Three-dimensional Thermal Model Research Articles

Investigation of Convective Heat Transfer and Stability on a Rotating Disk: A Novel Experimental Method and Thermal Modeling

Experimental and numerical investigations are conducted on a rotating disk from the perspective of convective heat transfer to understand the effect of heating on the stability of flow. A non-invasive approach with a thermal camera is employed to determine local Nusselt numbers for different rotational rates and perturbation parameters, i.e., the strength of the heat transfer. A novel transient temperature data extraction over the disk radius and an evaluation method are developed and applied for the first time for the air on a rotating disk. The evaluation method utilizes the lumped capacitance approach with a constant heat flux input. Nusselt number distributions from this experimental study show that there is a good agreement with the previous experimental correlations and linear stability analysis on the subject. A significant result of this approach is that by using the experimental setup and developed approach, it is possible to qualitatively show that instability in the flow starts earlier, i.e., an earlier departure from laminar behavior is observed at lower rotational Reynolds numbers with an increasing perturbation parameter, which is due to the strength of heating. Two experimental setups are modeled and simulated using a validated in-house Python code, featuring a three-dimensional thermal model of the disk. The thermal code was developed for the rotating disks and brake disks with a simplified geometry. Experimentally evaluated heat transfer coefficients are implemented and used as convective boundary conditions in the thermal code. Radial temperature distributions are compared with the experimental data, and there is good agreement between the experiment and the model. The model was used to evaluate the effect of radial conduction, which is neglected when using the lumped capacitance approach to determine heat transfer coefficients. It was observed that the radial conduction has a slight effect. The methodology and approach used in this experimental study, combined with the numerical model, can be used for further investigations on the subject.

LBM modeling of three-dimensional mixed convection in CZ crystal growth on curvilinear coordinates system

A three-dimensional (3D) thermal lattice Boltzmann model of crystal growth is presented to study the magneto-hydrodynamics (MHD) mixed convection in the melt of Czochralski silicon single crystal growth in this paper. In order to solve the problem of lattice Boltzmann method’s difficulty in solving the flow of 3D cylindrical cavity, the 3D physical model of crystal growth is transformed from the Cartesian coordinate system to the Curvilinear coordinate system. And the irregular grids in the Cartesian coordinate system are transformed into regular grids in the Curvilinear coordinate system to facilitate the establishment of the Lattice Boltzmann model. Under the above operations, two coupled distribution functions are established to solve the governing equations. Two D3Q19 models are adopted to solve the melt velocity and temperature. And the 3D lattice Boltzmann modeling of crystal growth with cylinder boundary is realized by interpolation in Curvilinear coordinate system. The comparison with the experiment and other references proves that the proposed model and boundary treatment scheme is correct and it proposes a new way for studying the 3D crystal growth or other similar 3D cylindrical cavity simulations. Furthermore, the unstable melt flow for two cases are also simulated in this paper and the critical Reynolds number are also obtained. Results show that the introduction of the transverse magnetic field enhances the stability of the crystal growth system and increases the adjustable range of crystal rotation parameter. The obtained conclusion has an important reference for adjusting the process parameters during the CZ crystal growth.

Numerical analysis and process optimization of electron beam melting for superalloys

This study aims to determine the optimal parameters for the electron beam melting process by employing a modified transient three-dimensional thermal model. The validity of the thermal model is confirmed through experimental results. Moreover, the proposed method establishes mathematical relationships between the resulting molten pool temperature and process parameters. A broader range of process parameters for a new Ni–Co-based superalloy was achieved by investigating the effects of scanning velocities (10–100 mm/s), scanning radius (20–60 mm), and melting mass (1500–3100 g) on temperature at various electron beam power levels (10–30 kW). Regression models were established between scanning velocities-temperature, and scanning radius-temperature under different electron beam power levels. These models laid the foundation for real-time automatic control of molten pool temperature. Significantly, orthogonal experimental design and response surface method are employed to conduct a multi-objective optimization based on sixteen experiments and three parameters. The results of multi-objective optimization indicate that with a smelting mass of 1.5 kg, an electron beam power of 11 kW, a scanning radius of 60 mm, and a scanning velocity of 75 mm/s, the energy consumption is 34.95 kW h, and the theoretical mass loss of Ni element is 0.002 kg. The desirability is 91.2 %.

