Modeling Of Thermal Processes Research Articles

Strong Skin Cooling and Its Impacts on Lake Thermal Processes in a Large Lake on the Tibetan Plateau

Abstract Skin cooling, wherein the surface temperature of a water body Tskin is lower than the temperature below the surface, is a widespread phenomenon. Previous studies have almost ignored this effect on the Tibetan Plateau (TP), despite the presence of thousands of lakes on the TP and the fact that extraordinary solar heating leads to very strong energy exchanges on the lake surfaces. This study utilizes in situ observations and MODIS-derived Tskin data at Lake Nam Co, one of the largest lakes on the TP, to quantify the skin cooling effect. The observed nighttime skin cooling is approximately 0.52°C on average, with the maximum of about 1°C, during the lake water turnover period (from October to mid-November), which obviously surpasses reported values for oceans (less than 0.4°C). To understand the impact of the skin cooling on the lake thermal processes, a skin cooling parameterization is validated and incorporated into the WRF-lake model. Simulations with the updated model show that accounting for the skin cooling process systematically lowers sensible and latent heat fluxes by a few watts per square meter, which yields an increase in water temperature by 0.45°C at the end of December and may delay the onset of lake freeze. Finally, we show that the inclusion of the skin cooling process in a lake model needs simultaneous adjustment of the parameterization of heat/water vapor transfer. Significance Statement Skin cooling is a widespread phenomenon for a water surface, and its intensity depends on the energy flux exchange of the water surface. The Tibetan Plateau possesses the presence of thousands of lakes, but early studies have ignored the skin cooling effect. We found that the nighttime skin cooling magnitude during the lake water turnover period in this region obviously exceeds reported values for oceans, due to the strong surface energy exchange in the Tibetan Plateau. Neglecting the skin cooling process may lead to systematic overestimation of turbulent heat fluxes and underestimation of water temperature. We highlight that accounting for this skin cooling process is crucial to select appropriate parameterization schemes for heat/water vapor transfer in lake thermal process modeling.

Review of Modeling Approaches for Conjugate Heat Transfer Processes in Oil-Immersed Transformers

This review addresses the modeling approaches for heat transfer processes in oil-immersed transformer. Electromagnetic, thermal, and hydrodynamic thermal fields are identified as the most critical aspects in describing the state of the transformer. The paper compares the implementation complexity, calculation time, and details of the results for different approaches to creating a mathematical model, such as circuit-based models and finite element and finite volume methods. Examples of successful model implementation are provided, along with the features of oil-immersed transformer modeling. In addition, the review considers the strengths and limitations of the considered models in relation to creating a digital twin of a transformer. The review concludes that it is not feasible to create a universal model that accounts for all the features of physical processes in an oil-immersed transformer, operates in real time for a digital twin, and provides the required accuracy at the same time. The conducted research shows that joint modeling of electromagnetic and thermal processes, reducing the dimensionality of models, provides the most comprehensive solution to the problem.

Numerical modelling of the warping behaviour at the first layer-build plate interface in 3D-printed models produced via the fused deposition modelling process

The material structure of 3D-models printed via the fused deposition modelling (FDM) technique is mainly affected in the z-direction of the 3D-print as a result of the layer-by-layer approach which tend to exhibit a deformation behavior corresponding to a type of transversely orthotropic material. Moreover, uncontrolled parameters such as printing temperature and printing speed have been reported to adversely affect 3D-print quality leading to undesired effects such as distortion and warpage. The additive manufacturing process is a relatively new field in advanced manufacturing where further research and innovation are required to overcome the limited strength and structural performance observed in presently 3D-printed components. In line with the above, this study proposes the numerical investigation of the warping behavior in PLA (Polylactic acid) - based 3D printed models by considering the finite element method (FEM) software of LS-DYNA. The warping investigation was specifically centered on the cooling cycle prevailing between the layer-by-layer structures. The findings of this study showed that warpage would most likely occur in the thermal process model corresponding to abrupt change in temperature due to a buildup of strain between the bottom most layers of the 3D model and the build plate. The findings of this study, which shed light on the warping behaviour in 3D-models, has direct implications on the final quality of 3D-printed components.

