Dynamic Heat Generation Research Articles

Research on thermal characteristics modeling of CNC machine tools based on submodel method

To improve the accuracy of thermal characteristics analysis of CNC machine tools, a modeling method for the thermal characteristics of CNC machine tools based on submodel method is proposed in this paper. In this method, the thermal-structural coupling calculation of the feed system and spindle system is initially completed in ABAQUS to obtain temperature and deformation results of the submodels. Subsequently, User Define Function (UDF) in Fluent is used to extract the temperature information from the surface of the submodels. The obtained surface temperature data is then imported into the overall machine model for fluid-structure coupling heat transfer calculation. The model developed in this study takes into account factors such as the dynamic heat generation of the heat source, the cooling fan system, and the secondary heat source effect of the cutting fluid. To validate the approach, a thermal characteristics experiment was conducted, and the research results demonstrate that the thermal analysis model established in this paper exhibits both high accuracy and efficiency. During the 180 min of machine operation, the thermal displacement between the tool tip and the workpiece increased. The maximum thermal deformation of the machine tool tip was 40.83 [Formula: see text], primarily observed in the X and Y directions.

Numerical simulation of multi-field coupling in geothermal reservoir heat extraction of enhanced geothermal systems

The coupled analysis of multi-field heat and mass transfer in geothermal reservoirs is a pivotal concern within the realm of geothermal rock exploitation. It holds significant implications for the assessment of thermal energy capacity and the formulation of reservoir optimization strategies in the context of geothermal rock resources. Parameters governing production, along with fracture network characteristics (such as injection well temperature, injection well pressure, fracture width, and fracture network density), exert an influence on enhanced geothermal systems (EGS) heat production. In this study, aiming to comprehend the dynamic heat generation of EGS during prolonged exploitation, a coupling of various fields including permeation within the rock formations of geothermal reservoirs and the deformation of these rocks was achieved. In this study, we formulated the governing equations for the temperature field, stress field, and permeability field within the geothermal reservoir rock. Subsequently, we conducted numerical simulations to investigate the heat transfer process in an enhanced geothermal system. We analyzed the effects of injection well temperature, injection well pressure, primary fracture width, and secondary fracture density on the temperature distribution within the reservoir and the thermal power output of the production well. The research findings underscore that ill-conceived exploitation schemes markedly accelerate the thermal breakthrough rate of production wells, resulting in a diminished rate of geothermal resource extraction from the geothermal reservoir rock. Variations in influent well temperature and secondary fracture density exhibit an approximately linear impact on the output from production wells. Crucially, injection well pressure and primary fracture width emerge as pivotal factors influencing reservoir output response, with excessive widening of primary fractures leading to premature thermal breakthrough in production wells.

A Fast Activation Energy Derivation (FAED) approach for Lumped Single Particle model in lithium-ion battery module-level heat generation prediction

The performance of electric vehicles (EVs) heavily relies on the durability and longevity of lithium-ion cells, which are strongly affected by operating temperatures. Various electrochemical models have been developed to investigate the impact of operating temperature on the dynamic heat generation at cell level. Among these, the Lumped Single Particle (LSP) model stands out due to its lower computational cost and higher accuracy under >1C-rates. However, key electrochemical parameters (i.e. the ohmic overpotential, exchange current, and diffusion time constant) in the LSP model are temperature-sensitive, requiring Arrhenius dependencies. Conventional activation energy measuring approaches, relying on testing under discrete fixed temperatures to obtain activation energies, are time-consuming. To address this, this paper proposes a FAED approach that fits the temperature-sensitive parameters and corresponding activation energies to experimental data with a single discharge process, reducing the testing time to a minimum of one hour. This approach was experimentally validated on a Tesla battery module (74P6S), demonstrating a good agreement between simulation and experimental results up to 1.5 C-rates, ranging from 16 ℃ to 46 ℃. Furthermore, this approach is suitable for cells with different lithium chemistries, formats, and properties, making it an effective method for thermal analysis of EV packs.

