Variable Heat Source Research Articles

Two Component Non-Darcian Benard Marangoni Convection with Uniform and Non-Uniform Temperature Gradients in a Composite Layer with Variable Heat Sources/Sinks

In a composite layer that comprises of a porous layer which is sparsely packed and saturated with two component incompressible fluid and above this porous layer lays a layer of the same fluid, with variable heat sources or sinks in both the layers double diffusive non-Darcian Benard Marangoni (DDNBM) convection is investigated. The upper surface of the composite layer has Marangoni effects which depend on temperature and concentration, whereas the lower surface is rigid. The inverted parabolic, parabolic and linear temperature profile is applied to this composite layer, which is surrounded by adiabatic boundaries. The appropriate thermal Marangoni numbers (TMANs) which are the eigen values (EVs) are calculated for all the three temperature gradients. The impact of different parameters on the EVs with respect to depth ratio is examined, thoroughly. The parameters that effect DDNBM convection are found.

Two Component Benard-Marangoni Convection in a Composite System Subjected to Variable Heat Source

Double diffusive convection is the phenomena that describes the convection driven by two differ-ent densities which have different rates of diffusion. A comparison of two temperature boundaries when i) both the surfaces are set at adiabatic temperature, and ii)upper free surface is adiabatic and lower rigid surface is isothermal cases, on surface tension driven double diffusive convection in a horizontal composite layer is studied analytically using exact method. For both cases i) and ii), the thermal Marangoni number (Tmn) is determined, which is the eigen value, for upper free and lower rigid velocity boundary conditions. The results indicate that the given system is a fluid dominant composite system and adiabatic-isothermal thermal boundary is more stable compare to adiabatic-adiabatic boundary condition.

Investigation and multi-objective optimization of vehicle engine-organic Rankine cycle (ORC) combined system in different driving conditions

Organic Rankine cycle (ORC) can improve the fuel efficiency of internal combustion (IC) engine. However, the dynamic characteristics of ORC system in driving conditions are not only affected by variable high-temperature waste heat source, but also have strong coupling correlation between operating parameters and performance. Under the superimposed influence, the performance of vehicle engine-ORC combined system has obvious nonlinearity and uncertainty. This paper first constructs a vehicle engine-ORC combined system model for the driving conditions. Based on different driving cycles, the combined system is verified. The influence of ORC system on engine performance in driving conditions is evaluated. The synergetic influence laws of operation parameters in driving conditions is systematically analyzed. Based on vehicle engine-ORC combined system for driving conditions model, simulation model with different coupling units and multi-objective optimization algorithm, this paper proposes an integrated multi-objective optimization framework of combined system with complex driving conditions. The real-time optimization of integrated system performance in driving conditions is realized. The trade-off and uncertainty correlation between combined system performance in driving conditions are analyzed. Finally, the improvement of IC engine performance by ORC system in driving conditions is quantitatively evaluated. The nonlinear optimization framework proposed in this paper can provide a practical solution for the analysis, evaluation and real-time optimization of vehicle engine-ORC combined system performance in driving conditions.

A testbed for performance studies of gas–liquid thermoelectric generators for waste heat harvesting

We describe a unique test platform for performance studies of thermoelectric generators (TEGs) with gas/liquid heat exchangers. The designed stand allows to simulate the real working conditions of TEG prototypes. It provides accurate measurements of key operational parameters of these devices in high precision laboratory regime.The testbed consists of a hot-gas control unit (HGCU) for examination of the heat exchanger (HHX) of the TEG, a cooling liquid control unit (CLCU), an automated control system (ACS) that allows to precisely set the requested experimental conditions, and a data acquisition system (DAS) that gathers data on temperature, fluids flow, pressure drops and electrical parameters of the TEG.The HGCU unit is a source of hot air, with mass flows in the range of 0–550 m3/h, maximum heat power PH of 15 kW, and temperature range between 15 °C and 800 °C. The CLCU unit controls the flow and temperature of the liquid medium in the range from 10 °C to 110 °C and the mass flow of water ṁwater in the range of 0.006 – 1.2 m3/h. The designed testbed allows to evaluate the most important TEG performance parameters, such as: efficiencies of its TE converters, the effectiveness of heat exchangers, power losses due to pressure drops, and net power Pnet generated, as well as the statistical uncertainties of the determination of these parameters.The testbed has been used for tests of various TEG prototypes. As an application example, we show results for a prototypical TEG with nominal power of 168 W designed for heat recovery from an automobile exhaust system. The device is based on a hexagonal, internally finned HHX, 24 TEM converters and 24 water-cooled cold heat exchangers (CHXs).The constructed testbed allows for a direct determination of all the factors which may influence the conversion efficiency of the TEG, as well as its net and gross electrical power output under varying heat source and heat sink parameters. The device allows to estimate the performance of the entire thermoelectric generation system as a whole and to identify individual components within the TEG which potentially need to be improved. Such a holistic approach to TEG parameter characterization was not presented or discussed in the literature so far.

