Numerical Thermal Analysis Research Articles

Numerical Thermal Analysis of Greased Rolling Bearing Considering Surface Topography and Plastic Deformation

ABSTRACTIn numerical studies of grease lubrication, thermal effect is often neglected and surface plastic deformation is almost not considered. This paper has developed a deterministic thermal plasto‐elastohydrodynamic lubrication (PEHL) model for grease‐lubricated rolling bearing. The influence of tangent modulus, rheological index and texture orientation on lubrication characteristics and temperature rise is analysed. The results show that increasing the rheological index of grease and decreasing the wavelength factor are obviously positive for improving lubrication behaviour. Since surface plastic deformation in the EHL state is at nanoscale, film thickness, friction coefficient and temperature rise of solid surfaces decline slightly with the decrease of tangent modulus.

Numerical thermal analysis and structural optimization of cascaded PCM heat sinks for thermal management of electronics

In the present study, an innovative cascaded phase change material (PCM) heat sink using organic PCMs was proposed for electronic thermal management. The design arranges multiple PCMs with progressively lower melting points along the heat transfer path, allowing active control of the melt front. A numerical model with 5 % accuracy was developed to evaluate thermal performance. Based on the validated model, the effects of PCM stage numbers, PCM volume fractions, fin types, and fin volume fractions were analyzed. The fin volume fractions were further optimized using a support vector machine (SVM) and genetic algorithm (GA) methods. Results showed that a three-stage PCM heat sink with pin fins and increasing configurations outperformed single-stage PCM heat sinks, enhancing heat transfer by up to 36.7 %. Additionally, the innovative cascaded PCM heat sink with a uniform 20 % fin volume fraction across the three stages achieved a 38.8 % improvement compared to single-stage configurations. When the fin volume fractions were set to 24.1 %, 17.6 %, and 13.0 % for the three stages, thermal performance of the innovative cascaded PCM heat sink was enhanced by up to 39.8 % compared to single-stage configurations. The findings provide valuable insights for the design and application of PCM-based thermal management systems, potentially leading to more efficient solutions for various engineering fields.

Prediction of the keyhole TIG welding-induced distortions on Inconel 718 industrial gas turbine component by numerical-experimental approach

Welding technologies represent a paramount joining process for ensuring the quality and reliability of critical industrial components; therefore, their innovation constitutes a driving force in realizing increasingly competitive products. A recently developed technology is the keyhole TIG welding, a new high energy–density alternative to the conventional TIG process. A key role in improving innovative manufacturing processes such as the keyhole TIG is covered by numerical simulation; indeed, it allows the development of a process digital twin able to support decisions and work as a predictive tool. Within this framework, the paper deals with the numerical-experimental investigation of the keyhole TIG technology, successfully employed on a simplified mock-up of an industrial gas turbine component consisting of two 6.5-mm-thick Inconel 718 rings. Numerical analysis aimed at predicting welding-induced distortions was performed employing two different computational approaches, namely the moving heat source and the simplified imposed thermal cycle methods. The numerical-experimental comparison of the results demonstrates an innovative approach in the field of the current keyhole TIG numerical simulation since, besides verification of numerical thermal analysis, further substantial validation of the post-weld distortion predictions is provided through comprehensive three-dimensional experimental data. Moreover, the comparative assessment of the two computational approaches and experimental evidence revealed that the imposed thermal cycle method implementation does not compromise the accuracy of welding distortion forecasting in industrial applications such as that investigated. Therefore, it can be regarded as a valuable tool for supporting the process engineer in designing the ideal set-up to comply with a variety of industrial requirements, among them strict design tolerances.

An air‐cooled cylindrical Li‐ion 5 × 5 battery module with a novel flow‐diverting arrangement and variable vent positions for electric vehicles: A numerical thermal analysis

AbstractThermal management of lithium‐ion batteries has received a lot of interest in the automobile sector. In commercial electric motor vehicles, an efficient battery cooling arrangement, particularly active cooling approaches, has been chosen as an ideal option. When building battery cooling systems, the physical structure and arrangement of the battery pack (BP) are vital. The current study presents a revolutionary design of a BP that incorporates cylindrical cells in a square duct and an air‐cooling (AC) medium circulated in its surroundings with the help of variable vents for inlet and outlet. A forced‐AC system is used to test lithium‐ion battery cells grouped in a 5 × 5 configured battery module. To investigate the impact of heat generation on battery thermal performance, a complete thermal analysis was performed at different discharge rates of 0.5, 1, 2, 3, and 4 C. As compared with both inlet vents at an equidistance configuration with an inlet velocity of 12 m/s and a flow rate of 1.210(−2) kg/s, the results show that the proposed design minimizes heat accumulation by enhancing the heat transfer. As a result, the peak temperature and temperature disparity decreased by 6.76% and 85.32%, respectively. A flow‐dispersing disc of 30 mm in size enhances temperature uniformity in comparison to the other intake vent design, hence improving battery safety and longevity.