Enhanced dropwise condensation on downward-facing cross-shaped pillar-structured surfaces with mixed wettability

In this paper, a novel downward-facing cross-shaped pillar-structured surface with mixed wettability is conceived for enhancing dropwise condensation. A three-dimensional thermal lattice Boltzmann model is employed to investigate the condensation performance on the downward-facing cross-shaped pillar-structured surface with mixed wettability and the associated enhancement mechanism of dropwise condensation. The numerical investigation shows that the cross-shaped pillar-structured surface with mixed wettability exhibits much better condensation performance than the square pillar-structured surface with mixed wettability and the flat surface with mixed wettability due to the synergistic effects of structural effects and mixed wettability, which can promote the droplet nucleation and accelerate the condensate removal. Moreover, for different contact angles of the pillar top (θtop), there exists a competition between the droplet nucleation and the condensate removal on the downward-facing cross-shaped pillar-structured surface. It is found that, when θtop=60°, an optimal droplet dripping rate can be achieved due to a suitable balance between a relatively large mass of detached droplets and a short condensation cycle time. Furthermore, the aspect ratio (γ) has an important influence on the droplet dripping rate, i.e., as γ increases, the droplet dripping rate first exhibits small fluctuations, then increases rapidly before γ=1.0, and after that experiences a slight variation. The large droplet dripping rate achieved at γ=1.0 is mainly attributed to the fact that an optimum structure of the concave corner can promote the droplet nucleation, increase the length of the triple-phase contact line, advance the appearance of droplet coalescence, and finally accelerate the condensate removal.

Experimental and simulation investigation of thermal runaway propagation in lithium-ion battery pack systems

Safety issues related to battery thermal runaway hinder the widespread adoption of electric vehicles. Thermal runaway propagation in a single cell within the modules and the entire battery system can be hazardous. Limited research has been published on thermal runaway propagation at the battery system level. In this study, thermal runaway propagation experiments were conducted at the battery system level for a comprehensive, multi perspective examination of the temperature, voltage, gas, and pressure changes during thermal runaway propagation in a battery system. Additionally, based on the fundamentals of heat transfer, a preliminary three-dimensional thermal runaway propagation model was developed for battery packs. This model exhibited high simulation accuracy and effectively captured the thermal propagation trends within modules. This research uncovers several of thermal runaway propagation characteristics in battery systems, providing valuable insights for the safe design of battery packs.

Postfire performance of pultruded wood-cored GFRP sandwich beams

Wood-cored sandwich components have been extensively used in constructions of buildings and bridges. However, the existing studies on the postfire behavior of these components are very limited. This study aims to quantitatively evaluate the postfire residual properties of the pultruded wood-cored GFRP sandwich (PWGS) beams. This paper mainly comprises three parts: (i) review of fire experiment of the PWGS beams; (ii) postfire bending experiments conducted on the PWGS beams with different fire scenarios and (iii) numerical study on thermal and postfire thermomechanical responses. It was found the failure modes mainly depended on the number of exposed sides and the fire damage degree. For the three-sided fire-exposed specimens (except for the one with a 25 mm-thick calcium silica board), the progressive tension rapture of the charred fibers was the dominant failure mode. The other specimens, however, exhibited the brittle in-plane shear failure of the web. Moreover, after cooling down from 250 °C to 20 °C, the GFRP and wood exhibited 68 % and 35 % of recoveries of elastic modulus respectively. A three-dimensional thermal model with kinetic thermophysical sub-models considering heat transfer, water evaporation and decomposition was developed. The developed thermal model accurately predicted the temperature responses and charring profiles. Furthermore, a thermomechanical model considering the material damage was developed to accurately predict the elastic modulus distribution, postfire residual bending capacity and failure modes. This study provides the basis for the retrofit and the reinforcement of the fire-damaged PWGS beams. In the future, study on the fire resistance of the PWGS components in fire will be required.

