Thermal Network Model Research Articles

Robust Design Optimization of Electrical Machines: A Comparative Study and Space Reduction Strategy

This article presents a comparative study on different types of robust design optimization methods for electrical machines. Three robust design approaches, Taguchi parameter design, worst-case design and design for six-sigma, are compared for low-dimensional and high-dimensional design optimization scenarios, respectively. For the high-dimensional scenario, the computational burden is normally massive due to the robustness evaluation of a huge number of design candidates. To attempt this challenge, as the second aim of this paper, a space reduction optimization (SRO) strategy is proposed for these robust design approaches, yielding three new robust optimization methods. To illustrate and compare the performance of different robust design optimization methods, a permanent magnet motor with soft magnetic composite cores is investigated with the consideration of material diversities and manufacturing tolerances. 3-D finite element model and thermal network model are employed in the optimization process and the accuracy of both models has been verified by experimental results. Based on the theoretical analysis and optimization results, a detailed comparison is provided for all investigated and proposed robust design optimization methods in terms of different aspects. It shows that the proposed SRO strategy can greatly improve the design optimization effectiveness and efficiency of those three conventional robust design methods.

Influence of Contact Pressure on the Thermal Contact Conductance of Layered AA3003 Aluminium

For the optimization of the annealing process of aluminium coils, simulation of the process is often performed. To simulate the process with higher accuracy, reliable input parameters are required and the thermal conductivity (thermal contact conductance) is one of them. In the present study, the thermal conductivity and thermal contact conductance of AA3003 alloy sheets were measured by a steady state comparative longitudinal heat flow method at different contact pressure. To evaluate the thermal conductance at the interface, thermal resistance network model' was applied. In addition, the surface roughness of the sheets was also investigated. Based on the measurement results, the semi-empirical equation for the relationship between thermal contact conductance and contact pressure was obtained

A Three-Dimensional Boundary-Dependent Compact Thermal Network Model for IGBT Modules in New Energy Vehicles

With the development of power electronics technology, power modules delivery considerably greater power density, which makes junction temperature an important parameter for reliable operation. Existing thermal models often ignore the influence of the thermal boundary conditions on the thermal parameter and cannot accurately predict junction temperature in various operating conditions. This article proposes a three-dimensional compact thermal network model that considers the thermal boundary conditions and can be obtained by the finite-element method (FEM). A novel two-step method for thermal parameter extraction is presented and the effects of boundary conditions on thermal network parameters are discussed in detail. The experimental results and FEM simulation show that the proposed thermal network model can accurately estimate the junction temperature in different thermal boundary conditions.

Energy-saving potential of 3D printed concrete building with integrated living wall

Large-scale concrete 3D printing and digital construction has brought enormous potential to expand the design space of building components (e.g., building envelope) for the integration of multiple architectural functionalities including energy saving. In this research, a modular 3D printed vertical concrete green wall system – namely the 3D-VtGW, was developed. The 3D-VtGW envelope was assembled with prefabricated (3D printed) multifunctional wall modular elements, which serves as the enclosure of the building as well as the backbone for a green wall system to improve building’s energy efficiency. Using this design concept and large-scale concrete 3D printing, a prototype commercial building was built in Nanjing, China. To quantify the energy-saving potential of the 3D-VtGW system, a thermal network model was developed to simulate the thermal behavior of buildings with 3D-VtGW system and for thermal comfort analysis. Whole-building energy simulation was carried out using Chinese Standard Weather Data (CSWD) of Nanjing, China. The simulation results indicate that the building with 3D-VtGW exhibited prominent potential for energy saving and improved thermal comfort. The integrated greenery system in 3D-VtGW largely reduces wall exterior surface temperature and through-wall heat flux via the combined effects of plant shading, evapotranspiration, and heat storage from soil. This study presents the immense opportunities brought by digital fabrication and construction to extend the design space and function integration in buildings.