An integrated smart thermo-chemical energy network

Managing the intermittency of renewable sources together with transient (hourly to daily to seasonal) energy demands is one of the principal challenges of delivering a net-zero energy system. Smart multifunctional thermo-chemical energy networks represent an alternative energy network and storage system, a solution based on the distribution of energy via thermo-chemical material rather than thermal energy, gas, fuels or electricity– an option that has scope for integrated short- and long-term energy storage. This is the first research work to realise such a system and demonstrate how it might operate using smart control strategies and how thermo-chemical fluids (TCFs) can be used as a medium for timely energy storage and distribution. The experimental study also describes the effect of steady and variable heat sources on TCF regeneration performance and estimates the potential of thermo-chemical energy networks, which would be particularly beneficial in buildings with high energy consumption for humidity control. This research proves the practicality of the design idea for such a network, which would be governed by centralised control, regenerated by steady or transient heat loads and capable of supplying a variety of demands in an experimental setting. The energy and economic potential of the network were also assessed, identifying temperature and humidity control application scenarios with energy savings of more than 60% compared to conventional operation and payback periods of 6.6–9.7 years.

Effects of throughflow on thermosolutal penetrative convection in a fluid layer with variable gravity field

AbstractIn this study, the start of thermosolutal penetrative convection in a horizontal fluid layer heated and salted from below was investigated analytically and graphically in the presence of throughflow and changeable gravity field effects. The normal mode technique is used to test the system's stability properties. The mathematical expressions for stationary and oscillatory Rayleigh numbers are obtained as a function of the governing parameters. The analysis demonstrates that the vertical throughflow, gravity parameter, and heat source effect all have a considerable influence on the beginning of convective motion in double‐diffusive flow. The impacts of variable gravity, vertical throughflow, and heat source parameters, as well as other physical parameters such as Solutal Rayleigh numbers and Lewis numbers, on stationary and oscillatory convection, are studied and illustrated graphically, and some previously published results are recovered in the limiting cases.

Thermo-mechanical Analysis of Lithium-ion Batteries with Variable Reversible Heat Source

Thermo-mechanical Analysis of Lithium-ion Batteries with Variable Reversible Heat Source

Numerical simulation of a thermally enhanced EMHD flow of a heterogeneous micropolar mixture comprising (60%)-ethylene glycol (EG), (40%)-water (W), and copper oxide nanomaterials (CuO)

In the past decades, the thermal and rheological properties of nanofluids have attracted much attention from many investigators due to their numerous applications as promising enhanced working fluids. The present numerical analysis intended to evidence the main hydro-thermal and mass transport appearances featuring the convective flows of an exceptional non-homogeneous micropolar mixture (i.e., 60% of ethylene glycol, 40% of pure water, and copper oxide nanomaterials) over an impermeable horizontal electromagnetic surface (i.e., Riga plate), which is heated convectively in the presence of a particular variable heat source. For this purpose, several admissible physical theories and hypotheses are adopted herein to derive the foremost conservation equations based on the renovated Buongiorno's formulation and some more realistic boundary conditions. Further, the leading partial differential equations (PDEs) are transformed into a system of ordinary differential equations (ODEs), which are tacked thereafter numerically using an efficient GDQNRM procedure. After performing multiple validations with the recent literature results, the aspects of the studied EMHD convective micropolar nanofluid flow are spotted accordingly and then discussed comprehensively via multiple figures and tables. As prominent results, it is found that the micropolarity and electrically conducting trends of the nanofluidic medium play an important role in the hastening of the nanofluid motion. Also, it is explored that the thermally enhancing influence of the thermophoresis diffusive mechanism can be reinforced more by the existence of an internal heat source along with an appropriate convective heating process.

