Effects Of Variable Properties Research Articles

Effects of temperature-dependent property variations on the output capacity prediction of a deep coaxial borehole heat exchanger

This study aims to understand the effects of property variations on prediction discrepancies in the output capacity (i.e., output power) of deep coaxial borehole heat exchangers under different operational conditions. These properties include the specific heat and thermal conductivity of the water and the reservoir rock, as well as the density and dynamic viscosity of the fluid. Numerical simulation and grey relational analysis were combined to quantify the effects of the property variations on heat convection, heat conduction, and the heat exchanger’s predicted output capacity. The simulation results indicate that the average convective heat transfer coefficient of the water decreases, but the average thermal diffusivity of the rock increases with the extraction of geothermal energy. These changes further lead to an over-prediction of the output capacity. The grey relational analysis reveals that the flow rate and well depth are the principal factors causing over-prediction. The over-prediction increases with the rise of the injection flow rate and well depth. The results also show that the variability of the specific heat and the dynamic viscosity of the water are the two most significant factors causing a discrepancy in the predicted output capacity. The results from this research have highlighted the significance of considering property variations for a more practical prediction of the numerically modeled output capacity of deep coaxial borehole heat exchangers.

The effects of thermal and mechanical material properties on tumorous tissue during hyperthermia treatment.

Although there have been numerous reports in several articles about the viscoelastic properties of biological tissues, no effort has been made to investigate the combined thermal and mechanical behavior of the viscoelastic tissue. At present, the model of thermo-viscoelasticity theory with variable thermal conductivity and rheological properties of the volume is considered to investigate bio-thermo-mechanics behavior in living tissue within the context of the Lord-Shulman theory. The model is applied to a limited thickness, cancerous layer problem. The problem was solved analytically in the transformed domain using Laplace transform as a tool. The exact solution is obtained in the context of transformation Laplace. Numerical results are given and illustrated graphically for the distributions of temperature, displacement, and stress. Some correlations are produced with the results obtained for the absence of the thermal relaxation parameter. The effects of variable thermal and volume materials properties, blood perfusion rate on the behavior of various fields are examined.

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.

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.

The hemodynamics of variable liquid properties on the MHD peristaltic mechanism of Jeffrey fluid with heat and mass transfer

The current work intends to look into the effects of variable liquid properties on the magnetohydrodynamics of peristaltic flow exhibited by Jeffrey fluid through a compliant-walled channel. In order to make realistic approximations for the flow characteristics of blood, the channel is considered to be inclined and porous. Furthermore, convective boundary conditions and concentration slip have been employed in the analysis. The mathematical formulation is established on the grounds of low Reynolds number and long wavelength approximations. Perturbation solution is obtained for the resulting non-linear differential equations of momentum and energy for small values of variable viscosity and variable thermal conductivity, whereas exact solution is found for the concentration field. The impact of various parameters included in the study is displayed graphically. A rise in the parameter for variable viscosity is found to accelerate the fluid flow, hence resulting in an increased bolus size. For variable thermal conductivity, a similar influence on the heat transfer was observed. The behaviour of the skin-friction coefficient, Nusselt and Sherwood numbers have also been plotted for the pertinent parameters.

Numerical simulation of the evaporation characteristics of a dimethyl ether droplet in supercritical environment

The unsteady spherically symmetrical evaporation of a dimethyl ether droplet in supercritical environment is modelled, considering real gas effects, Soret and Dufour effect, variable thermodynamic properties effects and high- pressure vapor-liquid phase equilibrium. The interface between droplet and environment disappears when it reaches the critical temperature of dimethyl ether-nitrogen system. Subsequently, the evaporation becomes a pure diffusion issue. The calculated results indicate the solubility of the ambient gas in the liquid phase is significant under supercritical conditions, and the temporal evolution of the interface temperature, reduced droplet diameter and dimethyl ether mole fraction are obtained under supercritical conditions as well. The influence of ambient pressure and temperature above critical point on the droplet evaporation characteristics was systematically investigated. Supercritical environment leads to a larger initial swelling of the droplet, when the reduced ambient pressure is 2.0 and temperature is 1.5, the maximum swelling of droplet is 7.7% larger than the initial value. Higher ambient pressure also leads a shorter fuel droplet lifetime in supercritical environment, When the reduced ambient temperature is 1.5, and the reduced pressure is varying from 1.0 to 1.5, the droplet evaporation lifetime of the dimethyl ether is reduced by 11.1%. The ambient temperature affects the droplet evaporation characteristics in a similar manner as the ambient pressure.