Hybrid enhancement of silica and aramid pulp on improving performance and reducing dynamic heat generation of natural rubber composites

AbstractThe composites with excellent mechanical, low rolling resistance, and low heat build‐up are the potential materials for preparing green tires. In this study, we prepared silica‐natural rubber latex (silica‐NRL) masterbatch, which improved the processing and dispersion properties of silica in the natural rubber, proved by the rheological properties of composites. Furthermore, the idea of partial replacement of silica with low content modified aramid pulp (AP) for preparing hybrid enhanced natural rubber with high mechanical properties and low heat build‐up was put forward and evaluated the feasibility of this strategy. We find that replacing 5 phr silica with 1 phr AP, the performances of the rubber composites were all superior to the composites with only filled 50 phr silica, and replacing 10 phr silica with 2 phr AP, the mechanical and fatigue property was improved remarkably and dynamic heat generation was reduced the most at same time. The strategy of preparing silica‐NRL masterbatch and partial replacement of silica with AP provides a novel reference for the preparation of low heat build‐up green tire.

Optimal design of liquid cooling structure with bionic leaf vein branch channel for power battery

• ·The liquid cooling plate with BLVB channel for Li-ion battery is proposed. • ·The BLVB cooling system is conducted by using 16 orthogonal test schemes. • ·The liquid cooling influence factors are analyzed by using the range method. • ·Multi-parameter coupling of the liquid cooling plate is optimized based on NSGA-II. Effective thermal management is crucial for the thermal safety and uniformity of lithium-ion(Li-ion) batteries caused by high temperature. However, it is challenging for structural design and optimization method of cooling system especially considering dynamic heat generation of the battery. The liquid cooling plate with the bionic leaf vein branch(BLVB) channel which is sandwiched with a pouch Li-ion battery was proposed. The effects of multi-parameter coupling with inlet flow rate( M ), channel width( D ), channel angle( α ) and channel number( N ) of the cooling plate on the maximum temperature( T max ), the maximum temperature difference(Δ T max ) of battery and the average pressure drop of coolant(Δ P avg ) were investigated by using the orthogonal test range method. Based on the non-dominated sorting genetic algorithm-II(NSGA-II), the solution sets were optimized. Results show that the proposed BLVB channel is efficient for battery cooling. Even at 3C discharge, T max can be controlled within 33.34℃. Meanwhile, M and D are the main factors affecting the cooling performance, α and N are the secondary factors. However, with the increasing of α or the decreasing of N , T max and Δ T max are decreased due to the enhancement of backflow or vortexes near the outlet. The optimal results are T max =30.31℃, Δ T max =2.78℃ and Δ P avg =0.50kPa; while the optimal parameters are M= 0.10m/s, α= 159°, N= 15 and D= 2.60mm. Compared with the initial BLVB channel and the traditional parallel straight channel, T max with the optimum BLVB channel can be reduced by 0.23℃ and 1.12℃ respectively when M= 0.10m/s. The corresponding Δ T max is declined by 0.28℃ and 1.64℃, and Δ P avg is decreased by 65.56% and 8.77% respectively. The proposed BLVB channel can be used to provide a certain reference for the thermal design of battery liquid cooling system.

Research on electrochemical characteristics and heat generating properties of power battery based on multi-time scales

A comprehensive understanding of the mechanisms of battery is essential for the design of thermal management systems. In this work, a second-order equivalent circuit model considering the hysteresis effect of the battery was developed, and a combined EIS and HPPC characterization method was used for parameter identification. The results showed that the combining EIS and HPPC parameter measurement methods could extract and analyze the parameters of the battery with different time scales and improve the accuracy of the model. It was found that the polarization internal resistance (R1 and R2) of the battery shows a stronger temperature dependence than the ohmic internal resistance at low temperatures, with R1 being about 170 times higher at low temperatures (10 °C) than high temperatures (50 °C). At the same temperature, τ2 was approximately 100 times larger than τ1, which was two orders of magnitude difference between τ1 and τ2. In addition, the dynamic heat generation results showed that the heat generation rate of the battery increases with decreasing temperature. At 3C discharge rate, the heat generation rate of the battery at low temperature (−10 °C) was about 1.5 times higher than at room temperature (25 °C).

