Simulation Of Heat Flow Research Articles

2023: a soil odyssey–HeAted soiL-Monoliths (HAL-Ms) to examine the effect of heat emission from HVDC underground cables on plant growth

BackgroundThe use of renewable energy for sustainable and climate-neutral electricity production is increasing worldwide. High-voltage direct-current (HVDC) transmission via underground cables helps connect large production sides with consumer regions. In Germany, almost 5,000 km of new power line projects is planned, with an initial start date of 2038 or earlier. During transmission, heat is emitted to the surrounding soil, but the effects of the emitted heat on root growth and yield of the overlying crop plants remain uncertain and must be investigated.ResultsFor this purpose, we designed and constructed a low-cost large HeAted soiL-Monolith (HAL-M) model for simulating heat flow within soil with a natural composition and density. We could observe root growth, soil temperature and soil water content over an extended period. We performed a field trial-type experiment involving three-part crop rotation in a greenhouse. We showed that under the simulated conditions, heat emission could reduce the yield and root growth depending on the crop type and soil.ConclusionsThis experimental design could serve as a low-cost, fast and reliable standard for investigating thermal issues related to various soil compositions and types, precipitation regimes and crop plants affected by similar projects. Beyond our research question, the HAL-M technique could serve as a link between pot and field trials with the advantages of both approaches. This method could enrich many research areas with the aim of controlling natural soil and plant conditions.

Numerical simulation on the condensation heat transfer and flow characteristics outside smooth and enhanced tubes

Most of the current studies only conducts two-dimensional simulations of condensation heat transfer and flow outside enhanced tubes, which cannot accurately reflect the flow and heat transfer characteristics of liquid film outside enhanced tubes. In order to provide theoretical support for the design optimization of enhanced tubes, this study adopts the VOF multiphase model and Lee condensation model to simulate the condensation heat transfer(HTC) of refrigerants outside smooth and enhanced tubes. The instantaneous film flow characteristics of the liquid film outside the horizontal smooth and enhanced tubes are analyzed, and the thickness of the liquid film and the relationship with the condensation heat transfer coefficient of the smooth and enhanced tubes under different working conditions are calculated. The refrigerants are compared under the same working conditions, and the results are shown: The simulation results are in good agreement with the experimental data and the Nusselt analytical solution, and the error is all within 15%; the distribution of liquid film is highly sensitive to the magnitude of local condensation heat transfer coefficients, and the condensation HTC outside the enhanced tube is approximately six times of that of smooth tube. Combining the distribution of the liquid film and the thermophysical properties of the refrigerants, it was determined that R410A has the highest HTC, while R1234yf has the lowest HTC.

Integrated modeling to control vaporization-induced composition change during additive manufacturing of nickel-based superalloys

A critical issue in laser powder bed fusion (LPBF) additive manufacturing is the selective vaporization of alloying elements resulting in poor mechanical properties and corrosion resistance of parts. The process also alters the part’s chemical composition compared to the feedstock. Here we present a novel multi-physics modeling framework, integrating heat and fluid flow simulations, thermodynamic calculations, and evaporation modeling to estimate and control the composition change during LPBF of nickel-based superalloys. Experimental validation confirms the accuracy of our model. Moreover, we quantify the relative vulnerabilities of different nickel-based superalloys to composition change quantitatively and we examine the effect of remelting due to the layer-by-layer deposition during the LPBF process. Spatial variations in evaporative flux and compositions for each element were determined, providing valuable insights into the LPBF process and product attributes. The results of this study can be used to optimize the LPBF process parameters such as laser power, scanning speed, and powder layer thickness to ensure the production of high-quality components with desired chemical compositions.