Non-similar characteristics of mixed convective slip flow over a wedge with temperature-dependent thermo-physical properties

We examined heat and mass transfer characteristics of mixed convective slip flow over a wedge taking into account the effect of variable transport properties. Unlike other studies, we have utilized non-similar transformation to get the non-similar features of the mixed convective slip flow. For comparison, stream function formulation is used to reduce the governing equation into a convenient form for short- and long-time regimes. We have determined the series solutions by adopting the perturbation techniques. The agreement between the numerical and series solutions is found to be excellent. Numerical solutions reveal that the slip parameters augment the momentum, thermal and concentration boundary layers. The local skin friction coefficient, the local Nusselt number and the local Sherwood number are found to decrease for higher value of slip parameters. For the increasing value of the variable viscosity parameter, the velocity is stronger, but the temperature and concentration lessen. Contrary to this, this parameter diminishes the local skin friction coefficient, local Nusselt number and local Sherwood number. Due to the increase of mass diffusivity parameter, the velocity and concentration significantly increase whereas the temperature remains almost unaffected. Moreover, the mass diffusivity variation parameter leads to an increase in the local skin friction coefficient and local Nusselt number, but it reduces the local Sherwood number.

Impact of Variable Transport Properties and Slip Effects on MHD Jeffrey Fluid Flow Through Channel

The present paper aims at investigating the effects of variable transport properties and slip conditions on the MHD peristaltic mechanism of a Jeffrey liquid. The flow is considered to take place in an axisymmetric channel with compliant walls. The nonlinear momentum and energy equations are solved for small values of variable viscosity and thermal conductivity by utilizing the method of perturbation. Closed-form solutions are found for mass transfer equation. MATLAB programming is employed to get the pictorial representation of various parameters on axial velocity, streamlines, temperature and concentration profiles. The current investigation reveals that an increase in the value of the magnetic parameter reduces the velocity as well as temperature. Moreover, the size of the trapped bolus is seen to be a decreasing function of magnetic and Jeffery parameters.

Development of main components of device for measuring residual stresses

The paper presents the results of the study of the stress state of machine elements and structures in which there are residual stresses. Examines the use of overhead eddy current and magneto-elastic transducers, investigates the process of measurement of residual stresses. It is proved that the cause of measurement errors is the instability of the gap between the transducer and the surface of the object. It is proved that during calibration and measurements, the installation of the gap and its control should be carried out by the magnitude of the magnetic resistance. Undesirable effects of variable electromagnetic properties of the object material on the installation result can be eliminated by using the method of vortex currents. As a result, a device for measuring the stress state of objects made of ferromagnetic metals has been developed, which uses a magnetoelastic converter. Using the values of the frequency increment of the corresponding oscillator, it is possible to significantly reduce the impact of changes in operating conditions on the measurement result.

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.

Velocity and Temperature Profiles in Turbulent Channel Flow at Supercritical Pressure

Understanding the effects of property variations on velocity and temperature profiles is important for the accurate prediction of supercritical heat transfer in regenerative cooling channels. In this study, direct numerical simulations of a planar turbulent channel flow with a wall-normal temperature gradient were conducted to understand the mean temperature profiles that are affected by property variations at supercritical pressure. The working fluid used was supercritical nitrogen. The density ratios between two walls were four and eight. The Van Driest transformation for the mean velocity profiles holds true in the present conditions. This result implies that discussions based on a mixing length hypothesis are valid for the conditions that were studied. Mean temperature profiles in the viscous sublayer are correlated to those of incompressible constant-property flows using a local Prandtl number. For the mean temperature profiles in the logarithmic region, a new temperature transform equation that accounts for the variation in mean density and isobaric specific heat was introduced. It was demonstrated that the gradients of temperature profiles transformed by the transform equation coincide with the ones in incompressible constant-property flows in the logarithmic region.