Fractional Thermal Analysis in a Generalized two Dimensional Infinite half Space with Heat Source

A generalized time fractional thermoelastic study under one relaxation time consideration is presented here for the two dimensional model having infinite half space. To analyze the thermal response of the problem, the infinite space is subjected to periodical varying heat source with respect to time. Futher, time derivative involved in heat transfer equation is of Caputo type having order  . Certains thermomechanical boundaries are applied at lower surface. Here the solution is obtained directly by employing Laplace and Hankel transformation but inversion for Laplace is evaluated by numerical method as given by Gaver-Stehfast algorithm. Properties of Copper metal is selected for the numerical analysis and results of temperature and stress distributions are presented graphically by using MATLAB software.

Memory Response on the Elasto-Thermodiffusive Interaction Subjected to Harmonically Varying Heat Source

Enlightened by the Caputo type of fractional derivative, this research paper is the analysis of a mathematical model of generalized thermoelastic diffusion with memory-dependent derivative (MDD) for an isotropic infinite medium with a cylindrical cavity in the context of dual-phase lag model. The surface of the cavity is traction free and subjected to harmonically heat sources with constant angular frequency of thermal vibration. Laplace transform technique has been used to solve the problem. Later eigenvalue approach is used to obtain the analytical expressions for different physical fields in the transformed domain. Finally to obtain the solutions in the real-time domain, the Riemann-sum approximation method is used. According to the graphical representations corresponding to the numerical results, the effect of heat source speed on temperature, displacement, stress, mass concentration and chemical potential are studied. The effect of memory-dependent parameters, as well as in the absence of MDD on physical quantities are also demonstrated.

Variable heat source in stagnation-point unsteady flow of magnetized Oldroyd-B fluid with cubic autocatalysis chemical reaction

Understanding the flow behavior of non-Newtonian fluids required more research in terms of various aspects. Because the role of heat transfer in non-Newtonian flows is dominant due to its importance in technology. For these benefits, a theoretical investigation is carried out to analyze the time-dependent flow of non-Newtonian fluid with a focus on thermal and solutal transport. In the present study, we formulate a mathematical model for Oldroyd-B fluid by taking into account the effect of magnetic field. The governing flow field equations are constructed with the help of the rheological expression of Oldroyd-B fluid model. For physical relevance, the effects of non-uniform heat source/sink, Joule heating and thermal radiation with homogeneous-heterogeneous chemical reactions have been incorporated in stagnation point flow towards a stretching cylinder to modify the energy and concentration distributions. The highly non-linear ordinary differential equations are tackled analytically through the optimal homotopy analysis method (OHAM). Study reveals that, the strength of homogeneous and heterogeneous reactions leads to enhanced the concentration of the catalyst at the surface. Furthermore, the non-uniform heat source/sink parameter acts like a major controlling parameter for the heat transportation rate, and heat transport is also influenced by the surface-dependent heat source/sink.

Multi-objective performance optimization of regenerative S-CO2 Brayton cycle based on neural network prediction

• A finite time thermodynamic model for regenerative S-CO 2 Brayton cycle is set up. • Artificial neural networks and multi-objective optimization are used. • Four different optimization objectives are considered. • The thermal efficiency and net power output are increased by 31.15% and 43.29%. • The exergy efficiency is increased by 33.75%. The regenerative supercritical CO 2 Brayton cycle (RSCBC) has great development potential in waste heat recovery and utilization, and it is necessary to carry out performance analysis and optimization. This article first applies the theory of finite time thermodynamics to establish a RSCBC model with finite temperature difference heat transfer, irreversible compression, irreversible expansion and other irreversible factors under variable temperature heat source conditions, and then uses the data samples to construct the corresponding neural network model. Based on the NSGA-Ⅱ algorithm, the working fluid mass flow rate, the pressure ratio, the heat conductance distribution ratios of the regenerator and the heater are chosen as optimization variables, multi-objective optimization is carried out with the goals of cycle thermal efficiency, net power output, ecological function and exergy efficiency. The results show that the use of neural network models to predict cycle performance can save a lot of calculation time compared to traditional calculation methods; after optimization, the positive ideal point is not on the Pareto front, which shows that the four optimization objectives are mutually restricted and affect each other. The results by using Shannon Entropy method for decision-making have a lower deviation index, and those by using TOPSIS and LINMAP methods for decision-making are consistent with each other; for the results by using Shannon Entropy method for decision-making, the cycle thermal efficiency and net power output can reach 38.4% and 12.047 MW respectively, which can be increased by 31.15% and 43.29% compared to those for the initial design point respectively, and the ecological function and exergy efficiency can reach 7.6274 MW and 73.2% respectively, which are 4.2588 times and 33.75% higher than those for the initial design point respectively. The obtained results can provide some guidance for the optimal design of the RSCBC in real engineering.