NUMERICAL ANALYSIS OF TEMPERATURE DISTRIBUTIONS IN GLULAM BEAMS EXPOSED TO FIRE AND REINFORCED WITH ARAMID COMPOSITE

Currently, strengthening timber elements with the use of various materials has become popular.Reinforcements are used to repair existing elements or improve the static operating characteristicsof new elements. Fibre composites are being increasingly used as reinforcement. Investigationshave shown that the use of fibre composites influences the nature of static work. However, anunder-researched issue is the determination of the influence of composite reinforcement ontemperature distributions and, consequently, the depth and shape of charring in the cross-sectionduring fire. The article presents a numerical thermal analysis of cross-sections of glulam beamsreinforced with aramid materials in various forms. Fire action was assumed in accordance with theISO fire curve and the fire load on three of the four edges of the beams was modelled. Temperaturedistributions are presented for all analysed cases, which shows the beneficial effect of the use ofaramid reinforcement on the temperature distribution in the cross-section during a fire.

Numerical Simulation and Thermal Analysis of Pressurized Hydrogen Vehicle Cylinders: Impact of Geometry and Phase Change Materials

This comprehensive study investigates the nuanced aspects of pressurized hydrogen vehicle cylinders during refueling, employing numerical simulation and thermal analysis. The examination encompasses the intricate dynamics influenced by cylinder geometry, mass flow rate variations, and the integration of phase change materials (PCMs). Simulations involving cylinders with diverse length-to-diameter ratios and inlet diameters highlight the impact of these parameters on temperature control. Notably, smaller length-to-diameter ratios prove effective for temperature regulation, while larger inlet diameters mitigate temperature rise. The study further explores the role of varying mass flow rates, revealing that an increasing flow rate during refueling results in the lowest temperature rise. In addition to geometry and mass flow rate considerations, the integration of PCMs is a focal point. Modeling and parametric analysis are employed to assess the feasibility of incorporating these materials. The study contributes valuable insights into optimizing the thermal performance and safety of hydrogen fuel systems. The holistic approach considers the interplay of geometry, mass flow rate dynamics, and the innovative use of PCMs, offering a multifaceted understanding of the factors influencing pressurized hydrogen vehicle cylinders.

Numerical modeling and thermal performance analysis of deep borehole heat exchangers considering groundwater seepage

Exploitation of deep geothermal energy based on a deep borehole heat exchanger (DBHE) system significantly promotes green and low-carbon development. The DBHE is the core apparatus of this system, and many mathematical models have been proposed to investigate its thermal performance. However, groundwater seepage which is one of the most important factors has not been considered in most previous numerical models. In addition, the temperature distribution of rock and soil with different seepage velocities during the thermal recovery period is still unclear. Therefore, to fill this research gap, there is a strong need to propose a novel numerical model for DBHEs that considers groundwater seepage and can be solved quickly. In this paper, a computationally efficient numerical model that considers groundwater seepage is proposed. Compared with the experimental data from a field test, the model’s root mean square error is 1.33 °C. Moreover, the time required for the simulation of DBHE operation for one year using this model is only 47.3 s. Then, the effects of groundwater seepage on the DBHE and rocky soil are investigated. The findings demonstrate that when the seepage velocity is high, the thermal performance of the DBHE will be underestimated if groundwater seepage is neglected. At the seepage velocities of 1 × 10-7, 3 × 10-7 and 5 × 10-7 m/s, the heat extraction rate of the DBHE increased by 4.92 %, 10.83 %, and 15.34 %, respectively, compared to the heat extraction rate of the DBHE calculated without taking the groundwater seepage into account. Furthermore, groundwater seepage can increase the temperature recovery capacity of rock and soil. The natural temperature recovery rate of rock and soil without seepage is 86.20 %, and the temperature recovery rate is 93.11 % if the seepage velocity reaches 1 × 10-7 m/s. This study provides essential theoretical guidance for DBHE system design in areas with high groundwater seepage velocities.

