Heat Generation Model Research Articles

Analiza toplotnih efekata u postupcima frikcionog zavarivanja mešanjem

This paper describes the formation of an analytical model of heat generation and transfer during friction stir welding. By solving differential equations of heat transfer, adapted for friction stir welding, the foundations for the formation of an analytical model were laid. In order to vary the technological parameters of welding that affect the generated heat, certain approximations were performed and the stress state of the material was observed at elevated temperatures. The aim was to simulate heat transfer for thin and thick plates, by obtaining a planar and spatial temperature image for certain welding parameters. The formation of the analytical model was performed in the Python programming language.

Self-Excited, Electromagnetic Braking and Heating System for Electric Buses

New energy vehicles usually recover the braking energy and store it back into the battery using the electric motor. Such a regenerative braking system improves the vehicle mileage. In the process of regenerative braking, all components of the system dissipate a great amount of energy, especially in winter. On the other hand, heating the vehicle's cabin consumes electric energy, further reducing its autonomy. Based on this, we propose a novel Self-excited, electromagnetic Braking and Heating System (SBHS), to solve problem of the driving range dramatic decline of electric bus when heating the bus cabin in winter. The system converts the kinetic energy of the electric bus into heat, via electromagnetic braking, and uses it to warm the vehicle's cabin in winter. Our system improves the conversion efficiency of regenerative braking. We present the structure of the system and calculate the air gap magnetic density using the magnetic circuit method. We develop the braking heat generation model and obtain the heat generation performance at different speeds using J-MAG. To improve the braking energy utilization efficiency, we design a braking force distribution strategy based on a fuzzy control system. We also characterize the braking and built-in generator performances in a test bench, and obtain the braking and heating characteristic at different speeds. We implemented our EBHS and installed on a test electric bus. The test records include SOC, temperature inside the vehicle and distance. The results show that the SBHS can provide both sufficient braking torque for the vehicle and heat energy for the cabin.

Prediction on thermal performance of refrigerant-based battery thermal management system for a HEV battery pack

The thermal performance of refrigerant-based battery thermal management system (BTMS) for a real HEV battery pack in both the cooling and heating conditions is numerically and experimentally investigated in this paper. The heat generation model of battery cells and the numerical methodology for predicting the cooling performance of refrigerant-based cooling system are validated by experiments and the predicted results are consistent with experimental data. The effects of discharging C-rate, mass flow rate, initial temperature and vapor quality of refrigerant on thermal performance of battery pack are analyzed in detail. The thermal performance of refrigerant-based BTMS at a real driving cycle is also examined. The results indicate that the discharging C-rate has a significant impact on thermal performance of battery pack due to the distinctive heat transfer behaviors of battery pack at different discharging C-rates. Increasing mass flow rate of refrigerant is contributed to descend the maximum temperature and improve temperature uniformity of battery pack. Decreasing initial temperature of refrigerant is beneficial to reducing the maximum temperature of battery pack but is disadvantageous to temperature uniformity. The effect of vapor quality on thermal performance of battery pack is limited. The cooling performance of refrigerant satisfies the requirement of BTMS at the real driving cycle. The optimum heating power of the battery pack at heating condition ranges from 400 W to 460 W.

Thermal Error Analysis of Machine Tool Spindle Based on BP Neural Network

With the continuous improvement of the accuracy of machine tools, the proportion of the thermal error of machine tools in the total error is increasing. In this paper, the thermal error of horizontal machining center is analyzed by finite element simulation, a three-dimensional model is established in SolidWorks, and some details (such as bolt holes) are simplified and imported into ANSYS Workbench to determine the heat generation model, heat dissipation model, convection heat transfer coefficient and other boundary conditions. On the basis of the temperature field, the thermal-structural coupling analysis is carried out, and the temperature cloud field of the whole machine tool is obtained through the analysis, which provides a theoretical basis for the experimental design. Then, the data are divided into four categories by fuzzy cluster analysis, and finally, the thermal error model is established by BP neural network based on time series. It provides a theoretical reference for the compensation of thermal error.

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.