CFD modeling of thermal processes in the firebox and heat load distribution on the screen surface firebox

Using ANSYS FLUENT numerical modeling and mathematical modeling, the main characteristics of combustion processes during the combustion of natural gas were determined. In this work, the combustion processes and NOx formation in the firebox were modeled at different loads of the GM- 50-14/250 boiler. The temperature distribution along the height of the firebox and the heat load on the screen panels were determined. The results of calculations by two types of models were compared with each other and with the data of measurements on the operating equipment. The environmental performance of the firebox, namely the formation of NOx at different heat loads, was determined. The maximum boiler capacity at which its operation meets European environmental standards was determined. The deviation of calculations on the formation of NOx in the GM-50-14/250 boiler at 40% of the rated power compared to the results of field tests using ANSYS FLUENT modeling was 8%, and using the mathematical model - 27%. When operating at rated power, the deviations of the results decreased to 2% and 8%, respectively. The deviation of the results of thermal calculations of the combustion in the firebox by different types of modeling in the active combustion zone and at the outlet of the firebox is up to 3% at different loads.

Solving a nonlinear problem for a one-sided dynamically loaded sliding thrust bearing

The purpose of this study is to propose an efficient numerical method for solving the inverse nonlinear problem of the movement of the compressor rotor collar in a fluid film thrust bearing. Methods. A periodic thermoelastohydrodynamic (PTEHD) mathematical model of hydrodynamic and thermal processes in a bearing is constructed under the condition of the rotor collar motion. Within the framework of the model, an inverse nonlinear problem of determining the position of the collar under a given external load is formulated. An iterative solution method is proposed, which utilizes the solution of the direct problem. To reduce computational costs, a modified Dekker–Brent method is employed in conjunction with a modified Newton’s method. Results. Numerical experiments have been conducted, demonstrating the effectiveness of the proposed approaches. The suggested methods significantly reduce the required computational resources by minimizing the number of calls to the target function in the optimization problem. A software suite has been developed that allows for the calculation of the nonlinear system of rotor motion under various physical and geometric parameters. Conclusion. An efficient set of numerical methods for solving the inverse nonlinear problem of the motion of the rotor collar in the compressor fluid film thrust bearing is proposed. The method’s effectiveness lies in substantial savings of computational resources. The method’s efficiency has been demonstrated in numerical experiments.

MATHEMATICAL MODELING OF NON-STATIONARY HEAT PROCESSES IN THE GROUND HEAT PUMP SYSTEM

In the work, an analytical study of the efficiency of heat pumps using soil energy for heating, taking into account the climatic conditions of theregion of operation, is performed, which meets the tasks of energy saving and allows reducing emissions of harmful substances into the environment. The main attention is paid to increasing the efficiency of utilization of the technical potential of the soil energy source by the heat pump system using vertical soil heat exchangers. A methodology based on use of the mathematical modeling apparatus as a scientifically based toolkit for calculating non-stationary thermal processes, capable of ensuring the stability and reliability of the ground heat pump system in the short and long term, is proposed. The developed toolkit for calculation and analysis of heat exchange processes allows determining the power of the heat flow, which is removed from the soil, taking into account changes in climatic factors, temperature distribution in the soil around the soil tube and along its length over time, schematic and structural features of the soil tubes for further optimization of the parameters of the heat pump system . It was established that the power of the heat flow, which enters the evaporator of the heat pump from vertical soil pipes, depends on a number of influencing factors: the flow regime of the working fluid circulating in the soil circuit; physical properties of the working body; number of soil heat exchangers; temperature distribution in the soil around the soil tube along its entire length, which changes significantly during long-term operation of the system, affecting the course of heat exchange processes in the system elements. The proposed method makes it possible to perform numerical modeling of thermal processes in the elements of the heat pump, to determine the energy efficiency of the ground heat pump system, which is able to reliably provide consumers with heat during a long period of operation, which can be considered an innovative approach to the analysis of prospects for the development of heat pump heat supply.

Сomputational approach to thermal-stressed state modeling of tire based on the algorithm of its self-heating analysis. Part 2 – Practical results of applying the approach