Numerical simulation and thermal analysis of water circulation cooling pipe of pressurized hydrogen ship-board cylinders

In this paper, a direct cooling pipe for hydrogen inside the marine hydrogen storage cylinder (HSC) was designed, and the cooling pipe was simulated and analyzed under different cooling structures and different cooling fluids using ANSYS(Fluent) 2022 R2. The simulation results show that the effect of different cooling fluids on the temperatures were nearly the same. The heat transfer coefficients, however, of various fluids were different, and the cooling temperature was also different after cooling for the same time. The cooling structures mainly affect the cooling rate of the hydrogen due to the contact area with hydrogen inside the HSC. Among the three structures investigated in this study, the cooling capacity of the spiral layout was increased by 0.85 % and 0.63 %, respectively, compared to the rectangular and wavy layout. The rectangular layout has the certain cooling effect, however, in comparison to the spiral tube structure, it has too many corners, which increases the hindering effect on the flow of cooling medium inside the tubes and affects the cooling efficiency. The wavy layout has the largest contact area, but it has the problems of uneven cooling and occupying a large amount of hydrogen storage space. Among the three structures, comprehensively speaking, the spiral layout is considered to be the optimal. The optimal performance parameters were determined by comparing the simulation results of the three layouts during cooling process with hydrogen charging being performed. The results show that the cooling pipe can achieve the hydrogen temperature to be controlled within 358 K before the hydrogen pressure in the HSC reaches 70 MPa, and the maximum temperature is 336.07 K was obtained after the completion of hydrogen filling. This paper gives technical information for optimizing the thermal performance and safety of the hydrogen fueling system.

Bayesian optimization-based prediction of the thermal properties from fatigue test IR imaging of composite coupons

The prediction of the prevailing self-heat transfer parameters of a glass/epoxy composite coupon during fatigue testing in general and the distinction between viscoelastic- and frictional crack growth-related energy dissipation in particular, are not trivial problems. This work investigates the feasibility of predicting the convective film coefficient, the total work loss as well as the ratio between viscoelastic and fracture-induced damping from thermal images using Bayesian optimization in conjunction with 3D FE thermal analysis. To this end, glass fiber/epoxy biax coupons are pre-damaged by means of a drop weight impact machine and subsequently tested under uniaxial tension-tension high cycle fatigue conditions. IR images are taken of the self-heating thermal profile at steady-state conditions. Synthetic surface thermal images are generated by numerical thermal analysis of the damage distribution obtained by μ-CT scanning prior to testing. Bayesian optimization of the aforementioned parameters is conducted by minimizing the loss function between the as-measured and the synthetic IR image. The predicted work-loss is consequently validated against the measured hysteretic response, from which a very good agreement is found.

Numerical and optimal thermal analysis of non-Newtonian fluids flow over a wedge by using response surface methodology (RSM): Sensitivity analysis

The numerical and optimal thermal analysis of Casson fluid flow over a wedge is investigated in this work. To perform numerical and sensitivity analysis we have convert third order non-linear PDEs into set of ODEs by using similarity transformations along with boundary conditions. These equations are simulated using numerical technique Keller Box method and then compared the values of skin friction coefficient and Nusselt number with those existing in literature and found excellent agreement. Then by using these numerical data we have performed sensitivity analysis by using Response Surface Methodology (RSM). ANOVA tables are generated and developed a correlations between input parameters and output responses. The coefficient of determination for output responses skinfriction coefficient and Nusselt number are 96.50% and 99.51% respectively which shows the best fitted correlations. Finally, we have performed sensitivity analysis which reflects that skinfriction coefficient is more sensitive to Falkner–Skan exponent (m) and there is no effect of Prandtl number (Pr) on skinfriction coefficient. It is also concluded that Nusselt number is sensitive to Prandtl number (Pr) and obtains its optimum value with variation in Prandtl number (Pr).

Peculiar microstructural evolution and hardness variation depending on laser powder bed fusion-manufacturing condition in Ti–6Al–2Sn–4Zr–6Mo

This study aims to comprehensively analyze the phase and microstructure evolution and related hardness variations of the Ti–6Al–2Sn–4Zr–6Mo wt.% (Ti6246) alloy produced by laser powder bed fusion (LPBF) under various laser conditions and to gain insight into the mechanisms of these changes using numerical thermal analysis. Higher laser volumetric densities (VEDs) resulted in a finer α/α' microstructure and increased hardness, exhibiting a positive correlation with the VED, except under extremely high conditions. This contrary trend, reported for the first time, is attributed to the solid-phase transformation from the β phase to metastable α' martensite during LPBF induced by rapid cooling. Despite the finer microstructure, the samples under very high VED conditions showed lower hardness, deviating from the overall trend. The X-ray diffraction peaks in the high-VED samples suggested a partial decomposition of α' to α + β owing to laser-induced reheating of the underlying layers, which is considered a contributing factor to the hardness reduction. The numerical analysis showed that the underlying layer was exposed to high temperatures for a relatively long time under high-VED conditions. It was revealed that the hardness of LPBF-fabricated Ti6246 was influenced by unique thermal processes: rapid cooling and reheating of the pre-solidified part, leading to the formation of a metastable α' phase and partial decomposition into α + β. These findings provide insights for tailoring Ti6246 with desired physical properties via LPBF.

