Variable Fluid Properties Research Articles

Rheological effects on peristaltic transport of Bingham fluid through an elastic tube with variable fluid properties and porous walls

AbstractThe peristaltic pumping of non‐Newtonian material configured by a tube is quite interesting phenomenon to examine the behavior of physiological fluids. The present paper investigates the role of variable viscosity and thermal conductivity on the peristaltic mechanism of Bingham fluid in an elastic tube with porous and convective boundary conditions. The long wavelength and small Reynolds number approximation is used to obtain the analytical solutions for velocity, plug flow velocity, streamlines, flow rate, and temperature. The theoretical determination of flux is calculated using the equilibrium condition, and an application to flow through an artery is highlighted by using the tension relation in an elastic tube. It is observed that the rate of flow within the elastic tube declined with variation of variable viscosity. An enhanced temperature distribution near the tube axis has been observed with increment of variable viscosity. An increasing influence of the porous parameter in the bolus size can also be seen from the streamlines plotted.

A general multi-scale modeling framework for two-phase simulation of multi-stream plate-fin heat exchangers

Compact heat exchangers are among the vital components used in various industries. In this study, a general framework has been developed with a multi-scale point of view for three-dimensional simulation of multi-stream plate-fin heat exchangers. The most important features in the MSPFHEs simulation, such as phase change phenomena, multi-component mixtures, multiple streams, transversal, lateral and longitudinal conduction, non-uniformity of inlet flow, variable fluid properties, and heat leakage are simultaneously considered in this model. The modular form of the model structure has facilitated layer-by-layer simulation of cross flow heat exchangers as well as parallel flow ones. Our model has been successfully validated with numerical and experimental case studies. Periodic boundary conditions are developed for simulating heat exchangers with a high number of layers to reduce the computational cost. The results for a challenging six-stream test case show that when the number of layers for each stream is more than 15, results converge to the periodic boundary condition case. The total simulation time is decreased by 98.1% for a heat exchanger with 40 repeating unit cells. Liquefied natural gas production has been decreased by 5.8% due to the non-uniformity of natural gas at the entrance of the six-stream test case. Fluid temperature, and vapor quality distributions for a multi-component two-phase cross-flow MSPFHE have been presented. A dead zone is observed in the results of the cross-flow heat exchanger that does not have a significant contribution to the heat exchange. Results show that the total heat exchange between streams has been decreased by 8.5% in comparison to the parallel-flow ones.

Effects of Variable Fluid Properties on Oblique Stagnation Point Flow of a Casson Nanofluid with Convective Boundary Conditions

Oblique stagnation point flow of a Casson nanofluid over a heated stretching surface is examined under the influence of variable fluid properties. The impact of variable fluid properties on the flow field is examined by taking a convective boundary condition into account. Momentum, energy and concentration equations are transformed into the non-linear ordinary differential system through suitable similarity transformations and are solved analytically via Optimal Homotopy Analysis Method (OHAM). Effect of pertinent parameters on dimensionless velocity, temperature and concentration are depicted graphically. Numerical values of skin friction, Nusselt number and Sherwood number have been calculated for various parameters. The results indicate that the axial velocity decreases with an increase in variable viscosity whereas the dual impact of variable viscosity is observed on transverse velocity.

A New Computational Technique Design for EMHD Nanofluid Flow Over a Variable Thickness Surface With Variable Liquid Characteristics

The objective of paper comprises two key points: descriptive mathematical model for constant and variable fluid flows over a variable thickness sheet by inducting applied electric and magnetic fields, porosity, radiative heat transfer, heat generation/absorption and seeking their solution by constructing a novel numerical method, the Simplified Finite Difference Method (SFDM). We resort to similarity transformations to implicate partial differential equations (PDEs) into a set of ordinary differential equations (ODEs). Optimal results for a pair of ODEs obtained from SFDM are assessed by drawing a comparison with \emph{bvp4c} and existing literature values. SFDM has been implemented in MATLAB for both constant and variable fluid properties. Tabulated numerical values of the skin friction coefficient, local Nusselt and Sherwood numbers are measured and analyzed against different parameters. Influence of distinct parameters on velocity, temperature, and nanoparticles volume fraction have been explained in great detail via diagrams. The skin friction coefficient for variable fluid properties is greater than the constant fluid properties. However, the local Nusselt number is less for variable fluid properties when compare with constant fluid properties. Surprisingly, the high precision computational results are achieved from the SFDM.