A sigmoidal model for predicting soil thermal conductivity-water content function in room temperature

Apparent thermal conductivity of soil (λ) as a function of soil water content (θ), i.e., λ(θ) is needed to determine the heat flow in soil. The function of λ(θ) can be used in heat and water flow models for simplicity. The objective of this study was to develop a sigmoidal model based on logistic equation for entire range of soil water contents and a wide range of soil textures that can be used in simulation of heat and water flow in respected modes. Further, performance of the developed sigmoidal model along with two other models in literature was evaluated. In the proposed sigmoidal model, the constants of this model are estimated based on empirical multivariate equations by using soil sand content and bulk density. The sigmoidal model was validated with good accuracy for a wide range of soil textures, as the relationship between the measured and predicted λ showed slope and intercept values of nearly 1.0 and 0.0, respectively. Comparison of the results obtained by sigmoidal model with those obtained from Johansen and Lu et al. models indicated that, the sigmoidal model was superior to the other two models in prediction of λ for a wide range of soil textures and soil water contents. Furthermore, comparison with a recently proposed model by Xiong et al. indicated that our sigmoidal model is superior. Therefore, our developed sigmoidal model can be used in heat and water flow models to predict the soil temperature and heat flow.

Flexible and Thermally Insulating Porous Materials Utilizing Hollow Double-Shell Polymer Fibers.

The global climate change is mainly caused by carbon dioxide (CO2) emissions. To help reduce CO2 emissions and conserve thermal energy, sustainable materials based on flexible thermal insulation are developed to minimize heat flux, drawing inspiration from natural systems such as polar bear hairs. The unique structure of hollow double-shell fibers makes it possible to achieve low thermal conductivity in the material while retaining exceptional elasticity, allowing it to adapt to insulation systems of any shape. The layered system of porous mats reaches a thermal conductivity coefficient of 0.031 W∙m⁻¹∙K⁻¹ and enables to reduce the heat transfer. The results achieved using scanning thermal microscopy (SThM) correlate with the simulated heat flow in the case of individual fibers. This research study brings new insights into the energy efficiency of domestic environments, thereby addressing the growing demand for sustainable and high-performance insulation materials for saving energy loss and reducing pollution footprint.

Lattice-Based Boltzmann Simulation of a Two-Dimensional Heat Flow Involved in a Solid Oxide Fuel Cell with a Focus on Assessing Entropy Generation Depending on the Channel Shape

Lattice-Based Boltzmann Simulation of a Two-Dimensional Heat Flow Involved in a Solid Oxide Fuel Cell with a Focus on Assessing Entropy Generation Depending on the Channel Shape

Modelling and simulation of heat flow in indexable insert drilling

In machining, the heat generated during the process deforms the components and the final shape might not meet specified tolerances. There is therefore a need for a compensation strategy which requires knowledge of the workpiece temperature field and the associated thermal distortions. In this work, a methodology is presented for the determination of the heat load for indexable insert drilling of AISI 4140. Compared to previous research, this work has introduced a varying heat load. The heat load is extracted from thermo-mechanical finite element simulations for different nominal chip thicknesses and cutting speeds using the coupled Eulerian-Lagrangian formulation of an orthogonal turning process. The heat load is then transferred to a simplified 2D axisymmetric heat transfer model where the in-process temperature field in the workpiece is predicted. To verify the methodology, the predicted temperatures are compared to the experimentally measured temperatures for various feed rates. It is found that the model is capable of predicting the workpiece temperatures reasonably well. However, the methodology needs to be further explored to validate its applicability.

A new random walk method for simulating heat flow and temperature distribution in three-dimensional discontinuous systems

Numerical methods for analyzing diffusion phenomena involving strong discontinuities and complicated interfaces are of great scientific and technical importance. In this paper, we extend the existing step-balanced random walk, which overcomes the problem of detailed balance of a random walker in three-dimensional (3D), diffusion-tensor discontinuous systems, to particle density (ρ) discontinuous systems, and introduce volumetric heat capacity C and temperature T by considering ρ as heat density, i.e., ρ=CT, to apply it to thermal problems. Two types of thermophysical simulations are demonstrated: one is steady-state heat flow due to a temperature difference at the end surfaces on a two-phase slab model unit cell with periodic boundary conditions; the other is the time variation of temperature distribution due to heat diffusion from a point heat source in a repeated two-phase slab model with no periodic boundary conditions. We see the correct behavior of heat and temperature expected in 3D discontinuous systems composed of two phases with anisotropic thermal conductivity. The applicability to problems other than pure diffusion and the limitations of the method are also discussed.

