Transient Thermal Simulation Research Articles

Efficient sensitivity analysis of the thermal profile in powder bed fusion of metals using hypercomplex automatic differentiation finite element method

Rapid cyclic temperature fluctuation occurring in powder bed fusion of metals using a laser beam (PBF-LB/M) influences the formation of flaws in printed parts. Consequently, there is a pressing need to enhance the quality of printed parts by developing innovative methodologies that can predict thermal histories and help uncover the intricate relationships between process parameters and thermal profiles. Sensitivity Analysis (SA) emerges as an essential tool for this, offering the potential for process optimization and enhanced quality control. Nonetheless, conventional SA methodologies often incur in excessive computational costs and potential numerical approximation errors. To address this technical challenge, we present a novel method for SA that integrates the HYPercomplex-based Automatic Differentiation (HYPAD) technique with transient thermal simulations conducted via the finite element method (FEM). Leveraging this methodology, we efficiently and accurately perform SA for PBF-LB/M processes in a post-processing step. Compared to traditional methods like Finite Differences (FD), HYPAD-FEM required 96 % less computational time for obtaining sensitivities for 22 process parameters, under a comparative study conducted within the context of the 2018–02 AM benchmark of the National Institute of Standards and Technology. In summary, HYPAD-FEM offers superior efficiency and accuracy in SA over conventional methods, delivering the best sensitivity of a model without the need for step-size selection and problem or parameter-based implementations.

The Effect of Material Variations on Discbrakes to Reduce the Heat that Occurs When Braking Using Transient Thermal Simulation

The Effect of Material Variations on Discbrakes to Reduce the Heat that Occurs When Braking Using Transient Thermal Simulation

Hierarchical thermal modeling and surrogate-model-based design optimization framework for cold plates used in battery thermal management systems

The continued advancement of battery-powered electric vehicles (EVs) towards higher energy and power densities poses significant thermal challenges for batteries. This work proposes a generalized design optimization framework for battery thermal management systems (BTMS), responding to the need for EVs with enhanced battery thermal performance, safety, and lifetime. This framework combines hierarchical thermal modeling and surrogate-model-based design optimization, explicitly tailored for liquid-cooled cold plates commonly used in EV BTMS. The hierarchical thermal modeling component decouples the battery cell, battery module, and cold plate models to reduce computational modeling costs while preserving the relative thermal performance of different cold plate designs. The design optimization component leverages our pioneer deep encoder–decoder hierarchical (DeepEDH) convolutional neural network surrogate modeling methodology to predict the cold plate’s full pressure, velocity, and temperature fields. Computationally efficient DeepEDH neural networks replace costly transient thermal simulations of cold plates and compute the objectives for evolutionary optimization using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). This work’s novel modeling and optimization framework produces optimal cold plate designs that consider battery-module-specific design features, including distributed battery cell heat generation, packaging materials, and heat-spreading characteristics. The proposed framework is evaluated through a cold plate design for modular BTMS, thoroughly assessing the impact of optimization objectives, flow path constraints, modeling assumptions, and design variable choices. The results demonstrate the effectiveness of the combined hierarchical thermal modeling and design optimization framework, with the optimized cold plates achieving reductions of 6.26K, 6.29K (22.7%), and 16.16Pa (18.7%) for maximum temperature, maximum temperature difference, and pressure loss, respectively. Moreover, compared to other methodologies that apply direct optimization without hierarchical and surrogate models, our approach significantly reduces the computational cost — from approximately 4800h to 13.5h. Our generalized multi-objective optimization framework is an effective and efficient design tool that can be leveraged to advance thermal management innovations for next-generation battery systems.

Synthetic data generation using finite element method to pre-train an image segmentation model for defect detection using infrared thermography

AbstractThe vision of a deep learning-empowered non-destructive evaluation technique aligns perfectly with the goal of zero-defect manufacturing, enabling manufacturers to detect and repair defects actively. However, the dearth of data in manufacturing is one of the biggest obstacles to realizing an intelligent defect detection system. This work presents a framework for bridging the data gap in manufacturing using the potential of synthetic datasets generated using the finite element method-based digital twin. The non-destructive technique under consideration is pulse infrared thermography. A large number of synthetic thermographic measurements were generated using 2D axisymmetric transient thermal simulations. The representativeness of synthetic data was thoroughly investigated at various steps of the framework, and the image segmentation model was trained separately on experimental and synthetic datasets. The study results reveal that when carefully rendered, synthetic datasets represent the experimental data well. When evaluated on real-world experimental samples, the segmentation model pre-trained on synthetic datasets generalizes well to the experimental samples. Furthermore, another advantage of synthetic datasets is the ease of labelling a large amount of data. Finally, the robustness assessment of the model was done on two new datasets: one where the complete experimental setup was changed, and the other was an open-source infrared thermography dataset

