Modeling Of Heat Transfer Processes Research Articles

Modelling of Heat Transfer Processes in Heat Exchangers for Cardiopulmonary Bypass

A model of the heat exchange process in the heat exchanger of the cardiopulmonary bypass device is proposed which allows for automation of the process of temperature regulation in the cardiopulmonary bypass with an accuracy of ±1 °C during cardiac surgery under controlled cooling and warming of the patient’s heart and brain. The purpose of this research is to create a concept and model of the temperature control circuit using the MSC Easy5 system, the creation of mathematical models of blocks of the temperature control circuit, and the description of the principle of temperature control in the cardiopulmonary bypass circuit. The model of the temperature control loop in the heat exchanger of the heart-lung machine was created using the MSC Easy5 system with a programmable microcontroller. The microcontroller implements a specialized temperature control algorithm in the C language. The model allows the creation of a full-fledged virtual prototype of a temperature control device in a heat exchanger, and helps to conduct virtual tests of the developed device at the design stage. The model identifies control system flaws and influences decisions made before producing an official prototype of the product.

Numerical Model for Heat Transfer Processes in Dry Ash Conveyors

Abstract The dry handling of bottom ash from coal-fired power plants has become more and more important in recent years due to a lack of water availability at the location of power plants or for environmental reasons. Hence, it is crucial that a sufficient cooling of the bottom ash can be ensured by the dry cooling air. In this work, a numerical model for the assessment of heat transfer processes in dry ash conveyors is developed and implemented via the software wolframmathematica. The model uses a newly introduced representative geometric quantity for ash particle geometry. In addition to the ash, cooling air is considered as an own phase for which a temperature solution is obtained. A numerical example, considering geometrical and operational data of an existing facility, shows that the main heat transfer between the ash and the cooling air takes place in the ash hopper, where convective heat transfer from ash to cooling air outweighs the effects from coke combustion and radiation from the boiler outlet area. The convective heat transfer in the ash hopper predominantly depends on the geometrical appearance, i.e., size and shape, of the particles, the grain density, as well as on the falling time/velocity. Conservatism of the calculation approach is indicated based on comparison of computed temperatures with measured data and literature values. The derived model can be used in future designs and projections of dry ash handling systems.

Теоретичні основи процесу охолодження тушок птиці після забою

One of the most important parts of the technological chain for the production of poultry meat is chilling carcasses after slaughter. In Ukraine, a more economic method of cooling - water-contact one is mostly used, which however does not guarantee the proper quality of finished products and is not allowed in the European Union. Actuality of theme. This article concerns the introduction of advanced technologies in the domestic poultry industry. The subject of research - thermophysical characteristics of the chilling processes of broiler carcasses. Purpose of the article is to substantiate the feasibility of using in the poultry industry technology for chilling carcasses of broilers by the hydroaerosol-air method. Research methods. Experimental research was performed using the method of local modeling of heat transfer processes between carcasses and a cooling medium of different type, analytical research – using differential equations, criterion dependences and similarity theory. Research results. It is experimentally established that at the same temperature for all types of chilling media tmed = 3 С ÷ 0 С, the mass velocity of their movement was, respectively, for water - w ≈ 0.2 m / s, for air and hydroaerosols - w ≈ 2.5 m/s ÷ 2.8 m /s, the heat transfer coefficient from the carcasses was: for water-contact method of cooling -v≤ 550.0 W / m2K, for hydroaerosol – g≤ 200.0 W / m2K, for hydroaerosol-air – gр≤ 106.0 W / m2K, for air – р ≤ 34.1 W / m2K. According to the results of comparative analytical studies of carcass chilling processes, the expediency of using the hydroaerosol-air method as one that ensures the quality of poultry meat at moderate operating costs has been proven. An algorithm for calculating the parameters of this process is proposed.

Assessment of radiation heat transfer influence on parameters of temperature fields of various design fuel rods