Comparative Analysis of Loss Mechanism Localization in a Semi-2D SOEC Single Cell Modell: Non-Equilibrium Thermodynamics versus Monocausal-Based Approach

This study aims to theoretically analyze the local entropy production rate in a SOEC single cell at T = 1123.15 K and p = 1 bar. Local entropy rates signify loss mechanisms, crucial for cell design and optimization. A semi-2D SOEC model based on non-equilibrium thermodynamics is developed, supplemented by monocausal correlations for direct comparison. The model is validated using KeraCell III data and grid independence analysis. Simulations of electric current density, temperature, heat flow, and local entropy production for various SOEC operating modes are presented. Coupled transport mechanisms significance is discussed, highlighting the pronounced impact of the Peltier effect on heat flux and temperature. The importance of the Peltier effect in SOECs compared to SOFCs is emphasised. The effects of the Seebeck effect on the potential distribution are superimposed by the dominant ohmic losses in the electrolyte. The localization of entropy production rates shows for exothermic operation that 66.6% of the total losses are due to the predominantly dominant irreversible ion transport in the electrolyte, while the entanglements in the reaction layers contribute 33% and GDLs less than 1%.

Heat Transfer and Pressure Drop in Plate Fin Heat Exchangers: A Numerical Approach

An apparatus for transferring thermal energy across an impermeable barrier between two or more fluids is a heat exchanger. The effective transmission of heat from a hot fluid to a cold fluid is its primary goal. The temperature differential between the two fluids directly affects this heat transfer. Using CFD study with FLUENT 2020 R1, the performance characteristics of the compact plate fin heat exchanger's improved surfaces are examined. The simulation of heat transfer and flow encompassed a variety of velocities including completely turbulent regions. The pressure, temperature, and velocity contours were taken from the Fluent simulations. To determine the heat exchanger's flow and heat transfer performance, numerical analysis has been done. Since boundary conditions are crucial to CFD, they have been carefully chosen. The flow field, heat transfer, thickness, and wavelength were all predicted using the software code for a range of air to water velocities. Three distinct wavelengths of numerical simulations for a plate-fin heat exchanger were used in the study (10, 20, and 30). There were changes to the fin thickness, entry locations, and air and water entry velocities. Solid Works and Ansys were used to create the geometry for the three-level fin models that were placed inside the heat exchanger, both with and without a cover. For determining the heat exchanger's geometry and fin isometry, three levels measuring 19.6 mm in height and 53.64 mm in width were constructed. The fins have a thickness of 0.2 to 0.4 mm. As the air and water velocities vary, so does the temperature inside the heat exchanger. Because the topmost layer is a warm stream's flow channel, the temperature rises there, whereas the opposite effect is seen close to the bottom layer. Convection heat transmission to the surroundings and conduction heat transfer through the heat exchanger's side plates are the causes of fluid temperature fluctuations in the depth direction.

Computational Fluid Dynamics Calculations of Moderator Heat and Fluid Flow of Small Modular Heavy Water Reactor

Abstract The heavy water reactor concept Teplator is a pressure channel type reactor with independent systems for the primary coolant and the moderator. The present study analyses the low-pressure moderator cooling system of Teplator during full-power operation. The moderator is heated from neutron thermalization, gamma rays absorption, fission product decay, and decay of activation products. Additionally, heat transfer from the coolant channels has to be taken in the analyses of the moderator cooling system. Preliminary thermal-hydraulic analyses of the cooling system are supplemented by computational fluid dynamics (CFD) simulations of heat and fluid flow in the moderator's vessel, emphasizing flow-type regimes. Results from CFD simulations showed that the buoyancy-dominated flow (case MF-22) resulted in a higher thermal stratification and high moderator temperature close to the upper plate of the moderator vessel. The inertia-dominated flow regime MF-90 resulted in good mixing of the moderator and a low thermal stratification in the vessel. Finally, the midmass flow rate regime MF-45 was identified as a transitional region from a buoyancy-dominated to a mix-type regime.