Improving the ventilation of a classroom to achieve heating energy savings and better indoor air quality

Indoor air quality and heating energy consumption are closely linked, especially in densely occupied spaces, as classrooms. In a classroom of Rennes University, a transient thermal simulation highlights the impact of ventilation on heating consumptions for different cases: (1) without controlled mechanical ventilation (CMV), (2) with a single flow CMV (SF CMV) of a regulatory flow of 18 m3.h−1. person−1 during periods of occupancy, and (3) a double flow CMV (DF CMV) whose flow is during periods of occupancy either equal to 18 m3.h−1. person−1 or (4) to 35 m3.h−1.person−1. The infiltration flowrate was evaluated experimentally using CO2 concentration measurements in the first case, which corresponds to the actual situation. In the normal use of the classroom with 30 persons inside, CO2 concentration exceeds 5000 ppm and the heating energy consumption is equal to 52 kWh.m−2.year−1. In case (2) and (3), CO2 concentration has a maximum level of 1350 ppm and the energy consumption is equal to 65 and 53 kWh.m−2.year−1, respectively. In case (4), the maximum CO2 concentration stays in the range 800-900 ppm without excessive heating consumption (58 kWh.m−2.year−1). Finally, by limiting the fresh air flowrate to 18 m3.h−1.person−1 in DF CMV and coupling it to a façade insulation (extra Case 5), the heating consumption is reduced to 32 kWh.m−2.year−1. These results are valuable within the context of the upcoming energy renovation strategy of the campus. Practical application In most schools, in France and elsewhere, insufficient ventilation flowrates are often observed compared to regulatory requirements. If compliance with ventilation standards and the subsequent revision of CMV installations are necessary to ensure the health of users, it is important to evaluate the energy cost of these renovations, and to identify the best choice to reduce heating consumptions. Our contribution is to compare different renovation choices in terms of two indicators: energy consumption and indoor air quality evaluated using CO2 concentration.

A workflow for predicting radiofrequency-induced heating around bilateral deep brain stimulation electrodes in MRI.

Heating around deep brain stimulation (DBS) in magnetic resonance imaging (MRI) occurs when the time-varying electromagnetic (EM) fields induce currents in the electrodes which can generate heat and potentially cause tissue damage. Predicting the heating around the electrode contacts is important to ensure the safety of patients with DBS implants undergoing an MRI scan. We previously proposed a workflow to predict heating around DBS contacts and introduced a parameter, equivalent transimpedance, that is independent of electrode trajectories, termination, and radiofrequency (RF) excitations. The workflow performance was validated in a unilateral DBS system. To predict RF heating around the contacts of bilateral (DBS) electrodes during an MRI scan in an anthropomorphic head phantom. Bilateral electrodes were fixed in a skull phantom filled with hydroxyethyl cellulose (HEC) gel. The electrode shafts were suspended extracranially, in a head and torso phantom filled with the same gel material. The current induced on the electrode shaft was experimentally measured using an MR-based technique 3cm above the tip. A transimpedance value determined in a previous offline calibration was used to scale the shaft current and calculate the contact voltage. The voltage was assigned as a boundary condition on the electrical contacts of the electrode in a quasi-static (EM) simulation. The resulting specific absorption rate (SAR) distribution became the input for a transient thermal simulation and was used to predict the heating around the contacts. RF heating experiments were performed for eight different lead trajectories using circularly polarized (CP) excitation and two linear excitations for one trajectory. The measured temperatures for all experiments were compared with the simulated temperatures and the root-mean-squared errors (RMSE) were calculated. The RF heating around the contacts of both bilateral electrodes was predicted with ≤ 0.29°C of RMSE for 20 heating scenarios. The workflow successfully predicted the heating for different bilateral DBS trajectories and excitation patterns in an anthropomorphic head phantom.

