slip flow of Maxwell fluid subject to stretching, radiation, and variable properties

The viscosity of fluids varies according to changes in pressure, temperature, and shear rate. As a consequence, it is essential to look at specific qualities in the paper industry, plastics extrusion in Rayon and Nylon production, the textile sector, and other industries. In such a way, the model is more precisely anticipated when the flow configuration comprises the viscosity and thermal conductivity of the fluid as a function of temperature. Owing to the importance of variable viscosity and thermal conductivity, this article highlights the importance of the magnetohydrodynamic (MHD) flow of Maxwell fluid over a bidirectional stretched surface. Fluid is electrically conducting in the presence of an applied magnetic field. Heat transfer analysis is carried out in the presence of thermal radiation and heat generation/absorption. A system of ordinary differential equations is obtained by appropriate transformations. Numerical solutions are computed for the resulting nonlinear differential system by applying the shooting method with the RK-5 scheme. The impact of different parameters on the velocity, temperature, and concentration profiles is examined. Computations for surface drag force, heat, and mass transfer rates are presented and examined for the influences of pertinent parameters. It is observed that fluid velocity reduces for larger Maxwell fluid parameter. Increasing values of thermal radiation parameter correspond to the enhancement in temperature. Mass transfer rate enhances for larger Schmidt number while heat transfer rate is increasing function of Prandtl number.