High Heat Generation Rates Research Articles

An immersion flow boiling heat dissipation strategy for efficient battery thermal management in non-steady conditions

Aiming at the heat dissipation requirements of future high-power batteries under complex operating conditions, this paper adopts immersion flow boiling as the strategy to investigate battery thermal management performance under Nürburgring circuit condition of Porsche Taycan. A multi-filed coupled model is proposed to investigate its flow and heat transfer performance. The results show that batteries have a higher heat generation in non-steady conditions, which means that it is more crucial to investigate the battery thermal management performance under non-steady state. Immersion flow boiling can meet the thermal management requirements of batteries with high heat generation rate, which has significant advantages over single-phase liquid cooling, and the temperature uniformity can be further improved by means of roughing surface. Besides, flow velocity will completely change the heat transfer and flow mechanism of immersion flow boiling. The optimum flow regime can both exchange heat by liquid–vapor phase change and replenish the vaporized working medium by convection, achieving the lower temperature rise and better temperature uniformity in battery. Moreover, the boiling heat transfer in battery thermal management is in the partial nuclear boiling state, which is much lower than the critical heat flux, and thus can effectively inhibit high heat flux conditions such as thermal runaway.

A study on the geothermal circulation system of granite: An example from the Lancang area, Yunnan

This study assesses the geothermal water circulation process of a granite geothermal system in the Lancang area, Yunnan. Cycling processes are studied using water chemistry and isotope analysis techniques. The results show that the water chemistry type of the hot springs in Lancang is Na-HCO3, with TDS values ranging from 246 to 724 mg/l. The granite pluton, as the main heat source, has a high radiogenic heat generation rate (4.17 μW/m3 on average). δD and δ18O in Lancang are close to the global atmospheric and local precipitation lines, indicating that geothermal water originates from atmospheric precipitation. Moreover, the mountainous area from 1295.3 to 1624.5 m above sea level is the main precipitation recharge area. In addition, the main ions of geothermal water mainly come from the dissolution, weathering, and cation exchange of silicate minerals in granite, and Ca2+ and Mg2+ in the water are exchanged with Na+ and K+ in the reservoir, significantly increasing the Na+ and K+ concentrations in the water. The reservoir temperatures are 126.60 °C to 151.32 °C based on the SiO2 geothermometer, and the depths range from 2283.05 to 4024.59 m. The NW- and NE-oriented fault system in Lancang serves as a channel for geothermal water to exit the ground and form hot springs; this water is also mixed with cold water during upwelling, and the mixing ratios are 63 %-84 %. Finally, the model of geothermal water circulation in the Lancang is established.

A study on microchip cooling performance increment by using air jet impingement with one and double rows

The impinging jet technique is a high-performance cooling technology for microchips which are basic elements of computer systems and have high heat generation rates in small volumes. In this study, the improvement of heat transfer of the desktop microchips used in all technological products today by air-impinging jet flow was examined. For this purpose, numerical research was carried out on the cooling of copper plate surfaces with two different patterns, concave and roof shaped having 1000 W/m2 constant heat flux in rectangular cross-sectional ducts by one and double air jets with distances of Dh and 2 Dh between them. Numerical analysis was performed steady and in three dimensions with the k– ε turbulence model by the Ansys–Fluent program. The obtained results were compared with the numerical and experimental results of the study in the literature and it was seen that they are determined to be compatible. The results were presented as the mean Nu number for each of both patterned surfaces and the mean outlet temperature of the jet flow ( Tmoj) and the mean Nu number ( Num) of all patterned surfaces in single and double jet channels with different distances. Besides, pressure drop (Δ P), friction factor ( f), thermal resistance ( Rt) and thermo-hydraulic performance (THP) of concave and roof-patterned surfaces in the channels with different jet setup configurations were analyzed. Streamline and temperature contour distributions of the jet flow along the channel for different H/ Dh ratios and jet numbers were evaluated for both patterned surfaces. In H/ Dh = 4 and at Re = 7000, the average Nu number for roof-patterned surfaces was found to be 30.52% higher than concave patterned surfaces in the case of double jets with a distance of Dh. Rt reduction values of the roof and concave pattern surfaces with a double jet arrangement having 2 Dh distance at Re = 5000 and H/ Dh = 8 are 163.7% and 36.23% when compared to single jet, respectively.

