Dimensionless Temperature Research Articles

Simplified thermoelectric generator (TEG) with heatsinks modeling and simulation using Matlab and Simulink based-on dimensional analysis

<abstract> <p>Energy sustainability is becoming paramount today with the focus being on renewable and alternative energy. This manuscript therefore embarks on clean alternative energy rooted in thermoelectricity with focus on thermoelectric generator (TEG). However, a TEG do practically needs heat-exchangers or heatsinks to properly and reliably work but heatsinks present another problem—thermal resistance, which affects a TEG power output and efficiency and thus, must be addressed. Consequently, we investigate a TEG with heatsinks model based-on dimensional analysis using Matlab and Simulink. Our research has three unique contributions. Firstly, we derived the analytical formulas for direct calculations of TEG dimensionless hot and cold sides temperature and by introducing and applying a new dimensionless parameter, the dimensionless temperature difference (<italic>DT<sub>s</sub></italic>). Secondly, we simplified further the new TEG dimensionless hot and cold sides temperature analytical formulas to obtain simpler and simplest forms. Thirdly, we implemented a TEG with heatsinks Matlab/Simulink theoretical model, that employs the simplified dimensional analysis, in which a TEG with heatsinks parameters of interest can be simulated to variously determine the analytical, numerical and graphical results with various optimal options to opt for, before doing a practical design.</p> </abstract>

Concentration Flux Dependent on Radiative MHD Casson Flow with Arrhenius Activation Energy: Homotopy Analysis Method (HAM) with an Evolutionary Algorithm

Heat transfer analysis in nanofluids is an active research field due to its extraordinary physical and chemical properties. In the current study, the focus lies on the effects of Stefan blowing when a non-Newtonian Casson base fluid flows over a surface which stretches linearly. A uniform transverse magnetic field is employed. The chemical reaction in the fluid with activation energy and radiation effects have also been engaging the attention. Fundamental laws of conservation are employed to model governing equations of flow. Similarity transform is introduced to reduce the said system of partial differential equations to ordinary differential equations which are in turn tackled analytically using Homotopy Analysis Method with genetic algorithms to optimise the series solution. The impact of pertaining parameters on the dimensionless velocity, temperature and concentration were presented explicitly. This study relevant to remedies for malign tissues, cells or clogged arteries of the heart.

Thermography of ferromagnetic Walter's-B fluid through varying thermal stratification

Thermally induced damages (hypolimnion, metalimnion and epilimnion) are usually caused by thermal stratification; due to a fact that fluid flows at a low velocity with large temperature variances. In this manuscript, thermal stratification phenomenon is studied for unsteady flow of Walter's-B fluid subject to a consistent inclined magnetic field at an angle of inclination over the boundary of transverse xy-plane with fractional thermal transport. Non-singular and local fractional derivative is hauled in the constitutive equations for the thermal flux. Semi analytical solutions of the dimensionless temperature and velocity fields are recognized by using the Laplace inversion numerical algorithms Stehfest's and Tzou's. Temperature and rate of heat transfer for non-integer and integer order derivatives are computed. Finally, the influence of some flow parameters and fractional parameter α on the temperature and velocity fields are graphically underlined by using IMATHCAD software and discussed.

Thermal variable conductivity features in Buongiorno nanofluid model between parallel stretching disks: Improving energy system efficiency

In present investigation, the axisymmetric analysis for the Casson nano-material has been analyzed due to two parallel stretchable disks. The novel thermophoresis and Brownian aspects of nanofluid are studied by using Buongiorno nanofluid model. Similarity transformations are applied on the system of governing equations that renovate it into the problem into proper dimensionless form. The homotopic procedure is suggested for the determination of solution. The role of numerous parameters on dimensionless velocity and temperature are observed in very effective way. To study the effect of Brownian motion and thermophoresis diffusion parameter, Buongiorno model is adopted. Radial and axial velocity profile has increasing behavior for stretching ratio and Casson parameter. As the value of Biot number and thermophoresis parameter enhanced, the concentration profile also enhances and concentration profile declines due to increase in value of Brownian motion parameter. Temperature profile decreases as the value of Reynolds number and Prandtl number increased. The values of Sherwood number, Nusselt number and Skin friction are calculated at upper and lower disk to understand the behavior of stretching disks.