The influence of permeability anisotropy in the upper ocean crust on advective heat transport by a ridge-flank hydrothermal system

In this study, we highlight the importance of permeability anisotropy on the hydrogeological regime of a ridge-flank hydrothermal system. Our study site, North Pond, is a marine sediment pond on ∼8 Ma seafloor in the North Atlantic, and represents a low-temperature, end-member ridge-flank hydrothermal system. Previous simulations of North Pond elucidated long-standing hypotheses concerning hydrothermal fluid and heat transport in the upper volcanic crust but failed to fully explain observed patterns of seafloor heat flux in this area. Here we use variography, a geostatistical method, to quantify relations between seafloor heat-flux measurements, and coupled numerical simulations of fluid and heat flow to simulate the hydrogeologic regime. Directional variography shows that heat-flux observations are correlated along-strike of the regional crustal fabric. Three-dimensional simulations that include permeability anisotropy are able to replicate seafloor heat-flux patterns across North Pond. The simulations that result in the best match to thermal data incorporate permeability anisotropy in the horizontal plane. We find that the feedback between permeability anisotropy and the asymmetric geometry of North Pond combine to promote advective removal of heat and mass within the crustal aquifer. These findings suggest that permeability anisotropy in the oceanic crust may influence ridge-flank hydrothermal circulation more broadly.

Selected Aspects of Heat Transfer Study in a Gun Barrel of an Anti-Aircraft Cannon

The paper presents the results of computer simulations of the transient heat flow in the barrel wall of a 35 mm caliber cannon for a single shot and a sequence of seven shots for a selected 30HN2MFA barrel steel. It was assumed that the inner surface of the barrel does not have a protective layer of chromium or nitride. When calculating heat transfer in a barrel, constant and temperature variable values of thermal conductivity, specific heat and density (in the range from RT (Room Temperature) up to 1000) in the 30HN2MFA steel were assumed. The test results were compared for both cases. A barrel with a total length of 3150 mm was divided into 6 zones (i = 1,, 6) and in each of them, the heat flux density was calculated as a function of the time q _i (t) on the inner surface of the barrel. In each zone, the heat transfer coefficient, as a function of the time hi(t) and bore gas temperature as a function of the time Tg(t) to the cannon barrel for given ammunition parameters, was developed. A calculating time equaling 100 ms per single shot was assumed. The results of the calculations were obtained using FEM implemented in COMSOL Multiphysics ver. 5.6 software.

Image-based analysis of single jersey loop parameters

Quality Control is crucial when it comes to fine and technical knits. Digital Twins are common in product design and are necessary for heat and mass flow simulations of textile fabrics. In both cases primarily, the exact geometry of the knitted loop is necessary for following processes. Wale spacing W and course spacing C are the essential geometrical characteristics of the representative unit cell of single jersey fabrics. The loop parameters can be obtained manually by counting loops per unit length or by microscopic measurements, which both are time consuming and are not applicable in integrated digital processes. Therefore, a new method for automatic extraction of major loop geometry parameters is described. A state-of-the-art method, which analyzes the microscopic images automatically, works with Fourier-Transformation of the image brightness and is used as a benchmark. The new loop-based method extracts the geometrical data from the distances between the center points of the loops. The methods are evaluated on single jersey fabrics of three different yarns. In addition, the impact of magnification on the measurement is shown for one fabric. The new method gives same results as manual measurements and even more precise results as the benchmark method.

Multiscale fracture networks and their impact on hydroshearing response in the Canadian Shield (Kuujjuaq, Canada)

Understanding the natural fracture network is essential for geothermal-related investigations. However, the geometrical attributes depend on the scale of observation. Therefore, a multiscale characterization of the fracture network is essential to ensure that heat and flow simulations are based on stochastically generated discrete fracture network models representative of the natural fracture system observed. The objective of this project was to understand the scale effect of fracture data on the performance of a potential enhanced geothermal system in crystalline rock in northern Canada. This was accomplished by collecting and characterizing fracture data from core, outcrops and satellite image, and then constructing a discrete fracture network model which was used to simulate the performance of the geothermal system. The numerical simulations suggest that fracture length and spacing have an important impact on its performance. Thermal short-circuiting can be easily achieved if the fracture network is modelled based solely on satellite image data, and hydroshearing may be less effective if the DFN is constructed based solely on outcrop data. The simulations suggest that combining the different datasets provides the best compromise between heat extraction, water losses, hydraulic impedance and thermal drawdown. Despite the uncertainties, the fracture data used highlights the importance of multiscale fracture analysis for heat-flow simulations of geothermal reservoirs.