Variable profile heat source models for numerical simulations of arc welding processes

Numerical modeling of arc welding and correlated processes tend to be challenging, since they have complex physical phenomena. Several heat sources, with geometric parameters to be adjusted, have been developed to impose the energy input of the process. This study proposes two variable profile heat sources, with only two geometrical parameters, that intend to achieve good accuracy, regardless the welding process, base material and thickness of the welded plates. These sources are tested against GTAW and GMAW processes of butt joints of carbon and stainless steel plates with two different thicknesses. Numerical simulations are performed in ANSYS® APDL software, and performance of these new heat sources are compared with classical ones, namely the 3D Conical and the Double Ellipsoid. Weld profiles and thermal cycles from experiments are compared with numerical ones. Although all heat sources had difficulties to predict accurately results in cases of GMAW processes, numerical results of the new heat sources had equal or better agreement than the classical ones.

Impact of the KKL Correlation Model on the Activation of Thermal Energy for the Hybrid Nanofluid (GO+ZnO+Water) Flow through Permeable Vertically Rotating Surface

The thermal energy transfer characteristics during hybrid nanofluid migration are studied in the presence of a variable magnetic field, heat source, and radiation. The flow is governed by the conservation laws of mass, momentum, and energy, whereas it is modeled by the coupled set of nonlinear partial differential equations (PDEs). Suitable similarity transformations are employed to convert the developed set of PDEs to a nonlinear system of coupled ordinary differential equations (ODEs). The simplified system of ODEs is solved by using the well-established analytical procedure of homotopy analysis method (HAM). The effects of varying the strength of the physical parameters on the thermal energy transfer during hybrid nanofluid motion between two plates in which one of the plate is porous, rotating, as well as stretching are investigated through tables and two-dimensional graphs. The porosity is modeled through the Koo–Kleinstreuer model (KKL) correlation. The analysis reveals that the skin friction and Nusselt number augment with the increasing strength of the magnetic field and nanomaterials’ concentrations. The gradient in the fluid velocity has a dual dependence on the strength of the applied magnetic field and Grashof number and drops with the higher values of the unsteadiness parameter. The fluid velocity constricts with the enhancing magnetic field due to higher Lorentz forces, and it also drops with the increasing rotation rate. The enhancing buoyancy associated with higher Grashof number values augments the fluid velocity. The fluid’s temperature rises with the augmenting nanomaterial concentrations, Eckert number, nonsteadiness, heat source strength, and radiation parameter, while it drops with the higher Grashof number and Prandtl number. The applied technique of the HAM shows good convergence over a wide range of the convergent parameter. This work has potential applications in the development of efficient thermal energy transfer systems.

The effects of ultrasonic frequency pulsed arc on wire + arc additively manufactured high strength aluminum alloys

Ultrasonic frequency pulsed variable polarity TIG and conventional variable polarity TIG arc heat source were employed to fabricate WAAM 2024 aluminum alloy thin-wall structures. Heat treatment procedure was conducted to process the components. The microstructure, porosity and mechanical properties were comparatively investigated to reveal the effects of ultrasonic frequency pulsed arc on the properties of WAAM aluminum alloys. With ultrasonic frequency pulsed arc, the grain was refined, and the porosity was significantly reduced. The micro hardness and its uniformity increased. Ultrasonic frequency pulsed arc can particularly increase the vertical tensile properties of heat-treated components and improve property isotropy. The refined grains and lower porosity in WAAM aluminum alloy structure with ultrasonic frequency pulsed arc were the reasons for property and isotropy improvement.

Numerical investigation of a convective hybrid nanofluids around a rotating sheet

Hybrid nanofluids are formulated with various kinds of base fluids. They are designed to provide good heat transfer performance. They can achieve this by dispersing various kinds of nanoparticles in the base materials. This new technology of formulating hybrid nanofluids has a wide range of applications in various industries such as solar energy, medical equipment, and aerospace. Keeping these applications in view, this study provides an insight into the effects of convective heat transport on a Hybrid nanofluid, across a rotating sheet with a variable heat source. In this investigation, the governing boundary layer partial differential equations were modified into the ordinary differential equations, by using the proper similarity transformations. Later, they were solved numerically, with the support of the Lobatto IIIA technique in MATLAB. The influence of the Richardson number on flow parameters was studied, and it was discovered that increasing Ri increases the velocity while decreasing temperature and concentration profiles. The impact of various other flow parameters on the flow fields and also on the behavior of Nusselt number, coefficient skin friction, and Sherwood number were studied and represented graphically. The outcomes were found to be in excellent accord when compared with quoted studies.