Thermal Modeling and Prediction of The Lithium-ion Battery Based on Driving Behavior

Real-time monitoring of the battery thermal status is important to ensure the effectiveness of battery thermal management system (BTMS), which can effectively avoid thermal runaway. In the study of BTMS, driver behavior is one of the factors affecting the performance of the battery thermal status, and it is often neglected in battery temperature studies. Therefore, it is necessary to predict the dynamic heat generation of the battery in actual driving cycles. In this work, a thermal equivalent circuit model (TECM) and an artificial neural network (ANN) thermal model based on the driving data, which can predict the thermal behavior of the battery in real-world driving cycles, are proposed and established by MATLAB/Simulink tool. Driving behaviors analysis of different drivers are simulated by PI control as input, and battery temperature is used as output response. The results show that aggressive driving behavior leads to an increase in battery temperature of nearly 1.2 K per second, and the average prediction error of TECM model and ANN model is 0.13 K and 0.11 K, respectively. This indicates that both models can accurately estimate the real-time battery temperature. However, the computational speed of the ANN thermal model is only 0.2 s, which is more efficient for battery thermal management.

Heat-flow coupling variation in double-row tapered-roller bearings during the loss of lubrication process

Loss of lubrication (LOL) is a severe problem in transmission systems wherein the temperature increases continuously until failure. The temperature and flow-field distributions during this process are complicated. These distributions and the heat generation of the transmission system during LOL have not been adequately studied. In this study, we used computational fluid dynamics to establish an oil–gas, two-phase flow model for asymmetric bearings and calculated the oil volume fraction on the bearing surface. A dynamic heat generation calculation method was proposed based on the kinematic viscosity variation of the oil–air mixture during the LOL process. The temperature distributions of the large and small rollers and raceway surface during the LOL process were analyzed using a simulation method. The injection parameters were optimized to avoid the gluing of the large roller. The internal temperature distribution was found to have a strong positive correlation with the lubricant distribution during the LOL process. Moreover, the lubrication and temperature distributions on the large-roller side were worse than those on the small-roller side. A temperature reduction of approximately 25% can be achieved if the number of oil inlets is increased.

A Novel Electro-Thermal Model of Lithium-Ion Batteries Using Power as the Input

Considering that use of measured current as input of a battery model may cause distortion of the model due to low accuracy of the on-board current sensor and that power can be used to indicate energy transmission in an electric vehicle model, the power input internal resistance model is widely used in simulation of whole electric vehicles. However, since no consideration is given to battery polarization and electro-thermal coupling characteristics, the foregoing model cannot be used to describe the internal temperature change of batteries under working conditions. Three contributions are made in the present study: (1) ternary lithium-ion batteries were taken as the research objects and a second-order RC equivalent circuit model with power as the input was established in the present study; (2) A dynamic heat generation rate model suitable for RC equivalent circuits was built based on coupled electrical and thermal characteristics of lithium-ion batteries; (3) An electric model and a two-state equivalent thermal network model were further built and combined by using the heat generation rate model to form a power input electro-thermal model. Parameters of the model so formed were identified offline, and the battery model was verified with respect to accuracy under seven working conditions. The results show that the maximum root mean square error in voltage estimation, current estimation, and surface temperature estimation is 19.38 mV, 9.51 mA, and 0.19 °C respectively, which indicates that the power input electro-thermal model can describe the electrical and thermal dynamic behavior of batteries more accurately and comprehensively than the traditional power input internal resistance model.