Analysis of flow pattern change in horizontal mini-channel under electric field force

In this paper, the phenomenon of the flow pattern in the channel changes when the electric field force exists. Through the visual observation in the experiment, it is found that the study found that the bubble behavior was suppressed by the electric field force. When the electric field is large enough, the working fluid in the channel will always maintain a single-phase liquid flow. However, When there is enough superheat at the bottom of the mini-channel, the liquid film at the bottom of the liquid phase changes to a vapor phase, and the dryout appears in the channel, and it rapidly changes into a mist flow as the heating power increases. This phenomenon of flow pattern change due to electric field force is referred to herein as a flow pattern special phenomenon. Due to the existence of this special flow phenomenon, the temperature difference between the inlet and outlet of the working fluid in the channel has a large change. Through calculation, it is found that the dimensionless temperature difference between the inlet and outlet at a voltage of 200 V is 1.67 times that of 0 V. At the same time, the channel heat transfer coefficient increases with the increase of voltage.

Experimental study on the hot-melt adhesive pattern produced by melt blowing nozzle designs

The high-quality standards of bodily absorbent hygiene products require that the adhesive bond between layers be as uniform and consistent as possible. The final adhesive pattern of the product is determined by the dynamics of the adhesive fibre, which in turn depends on the nozzle geometry and on its operating conditions. In order to gain a better understanding of the dynamics of adhesive fibres and the deposited application pattern, an experimental study was conducted on two multi-hole melt blowing (MB) nozzles designed for producing hot-melt adhesives. To this end, the fibre dynamics were captured through the use of high-speed imaging (HSI). The main parameters that govern the fibre dynamics, including its frequency of oscillation, were quantified through use of image analysis. The effect of the operating conditions on the fibre’s frequency of oscillation at the nozzle exit region was studied and the results indicate that increasing air-polymer flux ratios [Formula: see text] and decreasing dimensionless temperature ratios [Formula: see text] both increase the fibre whipping frequency. Additionally, information on the fibre dynamics on the two planes of oscillation is obtained by studying the deposited application pattern of hot-melt applications. Other related matters are also treated throughout the article, such as fibre contact in adhesive patterns, which represent one of the major defects that the melt blowing technology of hot-melt adhesives is trying to mitigate. Experimental measurements are presented throughout the article to support the validity of the conclusions.

Adsorption Desorption Operations of Multilayer Desiccant Packed Bed for Dehumidification Applications (Dept.M)

In this work, the effect of design and operating parameters on the performance of a multilayer desiccant packed bed was theoretically and experimentally studied. In the experimental work, a silica gel packed bed of eight layers has been studied. The transient value of the mass of adsorbed water and desorbed water were measured for different values of the bed length. The theoretical model shows the dependence of the dimensionless value of water content in the bed on the dimensionless time. Also the model shows that the dimensionless temperature depends on the bed characteristics and bed water content. The effect of inlet air humidity and velocity on the adsorption process for each bed layer was studied at different inlet velocity and at different air humidity. The effect of inlet temperature on desorption process for each packed bed layer was also studied at different inlet temperatures. The theoretical model also introduces an equation which can be used to predict the optimum bed length. Good agreement between experimental and theoretical results was found.