Thermophoretic MHD free stream flow with variable internal heat generation/absorption and variable liquid characteristics in a permeable medium over a radiative exponentially stretching sheet

The current paper describes the impact of variable viscosity and thermal conductivity over an exponentially stretching sheet in MHD radiating free stream Newtonian fluid with internal heat generation/absorption in a porous medium. The underlying problem consists of mass, momentum and energy equations, which are transformed by implying appropriate similarity transformations into ordinary differential equations (ODEs). Using the shooting technique, the resulting problem has been solved numerically and tested with MATLAB built-in solver bvp4c. The numerical data produced for the coefficient of the skin friction, the local Nusselt number and the local Sherwood number are compared with the available literature and have been found to be in close agreement. In addition, the profiles of velocity, temperature, and concentration are discussed through graphically. It is noted that the skin friction coefficient increases for increasing values of viscosity parameter θr, magnetic parameter M and porosity parameter Kp which causes reduction in velocity of the fluid flow. On the other hand the local Nusselt number and local Sherwood number decreases for higher values of viscosity parameter θr and small thermal conductivity parameter ϵ. Heat transfer rate is higher for constant fluid properties when compared with variable fluid properties.

Numerical treatment for MHD viscoelastic fluid flow with variable fluid properties and viscous dissipation

Numerical and theoretical examinations of the viscous dissipation phenomenon on the viscoelastic fluid flow of type Walters’ liquid B model which is passing over a stretching sheet are described. The significance of both slip phenomenon and magnetic field in stimulating the heat transfer process is the main cause for considering them in this study. On the other hand, to gain high precision in our numerical study, some of fluid properties are assumed to depend on the fluid temperature. Since, both the viscosity and the conductivity of the fluid which are changing with temperature are taken into consideration, therefore, our obtained results are much more reliable than those the similar previous researches. In addition, this described physical problem is governed by three partial differential equations. After introducing suitable dimensionless variables, two differential equations are created: the first is of fourth order, whereas the second one is of second order. These two equations along with appropriate boundary conditions are then numerically solved via the shooting technique. Finally, in the light of the prominent outcomes, for both the viscoelastic and viscosity parameters growth, the enhancement of the sheet velocity is remarkable, whereas the drastically drop for the sheet velocity was observed for the magnetic parameter.

Entropy analysis of EMHD non-Newtonian fluid flow induced by Riga plate with slip and convective boundary phenomena

Our paper is consecrated to show the influence of variable fluid properties in EMHD non-Newtonian power-law fluid along a moving Riga plate. Slip velocity phenomenon is considered at the surface which is convectively heated. Entropy analysis is elaborated employing thermodynamic second relation. The governing nonlinear PDEs are altered into ODEs through adequate propinquity transformations which have been solved numerically via the shooting method with the fourth-order Runge–Kutta algorithm through Mathematica software (bvp4c). Characteristics of different basic parameters on velocity, temperature, entropy generation and Bejan number are highlighted through graphs. The outcomes exhibit that the minimum entropy rate in the flow system can be obtained either with rising viscosity parameter and slip parameter or declining dimensionless parameter and thermal conductivity parameter. The entropy rate is minimal for dilatant fluid when compared to pseudo plastic fluid with the most governing parameters. Contrast behavior on the thermal field is noticed for larger values of viscosity parameter and thermal conductivity parameter.

ANALYSIS OF PERISTALTIC FLOW OF RABINOWITSCH FLUID IN A NON-UNIFORM CHANNEL: ANALYTICAL APPROACH

The present paper examines the impact of heat and mass transfer on the peristaltic flow of Rabinowitsch fluid through a non-uniform channel. The effects of slip and variable fluid properties are taken into account. The impacts of wall rigidity, wall stiffness, and viscous damping force parameter are considered. The equations governing the flow are rendered dimensionless by using a suitable similarity transformation. The governing equations of momentum, motion, energy, and concentration are solved by utilizing long wavelength and small Reynolds number approximation. The MATLAB 2019a programming has been used to obtain the solutions for velocity and concentration profiles. The series solution technique has been utilized to get the expression for temperature. The influence of relevant parameters on velocity, temperature, concentration, and streamlines are examined for viscous, shear-thinning, and shear thickening fluid models. The examination uncovers that a rise in the value of variable viscosity and variable thermal conductivity improves the velocity and temperature profiles for Newtonian and pseudoplastic fluid models. Moreover, an increase in the volume of the trapped bolus is seen for an expansion in the estimation of the velocity slip parameter for all the three considered models.