VVER-1000 reactors use cylindrical smooth-core fuel rods. Previously, a model to determe the fuel rod temperature field in a two-dimensional problem statement has been developed and verified. However, modelling assumptions do not consider the influence of variable thermophysical properties, radiation heat transfer, and the opening in the fuel rod on the final parameters of the temperature fields. The impact assessment is an urgent task to improve the economic efficiency of the fuel cycle and the capacity of power units. To develop models and study the features of energy release in nuclear reactors, a numerical package of thermophysical modeling COMSOL Multiphysics software is used. The simulation of temperature fields is performed based on the heat equation with an internal heat source, under the boundary conditions of the second kind at the ends of the fuel rod and the boundary conditions of the third kind on the side surface of the rod. Аn axisymmetric model in two-dimensional problem statement and a three-dimensional model of the fuel rod are developed. The temperature distribution fields are determined by the finite element method. The results of calculations of various design fuel rods are presented. The results have showen that the radiation heat transfer significantly affects the maximum fuel temperature (UO2). The impact degree of variability of thermophysical properties and radiation heat transfer is determined. It was found that the temperature characteristics under different specified conditions have a difference in the range of 15,5–282,0 K (0,8–14,4 %). The developed models are reliable and confirmed by the previously verified model, the characteristics of the fuel assembly used on the VVER-1000 units. The results presented can be used for mathematical modeling of heat transfer processes, both during the modernization of the equipment in operation, and during the development, design, and operation, which will increase the efficiency of electric energy generation at the power unit of a nuclear power plant.

Substantiation of the Project of an Environment Protection Thermal Protective Product for Disabled People Taking into Account the Impact of Environmental Factors of the Natural and Technical Environment

The article presents the research results of the impact of various environmental factors on the design parameters of heat-protective products for the disabled. It is shown that the assessment of the environmental friendliness and safety of this type of clothing must be considered in the framework of the complex dynamic system «external environment – clothing – people». Detailed attention is paid to the research of the effects of thermo-physical factors on human body of people with limited motor capabilities in negative ambient temperatures. Based on the results of the analysis, a working hypothesis of research has been put forward and confirmed. It was established that the design of a heat-protective product must be carried out taking into account the individual characteristics of the body, which are manifested in the complex elements interaction of the subsystems of the specified system. In the framework of this thesis, the analysis of the relationship of factors is carried out and parametric assessment of the adaptation of the disabled people to temperature variations is given. To justify the choice of material types and structural elements of the product, a mathematical model of heat transfer processes has been developed to provide a qualitative forecast of the thermal state of the human body.

Computer simulation of heat transfer processes in aircraft landing gear braking mechanisms

Landing gear brakes – multi-disc brakes, as the responsible mechanism of the aircraft, must have the lowest possible weight and dimensions, high performance, increased service life and reduced life cycle cost. Solving these problems will reduce the design and development cycle of multi-disc chassis brakes. To perform the calculations, a computer mathematical model based on the use of the finite element method is proposed, replacing the classical version of the calculation based on currently used mathematical models, taking into account the heating of the aircraft landing gear braking mechanism, which will increase the speed, accuracy of calculations and reduce their labor intensity. We have developed a computer mathematical model of heat transfer processes occurring in the friction elements of multi-disc landing gear braking systems at the second stage of landing using the COMSOL Multiphysics program. Based on the calculations performed using this model, it is possible to take into account the influence of various system parameters such as the number of friction disks, their diameter and thickness, the medium in the interstitial space, the size of the solver grid on the maximum heating temperature of the brake mechanism, the cooling rate, the calculation time and the calculation error. On the basis of the obtained experimental data, we can conclude about the preferable construction of the brake mechanism. For example, it is possible to produce friction plates, steel with application to the surface of the composite friction material, allowing it to maintain the necessary friction and thus reduce the dimensions and maximum temperature, wet-disc brakes. The results of this work can be applied not only in the aviation industry, but can also be used to calculate the mechanisms of multi-disc oil-loaded brakes, which are used in agricultural, forestry, construction, quarry and other special equipment. In future work, the developed model will allow carrying out calculations taking into account the changes of material properties depending on temperature, refining the geometry of the brake mechanism, taking into account periods of reverse thrust engines and aerodynamic brakes.

Образование дендритной структуры в кристаллах NiFeGaCo при выращивании способом Степанова

The process of growing crystals of the Ni-Fe-Ga-Co alloy by the Stepanov method has been developed. It was found that the structural perfection is disturbed by the formation of dendrites, which are distributed inhomogeneously both along the length and in the cross sections of the crystals. The blocking effect on the dendrites of crystals of the martensite phase, which appears when the samples are cooled to the temperature of the transition of the crystal to the martensite state, is found. The elemental composition of dendritic formations was studied and it was shown that the iron content in the dendrite is approximately 30% higher, and the gallium content is 40% lower than in the matrix. Based on the modeling of heat transfer processes in the real growth zone, taking into account the experiments performed, recommendations were obtained for suppressing the formation of dendrites

