Heat-generating Element Research Articles

Analysis of the thermally stressed state of the heat-generating element in the form of an ellipsoid

The paper considers the thermally stressed state of fuel rods when their geometric shape changes. The temperature fields for the sphere and the ellipsoid are determined. It is shown that, while maintaining volumetric heat release, maximum stresses occur in fuel rods of circular cross-section. Similar results were obtained when changing the geometric shape of a spherical fuel element: all other things being equal, maximum thermal stresses occur in spherical fuel elements.

Numerical Simulation of Conjugate Mixed Convection in 3D Channel with Heat-Generating Flat Element and Symmetrical Solid Two-Fin System

This paper presents the numerical simulation results of conjugate mixed convection in a three-dimensional channel with a heat-generating element and solid fins. It should be noted that the symmetrical location of fins has been studied. The system of partial differential equations, presented in dimensionless form using velocity and vorticity vectors, has been solved by the finite difference method on a uniform grid. The central difference schemes have been used to approximate diffusive terms. In contrast, for an approximation of convective terms, the monotonic Samarskii difference schemes have been applied to improve the stable properties of central differences of the second order of accuracy. Analysis has been performed on a wide range of governing parameters, including the Reynolds number (200 ≤ Re ≤ 1000), the material of the fins (aluminum, copper, and iron), and the location of the fins on the heater surface, taking into account the identical distances between the fins and the nearest walls. Water has been considered a working cooling medium. The obtained outcomes characterize the most efficient heat removal from the surface of the energy source using the considered fin system. For example, by using copper fins, the cooling efficiency of the heating element can be increased. The average heater temperature decreases significantly with an increase in the Reynolds number. The distance between the fins also makes a significant contribution to the cooling phenomenon. It is noted that with the most successful choice of location, it is possible to decrease the temperature of the heater by more than 12%.

Natural Convection of Variable Viscosity Fluid in a Partially Porous Cube Having Heat-generating Element Under Local Thermal Non-Equilibrium Model

Natural Convection of Variable Viscosity Fluid in a Partially Porous Cube Having Heat-generating Element Under Local Thermal Non-Equilibrium Model

Heat exchange between the heat-generating element of the circular section of a nuclear reactor and its shell under boundary conditions of the fourth kind

The work is devoted to the heat exchange of a nuclear reactor. Attention was paid to the mathematical modeling of the temperature field of a heat-generating element of circular cross-section and surrounding it with a thin gas layer. It is assumed that the thermal contact between the solid–interlayer system is ideal. Differentiation and integration methods were used for numerical modeling.

Effect of MHD mixed convection on a heat-generating element cooling inside a ventilated square cavity filled with Fe3O4–water ferrofluid

This work groups a set of numerical results on the investigation of the external magnetic field effect on mixed convection in a ventilated square cavity with a heat source located in the middle of its bottom wall and filled with a ferrofluid. The behavior of the magnetic field was treated according to three different scenarios illustrated by magnetic Reynolds number value (Rm = 0.1, 0.001, and 0.00001). The dimensionless governing equations were solved numerically by the finite volume method and the SIMPLE algorithm was chosen for the treatment of coupling between the momentum and continuity equations using the QUICK scheme of Leonard. The numerical results for a large range of Hartmann numbers and volume fractions and for horizontal and vertical magnetic field directions are discussed in terms of streamlines, isotherms, Nusselt numbers, and maximal temperature of fluid and heat source. The results highlighted different scenarios showing the heat exchange rate enhancement and heat source cooling as a function of the magnetic field strength and direction and as a function of the internal fluid constitution and behavior. The diversity of these results as a function of the magnetic Reynolds number also underlines the limitation of theory based on low-Rm model in the treatment of MHD flows.

