Study Of Heat Transfer Processes Research Articles

Influence of filler topology on the thermal transport of composite materials based on similarity principle modeling: A cross-scale simulation study

The thermal conductivity parameter of the materials is a fundamental parameter for thermal design and study of heat transfer processes. In our study, we combined the homogenization theory based on the finite element with the thermal conductivity order-of-magnitude analysis and similarity principle, to construct structural models of fibers, spheres, ellipsoids, sheets, and interfaces, and establish the topology of intermingling and encapsulation of different structures. Combined thermal conductivity calculations of mesoscopic composites and microscopic interface models using finite element and molecular dynamics methods. The anisotropy model of thermal conductivity was established by coordinate transformation. Based on the numerical verification of the reliability of the method, the mechanisms of the influence on the thermal transport of composites were analyzed for parameters such as volume fraction of different structural fillers, structural shape, thermal conductivity ratio, thickness of highly thermally conductive coatings, and spatial orientation distribution. The results showed that the effective thermal conductivity (ETC) of the continuous structural reinforced composite was mainly influenced by the volume fraction of the filler; the modulation of ETC with ellipsoidal particle structure form and distribution mode was comparable to the effect of changing the volume fraction modulation; the mutual fusion between ellipsoids randomly distributed in the plane could effectively enhance the heat transport effect of the composite, and as the volume fraction increased to more than 3%, the heat transport gain from mutual fusion was more obvious; spraying high thermally conductive copper coating on ellipsoidal particles could significantly enhance the ETC of the composites. The present work could provide reference for composites in terms of structural improvement and thermal performance enhancement.

Energy Saving through Automation of the Lightweight Floor Heating System

The overview of the literature sources showed that over the last decade, the attention to the study of heat transfer processes with the automation and periodic use of underfloor heating systems has increased significantly. The aim of this study was to investigate the heat flux density from the surface of the lightweight floor heating system dependence on different parameters. These parameters are material of the finishing coating, average temperature difference between indoor air and heat carrier, heat carrier temperature and its flow rate, thickness of the thermal insulation layout under the lightweight floor heating system. The article shows results of both experimental and computational modelling studies of the lightweight floor heating system which was operated in different regimes and with different (ceramic tile and laminate) finishing coatings. A new experimental stand has been created in the thermophysical laboratory of the Institute of Engineering Thermophysics of the National Academy of Sciences of Ukraine for the purposes of experimental studies. For the purposes of comparison of different operational regimes as well as the determination of the energy saving through automation of the operation regimes of the lightweight floor heating system, the CFD modelling was conducted. The results showed that such systems have significant potential for automation and heat supply purposes of different premises since they have low thermal inertia due to the absence of the concrete screed monolith. On the other hand, the research showed that use of quantitative regulation of the lightweight floor heating system, by reducing the flow of the heat carrier is more effective in this case than qualitative with change of heat carrier temperature.

ЕКСПЕРИМЕНТАЛЬНІ ТА ЧИСЕЛЬНІ ДОСЛІДЖЕННЯ ТЕПЛОВІДДАЧІ ЗІ СКЛОПАКЕТА З ЕЛЕКТРОНАГРІВОМ ЙОГО ПОВЕРХНІ

The results of experimental and theoretical studies of heat transfer processes through a two-chamber double-glazed window (4i-10-4M1-10-4i) with electric heating are presented. Electric heating was carried out on the inner surface of the inner glass by applying a voltage to its low-emission coating. A thermophysical heat transfer model has been cre-ated through an electrically heated double-glazed window. This made it possible to determine the characteristics of the thermal regime of double-glazed windows with electric heating. Verification of the created numerical model was car-ried out using the data of experimental studies. The obtained distributions of heat fluxes and temperatures on the outer and inner surfaces of a double-glazed window with electric heating are analyzed. Ref. 12, fig. 8.