Characteristics of Magnetohydrodynamics Nanofluid Flow in the Presence of Porous Medium Towards a Stretching Sheet with a Convective Boundary Condition

With the effects of variable viscosity and convective boundary conditions, the contemporary studies work ambitions to investigate the together effects of the magnetic field and porous medium on non-Newtonian nano fluid flow to a stretching layer. In this latest work, to examine the impact of thermophoresis and Brownian motion, the nanofluid model is utilized. To lessen the basic governing coupled non-linear PDE’s for velocity (momentum), temperature (energy), and nanoparticle concentration to an assortment of ordinary non-linear differential equations, the necessary transformations are used. Utilizing the fourth-fifth order Runge-Kutta-Fehlberg strategy, the resulting reshaped conditions are tackled mathematically. The effects on the dimensionless temperature, velocity, nanoparticle concentration profiles of various engineering parameters are discussed and graphically analyzed. The numerically computed values of skin-friction, coefficients of heat transfer rate and mass transfer are tabulated. The numerical findings got are contrasted and the outcomes recently detailed as unique instances of the current examination and viewed as in reasonable consistence.

Dual Solutions Analysis of Melting Phenomenon with Mixed Convection in a Nanofluid Flow and Heat Transfer Past a Permeable Stretching/Shrinking Sheet

The 2-D MHD nanofluid with mixed convection above a stretching/shrinking plate has been investigated. Melting heat transfer near surface is contemplated. Consider the saline water as base fluid with containing single SWCNTs as well as MWCNTs. Suitable similarity variables are employed to transform the governing PDEs into ODEs. These transformed equations which are coupled, and of high nonlinearity, have been solved through applying the bvp4c solver. The consequences of the relevant parameters like, the MHD parameter, mixed convection parameter, melting parameter, volume fraction on the flow field along with the skin friction and heat transfer rate are displayed in graphical form. Results show that the thin layer thickness diminishes as magnetic parameter enhances and at the same time temperature increases with magnetic parameter. It is also demonstrated that the melting parameter leads to a reduction in the thin layer thickness as well as dimensionless temperature. Obtain dual solutions for flow fields which delineates to identify the stable solution.

A method to solve the heat transfer problem for laminar flow of Phan-Tien-Tanner fluid in a flat channel

The paper presents a solution to the heat transfer problem for a flow of a four-mode viscoelastic linear Phan-Tien Tanner fluid in flat channels at a constant wall temperature. A special feature of this solution is the parametric representation of dependence of an axial velocity and temperature on coordinates. To obtain a solution to the energy transfer equation, we used the method of separating variables and decomposing the sought-for function into series by parameter. For a specific liquid, the profiles of dimensionless velocity and distribution of dimensionless temperature, Nusselt numbers, and other heat transfer characteristics for various Weissenberg numbers are presented.

Can the shape influence entropy generation for thermal convection of identical fluid mass with identical heating? A finite element introspection

PurposeThis paper aims to investigate the role of shapes of containers (nine different containers) on entropy generation minimization involving identical cross-sectional area (1 sq. unit) in the presence of identical heating (isothermal). The nine containers are categorized into three classes based on their geometric similarities (Class 1: square, tilted square and parallelogram; Class 2: trapezoidal type 1, trapezoidal type 2 and triangular; Class 3: convex, concave and curved triangular).Design/methodology/approachGalerkin finite element method is used to solve the governing equations for a representative fluid (engine oil: Pr = 155) at Ra = 103–105. In addition, finite element method is used to solve the streamfunction equation and evaluate the entropy generation terms (Sψ and Sθ). Average Nusselt number () and average dimensionless spatial temperature () are also evaluated via the finite element basis sets.FindingsBased on larger , larger and optimal Stotal values, containers from each class are preferred as follows: Class 1: parallelogrammic and square, Class 2: trapezoidal type 1 and Class 3: convex (larger , optimum Stotal) and concave (larger ). Containers with curved walls lead to enhance the thermal performance or efficiency of convection processes.Practical implicationsComparison of entropy generation, intensity of thermal mixing () and average heat transfer rate give a clear picture for choosing the appropriate containers for processing of fluids at various ranges of Ra. The results based on this study may be useful to select a container (belonging to a specific class or containers with curved or plane walls), which can give optimal thermal performance from the given heat input, thereby leading to energy savings.Originality/valueThis study depicts that entropy generation associated with the convection process can be reduced via altering the shapes of containers to improve the thermal performance or efficiency for processing of identical mass with identical heat input. The comparative study of nine containers elucidates that the values of local maxima of Sψ (Sψ,max), Sθ (Sθ,max) and magnitude of Stotal vary with change in shapes of the containers (Classes 1–3) at fixed Pr and Ra. Such a comparative study based on entropy generation minimization on optimal heating during convection of fluid is yet to appear in the literature. The outcome of this study depicts that containers with curved walls are instrumental to optimize entropy generation with reasonable thermal processing rates.