Cooling of a periodic heat-generating solid element in an electronic cabinet using a non-Newtonian pseudoplastic nanofluid and a heat-conducting substrate

PurposeNowadays, the most important challenge in mechanical engineering, power engineering and electronics is a development of effective cooling systems for heat-generating units. Taking into account this challenge, this study aims to deal with computational investigation of thermogravitational energy transport of pseudoplastic nanoliquid in an electronic chamber with a periodic thermally producing unit placed on the bottom heat-conducting wall of finite thickness under an influence of isothermal cooling from vertical side walls.Design/methodology/approachThe control equations formulated using the Boussinesq approach, Ostwald–de Waele power law and single-phase nanofluid model with experimentally based correlations of Guo et al. for nanofluid dynamic viscosity and Jang and Choi for nanofluid thermal conductivity have been worked out by the in-house computational procedure using the finite difference technique. The impact of the Rayleigh number, nanoadditives concentration, frequency of the periodic heat generation from the local element and thickness of the bottom solid substrate on nanoliquid circulation and energy transport has been studied.FindingsIt has been found that a raise of the nanoadditives concentration intensifies the cooling of the heat-generating element, while a growth of the heat-generation frequency allows reducing the amplitude of the heater temperature.Originality/valueMathematical modeling of a pseudoplastic nanomaterial thermogravitational energy transport in an electronic cabinet with a periodic thermally generating unit, a heat-conducting substrate and isothermal cooling vertical surfaces to identify the possibility of intensifying heat removal from a heated surface.

Modeling of thermal processes in the contact zones of fuel elements

In this work, using two specific examples, a general approach to the mathematical modeling of thermal processes in the contact zones of fuel elements in the development and optimization of 
 various technological processes, systems and devices is considered. In the first example, a mathematical model of heat transfer in the contact zone (metal-hybrid thermal interface) between the heat-generating element and the heat-dissipating radiator is considered. In the second case, the thermal process in the processing of materials with a bonded diamond tool in the contact zone "diamond grain – binder – processed material" is considered and analyzed. The general approach to modeling thermal processes in the contact zones of various fuel elements makes it possible to optimize the parameters of technological processing modes and the correct operating conditions for products and systems

Thermogravitational Convective Flow and Energy Transport in an Electronic Cabinet with a Heat-Generating Element and Solid/Porous Finned Heat Sink

Heat transfer enhancement poses a significant challenge for engineers in various practical fields, including energy-efficient buildings, energy systems, and aviation technologies. The present research deals with the energy transport strengthening using the viscous fluid and solid/porous fins. Numerical simulation of natural convective energy transport of viscous fluid in a cooling cavity with a heat-generating element placed in a finned heat sink was performed. The heat-generating element is characterized by constant volumetric heat generation. The Darcy–Brinkman approach was employed for mathematical description of transport processes within the porous fins. The governing equations formulated using the non-primitive variables were solved by the finite difference method of the second-order accuracy. The influence of the fins material, number, and height on the flow structure and heat transfer was also studied. It was found that the mentioned parameters can be considered as control characteristics for heat transfer and fluid flow for the cooling system.

A New Heat-Generating Element Based on Al–Ni–Fe3O4 Nanosized Powder Energetic Materials for Autonomous Thermoelectric Generators

Energy sources that can operate at extreme ambient temperatures and high humidity, as well as in an airless space, are one of the promising areas for research in electronics. The possibility of creating an autonomous thermoelectric generator with a fuel element based on nanosized powder Al–Ni–Fe3O4 energy materials is considered. Using bomb calorimetry and high-speed video filming, the influence of the composition of the energetic material on the thermal effect of the reaction and the nature of combustion has been investigated. Variants of designs of autonomous thermoelectric generators were proposed and experimental studies of their output characteristics were carried out using various fuel elements. Evaluation of the efficiency of the device was carried out and a working prototype was created.

Influence of the Fin Shape on Heat Transport in Phase Change Material Heat Sink with Constant Heat Loads

Nowadays, the heat transfer enhancement in electronic cabinets with heat-generating elements can be achieved using the phase change materials and finned heat sink. The latter allows to improve the energy transference surface and to augment the cooling effects for the heat sources. The present research deals with numerical analysis of phase change material behavior in an electronic cabinet with an energy-generating element. For an intensification of heat removal, the complex finned heat sink with overall width of 10 cm was introduced, having the complicated shape of the fins with width of 0.33 cm and height H = 5 cm. The fatty acid with melting temperature of 46 °C was considered as a phase change material. The considered two-dimensional challenge was formulated employing the non-primitive variables and solved using the finite difference method. Impacts of the volumetric heat flux of heat-generating element and sizes of the fins on phase change material circulation and energy transference within the chamber were studied. It was shown that the presence of transverse ribs makes it possible to accelerate the melting process and reduce the source temperature by more than 12 °C at a heat load of 1600 W/m. It should also be noted that the nature of melting depends on the hydrodynamics of the melt, so the horizontal partitions reduce the intensity of convective heat transfer between the upper part of the region and the lower part.