Study of Heat Transfer Processes in a System Containing Fe–Rh Microwires

Study of Heat Transfer Processes in a System Containing Fe–Rh Microwires

Numerical Study of Heat Transfer Processes in a Reservoir–Hydraulic Fracture System in the Constant Extraction Mode

Numerical Study of Heat Transfer Processes in a Reservoir–Hydraulic Fracture System in the Constant Extraction Mode

Calculation of temperature waves in kurums

The article indicates the relevance of the study of heat transfer processes in kurums. Boundary value problems of vertical temperature change in kurums and in the underlying rock base are solved, when the temperature on the surface of kurums changes according to a given periodic law, which simulates daily and seasonal temperature fluctuations. The cases when the rock base is a heat-conducting medium and permafrost are considered. Some regularities of temperature propagation along the depth are revealed.

Heat generation in devices for magnetic-pulse processing of materials

The problem of analysis of non-stationary heat generation due to the flow of electric current in devices for magnetic-pulse processing of materials is considered. An analysis of the available information sources led to the conclusion that a large number of studies in this area are devoted to the study of heat transfer processes during technological operations of induction heating. In other technological operations of magnetic-pulse processing of materials, heat release is also significant. In this case, a non-stationary inhomogeneous temperature field can lead to significant temperature deformations. This, in turn, can cause a loss in the performance of the device due to destruction or irreversible deformation. Adequate modeling of non-stationary temperature propagation in this case is an obligatory step in carrying out computational analysis in the process of designing technological devices. A general strategy is proposed for determining the propagation of a non-stationary temperature field in the presence of a non-stationary non-uniform electromagnetic field. The proposed strategy presupposes a general solution of the problems of the propagation of the electromagnetic field and the temperature field within the framework of a unified design scheme. The use of the finite element method is proposed as a numerical method. The finite element method, when used in such problems, allows one to draw up iterative procedures that can be used to take into account the nonlinear effects associated with the influence of temperature on the electro-physical properties of materials. The problem of sequential determination of a non-stationary, non-uniform electromagnetic field and a non-stationary temperature field in composite matrices intended for electromagnetic pressing of powders of super-strong refractory materials is considered. The distribution of some quantitative characteristics of the electromagnetic field, as well as the dependence of temperature on time are presented.

Parallel Implementation of the Algorithm to Compute Forest Fire Impact on Infrastructure Facilities of JSC Russian Railways

Forest fires have a negative impact on the economy in a number of regions, especially in Wildland Urban Interface (WUI) areas. An important link in the fight against fires in WUI areas is the development of information and computer systems for predicting the fire safety of infrastructural facilities of Russian Railways. In this work, a numerical study of heat transfer processes in the enclosing structure of a wooden building near the forest fire front was carried out using the technology of parallel computing. The novelty of the development is explained by the creation of its own program code, which is planned to be put into operation either in the Information System for Remote Monitoring of Forest Fires ISDM-Rosleskhoz, or in the information and computing system of JSC Russian Railways. In the Russian Federation, it is forbidden to use foreign systems in the security services of industrial facilities. The implementation of the deterministic model of heat transfer in the enclosing structure with the complexity of the algorithm O (2N2 + 2K) is presented. The program is implemented in Python 3.x using the NumPy and Concurrent libraries. Calculations were carried out on a multiprocessor cluster in the Sirius University of Science and Technology. The results of calculations and the acceleration coefficient for operating modes for 1, 2, 4, 8, 16, 32, 48 and 64 processes are presented. The developed algorithm can be applied to assess the fire safety of infrastructure facilities of Russian Railways. The main merit of the new development should be noted, which is explained by the ability to use large computational domains with a large number of computational grid nodes in space and time. The use of caching intermediate data in files made it possible to distribute a large number of computational nodes among the processors of a computing multiprocessor system. However, one should also note a drawback; namely, a decrease in the acceleration of computational operations with a large number of involved nodes of a multiprocessor computing system, which is explained by the write and read cycles in cache files.

Research methods in the study of heat transfer coefficient during flow in minichannels

The paper presents the specification of research methods commonly encountered in the studies of heat transfer processes in minichannels. In particular the following methods have been emphasized: electrochemical limiting current method as well as the thermal balance method. In thermal balance method the mean heat transfer coefficient is determined by the set of experimental thermal measurements of the investigated heat exchanger. In turn, limiting current method is based on heat and mass transfer analogy. The discussed research methods have been implemented on two specially designed and constructed test facilities with compact minichannel heat exchangers, which have been presented and described in details. In order to validate the designed setup, the preliminary experimental measurements of two minichannel heat exchangers with hydraulic diameter of 2 mm and rectangular cross sections during single-phase liquid flows have been carried out. In further perspective it is planned to extend the experimental studies of minichannel heat exchangers and to compare the results obtained by both methods described.