Numerical Investigation on Reduction Characteristics of Welding Deformation According to Standoff Distance in Heat Sink Welding Process

Welding with a trailing heat sink process is proposed as a useful technique to reduce welding deformation without a significant loss of manufacturing efficiency. In particular, this method is effective than the existing mechanical or thermal correction method in thin plate steel structures with low stiffness. In this study, a three-dimensional thermal elastic-plastic finite element model using a 3-mm thick 304L stainless steel sheet was developed to simulate heat sink welding. The reduction characteristics of welding deformation according to the standoff distance between the welding heat source and the heat sink zone was investigated in the numerical simulation. The results confirmed that the longitudinal and angular deformations were significantly reduced compared with those by conventional welding. The longitudinal deformation was reduced by approximately 60%, from 5.50 mm to 2.22 mm, and the angular deformation was reduced by approximately 70%, from 1.68 mm to 0.51 mm. The overall results obtained in the numerical analysis indicated that welding deformation significantly decreased as the standoff distance was shorter owing to the temperature cooling effect of the welds.

Modelling and optimization analysis of a novel hollow flexible-filler-based bulk thermoelectric generator for human body sensor

Thermoelectric generator (TEG) is a promising technology for self-powered wearable electronics and sensors. Usually, polydimethylsiloxane (PDMS) is selected as bulk thermoelectric gap filler to make the TEG flexible. However, PDMS has much higher thermal conductivity than air causing considerable thermal shortcut and efficiency degradation. In this study, a novel hollow PDMS-filler design is proposed to enhance the TEG performance. A well-validated three-dimensional thermal and electrical coupled model is developed to assess effects of longitudinal and transverse hollow structures on maximum output power and corresponding optimal fill factor of the flexible TEG, and to reveal impact of key geometrical and physical parameters on design optimization of the TEG. Results show that, (1) as height of the hollow structure increases, the output power increases linearly, while the optimal fill factor decreases sharply; (2) the transverse-hollow structure is more effective than the longitudinal-hollow structure to create higher power; (3) the transverse-hollow structure can approximately double the output power while halve the optimal fill factor; (4) the transverse-hollow structure combined with both-sides high-thermal-conductivity layers can increase output power up to 137.34 μWcm−2. Such design of hollow PDMS filler could open a window of opportunity to the next generation efficient yet low-cost flexible TEG.

A thermal network model considering thermal coupling effect and TIM degradation in IGBT modules

Thermal interface materials (TIMs), as important materials for heat dissipation of insulated gate bipolar transistor (IGBT) modules, degrade under long-term thermal cycling, resulting in elevated junction temperatures and threatening the safe operation of IGBT modules. In consideration of the thermal coupling effect in IGBT modules, this paper proposes a three-dimensional thermal network model characterizing the TIM degradation. An IGBT module with the TIM is adopted to establish the finite element method (FEM) model, in which the TIM layer is divided into regular areas. The thermal network is established by simulating the heat transfer paths. The thermal impedance in each path is extracted according to the heat flow through its area considering the TIM degradation. Thereby, the impact of thermal coupling and TIM degradation on junction temperature of IGBT modules could be characterized. Furthermore, the proposed thermal network is verified by simulation from calculation accuracy of junction temperature and TIM temperature.

Dynamic IGBT Three-Dimensional Thermal Network Model Considering Base Solder Degradation and Thermal Coupling Between IGBT Chips