Elastomers and their composites are widely used in modern innovative technology: for the production of aviation and automobile tires, anti-vibration elements (rubber, rubber-metal springs), dampers, elastomeric bearings. Also they are used in shaft suspensions, as spacers between structural parts, supporting parts and fasteners. Elastomeric elements of structures have a high dynamic load, in particular of a cyclic nature, which is accompanied by the formation of hysteresis loops and, as a result, the occurrence of the phenomenon of self-heating. An increase in temperature in the middle of materials causes significant changes in their mechanical properties, reduces strength characteristics, accelerates aging and degradation processes, and has a significant impact on fatigue processes. In addition, an increase in temperature causes an additional thermal stress state, capable of significantly changing the qualitative picture of the structure's deformation characteristics' distribution. Thus, the purpose of this study is development of approach to assessing the thermal stress state of structures made of elastomeric materials for the possibility of further analysis of its influence on the structure work as a whole. The appropriate approach was built on the basis of numerical modeling of thermal and deformation processes which takes place into the structure during operation. The proposed approach includes several related calculations by using FEM and is based on the fundamental approaches of the theories of elasticity and viscoelasticity, thermal conductivity and thermo-elasticity. Thus, the article presents an approach to the analysis of the thermal stress state of structural elements under operating conditions. This approach was applied to determine the thermo-strain-stress characteristics of a pneumatic tire and corresponding pictures of its distribution were obtained.

Modeling of thermal processes in vertical heat exchangers of ground-source heat pump

The basic directions for perfection heat supply systems are the tendency of transition to the low-temperature heating systems based at application heat pump installations. We consider heat supply systems with ground-source heat pump. The paper considers modeling the efficiency of ground-source heat pumps with the account of Ukrainian climate conditions. The paper presents the energy performance criteria which show the way to rational implementation of ground-source heat pumps for heating. A computational model based at non-stationary heat exchange processes in elements of ground-source heat pumps is developed. Generalization and analysis of theoretical and experimental dates allow establishing nature of dependence thermophysical properties on temperature insoil around ground heat exchangers during long term operation of the system. Numerical simulation of thermal processes in vertical ground pipes for ground-source heat pump working with low-temperature heating systems has been worked out. The results of numerical modeling demonstrated perfection and technical adaption of ground-source heat pump for low-temperature heating systems with rational using ground energy potential. The novelty of our method is complex usage theoretical and experimental results which enable to prevent freezing in the ground during long term exploitation This provides insights at effects of different resource mixes and may serve as a new approach to analysis of future heat pump systems using ground source energy development.The proposed method contributes to the field of creation and implementation the sustainable heating technologies using renewable energy sources. The ground heat exchange pipes quantities that are necessary for effective operation heat pump installation, capacity and coefficient of performance with the account of climate conditions are calculated.

Plasma spraying of Al2O3‑Al composite coatings

The article presents the results of modeling and analysis of thermal processes during plasma spraying of Al2O3–Al composite coatings. Modeling was carried out for composite particles with spherical symmetry, taking into account the influence of phase transitions during the melting and evaporation of dissimilar materials in the aluminum‑aluminum oxide system and various particle sizes based on a mathematical model of non‑stationary thermal conductivity, taking into account internal heat sources during phase transitions. The results of studies of the microstructure of composite coatings after plasma spraying of Al2O3–Al based powders, synthesized during metallurgical processing of aluminum matrix quartz‑containing compositions, are presented.

Dynamic ideality for electron beam welding

Experimental methods for evaluating performance of electron beams are both time consuming and costly, with favourable parameters chosen based on a subjective standard. Correlation of the weld geometry against conventional machine input parameters such as voltage, focus, and current involves complex interaction phenomena. This renders it difficult to deconvolute the influence of these inputs against applied energy distributions within a setup. In this work, a process window was generated across a range of weld powers and speeds with focal positions adjusted to achieve the same nominal spot size and hence mitigate input parameter interaction phenomena. The variability of spot size using this method can be reduced by 90% against using the conventional method of optically acquiring weld focus. To reduce reliance on empirically derived heuristics in parameter selection, weld performance was quantified through an aggregated output quality termed ‘ideality’ as a function of conventional weld geometry, imperfections, and characteristic microstructural evolution/transformation. The ideality metric was shown as a method of achieving the least harmful compromise of parameter conflicts. A method of using a thermal process model to perform subsequent optimisation of ideality was presented. The ability to characterise inputs as a function of beam properties rather than machine inputs serves as a useful method to optimise weld procedures and serve as a basis for comparison between setups. While electron beam welding is used in this study to propose ideality, process outputs and inputs can be substituted for other process-specific outputs and inputs, enabling adoption for most manufacturing processes.