Thermo-electrical modelling of the ATLAS ITk Strip Detector

In this paper we discuss the use of linked thermal and electrical network models to predict the behaviour of a complex silicon detector system. We use the silicon strip detector for the ATLAS Phase-II upgrade to demonstrate the application of such a model and its performance. With this example, a thermo-electrical model is used to test design choices, validate specifications, predict key operational parameters such as cooling system requirements, and optimize operational aspects like the temperature profile over the lifetime of the experiment. The model can reveal insights into the interplay of conditions and components in the silicon module, and it is a valuable tool for estimating the headroom to thermal runaway, all with very moderate computational effort.

Time-varying reliability prediction modeling of positioning accuracy influenced by frictional heat of ball-screw systems for CNC machine tools

Thermally induced elongation of a screw is the primary cause of deterioration in the positioning accuracy of half-closed-loop screw systems in machine tools. The failure mode of ball-screw feed-drive systems in relation to the positioning accuracy is defined as the response error of the carriage exceeding the axial tolerance. It is still challenging to accurately predict the thermal errors using conventional methods because the randomness of the influencing factors is not considered. This paper presents an improved random thermal network model subjected to dynamic thermal excitation for calculating real-time transient temperatures of ball-screw systems. Furthermore, a time-varying reliability model is proposed for estimating the gradual reliability of the thermally induced positioning accuracy of ball-screw systems with random thermal boundary parameters using the random thermal network. A ball-screw system of a computerized numerical controlled lathe is used as an example to show the practical application of the proposed model. Repeated experiments demonstrate the accuracy retaining ability and robustness of this method. This work provides the theoretical and practical method for real-time monitoring of the positioning accuracy reliability index for ball-screw systems and it has high accuracy considering the random parameters.

Thermal Model and Countermeasures for Future Smart Glasses.

The market for wearable devices such as smart watches and smart glasses continues to grow rapidly. Smart glasses are attracting particular attention because they offer convenient features such as hands-free augmented reality (AR). Since smart glasses directly touch the face and head, the device with high temperature has a detrimental effect on human physical health. This paper presents a thermal network model in a steady state condition and thermal countermeasure methods for thermal management of future smart glasses. It is accomplished by disassembling the state by wearing smart glasses into some parts, creating the equivalent thermal resistance circuit for each part, approximating heat-generating components such as integrated circuits (ICs) to simple physical structures, setting power consumption to the heat sources, and providing heat transfer coefficients of natural convection in air. The average temperature difference between the thermal network model and a commercial thermal solver is 0.9 °C when the maximum temperature is 62 °C. Results of an experiment using the model show that the temperature of the part near the ear that directly touches the skin can be reduced by 51.4% by distributing heat sources into both sides, 11.1% by placing higher heat-generating components farther from the ear, and 65.3% in comparison with all high conductivity materials by using a combination of low thermal conductivity materials for temples and temple tips and high conductivity materials for rims.

Fast heat conduction-based thermal error control technique for spindle system of machine tools

In view of the thermal declination of spindle system caused by the uneven heating, this paper proposed a thermal error reduction strategy by optimizing the thermal conductivity of the material. Firstly, according to the structural size and material characteristics of the spindle system, the thermal resistance and thermal contact resistance of each component are calculated, thereby establishing a spindle-housing thermal resistance network model and calculating temperature values of the key points. Then, heat conduction and insulation device are properly installed in the headstock, so that the heat in the high temperature zones can be quickly conducted to the low temperature zones, and the temperature field of the headstock is balanced. Finally, the multi-objective optimization method is used to optimize the size, material properties, and surface parameters of the device to achieve optimal heat balance. Verification was performed by numerical simulation and experiments. The results demonstrate that the thermal conductivity optimization strategy can effectively improve the temperature nonuniformity of the headstock and reduce the thermal tilt of the spindle.