Mathematical modelling of heat transfer processes in a two-phase material with inclusions in the form of a ball layer absorbing penetrating radiation. 1. Hierarchy of simplified analogs of the heat transfer basic model

Mathematical modelling of heat transfer processes in a two-phase material with inclusions in the form of a ball layer absorbing penetrating radiation. 1. Hierarchy of simplified analogs of the heat transfer basic model

Generation of Supercontinuum in Filamentation Regime in a Water Droplet Containing Silver Nanoparticles at Low Temperature

Generation of supercontinuum (SC) was studied experimentally both in water droplets containing silver nanoparticles (NP) in the temperature range from 2 to 22°C and in droplet ice floes frozen to –15°C. It is established that intensity of SC emission exponentially decays along the droplet diameter following excitation by a train of femtosecond laser pulses and linearly increases with increase in NP concentration. Spectrum of SC emission generated in a water droplet containing NPs is investigated in the presence of localized plasmons producing fluorescence in the vicinity of 430 nm. Propagation of a thermal wave along the diameter (d = 1.0 mm) of a small frozen droplet at a speed of 190 mm/s accompanied by exponentially decaying SC emission is discovered. Mathematical model of heat-transfer processes in an ice floe upon thermal-wave formation is proposed.

Fractional order, discrete model of heat transfer process using time and spatial Grünwald-Letnikov operator

Fractional order, discrete model of heat transfer process using time and spatial Grünwald-Letnikov operator

Variations of low temperature fumaroles as a tool for detecting changes in volcanic activity state: a brief overview

Abstract. Fumarolic fields, especially those with near-surface soil temperature <100 ∘C, are very common features of active or quiescent volcanoes, with both open or closed conduits. Their spatial extent, as well as the time variability of their temperature, are conditioned by three main factors: (1) Local hydro-meteorological conditions; (2) Vapor flow from the underlying volcanic-hydrothermal system; (3) Permeability variation induced by stress field changes and/or deposition dissolution cycles of hydrothermal alteration minerals. Once depurated from the exogenous noise, time variations of the thermal signal, in term of both short-lasting transients and medium/long term trends, reflect changes in the activity state of the related volcanic system, and/or of seismic activity, also of tectonic origin, affecting volcanoes. Theoretical models of heat transfer processes are discussed, highlighting how it is very difficult distinguish between conductive and convective mechanisms or calculating heat fluxes: as a consequence, thermal data from low temperature fumaroles should be used as qualitative proxies of volcano-tectonic phenomena acting on the monitored volcanoes. Following the description of the measuring systems and of the criteria for designing a performing network for thermal monitoring of fumaroles, some case histories from Italian volcanoes (Vulcano, Stromboli, Mt. Etna, Mt. Vesuvius) are presented, illustrating how in the last years the monitoring of low temperature fumaroles have given useful insights on the evolution of the activity state of these volcanoes.

Modeling heat transfer processes in heating systems for surface of highways

At present, icing of the road surface has a significant impact on traffic safety, which reduces the coefficient of adhesion of tires by 5–10 times. In order to reduce this negative effect in winter, frictional, chemical, physical-chemical and combined methods of struggle are used. In this case, one of the most promising ways to combat icing is to use a hydraulic system for snow melting. This is due to the possibility of laying not only individual systems of snow melting under the road surface, but also urban heat communications on road sections subject to frequent ice formation. In this regard, the modeling of heat transfer processes in heating systems for road surfaces is relevant. The proposed mathematical description, as well as its implementation in the Abaqus software package based on finite element calculations, makes it possible to determine the temperature on the surface of the highways taking into account the coolant supply, the location of pipes, their diameter and depth, air convection temperature and a number of other parameters. In this regard, the developed simulation model of the hydraulic system for heating the surface of highways will be widely used in the reconstruction of road surfaces, as well as for the optimization of heating network laying systems.