Flash flooding on Mars could be linked to large fault slip events

Studies of Martian fault-related landform morphology have noted an interesting phenomenon associated with large thrusts — isolated channels that run from the crests of these landforms down their slopes. One such example is Ogygis Rupes, an east-verging, 180 km long thrust-fault-related landform located near 55°W, 33°S. Geometric modeling efforts have indicated the fault underlying this landform has experienced approximately 2850 m of slip, and a large anticlinal fold has grown above the fault. We mapped 72 channels on back and front slopes of this massive landform at 1:24,000 scale on 10 mosaiced Context Camera images (6 m/pixel) and one High-Resolution Imaging Experiment image (2.5 m/pixel). The morphology of these channels indicates that they formed through flash flood events that originated near the hinge of the fold. We propose that these flooding events were due to the melting of subsurface ice during fault slip. We apply a thermodynamic model for heat generation along the fault surface during slip events of various magnitudes to estimate the volumes of water produced during each hypothetical event. By comparing these estimates to channel discharge values estimated from channel morphologies, we resolve fault slip magnitudes that could produce the channels. We find that slip events of approximately 28 m produce enough heat to melt the ice associated with channel flow (4.867 × 109 m3). This estimate is based on slip within a 1 m basaltic fault zone, with a friction coefficient of 0.6 where all pore space is occupied by water ice. Results indicate that only mature faults with well-developed, fractured hinges are capable of both (1) melting enough subsurface ice and (2) transporting the water to the surface to result in flooding, explaining why this impressive phenomenon remains a rare but important hazard of which to be aware during planning of the exploration and settlement of Mars.

Topology optimization for liquid-based battery thermal management system under varied charge rates

Multi-objective topology optimization (TO) has been adopted recently in the thermal-fluidic problem, resulting in cooling devices with non-intuitive and complex flow paths, yet revealing a significant improvement in the thermal performance. Although previous works utilized the multi-objective TO to design a cooling plate for the Battery Thermal Management Systems (BTMS), the effect of the heat loads from different charge/discharge rates on the optimized flow paths has not been fully assessed. Therefore, the present study implemented the two-step numerical framework coupling battery heat generation model with the multi-objective TO. We found that the lumped battery model could provide a reasonable estimation of the heat generation, especially at the C-rates between 1C and 3C, where the maximum deviation between numerical prediction and experiment was <2 %. In addition, the optimized cooling plate was affected greatly by the choices of heat loads and weighted objective functions. A higher heat load led to a more complex channel and narrower flow paths. In addition, by comparing with the benchmark model of the straight channels, the optimized model could reduce the pressure drop by 20–40 %. Furthermore, the hot spots in the system became more alleviated thanks to the optimized flow channels. The maximum temperature in the optimized model could be lower than that of the benchmark by up to 14 K at the charge rate of 3C. Additionally, by performing a cross-verification, the optimized plate under a high C-rate could reduce the maximum temperature to be lower than the allowable temperature of 323.15 K even when it was used under other charge rate conditions. Thus, the optimized plate under a high charge rate was found to be suitable for other C-rates as well. In summary, the present work established and validated the effective numerical framework which could be used to design a high-performance BTMS.

Thermal Dynamic Exploration of Full-Ceramic Ball Bearings under the Self-Lubrication Condition

A silicon nitride ceramic bearing has good self-lubricating characteristics. It still has a good operational status under the condition of a lack of oil. However, the temperature distribution of a silicon nitride ceramic bearing during its operation is unclear. To clarify the thermal distribution of a full-ceramic ball silicon nitride ceramic bearing under self-lubricating conditions, the changing trend of the rolling friction temperature between the rolling elements and channels with different accuracies is analyzed using the friction testing machine. The bearing heat generation model based on the silicon nitride material coefficient is established, and the life test machine measures the temperature of the bearing to verify the accuracy of the simulation model. The results show that the friction temperature between the ceramic ball and channel decreases with the increase in ceramic ball level. With an increase in the ceramic ball pressure and temperature, the friction temperature rises. Under self-lubrication, when the bearing bears a heavy load, the influence of the rotating speed on temperature rise tends to decrease. Under the condition of high speed, with the increase in load, the change range of temperature rise shows an upward trend. The important relationship between the bearing’s heat and bearing’s load and speed is revealed. It provides some theoretical guidance for the thermal analysis of a silicon nitride ceramic ball bearing under the self-lubricating condition to improve the service life and reliability of full-ceramic ball bearings.

Experimental study on the mechanism of frequency-dependent heat in AC preheating of lithium-ion battery at low temperature