Modelling a Loop Heat Pipe as Heat Switch for Transient Application in Space Systems

Heat switches are devices for controlling heat flow in various applications, such as electronic devices, cryogenic cooling systems, spacecraft, and rockets. These devices require non-linear transient thermal simulations, in which there is a lack of information. In this study, we introduce an innovative 1D thermo-hydraulic lumped parameter model to simulate loop heat pipes as heat switches by regulating the temperature difference between the evaporator and the compensation chamber. The developed thermo-hydraulic model uses the continuity, energy, and momentum equations to represent the behaviour of loop heat pipes as heat switches. The model also highlights the importance of some thermal conductance parameters and correction coefficients for accurately simulating the different operational states of a loop heat pipe. The simulations are conducted using the proposed 1D model, solved through the application of the Mathcad block function. The numerical model presented is successfully validated by comparing the temperatures of the evaporator and condenser inlet nodes with those of a referenced loop heat pipe from the literature. In conclusion, in this research, the mathematical modelling of loop heat pipes as heat switches is presented. This is achieved by incorporating correction coefficients with Boolean logic that results in non-linear transient simulations. The presented 1D thermo-hydraulic lumped parameter model serves as a valuable tool for thermal system design, particularly for systems with non-linear operational modes like sorption compressors. The graphical and nodal representation of this proposed 1D thermo-hydraulic model further enhances its utility in understanding and optimising loop heat pipes as heat switches across various thermal management scenarios.

Parametric analysis on temperature influence on brake squeal generation in a single-seater off-road vehicle’s disc brake

Brakes are a critical component of automobiles, responsible for converting kinetic energy into heat and vibration. The phenomenon of brake squeal, which produces uncomfortable noises, has been extensively studied in both drum and disc brakes. Many studies have evaluated the influence of material and operational parameters on brake instability to reduce squeal. However, the effect of temperature, a key factor in brake performance, is often overlooked. This study aims to fill this gap by analyzing a single rear-axle disc brake from an off-road single-seater vehicle using a parametric approach. Two branches were developed in ANSYS software. The first branch consisted of a finite element model of the brake with disc, pads, and backplates. A static structural analysis was performed to simulate a real braking pressure situation, and the resulting pre-stress state was used to conduct complex modal analysis, which extracted eigenvalues and values responsible for stability. The second branch involved a transient thermal simulation before the static analysis, also considering a real braking situation, to create a gradient of temperature and change component pre-stress reactions accordingly. A design of experiments process was used to explore geometric, thermal, and operational variables. The results showed that temperature and its parameters (convection and emissivity coefficient) increase brake squeal. Thus, considering the effect of temperature is crucial when evaluating brake instability, and optimizing temperature control can help reduce brake squeal, improving safety and comfort for drivers and passengers.

Evaluation of the cooling potential of a vertical greenery system coupled to a building through an experimentally validated transient model

Despite several studies showed that Vertical Greenery Systems (VGSs) have relevant thermal benefits at urban and building scales, researches devoted to investigate the benefits of a green facade through detailed transient thermal simulations are scarce. Furthermore, a study comparing the effectiveness of different plant types is still missing. The present paper aims to fill such gaps by studying the effectiveness of a green façade to improve the thermal behaviour of a well-insulated lightweight building in the Mediterranean area, as well as the perceived indoor thermal conditions, based on both on-site experimental measurements and dynamic thermal simulations with a novel Type in TRNSYS validated through the monitoring campaign. To this aim, two identical full-scale prefabricated modules were installed and monitored at the University Campus of Catania (Italy), differing from each other because one of them hosted a climbing plant species in its west façade. The validated numerical model was then used to appraise the cooling effect of the green façade with two different plant species commonly used in Mediterranean countries (Trachelospermum Jasminoides and Hedera Helix namely). Results show that Hedera helix ensures the best performance when the foliage layer is at an intermediate state of its growing process, while under full foliage development the species investigated show almost the same performance. The incoming heat flux can be strongly attenuated, showing a quite flat daily profile, while the peak value of the internal and external surface temperature of the wall can be reduced by up to 1.6 °C and 10.5 °C, respectively.