Lubricated Loaded Tooth Contact Analysis and Non-Newtonian Thermoelastohydrodynamics of High-Performance Spur Gear Transmission Systems

Energy efficiency and functional reliability are the two key requirements in the design of high-performance transmissions. Therefore, a representative analysis replicating real operating conditions is essential. This paper presents the thermoelastohydrodynamic lubrication (TEHL) of meshing spur gear teeth of high-performance racing transmission systems, where high generated contact pressures and lubricant shear lead to non-Newtonian traction. The determination of the input contact geometry of meshing pairs as well as contact kinematics are essential steps for representative TEHL. These are incorporated in the current analysis through the use of Lubricated Loaded Tooth Contact Analysis (LLTCA), which is far more realistic than the traditional Tooth Contact Analysis (TCA). In addition, the effects of lubricant and flash surface temperature rise of contacting pairs, leading to the thermal thinning of lubricant, are taken into account using a thermal network model. Furthermore, high-speed contact kinematics lead to shear thinning of the lubricant and reduce the film thickness under non-Newtonian traction. This comprehensive approach based on established TEHL analysis, particularly including the effect of LLTCA on the TEHL of spur gears, has not hitherto been reported in literature.

Modeling of double-layer triangular microchannel heat sink based on thermal resistance network and multivariate structural optimization using firefly algorithm

The micro-channel heat dissipation system has minor specifications and good thermal conductivity per unit, which is the best choice for heat dissipation of micro-chips. By optimizing the cross section of microchannel, the heat exchange efficiency and temperature uniformity can be effectively improved. In this article, a double-layer triangular microchannel heat sink is proposed, which uniquely combines triangular cross section and double-layer structure to obtain a better heat dissipation performance. A new thermal resistance network model is established. At the same time, the model of pressure drop in microchannel heat sink is obtained by use of fluid theory. Taking thermal resistance and pressure drop as optimization objectives, the thermal resistance of double-layer triangular microchannel heat sink is 0.284 K/W and the pressure drop is 1386.89 Pa by using the firefly algorithm based on the Pareto optimal solution set, obtaining the optimal structural parameters. The thermal-flow-solid coupling simulation analysis shows that the thermal resistance and theoretical analysis error is 5.19%, and the pressure drop and theoretical analysis error is 9.49%, which can verify the accuracy of the thermal resistance network model. This article has a guiding significance for the thermal resistance analysis and heat dissipation improvement of non-rectangular cross section microchannel heat sinks.

Online Estimation Method for Permanent Magnet Temperature of High‐Density Permanent Magnet Synchronous Motor

Since it can be difficult to directly estimate the temperature of permanent magnets (PM) in high‐density permanent magnet motor rotors, this paper proposes a method based on lumped parameter thermal networks (LPTN) for online estimation of PM temperature. Firstly, a parameter model is established that contains a four‐node thermal network model and a loss model. For the online estimation, an extended Kalman filter algorithm with fading factor is used to dynamically update the thermal network parameter model in order to estimate the PM temperature. The simulation and experimental results show that the parameter model can quickly converge to a value that is close to the true value. Therefore, this online estimation method for PM temperature can accurately monitor the PM temperature online without increasing the required motor hardware; thus not affecting the motor operation. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Analytical model for predicting the junction temperature of chips considering the internal electrothermal coupling inside SiC metal–oxide–semiconductor field‐effect transistor modules

Owing to their excellent characteristics, silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor modules are expected to have broad application prospects in various types of power conversion equipment in the future. Accurate prediction of the internal chip junction temperature of SiC module is of great value for the usage of the modules in the power conversion equipment. In this study, taking the electrothermal coupling process, and the thermal characteristics of the chips into consideration, the power loss model under unipolar and bipolar sinusoidal pulse-width modulation control was developed. A star-shaped equivalent thermal network model based on virtual temperature was established. Moreover, an analytical junction temperature predicting model was proposed. To obtain the temperature dependence of static and dynamic parameters for the models, power device analyser was used, and the double pulse test bench was established. To validate the effectiveness and accuracy of the above models, the finite element method was used to calculate the junction temperature of a commercial 1200 V/300 A full SiC module under different working conditions. The results show that the relative error is very small and the proposed model is effective

Numerical investigation on the thermal performance of Alpha Magnetic Spectrometer main radiators under the operation of International Space Station