MATHEMATICAL MODELING OF THE HEAT TRANSFER PROCESS IN THE SYSTEM OF MULTILAYER CYLINDRICAL SOLID BODIES CONSIDERING INTERNAL SOURCES OF HEAT

The article is devoted to the application of the direct method to the study of heat transfer processes in the "continuous cylinder inside a multilayer cylindrical shell" system. To solve the initial problem, an auxiliary problem is posed with a “remote” cylinder of sufficiently small radius. The solution is based on the reduction method, the concept of quasiderivatives, the Fourier scheme using the modified eigenfunctions method. The solution to the original problem was obtained by following the radius of the remote cylinder to zero.

Numerical study of heat transfer process during electroslag welding by two-dimensional particle method

Numerical study of heat transfer process during electroslag welding by two-dimensional particle method

INFLUENCE OF IMPERFECT THERMAL CONTACT ON HEAT EXCHANGE IN THE SYSTEM OF MULTILAYER CYLINDRICAL BODIES

Introduction. Solving the problem of heat transfer in multilayer structures devoted a large number of works. The vast majority of them are limited to the case of perfect thermal contact between the layers. However, according to the authors, the problems of thermal conductivity in multilayer structures using into account the imperfect thermal contact are insufficiently studied. The number of such studies is quite limited. Also, known studies are usually limited to two layers. That is because the increase in the number of layers (given the choice of methods of practical implementation) leads to several computational difficulties. Therefore, the problem of constructing an effective analytical scheme for the study of heat transfer processes in multilayer structures in the presence of imperfect thermal contact between the layers remains an urgent task.Purpose. Application of the direct method to the study of heat transfer processes in the system "continuous cylinder inside a multilayer cylindrical shell" with imperfect thermal contact.Methods. An auxiliary problem set for the distribution of the temperature field in a multilayer solid cylindrical hollow body (a cylinder of the sufficiently small radius is "removed") taking into account the imperfect thermal contact between the individual layers. According to the already known scheme of the direct method solve this problem.Results. Boundary transition obtained the solution of the original problem. Boundary transition: the radius of the"removed" cylinder, with the centre at the origin, goes to zero. This approach established that the solution to the problemis limited in the whole structure. In this case, the solution obtained explicit formulas.Conclusions. Effective analytical scheme constructed for application of the direct method to the study of heattransfer processes in multilayer hard cylindrical solids taking into account the non-ideal thermal contact between thelayers. The number of layers, their size and arrangement are considered arbitrary.

MODELING THE PROCESS OF OPERATION OF HIGH-SPEED EQUIPMENT AND THE INFLUENCE OF THERMAL PARAMETERS ON WORKING BODIES

Introduction. The article is devoted to the study of heat transfer processes occurring in space and time. Therefore, the study of thermal conductivity is reduced to the study of space-time temperature changes. Distinguish between stationary and non-stationary temperature fields. A non-stationary temperature field is a field whose temperature changes not only in space, but also over time. A stationary temperature field is a field whose temperature at any point does not change over time. Materials and methods. To solve problems associated with finding the temperature field, it is necessary to have a differential equation of thermal conductivity, which gives the relationship between temperature, time and coordinates of the elementary volume. The differential heat conduction equation describes the transfer of heat inside the body. In order to find the temperature field inside the body at any moment of time, that is, to solve the differential equation, it is necessary to know the geometric shape of the body and the boundary conditions. Boundary conditions consist of initial and boundary conditions. Research results. As a result of modeling the process of upsetting during stage-by-stage deformation, including 30 steps at each impact (total of 3 impacts) using the QForm-2D software package, maps of stress and strain distribution over the volume of the workpiece were obtained. Discussion and conclusions. The main process parameters influencing the nature of the technological force are the accumulated deformation and the resistance of the material to plastic deformation. From the analysis of the obtained pictures of the distribution of deformation over the cross section of the sample after upsetting, that under the accepted conditions it is uneven. The greatest accumulated deformation is observed in the center and in the peripheral layers on the contact surface, and in other areas its value is less than 0.1. The same unevenness is shown by the stress distribution pattern. This is explained by the fact that with an increase in the degree of deformation, the rate of heat release decreases in the same zones where the maximum accumulated deformation is concentrated.