Thermal convection and radiation in a rotating cabinet with time-dependent heat-generated solid element and heat-conducting solid walls

Purpose This paper aims to study numerically the simulation of convective–radiative heat transfer under an effect of variable thermally generating source in a rotating square chamber. The performed analysis deals with a development of passive cooling system for the electronic devices. Design/methodology/approach The domain of interest of size H rotating at a fixed angular velocity has heat-conducting solid walls with a constant cooling temperature for the outer boundaries of the vertical walls and with thermal insulation for the outer borders of the horizontal walls. The chamber has a heater on the bottom wall with a time-dependent volumetric heat generation. The internal surfaces of the walls and the energy element are both grey diffusive emitters and reflectors. The fluid is transparent to radiation. Computational model has been written using non-dimensional parameters and worked out by the finite difference technique. The effect of the angular velocity, volumetric heat generation frequency and surface emissivity has been studied and described in detail. Findings The results show that growth of the surface emissivity leads to a diminution of the mean heater temperature, while a weak rotation can improve the energy transport for low volumetric thermal generation frequency. Originality/value An efficient computational approach has been used to work out this problem. The originality of this work is to analyze complex (conductive–convective–radiative) energy transport in a rotating system with a local element of time-dependent volumetric heat generation. To the best of the authors’ knowledge, an interaction of major heat transfer mechanisms in a rotating system with a heat-generating element is scrutinized for the first time. The results would benefit scientists and engineers to become familiar with the analysis of complex heat transfer in rotating enclosures with internal heat-generating units, and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors and electronics.

Model of an electronic equipment cooling system based on the joint use of high-current thermoelectric semiconductor batteries and a thermal thermosipho

Objective. The objective of the study is to develop a design model of the electronic equipment cooling system based on the combined use of high-current thermoelectric semiconductor batteries of layered design and an evaporative-condensing thermal thermosyphon, as well as to study the thermophysical processes occurring during its operation.Methods. A mathematical model of the electronic equipment cooling system based on the combined use of high-current layered thermoelectric batteries and an evaporative-condensing thermal thermosyphon is presented. The design model includes a description of heat exchange processes in a layered thermoelectric element at various supply currents, determination of the amount of heat transferred through the cross-section of the channel of a thermal thermosyphon per unit of time, and the temperature values at each channel point.Result. A 2D dynamic heat conduction problem is solved for a complex system with rectangular geometry of fragments and heat sources. The temperature distribution of a thermoelement along its longitudinal axis at different values of the supply current and the change in the heat flow along its length in a thermal evaporation-condensation thermosyphon are studied.Conclusion. The results of the research have shown the effectiveness of combined use of high-current layered thermoelectric batteries and a thermal thermosyphon in electronic equipment with dense element packaging. It is shown that to increase the efficiency of electronic equipment and reduce the heat losses that occur in the heat line when the heat-generating element of radio-electronic equipment and thermoelectric semiconductor batteries are separated by a sufficiently large distance (over 0.6 m), it is advisable to use an evaporative-condensing thermal thermosyphon as a heat line.

Cooling System with Porous Finned Heat Sink for Heat-Generating Element

The present study deals with computational investigation of natural convection in a porous chamber having a copper finned heat sink and a thermally producing element of finite thickness and heat conductivity. The enclosure is cooled from the external vertical and upper horizontal walls, whilst the remaining borders are considered to be thermally insulated. Newtonian and heat-conducting liquid with temperature-dependent viscosity is assumed as a working medium. Governing equations are written in non-dimensional variables «stream function—vorticity—temperature» and they are worked out by the finite difference technique. The temperature distribution, streamlines and the dependences of the integral characteristics on the governing characteristics, such as the Darcy and Ostrogradsky numbers and geometric characteristics of the radiator have been illustrated. Presented results can be used for the development of passive cooling systems.