With the development of power electronic technology, the thermal characteristics of high-power insulated gate bipolar transistor (IGBT) module are vital information for thermal management of power electronic equipment, reliability analysis, and thermal design of power electronic system. However, the present commonly used lumped thermal network model based on thermal resistance and heat capacity still has some limitations in accurately predicting the junction temperature of IGBT modules, significantly once considering the degradation of base solder in high-power IGBT modules. In this paper, the thermal behavior of high-power IGBT chips under different base solder degradation is studied by the finite element method (FEM). The results show that the degradation of the base solder has effects on the thermal impedance between the junction and the case, which should be fastidiously thought about within the thermal network model modeling. As a result, a dynamic three-dimensional thermal network model that takes into account the thermal interaction between IGBT chips, as well as the degradation of the base solder, is proposed in this paper. The proposed thermal network model can estimate the junction temperature of a high-power IGBT module correctly and fast based on the real degradation of the base solder. Finally, finite element simulation and experimental findings are used to validate the proposed dynamic three-dimensional thermal network model. The results show that the dynamic three-dimensional thermal network model has comparable accuracy to finite element simulation and test results. At the same time, the dynamic three-dimensional thermal network model responds faster than the finite element simulation.

A Large-Scale Identification Approach for Thermal Parameters of Multichips IGBT Modules Based on LLSO-SQP Algorithm

This paper proposes a large-scale optimization approach for identifying thermal parameters of multi-chip IGBT modules. State-space equation, in which the coefficient matrix comprises the thermal resistance and capacitance, is provided to represent the compact three-dimensional thermal network model. Then, the level-based learning swarm optimization (LLSO) algorithm is firstly utilized to identify large-scale thermal parameters. Additionally, to solve the inefficient convergence problem, the optimization results obtained from the LLSO is provided as the initial value of the sequential quadratic programming (SQP) algorithm to find the global optimal solution. Hence, the proposed LLSO-SQP algorithm can identify the large-scale thermal parameters efficiently and accurately. The training dataset for the algorithm is derived from the transient temperature response of a finite element model (FEM) of the IGBT module under power step excitation. Since only one-time simulation is in-demand, this approach needs less computational effort than others. The identified thermal network model is utilized to estimate junction temperature profiles taking a two-level inverter as a case study. In comparison to that of the experiment and FEM, the results validate the feasibility and accuracy of the junction temperature estimation method based on the compact three-dimensional thermal network model.

Temperature distribution in the crust and upper mantle of the territory of Ukraine

The study aims to build a three-dimensional thermal model of the crust and upper mantle of the territory of Ukraine. Its basis is a scheme of deep processes in the tectonosphere, which, first of all, considers the results of heat and mass transfer during modern activation. They are superimposed on the models of the platform (except for the territory of the East European platform; the Donbas is also included in it), the Alpine geosyncline of the Carpathians, and the Hercynian-Cimmerian geosyncline of the Scythian plate. The incomplete process of modern activation cannot be accurately described by the geological theory used by the authors. Gravity modeling was previously conducted on a system of profiles around the northern hemisphere with a total length of more than 30,000 km, crossing Eurasia, North America, as well as the Atlantic and Pacific oceans to select an adequate scheme of heat and mass transfer. The paper distinguishes the most realistic scheme of the process . It is applied for Ukraine, and the more accurately the activated area is determined. Such a task was solved for the first time. In the south, the model is limited by the Black Sea depression, at a depth of 400 km. Temperatures in the transition zone to the lower mantle were not considered. Test thermal models are compared with geothermometers. The error (50°C) of calculation and cross-section of isotherms is determined (150°C for depths from 50 to 400 km, at a depth of 25 km the error is lower, the cross-section of isotherms is 100°C). Zones of partial melting of the rocks of the crust and upper mantle have been established. They are distributed in the middle part of the crust, in the upper horizons of the mantle (50-100 km). At a depth of about 400 km, partial melting occurs only under the non-activated part of the platform. Differences in the model from the presented one are described. They are associated with possible variations in the age of the process and its peculiarities at different levels of heat and mass transfer. Practical significance. The study emphasizes that mineral deposits are characteristic to thermal anomalies and other environmental parameters.