Effect of Density Variation on Rarefied and Non-rarefied Gaseous Flows in Developing Region of Microtubes

The present study analyzes the rarefaction and non-rarefaction effects on heat transfer characteristics of hydrodynamically and thermally developing air flow through microtubes having a constant wall heat flux boundary condition. The problem is especially simulated with two microtubes having diameters 50 µm and 150 µm. The rarefaction effect is taken into consideration using Maxwell slip flow and temperature jump boundary conditions. The fluid property variation is considered as a non-rarefaction effect which plays a significant influence on convection through a microtube. It is observed that the rarefaction and non-rarefaction effects significantly affect the convective heat transfer. The non-rarefaction effect decreases the Nusselt number (Nu) as compared to constant property solution; however, the rarefaction effect increases the Nu compared to constant property solution.

Similarity solution of MHD slip with energy mass transport through chemically reacting stretching permeable surface in porous media with variable properties

In this paper, a mathematical model is presented for magnetohydrodynamic viscous incompressible boundary layer flow of an electrically conducting chemically reacting fluid over a moving permeable flat vertical surface in a porous medium with variable fluid properties. A linear momentum slip boundary condition is included. Temperature and concentration difference between the wall and the environment are assumed to vary with the axial distance according to power law forms. Furthermore, a concentration-dependent mass diffusivity is featured to provide for a more realistic simulation of relevance to materials processing systems. The governing equations with associated boundary conditions are transformed into similarity equations using appropriate variables furnished with Lie group algebraic methods. The resulting nonlinear differential ordinary boundary value problem is then solved numerically with a Runge–Kutta–Fehlberg fourth–fifth order numerical method. The effects of the governing parameters on the boundary layer flow characteristics (velocity, temperature, concentration, wall shear stress, heat and mass transfer rates) have been investigated, displayed graphically and discussed. The computations indicate that variable mass diffusivity plays a significant role on transport characteristics. It is also shown that concentration magnitudes increase whereas the rate of mass transfer at the wall decreases with increasing mass diffusivity. Comparison of numerical and analytical results with results from the open literature show excellent agreement. Further verification of the general model is conducted with the Spectral Relaxation Method (SRM). The study is relevant to electroconductive polymeric sheet processing in manufacturing operations and smart coating systems.

The temperature decomposition method for periodic thermal flows with conjugate heat transfer

Periodic structures are often found in many industrial applications. Simulations for such systems can be performed over a one-module domain when neglecting variation in fluid properties, and the results can be applied to a multiple-module flow passage. This approach is widely found in previous studies; however, it is limited to systems with relatively simple boundary situations: either the temperature or heat flux can be specified over the wall surfaces. Recently Li and Zhang (J. Heat Transf. 140:112002, 2018; Numer. Heat Tr. B Fund. 74:559, 2018) have proposed a temperature decomposition method, which makes the one-unit simulations possible for the above situations. However, the conjugate heat transfer, for example, between the flowing fluid and the structure materials (solid structure), has not been considered. In this study, we extend the temperature decomposition method to periodic thermal flows with conjugate heat transfer between the fluid and structure. The physical temperature is split into two parts, namely the transient part and the equilibrium part. The governing equations and conjugate relations at the interface for each temperature parts are established, and the corresponding inlet/outlet boundary conditions are proposed. It can be mathematically shown that the temperature obtained from this method satisfies the original energy equation in the fluid and solid domains, the thermal boundary conditions on the system walls, and the conjugate relations at the solid-fluid interfaces. Physical interpretations and numerical implementation steps are also provided. Several simulations are conducted to verify and demonstrate the validity, accuracy, and potential usefulness of our method, and the results and discussions clearly show that the TDM method correctly reflects the underlying relationship in temperature, which otherwise is not available, for conjugate periodic thermal systems.

Graph theory-based heat current analysis method for supercritical CO2 power generation system

Supercritical carbon dioxide (sCO2) power generation system holds tremendous potential in energy utilization fields featuring with its high efficiency, compactness, and security. However, dramatic variations in sCO2 thermophysical properties make the existing constant property analysis methods imprecise. In this contribution, inlet temperature difference-based thermal resistance transforms the nonlinear governing equations of heat transfer process into linear forms, and applying the graph theory builds the heat current model of a sCO2 recompression cycle with consideration of fluid property variation, which is analogous to electric circuit. Therefore, utilizing the electric circuit principle offers the overall heat transport and conversion laws in the whole system and gives the integral mathematical relations of all independent variables, which are solved by the newly proposed iterative divide-and-conquer solution algorithm. Finally, optimization of a typical sCO2 recompression system under different boundary conditions shows the applicability and conciseness of the heat current method compared to the existing analysis methods.