Effect of Porous Medium and Copper Heat Sink on Cooling of Heat-Generating Element

Cooling of heat-generating elements is a challenging problem in engineering. In this article, the transient free convection of a temperature-dependent viscosity liquid inside the porous cavity with copper radiator and the heat-generating element is studied using mathematical modeling techniques. The vertical and top walls of the chamber are kept at low constant temperature, while the bottom wall is kept adiabatic. The working fluid is a heat-conducting liquid with temperature-dependent viscosity. A mathematical model is developed based on dimensionless stream function, vorticity, and temperature variables. The governing properties are the variable viscosity, geometric parameters of the radiator, and size of thermally insulated strip on vertical surfaces of the cavity. The effect of these parameters on the energy transport and circulation patterns are analyzed numerically. Based on the numerical results obtained, recommendations are given on the optimal values of the governing parameters for the effective operation of the cooling system. It is shown that the optimal number of radiator fins for the cooling system configuration under consideration is 3. In addition, the thermal insulation of the vertical walls and the increased thickness of the radiator fins have a negative effect on the operation of the cooling system.

Influence of the chamber inclination angle and heat-generating element location on thermal convection of power-law medium in a chamber

PurposeThis paper aims to study the mathematical modeling of passive cooling systems for electronic devices. Improving heat transfer is facilitated by the correct choice of the working fluid and the geometric configuration of the engineering cavity; therefore, this work is devoted to the analysis of the influence of the position of the heat-generating element and the tilted angle of the electronic cabinet on the thermal convection of a non-Newtonian fluid.Design/methodology/approachThe area of interest is a square cavity with two cold vertical walls, while the horizontal boundaries are adiabatic. An element of constant volumetric heat generation is placed on the lower wall of the chamber. The problem is described by Navier–Stokes partial differential equations using dimensionless stream function and vorticity. The numerical solution is based on the developed computational code using the finite difference technique and a uniform rectangular grid.FindingsThe key conclusions of this work are the results of a detailed analysis of streamlines and isotherms, the average Nusselt number and profiles of the average heater temperature. It was found that more intensive cooling of the heat-generating element occurs when the cavity is filled with a pseudoplastic fluid (n < 1) and not inclined (α = 0). The Rayleigh number of Ra = 105 and the thermal conductivity ratio of k = 100 are characterized by the most positive effect.Originality/valueThe originality of the research lies in both the study of thermal convection in a square chamber filled with power-law fluid under the influence of a volumetric heat production element and the analysis of the influence of geometric and thermophysical parameters characterizing the considered process.

Effect of porous insertion on convective energy transport in a chamber filled with a temperature-dependent viscosity liquid in the presence of a heat source term

Development of electronic devices demands to create an effective cooling system using optimal working liquid and porous insertions near the heat-generating elements. Such features allow intensifying the heat disposal from the heated element area. In this study, the unsteady convection of a variable viscosity liquid within a chamber having a heat-generating element under the impact of porous insertion is investigated. A porous layer surrounds the energy source located on the lower surface. The horizontal and vertical walls are thermally insulated, kept at constant cooling temperatures, respectively. Partial differential equations written in non-dimensional non-primitive variables with appropriate additional conditions are worked out by the finite difference method. The governing characteristics are the non-dimensional medium permeability, volumetric heat flux, variable viscosity and thickness of the porous insertion. The influence of these properties on local and mean fields’ characteristics for the energy transport and flow structures are studied in details. The calculations demonstrate that the inclusion of a porous insertion and the variation of its properties lead to more essential cooling of the heater.

Natural Convection of Non-Newtonian Power-Law Fluid in a Square Cavity with a Heat-Generating Element

Development of modern technology in microelectronics and power engineering necessitates the creation of effective cooling systems. This is made possible by the use of the special fins technology within the cavity or special heat transfer liquids in order to intensify the heat removal from the heat-generating elements. The present work is devoted to the mathematical modeling of thermogravitational convection of a non-Newtonian fluid in a closed square cavity with a local source of internal volumetric heat generation. The behavior of the fluid is described by the Ostwald-de Waele power law model. The defining Navier–Stokes equations written using the dimensionless stream function, vorticity and temperature are solved using the finite difference method. The effects of the Rayleigh number, power-law index, and thermal conductivity ratio on heat transfer and the flow structure are studied. The obtained results are presented in the form of isolines of the stream function and temperature, as well as the dependences of the average Nusselt number and average temperature on the governing parameters.