Thermoelectric Installation for Dehumidification and Heating of Air in Livestock Premises

General supply and exhaust ventilation is used to combat high humidity in livestock premises. The possibilities of this method in maintaining the air parameters within the required limits are limited. Dehumidifiers based on various physical principles help solving the problem of high humidity. (Research purpose) The research purpose is in substantiation of a rational functional and technological scheme for the installation of dehumidification and heating of air based on Peltier elements in the premises of agricultural production, based on the results of its physical modeling, developing, and testing of a working sample. (Materials and methods) Authors used methods of system analysis and synthesis of existing knowledge in the research field on the development of energy-efficient dehumidifier and air heater based on the theory of heat and mass transfer and thermoelectricity. The article presents a functional and technological scheme of the dehumidifier and air heater based on thermo-electric Peltier elements. Authors developed a prototype sample and performed physical modeling of heat transfer processes from thermoelectric assembly to heat carriers. The article presents a method for calculating the heat and power design parameters of heat exchange devices on the cold and hot sides of the thermoelectric assembly. (Results and discussion) It was found that the heat energy withdrawn by the hot circuit and directed to heating the dried air exceeds the energy consumed from the electrical network by 20-30 percent. (Conclusions) This design solution reduces the energy consumption of a thermoelectric dehumidifier compared to traditionally used equipment. Thermoelectric dehumidifiers are environmentally safe and are intended for small-scale agricultural areas with an air capacity of up to 500 cubic meters per hour.

Численное усреднение для задач теплопереноса в условиях криолитозоны

В работе рассматриваются задачи теплопереноса с учетом фазовых переходов влаги в промерзающем/протаивающем грунте. Математическая модель процессов теплопереноса с фазовым переходом описывается классической моделью Стефана и представляет собой нелинейное параболическое уравнение. Для решения задачи предложен метод численного усреднения для нелинейной задачи с использованием эффективных коэффициентов теплопроводности и объемной теплоемкости для талой и мерзлой зон. Вычисления эффективного тензора теплопроводности проводится в локальных областях (ячейки грубой сетки) и используются при построении аппроксимации на грубой сетке методом конечных элементов. Численная реализация конечно-элементной аппроксимации проведена с помощью вычислительной библиотеки FEniCS. Представлены численные результаты для двумерной и трехмерной модельных задач. The work considers heat transfer problems taking into account phase transitions of moisture in the soil. The mathematical model of heat transfer processes with phase transition is described using the classical Stefan model and is a nonlinear parabolic equation. To solve the problem, a numerical homogenization method is proposed for the nonlinear problem using the effective thermal conductivity coefficient for thawed and frozen zones. The calculation of the effective thermal conductivity tensor is carried out in local domains (coarse mesh cells) and is used to construct the approximation on a coarse mesh by the finite element method. Numerical implementation was carried out using FEniCS computational library for finite element approximation. Numerical results are presented for the model problem in two-dimensional and three-dimensional formulations.

Краевая задача для уравнения параболического типа в нецилиндрической области

Излагается применение метода разложения по собственным функциям самосопряженного дифференциального оператора к решению одной нестационарной задачи теплообмена с фазовым переходом на примере процесса промерзания некоторой сплошной среды. Получено приближенно-аналитическое решение задачи в неавтомодельной постановке при специальных начальных условиях. Решение задачи начинается с ее преобразования к области с неподвижными границами, затем для решения преобразованной задачи строится конечное интегральное преобразование с неизвестным ядром, нахождение которого связано с постановкой и решением соответствующей спектральной задачи через вырожденные гипергеометрические функции. Находятся собственные значения и собственные функции, а также формула обращения для введенного интегрального преобразования, что позволяет выписать аналитическое решение задачи. В ходе решения задачи устанавливается параболический закон движения границы раздела двух фаз. Задачи подобного типа возникают при математическом моделировании процессов теплообмена в строительстве, особенно в районах вечной мерзлоты, в нефтегазодобыче при бурении и эксплуатации скважин, в металлургии и т.д. We present an application of the method of the eigenfunction decomposition of a self-adjoint differential operator to the solution of a non-stationary heat transfer problem with phase transition with the freezing process in a continuous medium as an example. An approximate analytical solution of the problem in a non-automodel formulation under special initial conditions is obtained. The solution of the problem starts with its conversion to a region with fixed boundaries. Then, for the solution of the transformed problem, we construct a finite integral transform with unknown core, finding of which is associated with formulation and solution of corresponding spectral problems using the degenerate hypergeometric functions. We find the eigenvalues and eigenfunctions, as well as an inversion formula for the introduced integral transform, which allows us to obtain an analytical solution to the problem and consider a number of special cases. While solving the problem, we establish the parabolic law of motion of the interface between the two phases. Problems of this type arise in the mathematical modeling of heat transfer processes in construction, especially in the permafrost areas, in oil and gas production during drilling and operation of wells, in metallurgy, etc.