Finite element analysis of water-based Ferrofluid flow in a partially heated triangular cavity

PurposeThis study aims to deal with the numerical investigation of ferrofluid flow and heat transfer inside a right-angle triangular cavity in the presence of a magnetic field. The vertical wall is partially heated, whereas other walls are kept cold. The effects of thermal radiation are included in the analysis. The governing equations including continuity, momentum and energy equations are converted to nondimensional form using viable variables.Design/methodology/approachFinite element method (FEM)-based simulations are performed using finite element approach to investigate the effects of the volume fraction of ferroparticles (Fe3O4), the length of the heating element and the dimensionless numbers including Rayleigh and Hartmann numbers on the streamlines, isotherms and Nusselt number.FindingsIt is demonstrated that both horizontal and vertical velocity components increase with the length of the heating element, whereas the dimensionless temperature decreases the heating domain. It is observed that an increase of 10% in the volume fraction of ferroparticles increases Nusselt number more than 12%, and 20% increase in the volume fraction of ferroparticles increases more than 30%, depending upon the length of the heating element.Originality/valueThis is a new study showing the significance of the magnetic nanoparticles for the enhancement of heat transfer rate in a triangular cavity.

Thermal analysis of a convective–conductive–radiative annular porous fin with variable thermal parameters and internal heat generation

The thermal characteristics of annular porous fins with rectangular and hyperbolic cross-sections and internal heat generation were comprehensively studied by the homotopy perturbation method (HPM). The convective–conductive–radiative mode of heat transfer was considered in the current analysis. All thermal parameters were considered as a function of temperature. An approximate closed-form solution was obtained by solving the nonlinear heat transfer equation using HPM. Darcy’s model was employed to formulate the governing equation of heat transfer through porous media. Unknown constants were the initial approximations of the solution and were evaluated based on the boundary and initial conditions of the problem. The effects of pores and different thermal parameters on the dimensionless temperature distribution and the fin efficiency were graphically presented. In order to evaluate the accuracy of the closed-form solution, the obtained results (for both dimensional and non-dimensional forms) were validated by numerical solutions.

Numerical investigation of Von Karman swirling bioconvective nanofluid transport from a rotating disk in a porous medium with Stefan blowing and anisotropic slip effects

In recent years, significant progress has been made in modern micro- and nanotechnologies for micro/nano-electronic devices. These technologies are increasingly utilizing sophisticated fluid media to enhance performance. Among the new trends is the simultaneous adoption of nanofluids and biological micro-organisms. Motivated by bio-nanofluid rotating disk oxygenators in medical engineering, in the current work, a mathematical model is developed for steady convective von-Karman swirling flow from an impermeable radially stretched disk rotating in a Darcy porous medium saturated with nanofluid doped with gyrotactic micro-organisms. Anisotropic slip at the wall and blowing effects due to concentration are incorporated. The nano-bio transport model is formulated using nonlinear partial differential equations, which are transformed to a set of similarity ordinary differential equations (SODEs) by appropriate transformations. The transformed boundary value problem is solved by a Chebyshev spectral collocation method (CSCM). Impacts of key parameters on dimensionless velocity components, concentration, temperature and motile microorganism density distributions are investigated and graphically visualized. Validation with previous studies is included. It is found that that the effects of suction provide a better enhancement of the heat, mass and microorganisms transfer in comparison to blowing. Moreover, physical quantities decrease with higher slip parameters irrespective of the existence of blowing. Temperature is suppressed with increasing thermal slip, while nanoparticle concentration is suppressed with increasing wall mass slip. Micro-organism density number increases with the greater microorganism slip. Radial skin friction is boosted with positive values of the power law stretching parameter, whereas it is decreased with negative values. The converse response is computed for circumferential skin friction, nanoparticle mass transfer rate and motile micro-organism density number gradient. Results from this study are relevant to novel bioreactors, membrane oxygenators, food processing and bio-chromatography.

