Variable Thermal Conductivity Research Articles

Medium office energy consumption optimization using EnergyPlus

This research paper studies the impacts of HVAC system scheduling and building envelope material properties on the building energy efficiency in the downtown New York City, metropolitan area, that is highly associated with Urban Heat Island. By utilizing EnergyPlus for whole energy building simulation, the research compares two HVAC operational cases: a baseline case with constant temperature setpoints, and an occupancy-based temperature setpoint schedule. The study also investigated the influence of thermal conductivity variations in stucco exterior wall materials, with three cases, the default baseline thermal conductivity and a 15% variance, respectively. Results indicate that occupancy-driven scheduling significantly reduces energy consumption by approximately 16% annually compared to baseline. Conversely, the influence of thermal conductivity on energy consumption is minimal, with only a 0.35% deviation noted in response to a 15% variation in thermal conductivity. This suggests that both optimizing HVAC scheduling and the thermal conductivity of building envelope materials can save building energy consumption while optimizing HVAC scheduling has a relatively stronger impact than optimizing the thermal conductivity with a 15% variance in downtown New York City.

Reflection of Waves in a Two-Temperature Magneto-fiber-Reinforced Solid with Memory-Dependent Derivative Using Different Theories

Abstract Purpose The problem is concerned with the analysis of the reflection of the waves through a fiber-reinforced thermoelastic medium under the effect of the magnetic field, gravity, and the initial stress. The problem is discussed in the context of the three-phase-lag model and Green-Naghdi theory of type II and III with the memory-dependent derivative and variable thermal conductivity. Methods The harmonic representation of waves is used to find the solution to the problem. Based on the solution, it is concluded that after reflection three quasi-waves propagate through the medium. Results Numerical computations were performed using MATLAB software. The reflection coefficient ratio variations with the angle of the incident are shown graphically. Conclusion Comparisons are made with the results predicted for different values of the thermal conductivity parameter, two-temperature parameter, initial stress, gravity field, and different values of the magnetic field.

Design and Additive Manufacturing of TPMS Heat Exchangers

Triply periodic minimal surface (TPMS) heat exchangers (HXs) have been investigated in this paper along with additive manufacturing (AM). Heat transfer coefficients, pressure drops, and thermal capacity were systematically evaluated as functions of wall thickness, lattice cell density, and materials. It turns out that when thermal conductivity is above 100 W/m·K, gyroid HXs are less sensitive to variations in thickness and thermal conductivity. Additive manufacturing of 20 kW aluminum heat exchangers was successful and testing results are comparable with theoretical prediction. To the best of our knowledge, this is the first demonstration of a working prototype of TPMS HXs.

MHD Maxwell dusty fluid in thermally stratified radiative flow with temperature-dependent thermal conductivity and Cattaneo-Christov model

It might be very important for the polymer processing industries to comprehend how Maxwell fluids behave on a stretched cylinder. Optimizing the extrusion and drawing processes can ensure the desired product qualities while avoiding faults. The objective of this study is heat transfer analysis on a Maxwell dusty fluid flow cylindrical surface with the Cattaneo-Christov concept. We immerse the cylinder in porous media, with a two-dimensional fluid regulating the flow. Our mathematical model further considers the effects of variable thermal conductivity, radiation, viscous and joule heating, magnetic field, thermal stratification, and slip velocity. Based on the presumptions,partial differential equations(PDE’s) have been used to evolve the mathematical model.Using similarity transformations, the PDE’s for heat and momentum for both phases are transformed into highly nonlinear ODE’s.The numerical results have been obtained on these ordinary differential equations by using the RKF-45 method. This issue's main characteristic is that it examines the scenario's liquid and dust phases throughout. Results are given both visually and tabularly for the major parameters over a velocity, temperature, skin friction coefficient, and Nusselt number. When we compared our method to a previously published paper, we discovered a decent match. The findings, which were obtained for our system, show that the velocity and thermal gradient of both the phases of fluid and dust behave in an opposite trend in favor of rising Maxwell parameter, where the curvature parameter makes the rise in the same manner. Furthermore, the thermal transport profiles for both phases decline for the rising thermal time relaxation parameter.