Mathematical Modeling of Heat Transfer Processes in a Solid With Spherical Layer-type Inclusion to Absorb Penetrating Radiation

The paper deals with determining a temperature field of an isotropic solid with inclusion represented as a spherical layer that absorbing penetrating radiation. A hierarchy of simplified analogues of the basic model of the heat transfer process in the system under study was developed, including a “refined model of concentrated capacity”, a “concentrated capacity” model, and a “truncated model of concentrated capacity”. Each of the mathematical models of the hierarchy is a mixed problem for a second-order partial differential equation of the parabolic type with a specific boundary condition that actually takes into account the spherical layer available in the system under study.The use of the Laplace integral transform and the well-known theorems of operational calculus in analytically closed form enabled us to find solutions to the corresponding problems of unsteady heat conduction. The “concentrated capacitance” model was in detail analysed with the object under study subjected to the radiation flux of constant density. This model is associated with a thermally thin absorbing inclusion in the form of a spherical layer. It is shown that it allows us to submit the problem solution of unsteady heat conduction in the analytical form, which is the most convenient in terms of both its practical implementation and a theoretical assessment of the influence, the spherical layer width has on the temperature field of the object under study.Sufficient conditions are determined under which the temperature field of the analysed system can be identified with a given accuracy through the simplified analogues of the basic mathematical model. For simplified analogues of the basic model, the paper presents theoretical estimates of the maximum possible error when determining the radiated temperature field.

The Morphology and Mechanical Properties of ESD Coatings before and after Laser Beam Machining.

Electro-spark deposition (ESD) and laser beam machining (LBM) are the technologies using the concentrated energy flux. This paper deals with the issue of the impact of laser modification on the morphology and mechanical properties of carbide/copper coatings produced by electro-spark treatment. The coatings were applied to C45 carbon steel samples using the EIL-8A device. The following three types of electrodes made using the powder metallurgy (PM) hot pressing technique, from copper and tungsten carbide powders of different percentage compositions, were used for the coatings: 25% WC and 75% Cu; 50% WC and 50% Cu; and 75% WC and 25% Cu. Laser modification of the surface layers was performed with an Nd:YAG laser. The research focused on the analysis of the morphology of coatings applied by electro-spark technology before and after laser processing. The analysis of the morphology of electro-spark coatings revealed that the coatings had microcracks and pores. The laser beam machining of ESD coatings led to the homogenization of chemical composition, fragmentation of the structure, and elimination of microcracks. In addition, measurements of porosity, microhardness, adhesion, and analysis of XRD phase composition of the electro-spark coatings were performed. Laser processing proved to have a positive effect on improving the adhesion of coatings and reducing their porosity. This paper also presents a simulation model of heat transfer processes for the case of laser radiation impact on a WC-Cu coating. The developed numerical model, describing the influence of laser treatment on the distribution of temperature fields in the heated material (at a given depth) is of significant importance in the development of treatment technologies. Laser-modified ESD coatings perform anti-wear and protective functions, which enable their potential application in means of transport such as rolling stock.

The mathematical description of process of heat exchange particles of oil shale and ash the coolant in the semi-coking conditions in a rotating drum reactor installation with solid heat carrier

The article deals with the modeling of heat transfer process in a drum reactor of a semi-coking unit of oil shale with a solid coolant between ash and shale particles in the conditions of constant separation of vapor-gas products. The dominant role of the convective component of the process is revealed and the curves of heating of shale particles are obtained taking into account the endothermic effect.It is established that the smallest fraction of fuel warms up within 30-60 seconds and further serves as a source of heat for other fractions. In the interval of 400-600 seconds, the heating of the largest fraction is completed. The further stay of the shale mixture in the reactor is caused by the lagging rate of the thermal decomposition process from heat exchange, and the temperature decrease by 20-250C by the presence of the endothermic effect of the decomposition of organic matter.

Methods for optimization of time redundancy of prosumer in district heating systems

The paper deals with the problem of operating the reliability of prosumers as part of a district heating system, taking into account overload time redundancy that they possess. This time redundancy can be both passive, caused by heat accumulating effect and use of thermal energy storages, as well as an active time redundancy, which is provided by additional heating by its own heat source. Methods to determine the optimal level of this time redundancy of heat prosumer were developed based on search the minimal cost of ensuring required values of restoration rates of system components, taking into account the functions of prosumers. Methodology is based on the use of nodal reliability indices, models of Markov processes, aggregated model of heat transfer processes in heating of consumers, Rossander equation, models of the theory of hydraulic circuits.

Non integer order, state space model of heat transfer process using Atangana-Baleanu operator

Non integer order, state space model of heat transfer process using Atangana-Baleanu operator