Numerical simulation and thermal analysis of ecological energy-saving ground source heat pump design

By constructing the heat transfer model of the buried tube heat exchanger, using the mathematical method and numerical calculation software, the temperature of the buried tube heat exchanger is calculated numerical, so as to better understand the temperature effect of the buried tube heat exchanger on the surrounding soil. This paper establishes a mathematical model of a vertically buried heat transfer system based on the principle of thermal equilibrium and the thermal conductivity differential equation. Conduct research on the temperature field around single pipes in different soil (geological conditions), temperature field under different drilling backfill materials, and the temperature around buried pipelines in both short-term and long-term operation of the system. The experimental results show that the simulation results of the system?s short time (10 days) and long time (90 days) performance show that the cooling and temperature cycles in different areas directly affect the heat radius of the buried pipe and the heat accumulation near the buried pipe. The thermal action radius of the short-term operation system is about 1.8 m, and the long-term operation reaches 4.5 m.

Fatigue damage reconstruction in glass/epoxy composites via thermal analysis and machine learning: A theoretical study

This study introduces an advanced, non-contact diagnostic tool for structural health monitoring of fatigue damage in fiber/polymer composite materials. The approach combines thermal image recognition of fatigue self-heating hotspots with high-fidelity thermal modeling to quantitatively assess subsurface fatigue damage distributions by machine learning. To this end, artificial thermal images are generated through 3D numerical thermal analysis of an inherent fatigue damage heat source within a glass/epoxy composite, derived from sampling a multivariate Gaussian distribution of microcracks. Subsequently, these synthetic thermal images are employed to train three distinct regression models: a convolutional neural network, a Gaussian processes regressor, and a straightforward least squares model. Various image augmentation techniques are applied to expand the dataset efficiently. All models accurately predict the size of the damage and – most importantly – the maximum temperature within the damage deep inside the composite. The regression methods estimate the diagonal elements of covariance matrix components of the Gaussian distribution, with accuracies ranging from 86% to 99%. The findings presented in this work contribute to establishing a solid foundation for non-destructive subsurface fatigue damage assessment in composite materials, with many practical applications in experimental composites fatigue research.

Numerical thermal analysis of synchronous reluctance generator for wind energy application

AbstractThis paper focuses on the thermal analysis of the synchronous reluctance generator with a rating of 2.1 kW. It mainly uses explicit, and implicit finite difference methods for thermal analysis to reduce the complexity of thermal calculation for the machine's components. It compares the results with the results obtained using a finite element analysis (FEA) and includes the experimental verification of the obtained results. The explicit, and implicit finite difference thermal analysis is relatively simple and computationally fast. Once the design parameters are known, the electric losses and iron losses of the synchronous reluctance generator are evaluated. These machine parameters are utilized in developing the explicit finite difference (EFD), an implicit finite difference (IFD), and a 3D FEA model for thermal analysis. It is observed that the obtained results from the EFD, IFD, FEA, and experiments are very close to each other, and the temperature rise for the designed machine is within the desired and acceptable range.

Numerical and experimental thermal stress analyses of dissimilar GTA welded joints

Numerical and experimental thermal stress analyses of dissimilar GTA welded joints

New Method for Fine Calculation of Bridge Temperature Field Based on BIM Solar Radiation Analysis

Fine calculation of bridge temperature fields is significant for accurately evaluating thermal actions in bridge structures. Determining thermal loads on bridge surfaces caused by solar radiation is the most challenging part of the numerical thermal analysis because the sunlit and shaded areas on bridge surfaces change continuously with the sun’s rotation. Existing methods have low accuracy in determining thermal loads and cannot be applied to complex bridges. This study presents a new method for calculating temperature fields based on the advantages of building information modeling (BIM) technology in solar radiation analysis (SRA) and information sharing. This method starts with obtaining an accurate hourly insolation distribution on bridge surfaces through SRA implemented in a BIM system. Then, a Python script seamlessly maps the insolation information to finite element surfaces as thermal loads. This paper details the new method’s implementation steps and technical details, and a practical application on a concrete box girder demonstrates its applicability and effectiveness. Compared with previous methods, the proposed method has significant advantages, such as a more accurate calculation for solar radiation, a lower technical threshold, a higher degree of automation, less computational time, and easier finite element modeling.