Entropy production on mixed convection stagnation point flow of nonlinear radiative fourth-grade hybrid nanofluid through a stretchable Riga surface

The purpose of the current study is to inspect entropy generation, mixed convective stagnation point flow, and thermal transfer features of nonlinear radiative fourth-grade hybrid nanofluid (NF) confined by a convectively heated Riga surface. The heat transport is examined with the existence of two disparate heat source modulations, variable thermal conductivity, and viscous dissipation. The original flow equations are first transmuted using appropriate transformations into non-dimensional ordinary differential equations, which are then solved via an overlapping grid-based spectral collocation scheme. The upshots of various pertinent parameters on velocity, temperature, entropy generation, and valuable engineering quantities are deliberated. Pivotal results obtained reveal that speedily flow of fluid and skin friction can be accelerated by strong magnetic force, rising mixed convection, and material parameters. Also, convective boundary conditions, along with nonlinear radiation and fluctuating thermal conductivity, are recommended for boosting fluid temperature, rates of entropy generation and heat transport. Thermal mechanism in hybrid NF is dominant over simple NF, which implies that performance of hybrid NF is better than that of simple NF. The outcomes of this study can be useful in enriching thermal performance of the working fluid, assisting in diagnosing causes of incompetency in thermal systems, and discovering suitable means of minimizing entropy generation with the intention of mitigating the loss of useful and scarce energy resources.

Analysis for bioconvection due to magnetic induction of Casson nanoparticles subject to variable thermal conductivity

Owing to valuable significance of bioconvective transport phenomenon in interaction of nanoparticles, different applications are suggested in field of bio-technology, bio-fuels, fertilizers and soil sciences. It is well emphasized fact that thermal outcomes of nanofluids can be boosted under the consideration of various thermal sources. The aim of current research is to test the induction of induced magnetic force in bioconvective transport of non-Newtonian nanofluid. The rheological impact of non-Newtonian materials is observed by using Casson fluid with suspension of microorganisms. The chemical reaction effected are interpreted. The thermal conductivity of material is assumed to be fluctuated with temperature fluctuation. The flow pattern is endorsed by stretching surface following the stagnation point flow. Under the defined flow assumptions, the problem is formulated. A computational software with shooting technique is used to present the simulations. A comprehensive analysis for problem is presented. It is claimed that the interpretation of induced magnetic force exclusively enhanced the thermal phenomenon.

Heat Transfer Characteristics in Non-Newtonian Fluids with Variable Thermal Conductivity and Cattaneo-Christov Model: A Spectral Collocation Approach Employing Legendre Wavelets Scheme

Heat Transfer Characteristics in Non-Newtonian Fluids with Variable Thermal Conductivity and Cattaneo-Christov Model: A Spectral Collocation Approach Employing Legendre Wavelets Scheme

Effects of Variable Thermal Conductivity on MHD Fluid Flow on Rotating Vertical Cone in the Presence of Darcy Forchheimer, Soret and Dufour Effects through a Porous Medium

This research investigated the effects of Variable Thermal Conductivity on MHD fluid on a Rotating Vertical Cone in the Presence of Darcy Forchheimer, Soret and Dufour effects through a porous medium. The system of nonlinear differential equations were transformed into first order differential equations and solved using shooting technique in Matlab package Bvp4c.Furthermore, the effects of various parameters over the main physical quantities are shown graphically and also extensively discussed. The result shows that Thermal conductivity increases Tangential Velocity, Temperature and decreases Normal Velocity. Dufour increases Tangential Velocity and decreases Normal Velocity. Radiation parameter R enhances Tangential Velocity and Temperature.

Heat Transfer Analysis of Memory-Dependent Derivative in Biological Tissue Subjected to a Moving Heat Source

Abstract A new bioheat transfer equation is developed by introducing the memory-dependent derivative into dual-phase lag model. The heat transfer process of memory-dependent derivative in biological tissue under a moving heat source is studied. Besides, thermal conductivity is usually no longer constant at high temperature. The nonlinear temperature governing equation with considering variable thermal conductivity is formulated and the solutions are obtained by the methods of Kirchhoff and Laplace transformations. The influences of heat source velocity, variable thermal conductivity, relaxation time, and kernel function on the variation of temperature are analyzed.