TEMPERATURE-DEPENDENT PHYSICAL CHARACTERISTICS OF THE ROTATING NONLOCAL NANOBEAMS SUBJECT TO A VARYING HEAT SOURCE AND A DYNAMIC LOAD

In this article, the influence of thermal conductivity on the dynamics of a rotating nanobeam is established in the context of nonlocal thermoelasticity theory. To this end, the governing equations are derived using generalized heat conduction including phase lags on the basis of the Euler–Bernoulli beam theory. The thermal conductivity of the proposed model linearly changes with temperature and the considered nanobeam is excited with a variable harmonic heat source and exposed to a time-dependent load with exponential decay. The analytic solutions for bending moment, deflection and temperature of rotating nonlocal nanobeams are achieved by means of the Laplace transform procedure. A qualitative study is conducted to justify the soundness of the present analysis while the impact of nonlocal parameter and varying heat source are discussed in detail. It also shows the way in which the variations of physical properties due to temperature changes affect the static and dynamic behavior of rotating nanobeams. It is found that the physical fields strongly depend on the nonlocal parameter, the change of the thermal conductivity, rotation speed and the mechanical loads and, therefore, it is not possible to neglect their effects on the manufacturing process of precise/intelligent machines and devices.

Interactions in a nonlocal thermoelastic hollow sphere with voids due to harmonically varying heat sources

The present work is devoted to discuss the transient wave propagation in an isotropic homogenous thermoelastic spherical body with voids due to harmonically varying heat sources in the context of nonlocal thermoelasticity. The constitutive relations and the governing equations are resolved by applying harmonic variations in time and transformed into coupled ordinary differential equations. The outer and the inner surfaces of the sphere are kept stress-free and free from void concentration. A harmonically varying heat source is supplied on the inner surface along the radial direction and the outer surface is assumed to be isothermal. Numerical simulations are implemented to the analytical results with the support of MATLAB software tool. Numerically, generated data are presented graphically for the field variables of interest (temperature, stresses, cubical dilation, displacement and void volume fraction field) and at the end analysis of these results are given.

A new boundary element-free Galerkin method using dual CSRBFI for 2D inhomogeneous heat conduction problems

It is established that the new boundary element-free Galerkin method, namely the virtual boundary element-free Galerkin method (VBEFGM), using dual compactly supported radial basis function interpolation (CSRBFI) for 2D inhomogeneous heat conduction problems with variable heat sources, whose solutions are divided into homogeneous and particular solutions. The virtual loads of the homogeneous solutions and undetermined coefficients of particular solutions are interpolated by CSRBFI. Its formula is established by the Galerkin method. The homogeneous solutions are obtained by the virtual boundary element-free method (VBEFM). The recommended method for 2D inhomogeneous heat conduction problems is real meshfree without background integration elements and exhibits the merits of the meshfree method, Galerkin method, and boundary element method. Its calculation scheme is deduced in detail and easily programmed. The coefficient matrix has symmetrical characteristics. The implementation steps and implementation flow-chart are also shown in detail. Seven numerical examples, such as exponential functionally graded material, are calculated and contrasted with other numerical methods. The precision and stableness of the proposed method for 2D inhomogeneous heat conduction problems are verified.

Thermoelastic behavior of an isotropic solid sphere under a non-uniform heat flow according to the MGT thermoelastic model

Moore-Gibson-Thompson (MGT) is an equation which appropriately describes the spread of sound waves in gasses and fluids as well as thermal/mechanical waves in elastic bodies. The objective of this article is to theoretically analyze the generalized thermoelasticity models that have been presented as the development of the Fourier’s law dealing with the paradox of unlimited propagation velocities of thermal waves. For this purpose, a new model is presented which combines the third type of Green and Naghdi model (GN-III) with the generalized theory including the relaxation time based on the MGT equation. The proposed model may be considered as a generalization of previous thermoelastic theories. To examine the introduced approach, the behavior of thermoelastic waves within a homogeneous isotropic sphere in which its surface is exposed to thermal shock with varying heat source is investigated. The variations in different physical fields of a given substance have been computed by means of Laplace transform technique and an efficient numerical technique is implemented in Laplace inversion procedure. The effect of different forms of heat source are also examined and several comparisons for various thermoelasticity approaches are comprehensively conducted.