• Controlled experiments to explore the source of frequency-dependent heat have developed. • The heat generation mechanism of lithium-ion batteries under high-frequency AC excitation is different from those under low-frequency. • Frequency-dependent heat partly due to current harmonics, and partly from an unknown mechanism. Lithium-ion batteries suffer severe energy loss, significant pulse power decline, and reduced life cycle under cold weather. It is imperative to preheat the lithium-ion batteries for electric vehicles (EVs) at low temperatures. At present, various internal alternative current (AC) heating methods have been proposed to achieve fast and high-efficiency battery preheating. However, there is still confusion in the selection of the AC frequency. Researchers have found that the simplified Bernardi heat generation model is not always suitable for AC preheating, especially at high AC frequencies. Under these scenarios, a frequency-dependent heat is generated, making the traditional thermal model inapplicable. In this paper, the source of frequency-dependent heat is analyzed experimentally. Based on the electrochemical impedance spectrum (EIS) data and entropy thermal coefficient of the cell in the experiment, controlled experiments in different frequencies are developed to compare the cell heat generation rate. The experiments showed that the heat generation rate is highly correlated to its frequency. Further analysis show that the frequency-dependent heat is not due to electrochemical reaction, partly due to Joule effect by current harmonics, and partly from unknown mechanism (nominate “extra-heat”).

Analysis of Temperature Field in the Dielectrophoresis-Based Microfluidic Cell Separation Device

Cell separation techniques based on dielectrophoresis are of high interest as an effective method of performing cell separation non-invasively on cells. However, dielectrophoresis devices have the problem that cells in the device are exposed to a high-temperature environment due to the generation of Joule heat caused by high-voltage application and dielectric-loss heat when the applied voltage is AC voltage. There is concern that the heat generated in the device may affect cell viability, cell cycle and apoptosis induction. In this study, the temperature field inside the dielectrophoretic cell separation device was experimentally and numerically investigated. The temperature rise at the bottom of the flow channel in the device was measured using the LIF method, and the thermofluidal behavior of the device was numerically simulated by adopting a heat generation model that takes the Joule and dielectric-loss heating into account in the energy equation. The temperature rise in the device was evaluated and the effect of the heat generation on cells in the device is discussed.

Surrogate models for lithium-ion battery heat generation based on orthogonal experiments by eliminating external wire connection effect

• Maximum overestimation of 39.9% in heat generation occurs due to the wire connection at 40 °C and discharge rate of 3C. • Heat generation rate is determined by C-rate, temperature and depth of discharge with ranking order of DR > T > DOD. • Average deviation of 6.90% was obtained between present surrogate model and experimental tests beyond 0.53 W. • Heat generation model of the battery was verified by comparing with experiment measurement under natural convection. In this paper, an experimental investigation on the heat generation rate is presented for the cylindrical lithium-ion batteries under different operation conditions such as changing temperature and depth of discharge by eliminating the external connection effect. The tests were conducted by placing the battery in the thermostat chamber and connecting to the charger instrument through external wires. The intermediate quantities including the overpotential, entropy heat coefficient and internal resistance were obtained by the corresponding orthogonal test in full matrix design. It is found that the maximum overestimation of 39.9% occurs at the highest temperature of 40 °C and discharge rate of 3C with the wire connection. As such, the wire connection effect must be examined and eliminated in the heat generation estimation. The consequent sensitivity analysis indicates that the discharge rate has the largest impact on the heat generation of battery, followed by the temperature and depth of discharge, namely, DR > T > DOD. The temporal heat generating surrogate models of the battery are correlated under different operation conditions with the depth of discharge, temperature, and discharge rate by the response surface analysis, which agrees with experiment results within 6.90% for heat generation rate beyond 0.53 W corresponding to the 1C discharge case. Moreover, the heat generation model is verified by comparing the numerically obtained battery temperature with experiment measurement under natural convection condition. The temporal temperature rise of the battery during actual operation conditions such as worldwide harmonized light vehicles test procedure (WLTP) can be estimated based on the present surrogate models.

(Digital Presentation) Modeling Thermal Behavior and Safety of Large Format All-Solid-State Lithium Metal Cells Under Thermal Ramp and Short Circuit Conditions

We are submitting this abstract in the understanding that a virtual option is likely to be offered for the Spring, 2022 ECS meeting. We are only interested in the virtual option for this presentation. It has often been posited that solid-state batteries are inherently safer than liquid electrolyte Li-ion batteries because there is no flammable organic solvent present in the battery. However, thermal safety is a multi-faceted issue with other considerations such as onset temperature, maximum temperature, total heat generation, maximum heating rate, etc. These considerations need to be looked at in greater detail, including their dependence on the volumetric and gravimetric energy densities. Safety concerns become even more important as stable graphite anodes are replaced with potentially highly reactive and energetic lithium metal anode. In this presentation, we will report on our work using differential scanning calorimetry (DSC) heat flow data to construct a transient, 2D model of heat generation and temperature distribution in a large format cell with a LixCoO2 cathode, Li7La3Zr2O12 solid electrolyte, and lithium metal anode. We will present on the thermal runaway behavior of this cell chemistry during a thermal ramp test in an oven and due to the formation of an internal short circuit. Our analysis will focus on the total amount of heat generated, onset temperature for self heating, maximum temperature, and maximum heating rate. We also analyze how the battery state of charge affects these properties. Related work in our group focuses on collecting DSC data for Li metal solid state cells and may also be highlighted.