Space Cooling Energy Potential of Domestic Cold Water before Household Consumption in Cold-Climate Regions

Space cooling energy consumption in residential buildings has tripled globally over the past three decades, leading to a significant increase in greenhouse gas (GHG) emissions and building operating costs. To reduce building cooling energy consumption, cooling energy can be recovered from domestic cold water (DCW) for space cooling by circulating DCW through thermally massive walls (herein “DCW-wall”) before regular household consumption (e.g., showers). This approach is more effective in cold climate regions since the DCW is cooler in these regions, yet its engineering design and effectiveness have not been evaluated previously. This study evaluated the cooling potential of DCW-walls in different operation scenarios (e.g., inlet temperatures, zone temperatures, and piping configurations). A typical DCW usage pattern and a daily amount of 1200 L were selected for evaluation. Three-dimensional transient thermal simulations were used to obtain the water outlet temperatures, average wall surface temperatures, and cooling potentials. The results showed that a DCW wall with a spiral piping configuration and DCW inlet at 12 °C can deliver 21.92 MJ of cooling energy daily to a zone at 25 °C. This amount of free energy can cover up to approximately 11% of the annual cooling energy demand of a four-person dwelling in Toronto, Canada, which has a warm and humid summer.

Electric Traction Motor Spray Cooling—Empirical Model Development and Experimental Validation

The growing interest in electric vehicles leads to new developments of efficient electric traction motors with high power density. Since a large part of the losses in an electric motor can occur in the windings, it is important to cool the windings to reduce the temperature and protect the winding insulation from thermal aging. Oil spray cooling systems are becoming more and more relevant for cooling the windings. In this work, an approach for heat transfer modeling of electric traction motors (power classes #2-4 with 60 to 180kW) with hairpin end windings is developed and tested. The model is developed with a testing rig for different flat jet spray nozzle arrangements for a hairpin electric traction motor. The model approach showed a good agreement with the measured temperatures of the end windings in the testing rig. A transient thermal simulation of the testing rig confirms the good agreement. In a second step the model approach is transferred to another electric traction motor with a different spray cooling system. The simulation results of the second electric traction motor also show good agreement with thermal quasi-static operating points and transient measurements at low and medium speed. At high speeds the deviations increased. Possible causes for this behavior are discussed.

Energy, economic, and environmental assessment of the integration of phase change materials and hybrid concentrated photovoltaic thermal collectors for reduced energy consumption of a school sports center

In this study, dynamic simulations of an existing school sports building located in a hot semi-arid steppe climate (BSh) were carried out to evaluate the energy, economic, and environmental performance of an inorganic phase change material (PCM) and a low-concentration photovoltaic thermal (LCPV/T) hybrid collector. For this purpose, transient thermal simulations incorporating software elements were used to model the passive and active technologies. Different scenarios applied in the building -the integration of PCM into the roof (C1), the use of the LCPV/T collector system (C2), and the simultaneous use of these technologies (C3)- were established, and their energy savings, economic feasibility, and environmental impact were obtained. The combination of the PCM with melting point of 23 °C and hybrid collectors reduced the annual building electricity up to 5.8%. C1 is the best option if the cost of the PCM23 decreases to 13% of the original price, with a SPB and IRR of 3.7 years and 27%, respectively. C3 is economically feasible if the collector price is also reduced to 80%, achieving a SPB and IRR of 12.1 years and 6.6%. Finally, the greenhouse gases prevented emissions of up to 162, 138, and 24 tonCO2e/year are for C3, C2, and C1, respectively.

Fast response characteristics of fiber Bragg grating temperature sensors and explosion temperature measurement tests

Transient temperature measurement technology with fast response, harsh measurement environment, and high technical challenges has attracted research interest in the field of temperature measurement. Based on the differential equation of heat conduction at the interface of an optical fiber, the dynamic-response-time formula of the optical fiber was derived, the dynamic response capability of the optical fiber with different diameters was analyzed, and the transient thermal response simulation of the optical fiber was conducted. The theoretical dynamic test response times of optical fibers with diameters of 80, 125, and 145 µm were 30.21, 60.78, and 85.97 ms, respectively. Fast-response fiber Bragg grating (FR-FBG) temperature sensors were designed and manufactured by femtosecond-fabricated FBGs with diameters of 80 and 125 µm. The average response times of the 80 and 125 µm-FR-FBG temperature sensors were 33.2 and 65.3 ms, and the errors between the data and theoretical values were 9.89 % and 7.44 %, respectively. From explosion experiments, it is concluded that the femtosecond grating can be applied to the monitoring of rapid temperature response during explosion, and the response time is related to the diameter of the grating.