MHD variable viscosity mixed convection of nanofluid in a microchannel with permeable walls

In this study, we examine the combined effects of buoyancy forces, pressure gradient, thermophoresis, Brownian motion, variable viscosity of nanofluid flow in a microchannel with suction and injection in the presence of uniform magnetic field imposed in cross-wise direction. It is assumed that the dynamic viscosity of the nanofluid is related with temperature exponentially and that the vertical parallel-plates temperature is held asymmetrically. Applying similarity transformation, the governing system of partial differential equations (PDEs) are transformed into a set of non-dimensional nonlinear partial differential equations whose solutions are obtained numerically by semi-discretization centered finite difference method along with Runge-Kutta Fehlberg integration technique scheme. Qualitative description of graphical results depicting the effect of thermophysical parameters on the dimensionless velocity, temperature, nanoparticles concentration, skin friction, Nusselt number and Sherwood number are presented.

Improvement of energy dissipative particle dynamics method to increase accuracy

In this article, dissipative particle dynamics with energy conservation eDPD is used for simulating hydrodynamic behavior and heat transfer of DPD particles in a two-dimensional channel with parallel planes. To this end, a Fortran programming code is developed and the results are presented as dimensionless velocity and temperature profiles on the cross section perpendicular to the flow direction inside the channel. For the indented geometry, thermal and dynamic boundary conditions have been considered. The dynamic boundary condition of solution domain in the flow’s direction is periodic, and for modeling the walls, freezing layers of DPD particles with Bounce-Back reflection has been used. For the thermal boundary condition, it is assumed that the wall temperature is constant and the temperature of each DPD particle in contact with the wall is the same as the wall temperature. In this article, for the first time, for modeling the walls four frozen layers with Bounce-Back reflection are used and the effect of particle exit on two and three-layers configurations is investigated. Furthermore, for the first time, modified velocity Verlet integration algorithm is improved by adding heat transfer equations. And considering λ = 0.65 in the algorithm; the indented geometry is well simulated. In order to validate the results, first, the effect of regular and random initial distribution is compared. Furthermore, the results of wall alignment are compared with those obtained from CFD approach. In this paper, in addition to studying the effect of wall alignment and initial particle arrangement, the influence of the size of cells for averaging and the time steps in the output results are investigated.

Numerical study of the nanofluid thin film flow past an unsteady stretching sheet with fractional derivatives using the spectral collocation Chebyshev approximation

In this work, a mathematical model of fractional-order in fluid will be analyzed numerically to describe and study the influence of thermal radiation on the magnetohydrodynamic flow of nanofluid thin film which moves due to the unsteady stretching surface with viscous dissipation. The set of nonlinear fractional differential equations in the form of velocity, temperature and concentration which describe our proposed problem are tackled through the spectral collocation method based on Chebyshev polynomials of the third-kind. This method reduces the presented model to a system of algebraic equations. The effect of the influence parameters which governs the process of flow and mass heat transfer is discussed. The numerical values of the dimensionless velocity, temperature and concentration are depicted graphically. Also, computations of the values of skin-friction, Nusselt number and Sherwood number have been carried out and presented in the same figures. Finally, our numerical analysis shows that both the magnetic and the unsteadiness parameters can enhance the free surface temperature and nanoparticle volume fraction.