Research of Tribological and Thermodynamic Parameters of the WC-Cu Braking System of the Experimental Modular Electric Vehicle

Abstract The authors of this manuscript present the development of a braking system with friction material base WC-Cu coating for the electric vehicle. This manuscript follows on from the original development of an AGV multi-disc braking system and an experimental investigation of the friction factor of WC-Cu coatings. In addition to developing the mechanical elements and construction of the electric vehicle, the tribological parameters of three samples of the steel substrate, the C45 with WC-Cu coating, were investigated in the tribological laboratory. A metallic coating of the WC-Cu base was applied on the C45 steel substrate using electro-spark deposition coating technology. The experiment used three samples with different percentage ratios of chemical elements in the coating structure. The tribometer working on a “Ball on Plate” principle was an investigation of the friction factor of all samples during the experiment. Subsequently, the surface of the samples was modified structure WC-Cu with laser technology. The microhardness of modified and unmodified coatings according to the Vickers methodology was investigated in the next stage. At the end of the experimental investigation, a braking simulation was created in the programming environment of the Matlab® software, considering all driving resistances. The researchers also focused on the simulation of heat conduction during braking for some considered driving modes with braking on a level and with a 20% slope roadway. The simulation of heat flow was carried out in the Matlab® programming environment using the Fourier partial differential equation for non-stationary heat conduction.

Numerical simulations of heat exchange and vapor flow in ice fractures on Enceladus

Cassini spacecraft observed plume of water vapor and ice particles above the south polar terrain (SPT) of Saturn's moon Enceladus in 2005. The area of the SPT is marked by four prominent linear depressions in the ice dubbed “tigers stripes” (TS) that appear to be the source of the plume. The area around TS is also the source of anomalously high heat flux. The current consensus based on analysis of Cassini observations and modeling suggests that TS are fractures in the ice that penetrate to warm sub-ice ocean. Escaping vapor laden with ice particles forms the visible plume and latent heat of condensing vapor serves as the source of the surface thermal anomaly. In the present work previously developed numerical model of vapor flow and heat exchange inside TS fractures is refined and used to explain Cassini observations. Model improvements include consideration of a possible snow layer on the surface and inclusion of surface ice sublimation into energy balance model. Results of the simulations with improved model suggest that Cassini observations of vapor mass flow and endogenic heat flux can be explained if the width of the ice fractures is in the range 0.05–0.1 m, similar to previously published results. Wider fractures are possible if only a small portion of TS total length produces vapor plume, but the whole ~500 km length of TS fractures still contributes to the surface thermal anomaly. Alternatively, wider fractures are also possible in fractures with high effective friction due to wall roughness or channel tortuosity. Simulated heat output of fractures with different widths and depths in the range of 1.5–3 km is ~2.5–3.0 GW and is only weakly dependent on fracture width. A 2-m-thick surface snow layer covering the fracture can significantly lower outgoing heat flux to 0.9–1.9 GW and reduce surface temperatures by 20–40 K. The total heat flow from different fractures (including conduction from the water-filled portion) is remarkably similar - it is ~3.3 GW and 2.3 GW for fractures without and with a surface snow layer, respectively. The simulated heat flow is lower than the observed heat flow, suggesting that each TS depression may host 2 to 6 narrow ice fractures. The long-standing puzzle of the large difference between the observed heat flow from near TS (~4.2 GW) and from the whole SPT (~15.8 GW) is explained by conduction of ~11 GW of heat from the ocean through the ~5 km-thick ice shell underlying the SPT. Predicted high surface temperatures near fracture exit result in high rates of ice sublimation, which may produce a secondary source of water vapor feeding the observed plume. Fracture outlet likely evolves into a cone-like cross-section widening towards the surface on timescales from 1 to 100 years.