Simulação de processos de transferência de calor aplicada à indústria alimentícia com enfoque em produtos cárneos


 
 
 
 O objetivo desse artigo é o estudo dos processos de transferência de calor em produtos cárneos. A metodologia adotada foi o fracionamento da carne do tipo “coxão mole”, a construção de uma malha igualmente espaçada nas coordenadas x e y e a aferição das temperaturas nas regiões nodais em diferentes intervalos de tempo. A partir da temperatura calculada no tempo zero, pode-se prever as temperaturas nos demais tempos, utilizando o método explícito das diferenças finitas e, assim, foi possível comparar os resultados obtidos com as temperaturas experimentais. Os erros encontrados entre os dados experimentais e os calculados foi da faixa de oitenta por cento, distorção que pode ser justificada pelos erros associados ao experimento. Ademais, por meio da aferição das temperaturas centrais pode-se estudar a cocção da carne e classificá-las como mal passadas, ao ponto ou bem passadas. Conclui-se que o experimento obteve êxito no estudo do método das diferenças finitas bem como na análise da importância dos fenômenos de transferência de calor na indústria alimentícia.
 
 
 

Experimental study of heat transfer processes during the operation of WWER steam generator in emergency mode on a single-tube model

The paper presents the results of experimental research of the heat transfer processes during the operation of a WWER steam generator in emergency condensation mode. The experiments are carried out at a research facility with a test section in the form of a single-tube model of a steam generator. The geometric characteristics of the tube and the main research parameters, such as temperature and pressure, are similar to the real steam generator. Several stages of research are planned: with pure water steam, with a fixed concentration of boiling boric acid and with a variable concentration of acid in the solution. The results of the first series of experiments performed on pure water steam are presented. As a result of research, the heat flux density is determined, and the values of the heat transfer coefficient during steam condensation in a single horizontal tube are calculated.

Дослідження процесу теплопередачі в циліндрах двигуна внутрішнього згоряння

The article analyzes scientific publications and literary studies of heat transfer processes in cylinders of internal combustion engines. The research of temperature fields in engines during their operation at different modes with the use of a software package and calculation module is presented. The results of modeling and thermo-metering in homogeneous and laminated engine cylinder liners are analyzed. Graphic dependencies and temperature distribution by cylinder wall thickness at maximum and minimum temperature on cylinder surface are given. On the basis of researches it is established that at laminating and pressing of inserts temperature fields in the engine cylinder change, temperature on an internal surface of the cylinder increases at laminating on 6,5 °С, and at pressing - on 4,5 °С. This is explained by the fact that the contact layer during plastification is in the zone of non-stationary mode, and when pressing the contact layer is in the zone of stationary mode and thus increases the thickness of the cylinder by 2 millimeters. It is established that the difference of minimum and maximum temperatures on the inner surface of the cylinder practically remains the same as that of a homogeneous cylinder. Thus, modeling becomes the most effective scientific tool in the development and implementation of long-term evaluation of options for improving ICE.

Temperature imaging of mobile BaMgAl10O17:Eu phosphor aggregates under high radiation flux

Planar laser-induced phosphorescence (PLIP) has been used for the temperature measurement of suspended phosphor aggregates. Two-dimensional surface temperature of fluidized phosphor aggregates was measured through a pair of spatial and wavelength resolved images in an environment where phosphors are heated by high-flux radiation. The heating was supplied by a multi-diode laser system which provides a well-characterized high-flux radiation up to 28.87 MW/m2. Phosphors made of BaMgAl10O17:Eu (BAM) were selected as the material and suspended in a fluidized bed. Single-shot temperature imaging of BAM aggregates were inferred and compared at several heat fluxes. With the increasing heat flux up to 28.87 MW/m2, the BAM aggregates were found to exhibit a wider range of temperature distribution, and the maximum average aggregate temperature achieved 723 K, while the maximum temperature of a single aggregate could reach up to 1063 K. The wider temperature distributions that observed under higher radiation fluxes were caused by the elevated temperature of cooling air and the non-uniform aggregate surfaces. This non-intrusive method of measuring temperature offers advantages over other available methods in the study of heat transfer processes involving high-temperature reactions.