THERMAL FIELD IN A HORIZONTAL WELL APPLIED TO THE DETERMINATION OF FLUID FLOW BY ACTIVE THERMOMETRY

Today, in the context of falling oil production and increasing water cut, the importance of geophysical control over field development is increasing. A promising method of production logging is active thermometry, it is based on the creation of a thermal disturbance area in the wellbore, for example, due to induction heating of a section of a metal pipe (liner or casing, depending on the design of the well). As a result of heat exchange with a locally heated pipe section, heat marks are formed in the liquid, moving along the wellbore. The article presents the results of physical modeling of thermal processes during local induction heating of a section of a horizontal well. It has been experimentally established that with an induction heater power of about 1 kW and flow rates in the pipe up to 50 m3/day, the heating of the pipe wall reaches 12 K. As part of the experimental studies, the movement of heat marks was monitored using two modules of temperature sensors distributed over the pipe cross section. It is shown that the nature of temperature change in time is determined by the position of the temperature sensor in the pipe section. The greatest thermal anomalies are noted for sensors pressed against the pipe in its upper part, the smallest - for sensors located in the lower part of the pipe. The fluid flow rate in the pipe was estimated from the rate of passage of the heat mark between the temperature modules. It is shown that the calculated flow rate is overestimated relative to the actual one due to the influence of natural thermal convection, which causes the occurrence of a natural convective fluid flow in addition to the forced movement with a given flow rate. A new analytical solution has been obtained for calculating the dynamics of the pipe temperature in the induction heating section, a comparison of the results of calculations using the analytical model with the experimental results showed good agreement. The results of experimental studies can be used in interpreting the results of field logging wells using active thermometry, in particular, the sensitivity of the pipe temperature in the induction heating section to the flow rate can be used to solve inverse problems of estimating the flow rate in a pipe by measuring its surface temperature using the obtained analytical solution.

Self-Similar Solution to the Problem of Unsteady Film Condensation on a Vertical Semi-Infinite Plate

Changes in the regimes of condensate film flow along the underlying surface in the presence of a body force are considered within the framework of a simplified physical and mathematical model of hydrodynamic and thermal processes occurring under unsteady film condensation on a vertical semi-infinite plate. The model is used to determine the applicability conditions of the zero-gravity approximation when considering film condensation. It is found that the validity of using the zero-gravity approximation to calculate the film thickness growth rate on any plate section depends not only on the magnitude of the body force, but also on time and distance between this section and the leading edge of the plate.

Математичне моделювання електричних і теплових процесів в графітованих гнотових електродах для дугових сталеплавильних печей постійного струму

Математичне моделювання електричних і теплових процесів в графітованих гнотових електродах для дугових сталеплавильних печей постійного струму

Investigation of structural-phase transformations of weld metal and in the heat-affected zone during laser welding

The use of laser equipment is one of the promising ways to create innovative and highly efficient technologies in the production of ship structures. The main advantages of using laser technologies in the production of marine equipment are increased productivity by increasing the speed and reducing the number of welding passes, improving the quality of welded joints due to the accuracy of the assembly of structures and the level of automation, reducing the level of residual stresses, warping and leash due to significant localization of the heating and penetration zone compared with arc welding technologies, a significant reduction in the consumption of welding materials or their complete exclusion due to the smaller dimensions of the geometry of the cutting edges and the width of the assembly gaps. The mechanical properties of the welded joint are determined by the composition of the steel and its structure. The structural- phase transformations of the weld metal are determined by the temperature-time parameters that occur in the seam zone itself and in the heat-affected zone. Laser welded joints are formed under conditions in which thermal cycles differ significantly in depth and width of the weld, so the mechanical properties of the joint are determined by local changes in the structure of the seam metal and heat-affected zone. The issues of formation of the phase composition of the seam zone and heat-affected zone during laser welding are examined in the paper. On the basis of numerical modeling of thermal processes and structural- phase transformations of weld metal and heat-affected zone accompanying laser welding, a method for quantifying the volume fraction of structural- phase components of weld metal and heat-affected zone is proposed. The proposed calculation algorithm avoids solving the equation for the amount of the volume fraction of the structural- phase components of the metal at each step of the calculations.

Achieving local overheating and length scale control in density-based topology optimization

The main defect of additive manufacturing technology based on laser melting is that large thermal deformation is easily generated inside the part during the forming process. The traditional method is to adjust the process parameters, stress relief annealing and other hardware methods. From the point of view of design, this paper proposed a method to reduce the deformation by changing the product structure and configuration without changing the process form and design goals. The layer-by-layer thermal process model is considered as a constraint in the SIMP topology method, and the MMA is applied as the optimization solver to take care of the multi-constraints topology optimization. Then, the Heaviside based morphological filter is applied to control the minimum length of the part in the optimization results. The validity of the proposed method is tested by the MBB beam and cantilever compliance minimization problems.