Simple Loss Model of Battery Cables for Fast Transient Thermal Simulation

In electric vehicles, currents with high-frequency ripples flow in the power cabling system due to the switching operation of power converters. Inside the cables, a strong coupling between the thermal and electromagnetic phenomena exists, since the temperature and Alternating Current (AC) density distributions in the strands affect each other. Due to the different time scales of magnetic and heat flow problems, the computational cost of Finite Element Method (FEM) numeric solvers can be excessive. This paper derives a simple analytical model to calculate the total losses of a multi-stranded cable carrying a Direct Current (DC) affected by a high-frequency ripple. The expression of the equivalent AC cable resistance at a generic frequency and temperature is derived from the general treatment of multi-stranded multi-layer windings. When employed to predict the temperature evolution in the cable, the analytical model prevents the use of complex FEM models in which multiple heat flow and magnetic simulations have to be run iteratively. The results obtained for the heating curve of a 35 mm2 stranded cable show that the derived model matches the output of the coupled FEM simulation with an error below 1%, whereas the simple DC loss model of the cable gives an error of 2.4%. While yielding high accuracy, the proposed model significantly reduces the computational burden of the thermal simulation by a factor of four with respect to the complete FEM routine.

Thermographic Inspection Simulation of One Kind of Rail Defects

Rail is an important foundation of rail transit, and defects on the rail may pose a serious threat to rail transit. As a new non-destructive testing method, thermographic detection shows an excellent application prospect. In order to verify whether thermographic detection technology can be used to detect the defects on the rail, especially the defects at the bottom of the rail. The ANSYS software is used to model the rails under different conditions, and the heat flow simulation experiment is carried out to obtain the temperature change results when the heat flow passes through the defects and when it does not. The existence and location of defects can be determined by observing how the heat flow changes due to the existence of defects.Although the results show that surface fracture defects and defects towards the bottom edge of the rail can be clearly detected by thermal modeling under laser heating conditions, for transverse cracks that exist near the center of the rail bottom, the simulation experiments still cannot distinguish the temperature differences at the same observation location under current parameters. So it may be necessary to further optimize the experimental process, or increase the experimental parameters, so that the thermal modeling method can be better applied for non-destructive testing of rail defects.

О вопросах верификации результатов моделирования теплового потока полевым методом

Purpose. One of the fire safety requirements is the creation of conditions for preventing fire spread between buildings. This requirement is implemented by observing fire prevention distances (breaks) between buildings and structures. Requirements for fire prevention distances (breaks) are established in regulatory documents. In some cases, the implementation of these requirements is either technically impossible, or associated with significant economic costs, when the further operation of the facility is impractical. To solve this problem, it is possible to reduce fire prevention distances (breaks) between facilities under protection, provided that the engineering calculation confirms the impossibility of fire spread to a neighboring facility by a heat flow. The accuracy of the results obtained by the method of calculating fire distance (break) directly affects the level of fire hazard in the facility under protection, and verification in the calculation models used within the framework of this method is an important stage in its development and improvement. Methods. For research, methods of analysis and computer simulation with the help of the Fire Dynamics Simulator (FDS) software product are used. Findings. The simulation of a heat flow during heptane pan burning is performed. The results obtained during the simulation are compared with the results of a full-scale experiment. Recommendations for setting FDS parameters for heat flow simulation are formulated. Research application field. The study results can be applied in the calculation of fire prevention distances (breaks) by the field method using Fire Dynamics Simulator software product. Conclusions. The model created by means of FDS requires mandatory refinement of the parameters, since not in all cases the default values correctly describe the simulated process. The study of the issue of heat flow simulation in FDS requires further research. In the course of numerical experiments, it is found that when calculating the incident heat flux, it is necessary to pay attention to setting such parameters as discretization of the solid angle, the fraction of energy spent on radiation, CO and soot release. For correct assessment of the incident heat flux, it is recommended to simulate combustion by solid angle correction with a step in 100 until the value of the incident heat flux stabilizes within a narrow range.