Nonlinear Radiation and Variable Viscosity Effects on Free Convection of a Power-Law Nanofluid Over a Truncated Cone in Porous Media With Zero Nanoparticles Flux and Internal Heat Generation

Abstract This study used numerical analysis to investigate the effects of nonlinear radiation and variable viscosity on free convection of a power-law nanofluid over a vertical truncated cone in porous media with Rosseland diffusion approximation considering zero nanoparticles flux and internal heat generation. The internal heat generation is of an exponential decaying form and the viscosity of the fluid is assumed to follow Reynolds viscosity model. The surface boundary conditions of vertical truncated cone is maintained at the uniform wall temperature (UWT) and the zero nanoparticle flux (ZNF) to cause the results to be more realistic and useful. The nanofluid model considered the effects of Brownian motion and thermophoresis. The nonsimilar governing equations are obtained by using a suitable coordinate transformation and then solved by Keller box method (KBM). Comparisons with previously published work obtained good agreement. Graphical and tabular presentations of numerical data for the dimensionless temperature profile and the local Nusselt number were presented for main parameters: dimensionless streamwise coordinate, thermophoresis parameter, Lewis number, radiation parameter, surface temperature parameter, viscosity parameter, power-law index of the non-Newtonian fluid, and internal heat generation coefficient. The local Nusselt number increased when the following parameters were increased: radiation parameter, surface temperature parameter, viscosity parameter, power-law index of the non-Newtonian fluid, and dimensionless streamwise coordinate. In contrast, the local Nusselt number decreased when the following parameters were increased: internal heat generation coefficient, thermophoresis parameter, and Lewis number. Besides, the physical aspects of the problem are discussed in details.

Numerical modeling of fractional viscoelastic non-Newtonian fluids over a backward facing step – Buoyancy driven flow and heat transfer

The unsteady flow and natural convection heat transfer of fractional Maxwell viscoelastic fluid over sudden expansion geometry such as vertical backward facing step is studied. The time–space fractional derivatives are calculated based on Caputo fractional derivative. The nonlinear governing equations are solved using finite difference method mixed with a L-1 algorithm. The step, upstream and downstream walls were set at a constant temperature. The range of step length is 0≤S≤0.5 and dimensionless temperature is 0.25≤θw≤1. The effects of velocity and temperature fractional derivatives (αand β) and various physical parameters, such as step length, dimensionless temperature, on Nusselt number, friction coefficient, profile of velocity and temperature, are investigated numerically. The results reveal that the fractional derivative parameters, the variation of wall temperature and step length have significant effects on the rate of heat transfer, the friction coefficient, the velocity and temperature of backward facing step. The average of Nusselt number variation increases with increasing of β and decreases of α parameters. The results show that the velocity and thermal boundary layer of the non-Newtonian fluid (ordinary Maxwell) is higher than Newtonian fluid. Also, the Nusselt number for the ordinary Maxwell fluid flow is greater than the Newtonian fluid flow. With the increase of the step length of backward facing step, the average Nusselt number, friction coefficient, velocity boundary layer, and temperature boundary layer increases. The obtained results can improve significantly the performance of the systems design that operate with the non-Newtonian fluids.

Selection of Optimum Heat Flux Distribution in Pipe Flow Under Laminar Forced Convection

The concept of non-uniform heat flux distributions has emerged because of its potential to make the design of thermal systems more flexible. Therefore, the current study highlights the impact of non-uniform heat flux distributions on the thermal characteristics of a high Prandtl number fluid for forced convective laminar flow regime in a horizontal pipe. The steady-state 2-D simulations have been employed using ANSYS Fluent. The variations in heat flux distributions as a wall boundary condition are systematically analyzed while keeping the total heat transfer constant. The results obtained for various distributions are compared in terms of a dimensionless maximum wall temperature (hot spot), local and average Nusselt numbers, and entropy generation rate. The analysis showed that the heat flux distributions significantly affected the heat transfer pattern. It was found that the hot spot temperature was lower for the descending heat flux boundary conditions compared to the ascending type of distributions. However, a higher entropy generation rate was observed for descending distributions as compared to ascending ones. It was also found that the ascending heat flux distributions provided higher average Nusselt number values than the descending cases of heat flux.