An equilibrium wall model for reacting turbulent flows with heat transfer

A wall model for reacting turbulent flows for predicting heat transfer in rocket engine combustion chambers is presented. The wall model is developed based on boundary layer equations and includes the effects of chemical reactions and variable properties. Assuming an equilibrium state near the wall, a simple set of momentum and enthalpy equation is formulated. A table look-up procedure is employed to calculate the contributions of chemical effects and mixture properties. For turbulence modeling of the inner layer, a modified mixing length model based on semi-local scaling is applied. The proposed equilibrium wall model is validated in two hydrogen/oxygen reacting cases. In the first validation case of a reacting turbulent channel flow, the equilibrium wall model accurately predicts the near-wall velocity and temperature fields. In contrast, the wall model when assuming frozen chemistry shows a discrepancy in temperature gradient and mixture properties. The heat flux balance in the equilibrium wall model highlights the important contributions of chemical effects. The second test case of a rocket combustion chamber shows that the equilibrium wall model is superior to the frozen wall model and wall function models in predicting wall shear stress and heat flux.

Effects of variable thermophysical properties on mixed convection slip flow over a wedge

AbstractThis paper reveals the characteristics of mixed convection slip flow of an electrically conducting fluid over a wedge subject to temperature dependent viscosity and thermal conductivity variations. The system of dimensionless nonsimilar governing equations has been solved by an implicit finite difference method. We also use stream‐function formulation to reduce the governing equations into a convenient form, which are valid for small and large time regimes. These are solved employing the perturbation method for small time and the asymptotic method for large time. Numerical solutions yield a good agreement with the series solutions. Because of the increase in the mixed convection parameter, the peak of the velocity profile increases whereas the maximum temperature decreases. In contrast, the local skin‐friction coefficient and local Nusselt number are found to increase with the mixed convection parameter. For higher values of the velocity slip and temperature jump conditions, the local skin‐friction coefficient and the local Nusselt number are found to increase. The viscosity parameter enhances the local skin friction and the local Nusselt number. But the converse characteristic is observed for the thermal conductivity parameter. The results could be used in microelectromechanical systems, fabrication, melting of polymers, polishing of artificial heart valves, etc.

Effect of Property Variation on the Fluid Flow and Thermal Behavior in a Vertical Channel

Effect of Property Variation on the Fluid Flow and Thermal Behavior in a Vertical Channel

Generalized solution of the thermoelastic problem for the axisymmetric structure with temperature-dependent properties

The purpose of this paper is to seek the generalized solutions of the thermo-elastic problem with variable material properties. The governing equations with temperature-dependent properties are proposed firstly by means of general C-T theory, where the dual-phase-lag heat conduction equation (DPL equation) is introduced to describe the micro-scale effect in time and space, induced in the rapid transient heat conduction. An analytical method, based on the partial expansion techniques along with a linearization approach, is then used to solve these nonlinear equations analytically. The thermo-elastic response of the axisymmetric structure with variable material properties and its boundary subjected to a sudden thermal shock, which is a typical problem commonly encountered in some extraordinary heat process, is solved by this method. The short-time solutions with variable material properties, described the heat transport and associated thermo-elastic response in micro-scale, are obtained. Utilizing these analytical solutions, the propagation of thermo-elastic wave and thermal wave, as long as the distributions of each physical field, is illustrated to qualitatively evaluate the effect of variable material properties on the heat transport and associated thermo-elastic behavior in micro-scale.

An analytical model of heat and mass transfer from liquid drops with temperature dependence of gas thermo-physical properties

An analytical model for heating and evaporation of a single component liquid drop is developed. The model accounts for the temperature dependence of density, diffusivity, thermal conductivity and specific heat of the gas species. The effect of variable properties on heat and evaporation rates is analysed and a comparison with the prediction of the classical constant property model is reported for six different species and different operating conditions. The model allows to evaluate the effect of the choice of the gas mixture averaging parameter (the relative weight of free stream and drop surface conditions) on the prediction of the constant property model, and a way to optimise the choice is proposed. The results can be extended to non-spherical drop and examples are reported.