Flow analysis of Williamson model over a moving surface with nonlinear convection/diffusion and variable thermal conductivity

This article analyses the flow across a moving surface using the magnetohydrodynamic (MHD) Williamson fluid model in detail, accounting for the effects of diffusion, nonlinear convection, and variable thermal conductivity. The heat transmission within the system is impacted by the changing thermal conductivity, which can also significantly alter the flow behavior. The effects of the moving surface on flow forms in porous media are explained here using the Darcy model. The similarity transformations are used to convert the underlying nonlinear partial differential equations into a collection of ordinary differential equations. The work uses a numerical RK4 technique to examine the complex incompressible fluid flow behavior on a moving surface. The study’s conclusions provide insight into the intricate flow patterns and shear layer forms brought on by the interaction of fluid and surface motion while taking varied thermal conductivity into account. The findings give important information for the design and optimization of engineering applications involving changeable thermal characteristics and advance our understanding of fluid dynamics in geophysical and atmospheric systems. Physical descriptions are used to depict how flow parameters behave in relation to velocity, temperature, and concentration distributions.

Thermal performance appraisal of hybrid and nanofluid flow between a cone and a disk with variable thermal conductivity, viscous dissipation, and Joule heating

In many engineering systems, hybrid and nanofluids are influenced by their respective thermophysical characteristics. Lately, several models have been envisaged to foresee the hybrid and nanofluid attributes. The properties of hybrid nanofluids (HNFs) as potential heat transfer fluids are controlled by numerous aspects such as solid part size, volume fraction, and temperature. Considering the interesting facts of the hybrid and nanofluid flows, we in this exploration examined the thermal performance comparison of both types of fluid flows. The nanofluid and HNF are composed of molybdenum disulfide (MoS[Formula: see text]/kerosene oil and silicon dioxide–molybdenum disulfide (SiO2–MoS[Formula: see text]/kerosene oil, respectively. The flows are taken in a canonical gap between the cone and the disk. Both the cone and the disk may be rotating or stationary. The novelty of the computational model is enhanced by discussing the effects of viscous dissipation, Joule heating, and the variable thermal conductivity with convective condition. The Tawari and Das model is designed to analyze the heat transfer performance of the assumed fluid flows. The assumed fluid model is transmuted into the set of differential equations that are dealt numerically with the bvp4c MATLAB approach. The results are displayed in tables and graphical forms. For elevating estimations of the Eckert number, the heat transmission rate is found to be more significant in the disk than cone. It is also learned that hybrid nanoliquid heat transfer performance outperforms nanoliquid. The fluid velocity increases by raising the nanoparticle volume fraction [Formula: see text], and is decreasing for a higher magnetic field parameter. With the elevating estimates of thermal conductivity, it is shown that the cone transmits heat more quickly whereas the disc transmits heat more slowly. The thermal conductivity parameter increases the probability of collision of the liquid particles, that ultimately upsurges fluid heat transmission rate.

Influence of variable fluid properties on mixed convective Darcy–Forchheimer flow relation over a surface with Soret and Dufour spectacle

Abstract The thermo-diffusion applications of nanofluid subject to variable thermal sources have been presented. The significance of Darcy–Forchheimer effects is attributed. The flow comprises the mixed convection and viscous dissipation effects. Furthermore, the variable influence of viscosity, thermal conductivity, and mass diffusivity is treated to analyze the flow. The analysis of problem is referred to convective mass and thermal constraints. The analytical simulations are proceeded with homotopy analysis method. The convergence region is highlighted. Novel physical contribution of parameters is visualized and treated graphically. It is noted that larger Brinkman number leads to improvement in heat transfer. The concentration pattern boosted due to Soret number. The wall shear force enhances with Hartmann number and variable thermal conductivity coefficient.

Overlapping Grid-Based Spectral Collocation Technique for Bioconvective Flow of MHD Williamson Nanofluid over a Radiative Circular Cylindrical Body with Activation Energy

The amalgamation of motile microbes in nanofluid (NF) is important in upsurging the thermal conductivity of various systems, including micro-fluid devices, chip-shaped micro-devices, and enzyme biosensors. The current scrutiny focuses on the bioconvective flow of magneto-Williamson NFs containing motile microbes through a horizontal circular cylinder placed in a porous medium with nonlinear mixed convection and thermal radiation, heat sink/source, variable fluid properties, activation energy with chemical and microbial reactions, and Brownian motion for both nanoparticles and microbes. The flow analysis has also been considered subject to velocity slips, suction/injection, and heat convective and zero mass flux constraints at the boundary. The governing equations have been converted to a non-dimensional form using similarity variables, and the overlapping grid-based spectral collocation technique has been executed to procure solutions numerically. The graphical interpretation of various pertinent variables in the flow profiles and physical quantities of engineering attentiveness is provided and discussed. The results reveal that NF flow is accelerated by nonlinear thermal convection, velocity slip, magnetic fields, and variable viscosity parameters but decelerated by the Williamson fluid and suction parameters. The inclusion of nonlinear thermal radiation and variable thermal conductivity helps to enhance the fluid temperature and heat transfer rate. The concentration of both nanoparticles and motile microbes is promoted by the incorporation of activation energy in the flow system. The contribution of microbial Brownian motion along with microbial reactions on flow quantities justifies the importance of these features in the dynamics of motile microbes.