Temporal and spatial temperature predictions for flexible pavement layers using numerical thermal analysis and verified with large datasets

The pavement temperature patterns play a significant role in the performance of flexible pavements containing asphalt concrete surface layers for several reasons. Since asphalt concrete behaves as a viscoelastic material at medium to high service temperatures, the structural response of the pavement is affected by the temperature history and the magnitude and duration of the wheel loads applied on the pavement. Therefore, predicting the pavement temperature patterns in a scalable manner (i.e., daily, seasonal, annual) is vital for a more accurate simulation of pavement response and performance, particularly the permanent deformation (rutting). This can result in more effective pavement designs. A numerical model was developed in this paper to predict the temperatures in asphalt layers by using the heat transfer theory and the Finite Element method with the help of proprietary software. A model that can predict the pavement temperatures continuously for one year covering all four seasons at time intervals that allow pavement distress prediction for each axle load cycle and calibrated with high-quality measured data is the main contribution of this study. Among the parameters that significantly affect pavement temperature prediction, the convective heat transfer at the air-pavement interface is of utmost importance. Therefore, the Convection Heat Transfer Coefficient (CHTC) for the air-pavement interface was also selected as an exploratory focus area for this paper. Two approaches were used to estimate the CHTC needed for the heat-transfer model. An error analysis was conducted to assess the accuracy of the pavement temperature prediction by using a large, measured dataset from a field test. The error of temperature predictions for the whole year was found to be minimum when the value of CHTC was equal to 21 W/(m2K). The error observed in winter predictions with the wind speed model of CHTC was minimized when a constant value of 60 W/(m2K) was used for CHTC. The significance of the convective heat transfer component in the FE model was identified through the improvements obtained by adapting the value of CHTC. Correlation analysis also identified a connection between the prediction error and relative humidity. Further research is underway to improve the temperature prediction model using additional parameters (i.e., relative humidity, cloud cover) and more refined data analytics approaches.

ADVANCED NUMERICAL FIRE DESIGN OF INDUSTRIAL COMPOSITE SLABS WITH UNPROTECTED STEEL BEAMS – A CASE STUDY

AbstractIn this paper, the development and the application of a framework for advanced numerical thermal and mechanical analysis of a composite slab with unprotected steel beams which is subjected to fire is described. A short overview over existing calculation methods is given to describe the state of the art in fire design of composite slabs. For the numerical model in the software framework SOFiSTiK, the main advantages, features and characteristics are described. To analyse the reliability of the model, the process of validation with existing fire tests is presented. Finally, the model is applied in an engineering project by means of a case study.

Direct microwave heating of alumina for different densities: experimental and numerical thermal analysis

AbstractMicrowave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single‐mode cavity, for different density levels. Even considering a constant incident power, the results show a complex evolution of the alumina temperature: first a two‐step increase, then a maximum, and finally a cooling stage. In addition, a density dependence of the heating efficiency is observed: a more efficient heating occurs for lower densities. Using the effective medium approximation (EMA) to derive the physical data as functions of density, the numerical simulations are in contradiction with the experiments, proving that the EMA approach is not able to correctly predict the imaginary part of the permittivity. Furthermore, the simulations do not accurately describe the first moments of the heating, nor the long‐term evolution of the temperature (cooling). We then explain the origin of this discrepancy: the need to adjust the movable stub on the one hand, and to account for heat exchange between the cavity and its surroundings on the other.

Numerical thermal performance analysis of light steel insulated walls under fire

Light-gauge steel-framed (LSF) walls are being adopted by the Algerian construction industry as a new alternative to the traditional infilled frames due to the advantages they provide. The strength-to-weight ratio of Cold Formed Section (CFS) leads to lighter structures and a decrease in the building cost. However, in the case of fire, the high shape factor combined with the loss of material properties of the unprotected, slender CFS can result in structural failure. Because of their conductivity, elevated temperatures have an effect on the thermal performance of panels, necessitating the use of appropriate insulation. The purpose of this paper is to perform a numerical analysis of the thermal behavior of LSF walls protected by plasterboard or magnesium oxide board, as well as cavity insulations. Numerical models are developed, using ANSYS software to simulate the thermal performance of LSF walls under ISO 834 fire. Thermal simulations are done to predict temperature profiles, maximum temperatures, and the estimated fire resistance level (FRL). This research has produced results to better evaluate the influence of different systems of protection and insulation used for the CFS under fire.