Dynamic, thermal, and vibrational analysis of ball bearings with over-skidding behavior

The term “over-skidding” indicates that the cage rotational speed ratio exceeds the theoretical value as ball purely rolls on the raceway. Different from the skidding phenomenon that occurs in low-load and high-speed bearing, over-skidding usually occurs in large-size angular contact bearings, and it is still difficult to suppress under high load conditions. The main forms of damage to the raceway by over-skidding are spinning and gyro slip. To further explore the vibration characteristics and thermal effects of this phenomenon, a set of over-skidding tests of an angular contact bearing with a bore diameter of 220 mm were conducted on an industrial-size test bench. Through the experiment, the influence of axial load, rotational speed, and lubrication conditions on the occurrence of over-skidding were determined. Based on a previous dynamics model, the heat generation and thermal network models were integrated in the present study to predict the over-skidding and its thermal behavior. The model was validated in terms of the measured degree of over-skidding and temperature rise. The results showed that the degree of over-skidding reaches up to 12% of the theoretical value, and the friction power loss of the ball-pocket accounts for 30% of the total power loss. The analysis of the vibration signal showed a strong correlation between the bearing vibration characteristics and over-skidding behavior, thereby providing a way to indirectly measure the degree of over-skidding.

An Overview of Heat Transfer Enhancement Based Upon Nanoparticles Influenced By Induced Magnetic Field with Slip Condition Via Finite Element Strategy

Abstract The mathematical model of heat generation and dissipation during thermal energy transmission employing nanoparticles in a Newtonian medium is investigated. Dimensionless boundary layer equations with correlations for titanium dioxide, copper oxide, and aluminium oxide are solved by the finite element method. Parameters are varied to analyze their impact on the flow fields. Various numerical experiments are performed consecutively to explore the phenomenon of thermal performance of the combination fluid. A remarkable enhancement in thermal performance is noticed when solid structures are dispersed in the working fluid. The Biot number determines the convective nature of the boundary. When the Biot number is increased, the fluid temperature decreases significantly. Among copper oxide, aluminium oxide, and titanium oxide nanoparticles, copper oxide nanoparticles are found to be the most effective thermal enhancers.

Numerical Study on Thermal Management of Air-Cooling Model for Diamond, Triangular and Rectangular Lithium-Ion Batteries of Electric Vehicles

To improve the safety of electric vehicles, this paper analyzes the way of cooling lithium-ion batteries of electric vehicles and proposes an air-cooling scheme. First, a heat-generation model for the lithium-ion battery is prepared for numerical simulation and a finned air-cooling model is designed, which combines cold air with fins to lower the temperature of lithium-ion batteries. Through feasibility analysis, it is proved that the heat-generation model can reflect the actual heat generation of lithium-ion batteries. The cooling effect of the finned air-cooling model is also evaluated. The temperature can be 23.6 °C lower than the maximum compared with lithium-ion batteries without cooling. The cooling effect is desirable for diamond, triangle and rectangular lithium-ion battery packs, among which the rectangular battery pack achieves the most desirable effect. To conclude, to ensure the safe operation of lithium-ion batteries in electric vehicles, air cooling can be used to control their temperature, with the cooling effect in the rectangular lithium-ion battery pack being the most desirable.

An Online SOC-SOTD Joint Estimation Algorithm for Pouch Li-Ion Batteries Based on Spatio-Temporal Coupling Correction Method

An SOC (state of charge)-SOTD (state of temperature distribution) joint estimation algorithm is established for a pouch lithium-ion battery. This method integrates the first-order RC model, distributed heat generation model, thermal resistance network model, and spatio-temporal coupling correction based on spatial restoration algorithm and dual Kalman filter (DKF). Unlike the traditional 1-D SOT estimation model, the proposed algorithm can accurately estimate the temperature distribution in the battery online by restoring the battery surface temperature distribution, calculating the battery internal temperature distribution, and jointly correcting the SOC and average internal temperature. Then, the proposed method is used for the SOC-SOTD estimation of a 25-Ah pouch battery at the ambient temperatures of 10, 20, and 30 °C under the worldwide light-duty test cycle and new european driving cycle driving cycles, and the estimated values are verified by experiment and 3-D simulation. According to the verification results, calculation errors of SOC are no more than 2.12%, and the maximum average calculation errors are 0.16 °C for the surface temperature and 0.24 °C for the internal temperature. However, the DKF is needed for the SOC-SOTD joint estimation because the single KF can only correct SOC or average internal temperature but cannot handle the inconsistency in temperature distribution.