Experimental study on evaluation of density, P-wave velocity, thermal conductivity, and thermal diffusion coefficient of granite after thermal treatments by using PCA

Temperature significantly influences the physical parameters of granite, resulting in variations in the rock's thermal conductivity. In order to examine the impact of changes in multiple physical parameters of granite at different temperatures on the thermal conductivity of rocks, Principal Component Analysis (PCA) was employed to determine the correlation between granite at different temperatures and various physical parameters, including density (ρ), P-wave velocity (P), thermal conductivity (KT), and thermal diffusion coefficient (KD). Utilizing the linear contribution rate, a single indicator 'y' was derived to comprehensively represent the thermal conductivity of rocks. Research findings indicate that within the temperature range of 150–450 °C, the 'y'-value is relatively high, signifying favorable thermal conductivity of the rock. Notably, longitudinal wave velocity demonstrates higher sensitivity to temperature changes compared to other physical parameters.

A Comparative Study of Newtonian and Non-Newtonian Nanofluids with Variable Thermal Conductivity Over a 3-D Stretching Surface

This study presents a comprehensive numerical and statistical analysis of the flow, heat/mass transfer management of Newtonian and non-Newtonian nanofluid over a bidirectional Darcy-Forchheimer stretching sheet. The external effects of MHD, Joule heating, thermal radiation, heat generation/absorption, Brownian motion, thermal diffusion and chemical reaction are taken into account. It is presumed that the thermal conductivity of fluid varies linearly with temperature. The non-linear coupled P.D.Es are converted into nonlinear coupled O.D.Es using similarity transformation. These equations are solved using MATLAB by implementing four-stage Lobatto IIIa formula and the outcomes of numerous flow parameters are presented graphically. In addition to numerical investigations, a comprehensive statistical analysis is performed using R-software to evaluate the sensitivity of key input parameters towards variable thermal conductivity. The values of local wall friction, local wall heat flux, and wall mass flux for various parameters are tabulated. The study reveals that the heat transmission is significant for dilatant fluids (156.8%) when compared to the pseudoplastic fluids (113.8%). Enriching the values of the Brownian motion parameter suppresses the molecular diffusion while a contrary nature is observed for the thermal diffusion parameter. Further, the mass transfer coefficient shows a very strong negative correlation with variable thermal conductivity parameter for Shear thinning fluids, whereas for Newtonian and Shear thickening fluids it shows a very strong positive correlation.

Insight into the peristaltic motion through a tapered channel with Newton’s cooling subject to viscous dissipation, Lorentz force, and velocity slip

Peristalsis has gained significant attention due to its numerous applications in the medical field, engineering, and manufacturing industries. Therefore, the current work intends to look into the effects of variable liquid properties on the magnetohydrodynamics of peristaltic flow exhibited by viscous fluid through a tapered channel. The viscosity of the liquid differs over the thickness of the channel, and temperature-dependent thermal conductivity is considered. The constitutive relation for energy is formulated with the addition of viscous dissipation and heat generation/absorption. The assumption of velocity slip along with the convective boundary condition energizes the thermal system as well as the flow phenomena. The mathematical formulation is established on the grounds of low Reynolds number and long wavelength approximations. Perturbation solution were obtained for the resulting non-linear differential equations of momentum and energy for small values of variable viscosity and variable thermal conductivity. The effects of various relevant parameters on flow properties were investigated through graphical analysis. The results show that the maximum velocity does not occur in the middle of the tapered channel, but moves toward the upper wall with the increase in the variable viscosity difference between the walls. The application of viscosity is essential in many engineering and industrial processes.