Analysis of fluid property variations across the Barnett and Eagle Ford Shale using fuzzy logic

The objective for this study is to perform an investigation of the areal and vertical geospatial fluid property variations across the Barnett and Eagle Ford based on publicly-available PVT data (97 Barnett wells and 153 Eagle Ford wells). A modified multi-contact recombination procedure has been implemented to the PVT data of the reported well stream compositions for Barnett to improve estimates of in-situ reservoir composition. The Eagle Ford data were utilised without modifications as this shale play is known to be highly under-saturated. The results of modified multi-contact recombination procedure for Barnett are plotted on a ternary diagram and show that the majority of the wells were dry gas to retrograde gas. For Eagle Ford, ternary diagrams indicated the fluid type, vertical variations of OGR, C7+ and API gravity. Maps were created to review areal variations of these properties (API gravity, C7+, and initial OGR). The study was further speculated by applying fuzzy pattern recognition algorithms. The application of fuzzy logic provided additional insight to the reservoir fluid's PVT behaviour in understudy shale formations. [Received: August 23, 2018; Accepted: May 6, 2019]

Analysis of fluid property variations across the Barnett and Eagle Ford Shale using fuzzy logic

The objective for this study is to perform an investigation of the areal and vertical geospatial fluid property variations across the Barnett and Eagle Ford based on publicly-available PVT data (97 Barnett wells and 153 Eagle Ford wells). A modified multi-contact recombination procedure has been implemented to the PVT data of the reported well stream compositions for Barnett to improve estimates of in-situ reservoir composition. The Eagle Ford data were utilised without modifications as this shale play is known to be highly under-saturated. The results of modified multi-contact recombination procedure for Barnett are plotted on a ternary diagram and show that the majority of the wells were dry gas to retrograde gas. For Eagle Ford, ternary diagrams indicated the fluid type, vertical variations of OGR, C7+ and API gravity. Maps were created to review areal variations of these properties (API gravity, C7+, and initial OGR). The study was further speculated by applying fuzzy pattern recognition algorithms. The application of fuzzy logic provided additional insight to the reservoir fluid's PVT behaviour in understudy shale formations. [Received: August 23, 2018; Accepted: May 6, 2019]

Steady flow of MHD Williamson fluid due to a continuously moving surface with viscous dissipation and slip velocity

This research attempts to draw a fuller understanding of the magnetohydrodynamic flow of Williamson fluid owing to a continuously moving permeable surface. A detailed illustration of the importance of the effects of viscous dissipation and the variable fluid properties phenomena are also given. Meanwhile, this work has also revived the interest of the slip velocity phenomenon. The success is met after formulating the thorough equations which describe this model, thus it is no longer difficult to get into the numerical solution for this model via the shooting method. By analogy, this interesting subject also stimulates us to pursue further details which can be obtained from both the drag force or the skin-friction coefficient and the rate of heat transfer. Based on our apparent results, the presence of magnetic field, suction phenomena and slip velocity was the reason to reduce the surface velocity. Also, the same parameters can serve as a helpful guide for governing the rate of heat transfer.

The flow resistance experiments of supercritical pressure water in 2 × 2 rod bundle

The flow resistance experiment of supercritical pressure water in a 2 × 2 rod bundle was performed with heated length of 2.5 m. Each rod was annular tube of 9.5 mm outer diameter, 6.5 mm inner diameter and the center distance between two adjacent rods was 10.5 mm. The data were obtained at the pressures above the critical point, mainly focusing on 23, 24 and 25 MPa, mass flow within the range from 600 to 1400 kg/m2s and heat flux up to 943 kW/m2. The data reduction method was introduced in details to account for the fluid property variation in heated channels of supercritical flow. The results showed that the friction coefficient of supercritical flow had the shape of “V” profile versus Reynolds number. The fluid property differences between the wall and the bulk fluid should be considered. The heat flux and mass flux would affect the friction coefficient through changing the material correction factor. Various friction correlations were compared with the experimental data and some suggestions were given. The data obtained from this experiment could be applicable for a reference estimation of flow resistance in SCWR rod bundles.