Design optimization of conformal cooling channels for injection molds: 3D transient heat transfer analysis

This research aims to enhance the design of an injection mold in order to minimize ejection time and increase temperature uniformity by repositioning cooling channels. For 3D transient thermal simulations, the ANSYS finite element method (FEM) program was employed, while the MATLAB program was used for optimization. It was discovered that the method could be used successfully to optimize the design of Conformal Cooling Channels (CCCs) in injection molds. The objective function value of the optimized model represents a near 40% improvement in relation to the initial model. The combined parameterization, simulation, and optimization method has proven beneficial for enhancing the arrangement of channels in an injection machine mold. The methodology is generalizable. As such, it can be employed in any industrial applications involving injection molding machines, for the improvement of the quality of the manufactured part.

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.

A numerical calibration of structure-function transient thermal measurement based on Cauer RC network

Structure functions were originally provided by V. Székely et al. as a nondestructive method for analyzing the thermal resistance of each layer. In this paper, we propose a numerical calibration of structure functions based on the Cauer RC network. The numerical calibration has practical physical significance and can be used as feedback to form a closed loop system in conjunction with the structure functions. A 3D finite element transient thermal simulation is analyzed by structure functions with different setting parameters to determine the feasibility of the numerical calibration. Furthermore, this numerical method can be used to obtain the transient thermal resistance of an ideal heat dissipation structure from the results of the transient dual interface measurement (TDIM).

A generalized alternating direction implicit method for transient thermal simulation of 2-D structures with locally refined grids

In this article, a generalized alternating direction implicit (ADI) method for transient thermal simulation of two-dimensional structures with locally refined grids is proposed. First, a flexible approach is employed to generate the semistructured grids with local refinement. The generalized ADI method is then derived based on these semistructured grids, in which two new directions are added to deal with the grid points in the transition regions. By this means, the ADI scheme is successfully extended to handle the transient simulation of objects with locally refined grids while maintaining the property of linear complexity in computation. The accuracy and high efficiency of the proposed method are verified by several typical examples.

Combined Thermal and Wear Analysis of Linear Rolling Guide Subjected to Rigid–Flexible Coupling Motion Stage

The local heat and wear generated due to friction in a precision motion stage in electronic packaging equipment have a significant impact on its positioning precision. In this paper, we studied the temperature changes over time and the wear of a linear rolling guide (LRG) in a rigid–flexible coupling motion stage (RFCMS), both analytically and experimentally, and we proposed an evaluation method for LRG wear in an RFCMS. According to Fourier’s law and the law of conservation of energy, the differential equation of heat conduction for the LRG and the thermal boundary conditions were established. Steady-state and transient thermal simulations were carried out using ANSYS Workbench to predict the temperature increase in the LRG due to friction. Finally, a test apparatus was built to demonstrate that an RFCMS reduced the operating temperature of the LRG, which also reduced the wear on the contact surface. Through response surface methodology, the levels of the influence of different flexure hinge thicknesses, strokes, velocities, and accelerations on the temperature change rate (TCR) of the LRG were obtained, as well as the approximate regression equation of four variables of the TCR. This provided a new research method for precision maintenance, life design, and operational parameter selection for high-precision motion stages.

Research on Bionic Fish Scale Channel for Optimizing Thermal Performance of Liquid Cooling Battery Thermal Management System

Liquid cooling battery thermal management systems (BTMSs) are prevalently used in electric vehicles (EVs). With the use of fast charging and high-power cells, there is an increasing demand on thermal performance. In this context, a bionic fish scale (BFS) channel structure optimization design method is proposed to optimize the thermal performance. The effects of different structural parameters of the liquid cooling plate in BTMS on its cooling performance, including BFS notch diameter (D), BFS notch depth (H), and BFS notch spacing (S), are investigated. To minimize the maximum temperature (Tmax) and the maximum temperature difference (ΔTmax) as optimization indicators, experimental tests and numerical calculations are performed for a battery pack consisting of 36 square cells. Sixteen sets of thermal performance are discussed for different structural parameters in the transient thermal fluid simulation by using orthogonal tests. Under the optimal structural parameters, Tmax decreases by 1.61 °C (10.8%) and ΔTmax decreases by 0.43 °C (16.7%). In addition, the maximum increase in outlet flow velocity is 2.72% and the pressure is reduced by 4.98%. Therefore, the proposed BTMS will have effective cooling performance in high-power dissipation.

Effect of different operation strategies on transient solar thermal power plant simulation models with molten salt as heat transfer fluid – Considering 5 cities under different climate zones – Dubai and Iran

Effect of different operation strategies on transient solar thermal power plant simulation models with molten salt as heat transfer fluid – Considering 5 cities under different climate zones – Dubai and Iran