Unsteady MHD Flow of Nanofluid with Variable Properties over a Stretching Sheet in the Presence of Thermal Radiation and Chemical Reaction

The unsteady magnetohydrodynamics (MHD) flow of nanofluid with variable fluid properties over an inclined stretching sheet in the presence of thermal radiation and chemical reaction is studied taking into account the effect of variable fluid properties in thermal conductivity and diffusion coefficient. The governing partial differential equations are transformed into ordinary differential equations by using similarity transformation. The numerical solutions of the problem are obtained by using the fourth order Runge-Kutta method in line with the shooting technique. It is found that the increase in both thermal conductivity and radiative heat flux decreases the heat transfer rate but increases the skin friction and mass transfer rates. It is further observed that the increase in porosity parameter and magnetic field reduces the skin friction, heat, and mass transfer rates.

Effect of variable liquid properties on peristaltic flow of a Rabinowitsch fluid in an inclined convective porous channel

The peristaltic mechanism of a Rabinowitsch liquid in an inclined porous channel is reported in the presence of variable liquid properties. The convective conditions at the boundary walls are considered. The governing nonlinear equations are rendered dimensionless and solved with the help of the perturbation technique. The analytical solutions for velocity, temperature and streamlines are obtained and analysed graphically. Also, the pumping characteristics are discussed, and MATLAB programming has been used to tabulate the pumping efficiency. Further, the impact of relevant parameters of interest on physiological quantities are analysed for dilatant, Newtonian and pseudoplastic fluid models. The obtained results show the presence of variable liquid properties and convective conditions have a significant role in understanding the rheological properties of shear thinning, viscous and shear thickening fluid models. The investigation further reveals that an increase in the value of porous parameters diminishes the occurrence of the trapping phenomenon for Newtonian and dilatant fluid models. On the other hand, opposite behaviour is noticed for pseudoplastic fluids.

Effect of variable liquid properties on peristaltic transport of Rabinowitsch liquid in convectively heated complaint porous channel

The present paper emphasizes the peristaltic mechanism of Rabinowitsch liquid in a complaint porous channel under the influence of variable liquid properties and convective heat transfer. The effect of inclination on the complaint channel walls has been taken into account. The viscosity of the liquid varies across the thickness of the complaint channel, whereas, thermal conductivity varies concerning temperature. The nonlinear governing equations are solved by using perturbation technique under the long wavelength and small Reynold’s number approximations. The expressions for axial velocity, temperature, the coefficient of heat transfer and streamlines are obtained and analyzed graphically. The above said physiological phenomena are investigated for a specific set of relevant parameters on dilatant, Newtonian and pseudoplastic fluid models. The results presented here shows that the presence of variable viscosity, porous parameter and slip parameter significantly affects the flow quantities of dilatant, Newtonian and pseudoplastic fluid models. The investigation further reveals that an increase in the value of variable viscosity and porous parameters enhances the occurrence of trapping phenomenon. Moreover, the size of trapped bolus can be eliminated with suitably adjusting the angle of inclination parameter.

Effect of variable fluid properties on the hydrodynamic and thermal characteristics of parallel flow microchannel heat exchanger

In this paper the parallel flow microchannel heat exchanger is numerically investigate and the effect of treating the properties of fluids as variables with temperature compared with constant fluid properties assumption on its performance is studied. A numerical simulation is made to solve 3D Navier stock equations in two fluids with temperature dependent properties and 3D energy equation in two fluids and solid walls taking into account the effect of entrance region and axial conduction in the walls. The properties entered to the main program by relations as a function of temperature using subroutines written to calculate the properties at the end of each iteration. The results obtained show that, treating the properties as a temperature dependent gives higher overall performance since it leads to obtain lower pressure drop and higher effectiveness compared with constant properties assumption.