The thermal environment of the space-borne instruments can be affected by their carriers. Investigation on those thermal effects has great importance for those payloads operating safely and stably. In the current work, the influences of the operation of International Space Station flight attitude adjustment on the thermal performance of the Alpha Magnetic Spectrometer main radiators are studied by numerical simulations. For that purpose, the thermal network model is developed and validated by the theoretical calculation from the mathematical model, based on which, the external heat flux absorbed and the temperature response characteristics under the three most frequent attitude adjustments are further studied. By the results, the error between the two models is less than 18.2% which proves the validation of the developed numerical model. The external heat flux varies obviously when changing the flight attitude and even reaches its maximum of 480 W/m2. The temperatures respond accordingly and may even cause the temperature anomalies in 44.8% of the selected cases with the minimum occurrence time of 6235 s. Moreover, the areas with the most drastic temperature variations are always located at the upper-right and the bottom positions of AMS main radiators, which is independent of the flight attitude adjustment.

A Generalized Mesh-Based Thermal Network Model for SPM Machines Combining Coupled Winding Solution

In this article, a new equivalent thermal network (ETN) model for surface-mounted permanent magnet machines is proposed by applying a mesh-based method with bidirectional coupled winding solution. The key is to couple the winding temperature distributions with thermal network meshes in stator dynamically. First, the meshing method is proposed and combined in the lumped parameter thermal model to obtain temperature distributions instead of the average temperature. The mesh elements have identical shapes and unified thermal conductivity, which can greatly enhance the modeling flexibility and efficiency. Second, the slot winding is established by a 2-D analytical solution method under segmented boundaries with a temperature gradient. Then, the winding solution is coupled with mesh nodes and integrated in the ETN model to accurately predict the temperature distributions in slot including the maximum temperature and position offset. Finally, the effectiveness of the proposed ETN model is verified by comparison with the finite-element analysis and experimental results.

Thermal resistance network model for heat conduction of amorphous polymers

Thermal conductivities (TCs) of the vast majority of amorphous polymers are in a very narrow range, 0.1 $\sim$ 0.5 Wm$^{-1}$K$^{-1}$, although single polymer chains possess TC of orders-of-magnitude higher. Entanglement of polymer chains plays an important role in determining the TC of bulk polymers. We propose a thermal resistance network (TRN) model for TC in amorphous polymers taking into account the entanglement of molecular chains. Our model explains well the physical origin of universally low TC observed in amorphous polymers. The empirical formulae of pressure and temperature dependence of TC can be successfully reproduced from our model not only in solid polymers but also in polymer melts. We further quantitatively explain the anisotropic TC in oriented polymers.

Modeling and thermal analysis of a canned permanent magnet machine with a novel network model

Due to use of cans in the airgap, the eddy current induction occurs and generates can loss. The loss on cans is considerably high and leads to excessive temperature rise of a canned motor, a fast and accurate temperature is necessary. In this paper, a compensation element assisted thermal model is proposed and stressed, due to the inaccuracy of tradition thermal network model. First, the studied canned motor is described. Second, the thermal analysis principle is studied. Then, the novel thermal network model with compensation element is studied, with thermal resistance calculation. Finally, compare motor temperature that is measured by thermal network model and finite element (FE). FE is used as reference and complement.

A Design Method of Air-Cooled Radiator Based on Electric Aircraft Controller

The air-cooled motor controller has been widely used in electric aircraft due to its simple heat dissipation structure and maintenance-free features. Being the main heating component of the electric propulsion system of electric aircraft, the weight and the volume of the air-cooled motor controller need to be strictly controlled. Due to the short power running time of the electric motor controller, there is a large weight and volume allowance margin for the air-cooled radiator-based on the rated power and heat dissipation requirements of the motor controller.This paper proposes an air-cooled radiator design method that can reduce its volume and weight by optimizing its structure based on the operating conditions of the electric aircraft under the heat dissipation requirements.The structure of the air-cooled motor can be optimized by optimizing the structure the minimum structure of the motor controller radiator constrained by the maximum temperature of the Insulated Gate Bipolar Transistor (IGBT) module,which can be determined using an algorithm called the motor controller thermal resistance network model. Experimental results obtained from a prototype test on a two-seat electric aircraft demonstrate the effectiveness of the optimization method. The air-cooled radiator designed using the proposed method can be reduced by 5% in weight while meeting the heat dissipation requirements of the motor controller of the electric aircraft.