A new laser welding method of two transparent plastic parts based on reflector assisted method

It is a challenging work to joint two transparent plastic parts using traditional laser welding because the absorptivity of transparent plastic on short wavelength (800–1000 nm) laser energy is very low. During the laser welding of two transparent plastic parts, although laser absorber and long wavelength (1600–2000 nm) laser can obtain the high-strength weld joint, the problems of unattractive weld joint or pollution will occur when laser absorber is used, and the laser energy utilization coefficient is about 70% when long wavelength laser energy is used. To address this issue, this paper proposes a new production method for the absorber-free laser welding of two transparent plastic parts based on reflector assisted method. From three-dimensional thermal model, it can be found that the simulation data of the modified Gauss cylindrical body heat source show better agreement with the experimental result than those of Gauss surface heat source and Rotary-Gauss body heat source. In addition, for the same the weld joint width on the contact surface, the reflector assisted laser welding method can decrease the laser energy consumption by about 20%. Moreover, the maximum shear force of weld joint can be up to 1315 N. Under the same process parameters, the reflector assisted method can increase the shear strength of weld joint by 15.3%. Hence, the reflector assisted method has good application and promotion value in laser welding two transparent plastic parts.

Research on accurate thermal network calculation model of modular permanent magnet motor

This paper proposes a thermal network model for calculating the modular permanent magnet motor’s temperature rise. Analyzing the actual heat flow path of motor Joule loss and considering the circumferential heat conduction of winding, the local three-dimensional thermal network model of winding is constructed. Based on the model, the motor parts’ steady and dynamic temperature rise is calculated and verified by the FEM. The thermal network model also applies to motors with short winding ends and complex stator yokes.

An investigation on thermal runaway behaviour of a cylindrical lithium-ion battery under different states of charge based on thermal tests and a three-dimensional thermal runaway model

A significant risk for lithium-ion batteries (LIBs) is fire and explosions caused by thermal runaway (TR). A TR model for LIBs with various states of charge (SOCs) can help design safer battery modules. In this work, the TR mechanism of a commercial Li[Ni5Co2Mn3]O2/graphite 18650 type cylindrical battery with various SOCs has been investigated through differential scanning calorimetry (DSC) tests on the single and mixed components. Then, a three-dimensional (3D) TR model is developed to predict the battery TR behaviours under different SOCs. This model fits well with the accelerating rate calorimetry (ARC) test results of the batteries with various SOCs. Furthermore, the validated model and ARC experiment results are employed to investigate the TR mechanism of different SOC batteries. The results show that the reaction onset temperature for cathode-anode and anode-electrolyte roughly advances as the SOC increases and the reaction enthalpy of the cathode-anode, anode-electrolyte and cathode increases with the increase of SOC. Cathode-anode, anode-electrolyte are the main heat generation in the process of battery TR, and their proportion of heat generation will decrease with the decrease of SOC.

Evaluation and Test of Impact-Resistant Overload Capability of Companion-Type Direct Cooling Motor

In the actual working process of the motor, there will be short-term overload conditions, which puts forward higher requirements for maintaining the overload capacity of the motor. Due to the limitation of the thermal limit on the overload capacity of the motor, taking a 250kW permanent magnet synchronous motor (PMSM) as an example, this paper proposes a thermal management scheme of companion-type direct cooling, and establishes a three-dimensional thermal network model considering the secondary circulation factor. At the same time, in order to explore the influence of the thermal management scheme on the overload capacity of the motor when there is an impact load, on the premise that there is a safety margin for the hottest spot temperature of the winding under the rated state of the motor, the impact load is simulated by setting the overload torque, the thermal network model is used to compare and analyze the temperature field of the motor based on the companion-type direct cooling and the indirect casing cooling, and combining with the insulation limit to quantitatively compare the overload capacity of the motor after impact load. Through the simulation test, it is verified that the motor based on the companion-type direct cooling has efficient heat dissipation and stronger impact-resistance overload capability. The proposal of the companion-type direct cooling scheme has important practical significance for excavating the load potential of the motor under actual operating conditions.