Procedure for simulating radiators of liquid cooling systems of avionics

Setting the problem. Analysis and assessment of the thermal mode of radioelectronic equipment (RES) in modern radioelectronic equipment is the most important task that is solved at the stage of design and development of the future device. Therefore, the choice of cooling system for heat-loaded structures is an integral component that must be solved in the early stages of design. The use of a modern set of computer-aided design tools (CAD) throughout the entire process of creating RES allows you to take into account all possible problem areas without resorting to the manufacture of a layout and prototype. Modeling of thermal characteristics and heat exchange processes provides for modeling procedures and ensuring the thermal regime mainly at the stage of design and topological design. At the same time, the analysis of thermal characteristics, as a rule, carried out after solving any design synthesis problem (placement, layout, selection and development of block structures, racks, etc.), if the modeling results are unsatisfactory, the design changes. Thus, in order to reduce time costs and reduce the iteration of the design process, it is necessary to solve the issues of ensuring the thermal regime in the early stages. Most often, the problem can be solved by increasing the area of the heat-emitting surface (radiator), but in some cases there is a need for additional cooling, in our case, additional use of liquid cooling. This is the reason for the relevance of the development of the methodology for modeling radiators of liquid cooling systems of the RES. Purpose. Present the methodology for simulating radiators of liquid cooling systems of the RES, the reliability of which could be confirmed by the results of analytical calculations and data of a full-scale experiment. Results. A mathematical statement has been formed, a modeling technique has been proposed and procedures for optimizing the cooling system have been implemented. Based on the developed 3D model of a radiator with a liquid cooling system, multivariable analysis procedures are implemented using modern computer-aided design tools. The liquid cooling system was optimized using modern software modeling tools, in particular the Solidworks Simulation program.

Heat flow influence on the Cauchy stress tensor in a thermal wave

Rational thermodynamics with relaxing heat fluxes is used in this work to obtain the constitutive equations of thermoelasticity. It is found that it is possible to formulate the governing equations of the medium where the density of internal energy per unit mass depends on the heat flux, while the density of entropy per unit mass may not depend on it. A situation where the density of the entropy per unit mass depends on the heat flux, while the density of internal energy per unit mass does not, is also possible. A model of a thermoelastic material with a relaxing heat flux, where the characteristic relaxation time of the heat flux is a constant of the material, is considered in detail in this paper. It is shown that the Cauchy stress tensor in this model is not only a function of the temperature and deformations of the medium, but also depends on the heat flux. This gives rise to new effects not present in the classical theory of thermoelasticity. The specific heat of the material will also depend on the magnitude of the heat flux.The paper considers the application of the theory to the modelling of thermal processes during ion plasma treatment of a polymeric material.

Modeling of Thermal Processes in Prostate Tumors

Modeling of Thermal Processes in Prostate Tumors

Thermodynamic Modeling of Thermal Processes Involving Radionuclides of Uranium, Plutonium, Europium on Heating of Nuclear Graphite in Air

Thermodynamic Modeling of Thermal Processes Involving Radionuclides of Uranium, Plutonium, Europium on Heating of Nuclear Graphite in Air

A Predictive Damage-Tolerant Approach for Fatigue Life Estimation of Additive Manufactured Metal Materials

Metal Additive Manufacturing (AM) allows the fabrication of intricate shaped parts that cannot be produced with conventional manufacturing techniques. Despite the advantages of this novel manufacturing technology, the main drawback is the inferior fatigue performance of AM metal materials and parts due to the presence of process-induced defects that act as initial cracks. Reliable fatigue modeling methods that can assist the design and characterization of AM components must be developed. In this work, a computational damage-tolerance framework for the fatigue analysis of the AM metals and parts is presented. First, thermal modeling of the AM process for the part fabrication is performed to predict the susceptible areas for defect formation in the parts. From the processing of results, the characteristics of the critical defect are determined and used as input in a fracture mechanics-based model for the prediction of fatigue life of AM metals and parts. For validation purposes, the framework is utilized for the fatigue modeling and analysis of AM Ti-6Al-4V and 316L SS metals of relative experimental test cases found in the literature. The predicted results exhibit good correlation with the available experimental data, demonstrating the predictive capability of the modeling procedure.