Effect of internal heat generation on free convective power-law variable temperature past a vertical plate considering exponential variable viscosity and thermal conductivity

The aim of this paper is to study the free convection boundary-layer flow with heat generation and variable fluid properties past a vertical plate. We incorporated the heat generation and variable viscosity are the exponential decay form and thermal conductivity is the linear form in the governing equation. Using similarity transformations, the governing coupled non-linear partial differential equations are transformed into a system of coupled non-linear ordinary differential equations and then solved using Maple symbolic software to execute the computations via dsolve. The effects of the temperature-dependent viscosity, the wall velocity power index, the thermal conductivity, the wall temperature parameter, and the Prandtl number on the flow and temperature fields are presented. The skin friction and the wall temperature gradient are also presented for different values of the physical parameters.

Influence of heat source/sink on MHD flow between vertical alternate conducting walls with Hall effect

The key object of this article is to present the impact of heat source/sink and Hall current on the completely advanced natural convection flow of a viscous incompressible and electrically conducting fluid through a vertical channel with the condition that one wall is conducting and other is non-conducting. The resulting system of non-dimensional linear equations has been examined with the help of theory of simultaneous differential equations. Finally, we have found the expressions for the fluid velocity, induced magnetic field and temperature field in the compact form. Also, we have derived the induced current density from induced magnetic field and with the help of velocity we found skin friction and rates of mass flow. The obtained results are presented through graphs for distinct values of the Hartmann number, Hall current and heat source/sink parameters. It is noted that the impact of the Hartmann number is to reduce the parts of the velocity and induced current density but improve the constituents of induced magnetic field. Further, the increase of the Hall current parameter leads to enhancement and reduces the primary and secondary constituents of the velocity and induced magnetic field respectively. The Hall current gives rise to a cross flow and the variable fluid properties have strong effects on the shear stress and the Nusselt number. Hall current is applicable in Hall accelerators, Hall effect sensors and constrictions of turbines, etc.

Magnetohydrodynamic Free Stream and Heat Transfer of Nanofluid Flow Over an Exponentially Radiating Stretching Sheet With Variable Fluid Properties

This paper deals with the MHD free stream nanofluid flow and heat transfer over an exponentially radiating stretching sheet accompanied with variable fluid properties. By integrating appropriate similarity transformations, the fundamental governing partial differential equations (PDEs) are transformed into nonlinear ordinary differential equations. The resulting equations are successfully solved by using shooting method and MATLAB built-in solver \emph{bvp4c}. The major effect of the skin friction coefficient, Nusselt number and Sherwood number on the flow field have been calculated. The alteration of fluid flow is governed by different parameters, magnetic parameter M, Prandtl number Pr, Lewis Number Le, thromophoresis paramter Nt, Brownian motion parameter Nb, radiation parameter Rd which are presented in tabulated format. Graphs are also plotted to observe the effects of different aforementioned parameters on velocity, temperature and concentration profiles.

Heat transfer characteristics of water flowing through micro-tube heat exchanger with variable fluid properties

The heat transfer characteristics of laminar single-phase forced convective water flow through a micro-tube heat exchanger are numerically investigated in this paper. Two-dimensional simulations are performed to find the effects of variable fluid properties on heat transfer for hydrodynamically and thermally developed flow. The effects of variable fluid properties on convective heat transfer coefficient (h) and Nusselt number (Nu) are significant for micro-convective flow. It is noted that the variation in temperature-dependent thermal conductivity [k(T)] greatly enhances the h as compared to the variation in temperature-dependent viscosity [µ(T)], although water viscosity–temperature sensitivity (SμT) is greater than that of thermal conductivity–temperature sensitivity (SkT). The effects of variation in wall heat flux (\(q_{\text{w}}^{\prime\prime}\)) and inlet temperature on heat transfer are investigated for variable fluid properties. It is noted that the Nu declines with an augment in \(q_{\text{w}}^{\prime\prime}\) for temperature-dependent density variation [ρ(T)]. The Nu increases with an increase in \(q_{\text{w}}^{\prime\prime}\) for µ(T) and k(T) variations. The results show that the Nu decreases with an increase in inlet temperature for variable fluid properties. The undevelopment and redevelopment of the flow are observed due to µ(T) variation. Additionally, the effects of wall heat flux, inlet temperature and inlet velocity on the variation of Nu/Pr1/3 with Re are examined for µ(T) variation.