Development of high-performance thermoplastic composites based on polyurethane and ground tire rubber by in-situ synthesis

The aim of this paper is to make full use of the hydroxyl groups on the ground tire rubber (GTR) surface to realize the high valuable utilization of waste tires in the field of high-performance polyurethane elastomers. In this work, the Polyurethane/Ground tier rubber (PU/GTR) thermoplastic composite with excellent performance was in-situ synthesized by adding untreated GTR to polyurethane. With incorporating 3.44 wt% GTR to polyurethane, the tensile strength of the PU/GTR thermoplastic composites was improved by approximately 166.7 % compared with pure PU. And the dynamic heat generation index (ratio of the tan δ at 90 °C and 30 °C) of the thermoplastic composites was reduced to 0.97, being far lower than that of pure PU (1.62), which exhibits this material has low dynamic heat generation when subjected to alternating stress. As expected, X-ray photoelectron spectra (XPS) results showed that the GTR indeed participated in the in-situ synthesis of polyurethane, thus, resulting in the GTR particles with micro size being evenly distributed in the polyurethane matrix via a network structure, which was proved by the morphology analysis and rheological measurement part. Additionally, the microphase separation of the PU matrix of the composites was greatly weakened according to Cole-Cole plots and the small angle X-ray scattering (SAXS) analysis. And the outcome of the study provided a low-cost and rational approach for recycling of waste tires while avoiding resource waste.

An improved resistance-based thermal model for prismatic lithium-ion battery charging

This study proposed a dynamic resistance-based thermal model to predict the temperature evolution of a prismatic lithium-ion battery in fast and regular charging strategies. The effects of battery temperature, state of charge (SOC), and charging current on resistance were investigated to form a dynamic heat generation model. This model included both the heat generation of battery body and the heat generation of electrodes. Then the charging resistance-based thermal model was used to predict the temperature distribution and temperature evolution of a 50 Ah prismatic battery under different charging strategies and ambient temperatures. The charging strategies included a multi-stage constant current-constant voltage (MSCC-CV) for fast charging and a constant current-constant voltage (CC-CV) for regular charging. Experiments verified the prediction accuracy of the proposed thermal model. The results showed that the dynamic thermal model accurately predicted the temperature distribution and its evolution under different charging strategies and ambient temperatures. With regard to temperature distribution prediction, the average root mean square errors (RMSEs) of temperature among the five test points were 0.43 °C for the MSCC-CV charging strategy and 0.3 °C for the CC-CV charging strategy. For the temperature prediction under various ambient temperatures, the average RMSEs at different ambient temperatures were 0.34 °C for the MSCC-CV strategy and 0.25 °C for the CC-CV strategy. Finally, the effect of the charging and discharging resistance on the temperature prediction under the MSCC-CV charging condition was studied. Although the discharging resistance-based thermal model could describe the temperature change with charging time, it showed higher predicted temperatures than the tested values and a larger estimation error than the charging resistance-based thermal model.

Dynamic Heat Generation of LiNi0.5Co0.2Mn0.3O2 Half Cell Under Cycling Based on an In Situ Micro-calorimetry

To further understand the thermal properties of lithium ion batteries, in situ measurement and calculation of the heat generation under operating condition are conducted. In this work, a novel micro-calorimeter with high accuracy is applied to study the heat flow of the LiNi0.5Co0.2Mn0.3O2/Li half cell. The dynamic heat generation and corresponding electrochemical data are detected out under isothermal environment from 30°C to 70°C with different current rates (0.2, 0.4, 0.6, 0.8 and 1.0 C) and electrode thicknesses (400, 200 and 100 μm). In addition, heat generation rate is calculated based on the measurement of entropy coefficient and internal resistance. It is found that the heat generation rises with the increase of thickness and current rate, due to concentration polarization and electrochemical polarization, respectively. The lithiation process is more sensitive to changes in current rate than delithiation. Appropriately increasing the temperature can improve the activity of material and reduce the energy consumption of the battery. Besides, the contribution of reversible heat to the overall heat generation should be taken into account especially at a lower current rate (< 0.5 C). The detailed analysis of heat generation and electrochemical performance can provide accurate data for thermal management systems.