Phase change heat transfer characteristics of an additively manufactured wick for heat pipe applications

This study presents the phase change heat transfer characteristics of an additively manufactured wick for heat pipe applications. For this study, a flat heat pipe is considered that is made of stainless steel 316L utilizing a fabrication process that yields a wick structure with multi-scale features. Using laser powder bed fusion, relatively large pore structures, similar to screen-mesh structures, are laser molten with micro-scale laser-sintered features on top of this – we refer to these as multi-scale features in this paper. To characterize the phase change processes at heat pipe operating conditions, an experimental facility was developed. For this aim, a test cell with an internal volume of 40 × 20 × 6 mm3 was fabricated. Different filling ratios with water as working fluid and heat inputs ranging from 0.75 to 82.5 kW/m2 were tested. Additionally, a thermal network model to predict the overall heat transfer performance of an additively manufactured flat heat pipe is presented. The model is based on the heat conduction through the wick and wall in both axial and radial directions. Validation by comparison to experimental data shows an excellent agreement for the operating temperature (adiabatic or vapour temperature). The fabricated wick structure exploits enhanced evaporation heat transfer; thin film evaporation occurs due to the multi-scale sintered powder features on top of the fabricated wick surface. Additionally, the optimal filling ratio for which the device has maximal thermal performance is determined. The evaporation superheat is determined and discussed for different filling ratios. Experimental results show the optimum thermal performance of the flat heat pipe for a filling ratio of 110%. Compared to conventional wick structures, additively manufactured wick design exhibits improved thermal performance at higher heat fluxes. The experimental results suggest that additive manufacturing is a promising technology to fabricate freeform porous structures for heat pipes in general.

Thermal-Fluid-Solid Coupling in Thermal Characteristics Analysis of Rolling Bearing System Under Oil Lubrication

Abstract It is necessary to use the thermal network method for thermal analysis of the bearing, but there are still some shortcomings. In this paper, a novel thermal network model of the bearing transient temperature is developed considering the thermal-fluid-solid coupling effects. First, the quasi-static analysis of the bearing is carried out considering the thermal expansion effect, and the heat generation, heat transfer, and heat dissipation are studied. Then, the coupling effects between the oil characteristics, heat generation, structure parameters, and temperature (thermal-fluid-solid) during the operation of the bearing are discussed, and the transient thermal network model of the bearing-shaft-bearing housing system is established. Test results indicate that the existing models (without thermal-fluid-solid coupling) have large temperature deviation, while the proposed model in this paper considering the thermal-fluid-solid coupling effects is much more accurate. Finally, the effects of rotational speed, load, oil temperature, and oil flowrate on the temperature rise are all achieved and discussed.

Computationally efficient thermal network model and its application in optimization of battery thermal management system with phase change materials and long-term performance assessment

This paper presents a simple 2D thermal network model for a battery thermal management system with phase change materials (PCMs). An equivalent electric circuit model is developed to solve heat transfer problems that include the processes of battery heat generation and PCM thermal storage. This thermal network model is compact and accurate. The simulation time is saved by 99% compared with a conventional numerical model, whereas the average prediction error of battery temperature is lower than 1 °C. This model is applied for the rapid optimization of the PCM properties to warm up a battery pack rapidly during cold starts. The results demonstrate that the PCM suitable for thermal management under low temperatures should have a melting point of approximately 40 °C, high thermal conductivity of over 5.4 W/m K, and a low latent heat storage density of less than 0.0145 kJ/m3. Utilizing its high computation efficiency and resolution for capturing the temperature distribution in 2D, the model can quantitatively assess the long-term effect of the thermal management system on the life of a battery module during a 10,000-hour charge–discharge cycle. A lifespan model that integrates a battery capacity fade model into the thermal network is developed and the simulation results verify that a lower temperature and temperature difference reduce the capacity loss in a multi-cell module. The thermal network model is efficient to design and optimize the thermal management system for a real-size battery pack, based on the assessment of its long-term impacts on battery performance.