Thermal Propagation Modelling of Abnormal Heat Generation in Various Battery Cell Locations

With the increasing demand for energy capacity and power density in battery systems, the thermal safety of lithium-ion batteries has become a major challenge for the upcoming decade. The heat transfer during the battery thermal runaway provides insight into thermal propagation. A better understanding of the heat exchange process improves a safer design and enhances battery thermal management performance. This work proposes a three-dimensional thermal model for the battery pack simulation by applying an in-house model to study the internal battery thermal propagation effect under the computational fluid dynamics (CFD) simulation framework. The simulation results were validated with the experimental data. The detailed temperature distribution and heat transfer behaviour were simulated and analyzed. The thermal behaviour and cooling performance were compared by changing the abnormal heat generation locations inside the battery pack. The results indicated that various abnormal heat locations disperse heat to the surrounding coolant and other cells. According to the current battery pack setups, the maximum temperature of Row 2 cases can be increased by 2.93%, and the temperature difference was also increased. Overall, a new analytical approach has been demonstrated to investigate several stipulating battery thermal propagation scenarios for enhancing battery thermal performances.

Fast and Slow Earthquakes in Alaska: Implications from a Three-Dimensional Thermal Regime and Slab Metamorphism

Fast and slow earthquakes are predominantly generated along faults constituting active plate boundaries. Characterized by repeated devastating earthquakes and frequent slow slip events and tremors, the Alaska megathrust presents a chance to understand the complicated dynamics of a subduction system changing from steep to shallow dips associated with enigmatically abundant fast and slow seismic events. Based on three-dimensional thermal modeling, we find that the downgoing metamorphosed oceanic crust containing bound water releases a large amount of fluid and causes the recurrence of fast and slow earthquakes by elevated pore fluid pressure and hydrofracturing. The seismogenic interface and the slow slip events (SSEs) identified beneath the Upper Cook Inlet coincide well with the slab metamorphic dehydration regions. The observed slow earthquakes with quasi-stable fault slips preferentially occur, accompanied by high dehydration and temperature downdip along the transition zone.

Research and numerical analysis on performance optimization of photovoltaic-thermoelectric system incorporated with phase change materials

In recent years, photovoltaic (PV) cells have been widely used to cope with the problem of global energy shortage. In the current researches, the PV-TEG-PCM (photovoltaic-thermoelectric generator-phase change material) system can improve the utilization of solar energy and the hybrid system shows better performance. Most of the previous studies were two-dimensional models or steady-state models, which could not accurately evaluate the system performance under fluctuating solar irradiation. This research constructs a three-dimensional thermal simulation transient model of the PV-TEG-PCM system. The model is simulated under fluctuating solar irradiation, model validity has been verified. This research completes and optimizes the theoretical researches of PV-TEG-PCM systems. This research will play a guiding role in the subsequent practical experiments and applications. The effects of PCM melting temperature, thickness and thermal conductivity are studied. The results show that the performance of PV-TEG-PCM system is better than that of PV-TEG or sole PV systems. At the peak sun-hour, the PV temperature was reduced for three types of PV-TEG-PCM systems compared to PV-TEG systems. Through simulation, the PCM layer with 30 mm thickness and melting temperature of 42 °C, can make the PV-TEG-PCM system established this time achieve the best thermal performance.

Three-dimensional thermal modeling of high-temperature primary lithium battery with nickel disulfide cathode

Thermal modeling is significant for high-temperature primary lithium batteries (thermal batteries) widely used in military hardware and aerospace equipment. Herein, the three-dimensional (3D) thermal model of a thermal battery with the novel cathode NiS2 and 48 cells is performed to observe the thermal behavior within 500 s from the single cell to the whole battery. From the perspective of unit cell, the Li–B/LiF–LiCl–LiBr/NiS2 cell shows exothermic reaction with the potential temperature coefficient of −0.405 mV K−1, so double heat sources exist in the cell during discharge. From the thermal field of battery stack, the temperature uniformity of the battery stack is the worst at the start of the discharge with a significant temperature gradient (about 90 °C) in the lead-out disks, but then improves with increasing discharge time. According to the thermal balance of the entire battery, the total heat generation is greater than the heat dissipation for the first 325 s and then becomes negative, as the increase in Joule heat is insufficient to offset the decrease in reversible reaction heat with decreasing temperature. This study could provide theoretical guidelines for the thermal design and management of thermal batteries with NiS2 cathodes and other novel materials.