The Influence of Surface Radiation on the Passive Cooling of a Heat-Generating Element

Low-power electronic devices are suitably cooled by thermogravitational convection and radiation. The use of modern methods of computational mechanics makes it possible to develop efficient passive cooling systems. The present work deals with the numerical study of radiative-convective heat transfer in enclosure with a heat-generating source such as an electronic chip. The governing unsteady Reynolds-averaged Navier–Stokes (URANS) equations were solved using the finite difference method. Numerical results for the stream function–vorticity formulation are shown in the form of isotherm and streamline plots and average Nusselt numbers. The influence of the relevant parameters such as the Ostrogradsky number, surface emissivity, and the Rayleigh number on fluid flow characteristics and thermal transmission are investigated in detail. The comparative assessment clearly emphasizes the effect of surface radiation on the overall energy balance and leads to change the mean temperature inside the heat generating element. The results of the present study can be applied to the design of passive cooling systems.

Impacts of Heat-Conducting Solid Wall and Heat-Generating Element on Free Convection of Al2O3/H2O Nanofluid in a Cavity with Open Border

Development of modern electronic devices demands a creation of effective cooling systems in the form of active or passive nature. More optimal technique for an origination of such cooling arrangement is a mathematical simulation taking into account the major physical processes which define the considered phenomena. Thermogravitational convection in a partially open alumina-water nanoliquid region under the impacts of constant heat generation element and heat-conducting solid wall is analyzed numerically. A solid heat-conducting wall is a left vertical wall cooled from outside, while a local solid element is placed on the base and kept at constant volumetric heat generation. The right border is supposed to be partially open in order to cool the local heater. The considered domain of interest is an electronic cabinet, while the heat-generating element is an electronic chip. Partial differential equations of mathematical physics formulated in non-primitive variables are worked out by the second order finite difference method. Influences of the Rayleigh number, heat-transfer capacity ratio, location of the local heater and nanoparticles volume fraction on liquid circulation and thermal transmission are investigated. It was ascertained that an inclusion of nanosized alumina particles to the base liquid can lead to the average heater temperature decreasing, that depends on the heater location and internal volumetric heat generation. Therefore, an inclusion of nanoparticles inside the host liquid can essentially intensify the heat removal from the heater that is the major challenge in different engineering applications. Moreover, an effect of nanosized alumina particles is more essential in the case of low intensive convective flow and when the heater is placed near the cooling wall.

Unsteady natural convection in a partially porous cavity having a heat-generating source using local thermal non-equilibrium model

PurposeThe purpose of this study is a numerical analysis of transient natural convection in a square partially porous cavity with a heat-generating and heat-conducting element using the local thermal non-equilibrium model under the effect of cooling from the vertical walls. It should be noted that this research deals with a development of passive cooling system for the electronic devices.Design/methodology/approachThe domain of interest is a square cavity with a porous layer and a heat-generating element. The vertical walls of the cavity are kept at constant cooling temperature, while the horizontal walls are adiabatic. The heat-generating solid element is located on the bottom wall. A porous layer is placed under the clear fluid layer. The governing equations, formulated in dimensionless stream function, vorticity and temperature variables with corresponding initial and boundary conditions, are solved using implicit finite difference schemes of the second order accuracy. The governing parameters are the Darcy number, viscosity variation parameter, porous layer height and dimensionless time. The effects of varying these parameters on the average total Nusselt number along the heat source surface, the average temperature of the heater, the fluid flow rate inside the cavity and on the streamlines and isotherms are analyzed.FindingsThe results show that in the case of local thermal non-equilibrium the total average Nusselt number is an increasing function of the interphase heat transfer coefficient and the porous layer thickness, while the average heat source temperature decreases with the Darcy number and viscosity variation parameter.Originality/valueAn efficient numerical technique has been developed to solve this problem. The originality of this work is to analyze unsteady natural convection within a partially porous cavity using the local thermal non-equilibrium model in the presence of a local heat-generating solid element. The results would benefit scientists and engineers to become familiar with the analysis of convective heat transfer in enclosures with local heat-generating heaters and porous layers, and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors and electronics.