Study of the thermal behavior of a battery pack with a serpentine channel

To effectively enhance the thermal security of the Li-ion battery packs used in the electric vehicle industry, novel cooling systems equipped with serpentine channels are established. Then, the heat generation model is established and verified experimentally. In this research study, the structure of the cooling channel, the coolant velocity, the coolant temperature, and the coolant flow direction are considered to be the influencing factors. The results demonstrate that, by adopting the serpentine cooling channel, a better thermal conductivity can be obtained, and the type-B cooling system possesses a more reasonable structure. For different types of liquid cooling systems, the coolant temperature has a small influence on the temperature nephogram; however, for the same type of system, the coolant temperature strongly influences the temperature distribution. Similarly, the temperature difference is only related to the type of cooling system, with ∼6.09 and 5.53 K obtained for the type-A and type-B cooling systems, respectively. Furthermore, allowing the coolant in the serpentine cooling channels to flow in opposite directions can lower the value of the maximum temperature and temperature difference.

Analysis of the effect of friction of hybrid ball bearings on grease evaporation in cold compressors

Bearings are the essential part of the cold compressor rotor system, which has a great influence on the operation of cold compressor. Hybrid ball bearing has been successfully applied in cold compressors with the lubrication of grease. With the high-speed rotation of the cold compressor, the bearing will be affected by the axial thrust of the impeller, which will cause friction, and the grease will be impacted by the frictional heat. To understand the influence of frictional heat on grease evaporation, it is important to study the bearing heat generation. In this article, the application of grease-lubricated hybrid ball bearings in cold compressors was introduced. Based on the parameters of a successfully applied impeller and a ball bearing of the cold compressor, the axial thrust of impeller was calculated, and a bearing frictional heat generation model was proposed, which considered the dynamic change of the axial thrust of the cold compressor impeller. The heat generation and temperature of the bearing was analyzed and calculated using the proposed model. According to the results of the calculation and practical experience, a test was performed on high-speed greases, and the adding amount of grease was estimated with reference to the bearing temperature.

Heat generation and surrogate model for large-capacity nickel-rich prismatic lithium-ion battery as against 18650 battery

Large-capacity lithium batteries are being widely used as the power sources of new energy vehicles due to the advantages of easy assembly and simplified electrical connections. However, the temperature rise and thermal safety issues would become more severe for larger capacity batteries with smaller specific areas due to more concentrated heat generation and accumulation thereof. In this paper, an experimental study is presented for the thermal characteristics and thermal performance of a commercial large-capacity lithium battery over 100 Ah. The orthogonal experiment protocol was designed to obtain the direct current internal resistance and entropy coefficient of battery under varying working conditions involving the temperature and depth of discharge. It was found that the discharge rate had little effect on the entropy coefficient and direct current internal resistance, and the average entropy coefficient of a battery with high nickel content and specific energy was lower. Meanwhile, the electrochemical impedance spectroscopy of a battery in different placement orientations was also tested. The results indicated that the ohmic impedance and charge transfer impedance of the battery in the upright orientation were slightly smaller than that in the lying-down orientation, which is preferred in practical operation. The battery heat generation rate is gained by combining the measured internal resistance and entropy coefficient terms. A third-order surrogate model of heat generation rate is correlated under different working conditions with the depth of discharge, temperature, and discharge rate by the response surface analysis (RSA). In addition, the volumetric heat generation rate of the present large-capacity prismatic battery is compared with a smaller 18650 battery. The battery temperature rise under natural convection condition was experimentally measured, together with the measured specific heat, to examine the validity of the present heat generation model. Finally, the heat generation surrogate model was applied in WLTC conditions, and the temperature rises of the battery under different depths of discharge were obtained and discussed.

Study of wear and friction heat generation models of finger seals based on energy theory of tribology system

Finger seals have a good application prospect in gas and steam turbine for power generation as an advanced contact flexible seal. The wear and friction heat generation properties of the finger seal have significant effects on leakage and life. In this study, a bilateral wear model and friction heat generation model were established to calculate the wear volume and temperature of the finger seal and rotor. In particular, the friction heat generation model considered the effect of wear and deformation (centrifugal and thermal) of both the finger seal and rotor. Both models were expressed as functions of the finger seal configuration, material properties, operating conditions, and several relevant parameters. To determine these parameters, a ball-disk friction and wear experiment and a finger seal wear and friction heat generation experiment were conducted. Both models were validated with experimental data, and both errors were less than 12%.