Virtual thermal tests of heating devices

To determine the values of the nominal indicators of heating devices, thermal tests are carried out. Analysis of the literature data has shown that, despite the widespread use of mathematical modeling for the study of heat transfer processes in heating devices, there is no comparison of test data and modeling. The purpose of this study is to test a heating device in a chamber (an indoor convector with a natural impulse of air movement) and compare it with the results of modeling. To assess the possibility of using and accuracy of modeling tests of heating devices, the data of tests of the indoor convector with natural convection “Golfstream” KRK 20.11.150 (LLC “Izoterm”), performed by the Institute “HLK Stuttgart” (Germany), were accepted. Modeling of the test chamber and convector is based on the FloEFD software package of “Axis Engineering” company. During virtual thermal tests of the convector, a heat flow was obtained that differs from the data of the convector tests on the test stand by 4.9%. It is concluded that it is possible to conduct virtual tests to optimize the design of heating devices and obtain the thermal characteristics of heating devices under all operating conditions and modes.

SIMULATION OF HEAT EXCHANGE IN A MULTILAYER FLAT STRUCTURE UNDER PERFECT THERMAL CONTACT IN FIRE CONDITIONS

The proposed work is devoted to the application of the direct method to the study of heat transfer processes in a multilayer flat structure. It is assumed that each layer is made of isotropic material of different thickness. There is an imperfect thermal contact between them, and the layers have internal heat sources. In this case, the isothermal surfaces are parallel planes, i.e the temperature changes in only one direction. On the outer surfaces of the structure there is a convective heat exchange with the environment, i.e the boundary conditions of the third kind are fulfilled. The coefficients of the thermal conductivity equation are considered to be piecewise constant with respect to the spatial coordinate. This is the first time the problem has been solved in this setting. The solution of the problem is realized by applying the method of reduction using the concept of quasi-derivatives and applying the theory of systems of differential equations with impulse action. The following is the procedure for separating Fourier variables using a modified method of eigenfunctions.Based on the physical content of the problem, the differential equation of thermal conductivity was written in the Cartesian coordinate system, but the solution scheme presented here without any fundamental difficulties extends to similar problems for multilayer bodies of basic geometric shapes by switching to appropriate coordinate systems. To illustrate the proposed method, a model example of finding the distribution of a nonstationary temperature field in a seven-layer flat structure under the influence of the hydrocarbon temperature of the fire is solved. The condition of ideal or non-ideal thermal contact is fulfilled between two adjacent layers. In addition, some layers have internal heat sources. The results of the calculations are presented in the form of a graph of temperature changes depending on timeand spatial coordinates.

Photoacoustic Spectroscopy for Curing Time Determination of an Acrylic Nanocomposite

Photoacoustic spectroscopy (PAS) has been widely used as a nondestructive and sensitive analytical technique used to determine the thermal diffusivity, effusivity and heat capacity of different materials. In this work, the open cell photoacoustic technique (OPC) technique was used for the kinematic study of heat transfer processes as a function of time for curing nanoresin composites. An exponential growth of the signal during the process of curing was observed. The nanoresin was based on silver nanoparticles (AgNPs) that were synthesized using a green method from an aqueous extract of Capsicum annuum var annuum as an Ag reducer and an acrylic resin. It was cured using a violet laser beam with a wavelength of 405 nm with an average power of 120 mW. The characteristic curing time was measured as a function AgNPs concentration of 0.0, 5.16, 7.27, 11.85, 14.50, 16.86 and 20.96 × 10−4 vol%. The results showed an increase in the curing time of composite resin containing the AgNPs compared to the pure resin. This study has applications in printing parts using laser stereolithography.