Comprehensive Analysis on Dynamic Heat Generation of LiNi1/3Co1/3Mn1/3O2 Coin Cell under Overcharge

To meet the requirement of fast charging and high energy density of lithium ion battery, it is critical to further study the impact of current and voltage on the heat generation. In this work, dynamic heat generation of LiNi1/3Co1/3Mn1/3O2 coin cell under different current rates and overcharge voltages is investigated in detail using an in-situ micro-calorimetry. Polarization is the main factor causing rapid increase of heat generation at high current rate. The internal resistance and entropy coefficient show a great consistency of tendency and magnitude between irreversible and total heat. The excessive delithiation accelerates the polarization of electrode and the oxidation of electrolyte, leading to larger amount of heat generation. Besides, the heat release rate of charging process gets a steep increase as the cutoff voltage exceeds 4.5 V. Under the voltage range of 2.8–4.9 V, the heat generation from abusive range contributes more than 58% to the whole process. With the degradation of electrochemical performance, crystal structure and thermal stability also become worse after 50 cycles under higher cutoff voltage. These results provide basic data for the design of current rate and voltage range and the improvement of thermal management system.

Investigation of dynamic heat generation and transfer behavior and energy dissipation for nonlinear synchronous belt transmission

Study on energy dissipation and temperature distribution of synchronous belt transmission is of great importance in industrial engineering field, which is highly related to transmission efficiency estimation, thermal fatigue life prediction, and product design. However, the complex behaviors of viscoelastic hysteresis and meshing friction make it much more difficult to investigate heat generation and transfer mechanism of synchronous belt than other products. To accurately predict temperature and energy dissipation, a thermo-mechanical coupling model was developed through combining experiment and finite element analysis method, in which material nonlinearity of rubber hyper-viscoelasticity, and contact nonlinearity of meshing interference were comprehensively considered. Meanwhile, the friction heat flux partition coefficient and convective heat transfer coefficient were theoretically computed and corrected. As a result, the temperature distribution, hysteresis and friction energy dissipation of synchronous belt could be computed accurately, the transmission efficiency was estimated as well. The simulation temperatures of various operating conditions were confirmed by testing results. The presented methodology can completely predict energy dissipation and temperature distribution of synchronous belt transmission, which has far-reaching consequences in the engineering application filed.

Dynamic thermal rating of power lines – Model and measurements in rainy conditions

The transfer capabilities of overhead power lines are often limited by the critical power line temperature that depends on the magnitude of the transferred current and the ambient conditions, i.e. ambient temperature, wind, precipitation, etc. To utilize existing power lines more effectively and more safely concerning the critical power line temperatures and to enforce safety measures during potentially dangerous events, dynamic assessment of the thermal rating is required. In this paper, a Dynamic Thermal Rating model that covers the most important weather phenomena, with special emphasis on rain, is presented. The model considers a dynamic heat generation due to the Joule losses within the conductor and heat exchange with the surrounding in terms of convection, radiation, evaporation, rain impinging and solar heating. The model is validated by comparison of the skin and core temperature of the power line with measurements under realistic environmental conditions.