Study of hybrid nanofluid flow in a stationary cone-disk system with temperature-dependent fluid properties

Cone-disk systems find frequent use such as conical diffusers, medical devices, various rheometric, and viscosimetry applications. In this study, we investigate the three-dimensional flow of a water-based Ag-MgO hybrid nanofluid in a static cone-disk system while considering temperature-dependent fluid properties. How the variable fluid properties affect the dynamics and heat transfer features is studied by Reynolds’s linearized model for variable viscosity and Chiam’s model for variable thermal conductivity. The single-phase nanofluid model is utilized to describe convective heat transfer in hybrid nanofluids, incorporating the experimental data. This model is developed as a coupled system of convective-diffusion equations, encompassing the conservation of momentum and the conservation of thermal energy, in conjunction with an incompressibility condition. A self-similar model is developed by the Lie-group scaling transformations, and the subsequent self-similar equations are then solved numerically. The influence of variable fluid parameters on both swirling and non-swirling flow cases is analyzed. Additionally, the Nusselt number for the disk surface is calculated. It is found that an increase in the temperature-dependent viscosity parameter enhances heat transfer characteristics in the static cone-disk system, while the thermal conductivity parameter has the opposite effect.

Phase change in a one-dimensional functionally graded material

Functionally graded materials (FGMs) are a class of materials with engineered microstructure to achieve spatial variation in properties so as to serve a desired function. While FGMs have been well-researched for their structural properties, there is a lack of investigation of FGMs in solid-liquid phase change heat transfer processes. A well-designed functionally graded phase change material (FG-PCM) may overcome some of the well-known limitations of the phase change process. In order to investigate this possibility, this work presents a theoretical model to predict phase change propagation in a one-dimensional FG-PCM containing an arbitrary spatial variation in thermal conductivity, thermal diffusivity and latent heat. The problem is solved using the method of eigenfunction expansion to determine the temperature distribution, wherein, spatial variation in thermophysical properties listed above is accounted for by deriving a first-order matrix ordinary differential equation in the coefficients of the series solution. Results are found to correctly reduce to the well-known Stefan solution under special conditions. The impact of variation in thermophysical properties is investigated in detail. It is found that while spatial variation in thermal conductivity and latent heat has a significant effect on the rate of phase change, the impact of the thermal diffusivity function is negligible for realistic values of the Stefan number. The effect of the Stefan number governing this problem on the rate of melting is investigated. The nature of phase change under linear (1+aξ), polynomial (1+aξn) and exponential (eaξ) functional forms of thermophysical properties is investigated. It is shown that an appropriate choice of these spatial functions may help overcome the well-known self-limiting nature of phase change and produce a nearly-linear phase change propagation curve. For example, results show 33% increase in phase change propagation for a linear (1+5ξ) variation in thermal conductivity compared to baseline. The theoretical tools developed here may help design and optimize functionally graded PCMs towards improved phase change heat transfer in applications of practical interest.

Enhancement of heat transfer due to nonlinear radiative Burgers nanofluid with triple diffusion and heat source effects

This investigation predicts the assessment of mass and heat transfer due to Burgers nanofluid. The investigation is further supported by triple diffusion flow. Variable thermal conductivity is accounted to endorse the thermal flow. In the heat equation, the extension is suggested by utilizing the external heat source and nonlinear radiated phenomenon. Computations for modeled problems are achieved by the shooting method. The fundamental role of parameters governing flow is noticed which is physically attributed. It is observed that the heat transfer rate is enhanced due to the modified Dufour number. The solutal concentration declined for the regular Lewis number. Furthermore, the nanoparticles concentration reduces due to the nano-Lewis number. The depicted results convey novel applications in chemical processes, cooling control systems, refrigeration, solar energy, extrusion processes, etc.

Variable thermal conductivity and mass diffusivity effects in a free convective flow of doubly stratified non-darcian porous medium over a vertical plate

The research in this article is carried out to study incompressible and unsteady free convective flow on a semi-infinite isothermal vertical plate in a doubly stratified non-Darcian porous media with variable mass diffusivity and variable thermal conductivity. The governing non-linear partial differential equations of flow were calculated by applying an implicit finite difference scheme of Crank-Nicolson type. Various parametric impacts on concentration profiles, temperature, velocity, as well Sherwood number, Nusselt number and skin friction, were examined and presented in graphs. It is examined that there exists a significant temperature decrease for high Darcy number in stratified fluids. Also, it is detected that the presence of stratification produces a considerable drop in skin friction while increases the mass and heat transfer rate. Comparison of current outcomes well agreed with the available solutions.