Steady state and transient analytical modeling of non-uniform convective cooling of a microprocessor chip due to jet impingement

Heat removal from microprocessor chips with multiple regions of dynamic heat generation remains a critical technological challenge. Excessive temperature rise is undesirable for performance as well as reliability. Jet impingement cooling has been widely investigated as a potential thermal management technique due to the capability of localized cooling and of dynamically following the heat generation distribution. A jet offers large local convective heat transfer coefficient, for which theoretical models and correlations have been proposed for a variety of scenarios. However, not much work exists on using this information to determine the resulting temperature distribution. This paper addresses this need by developing analytical steady state and transient heat transfer models that account for the spatial variation in convective heat transfer coefficient and for spatially non-uniform heat flux. The solution is derived in the form of an infinite series, the coefficients of which are determined by solving a set of algebraic equations. Temperature rise predicted by the models are found to be in excellent agreement with finite-element simulations, while offering faster computation time and easier integration with design and performance optimization tools used in microelectronics. The analytical model is used for predicting temperature rise in a variety of scenarios to examine interesting optimization problems such as the cooling of multiple hotspots with a single jet, determining the optimal location of a jet, etc. Results presented here may facilitate improved thermal design and real-time performance optimization of microprocessor chips.

Transient Temperature and Heat Flux Measurement in Ultrasonic Joining of Battery Tabs Using Thin-Film Microsensors

Process physics understanding, real time monitoring, and control of various manufacturing processes, such as battery manufacturing, are crucial for product quality assurance. While ultrasonic welding has been used for joining batteries in electric vehicles (EVs), the welding physics, and process attributes, such as the heat generation and heat flow during the joining process, is still not well understood leading to time-consuming trial-and-error based process optimization. This study is to investigate thermal phenomena (i.e., transient temperature and heat flux) by using micro thin-film thermocouples (TFTC) and thin-film thermopile (TFTP) arrays (referred to as microsensors in this paper) at the very vicinity of the ultrasonic welding spot during joining of three-layered battery tabs and Cu buss bars (i.e., battery interconnect) as in General Motors's (GM) Chevy Volt. Microsensors were first fabricated on the buss bars. A series of experiments were then conducted to investigate the dynamic heat generation during the welding process. Experimental results showed that TFTCs enabled the sensing of transient temperatures with much higher spatial and temporal resolutions than conventional thermocouples. It was further found that the TFTPs were more sensitive to the transient heat generation process during welding than TFTCs. More significantly, the heat flux change rate was found to be able to provide better insight for the process. It provided evidence indicating that the ultrasonic welding process involves three distinct stages, i.e., friction heating, plastic work, and diffusion bonding stages. The heat flux change rate thus has significant potential to identify the in-situ welding quality, in the context of welding process monitoring, and control of ultrasonic welding process. The weld samples were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to study the material interactions at the bonding interface as a function of weld time and have successfully validated the proposed three-stage welding theory.

Optimal experimental design for the parameter estimation of conduction heated foods

The objective of this paper was to estimate the volumetric heat capacity, ρc and the thermal conductivity k, of conduction heated foods simultaneously and uniquely by using the hot wire probe method. To meet this objective, the heat conduction in the probe and its environment was modelled by means of the finite element method. Optimal experimental design methodology was, then, applied and the information content of various static and dynamic heat generation profiles were evaluated towards obtaining unique estimates for the thermophysical properties of the food. Simulations indicate that informative experiments were obtained from pulse heat generation profiles and this was confirmed by implementing pulse-like block profiles. However, the accuracy of the estimates is highly dependent on some features of the setup and the heat transfer model.

P-2-226 - Correlation of intraoperative ultrasound, computed tomography, magnetic resonance imaging and histopathological findings

The transfer capabilities of overhead power lines are often limited by the critical power line temperature that depends on the magnitude of the transferred current and the ambient conditions, i.e. ambient temperature, wind, precipitation, etc. To utilize existing power lines more effectively and more safely concerning the critical power line temperatures and to enforce safety measures during potentially dangerous events, dynamic assessment of the thermal rating is required. In this paper, a Dynamic Thermal Rating model that covers the most important weather phenomena, with special emphasis on rain, is presented. The model considers a dynamic heat generation due to the Joule losses within the conductor and heat exchange with the surrounding in terms of convection, radiation, evaporation, rain impinging and solar heating. The model is validated by comparison of the skin and core temperature of the power line with measurements under realistic environmental conditions.