Study on Characteristics of Two Phase Flow Field in Grinding Zone of Large Spiral Angle Groove Wheel

Aiming at the high specific removal energy and heat generation rate in grinding process, and the low heat transfer efficiency in grinding arc zone of ordinary grinding wheel, the problems of local high temperature and grinding burn are easy to occur. In this paper, the plane grinding of grooving wheel with large spiral Angle is taken as the research object, and the numerical analysis model of gas-liquid two-phase flow field in wedge zone and grinding arc zone is established. The enhancement mechanism of heat transfer performance in grinding arc of large spiral Angle groove wheel was investigated. The results show that the flow of grinding fluid into the grinding arc will be hindered by the airflow around the grinding wheel, resulting in backflow and side leakage. Compared with ordinary grinding wheels without grooves, the backflow and side drainage in grinding zone of big spiral Angle grooves grinding wheels are significantly reduced, and a large amount of grinding fluid is transported in the heat exchange channel. The spiral groove has a good conduction effect on the grinding fluid, and the grinding fluid is easier to enter the grinding zone, thus significantly improving the heat transfer performance of the grinding zone and effectively reducing the grinding temperature during the grinding process.

Granite thermal reservoirs in Lingshui area of Hainan Island and their significance to geothermal resources, China

Hainan Island located at the southernmost tip of the continental crust of the South China Plate, has high terrestrial heat-flow values, widely-distributed hot springs, and rich geothermal resources. Intensified researches on the origin and potentials of geothermal resources can promote Hainan Island's development into a clean energy island. To determine the geological conditions for the formation of geothermal resources in southern Hainan Island, we collected core samples of granites from the Baocheng batholith in southern Hainan Island and conducted systematic analysis in respect of petrology, geochronology, geochemistry, and petrophysical property. The results of this study are as follows. The Baocheng batholith in the southern Hainan Island has a crystallization age of 98.42 ± 0.56 Ma, making it the product of magmatism in the early stage of the Late Cretaceous. It mainly consists of high-K calc-alkaline granites, which were intruded by intermediate-to-mafic veins. The Baocheng batholith has a high radioactive heat generation rate of 2.712–6.843 μW/m3, with an average of 3.846 μW/m3, a radioactive heat-flow value of 30.768 mW/m2 and a heat-flow contribution rate of 38.95%–43.95%. As shown by the results of their thermophysical property analysis, the granites have high thermal conductivity and can serve as high-quality geothermal reservoirs. In combination with previous geological and geophysical data, the geothermal model of the Lingshui area was established in this study. The deep structure indicates the presence of high-conductivity and low-resistivity layers in the basement of the Baocheng batholith. It can be inferred thereby that asthenospheric upwelling may occur and that there exist two magma vents at depth in the batholith. Therefore, magmatic heat at depth and granites with high radioactive heat generation rate serve as the main heat sources in the Lingshui area.

Experimental Study and Finite Element Analysis of Temperature Reduction and Distribution During Machining of Al-Si-Mg Composite Using Deform 3D

Composite materials are promising materials in the manufacturing industry due to the quality of their materials. However, in transforming these materials, the machining process experiences a high-heat generation rate, which has led to the study of temperature distribution, and reduction analysis at the cutting region. High-temperature generation during machining operation leads to thermal deformation on the developed component or parts, affecting the operation life span of the component. Thus, this study investigated the effect of mineral oil-based-Multi-walled carbon nanofluid (MWCNTs) compared to pure mineral oil in the turning of aluminum-silicon magnesium metal composite (AlSiMg) on temperature reduction and distribution. The nanofluid was prepared with 0.4g of MWCNT to 1 liter of mineral oil. The study employed the energy dispersive spectrometer to obtain the chemical composition of the developed nanofluid. Furthermore, Finite element software DEFORM 3D v11.0 uses a lagrangian incremental approach to simulate chip formation and temperature distribution on the workpiece. Also, to study the effects of the machining parameters on the temperature distribution. The experiment results showed a significant reduction of 11.9% in temperature when machining with nanofluid compared to pure mineral oil. The simulation results showed that the temperature increases as the cutting speed and feed rate increase. The minimum temperature via the DEFORM 3D Finite Element Model simulation was achieved at spindle speed 870 rpm, feed rate 2 mm/rev, and depth-of-cut 1 mm. In conclusion, the study recommends that the manufacturing industry employ the optimized machining parameters during the turning of AlSiMg metal matrix composite for a sustainable machining process.

3D thermal modelling of the Oslo-Asker area, Norway

The pressing need for renewables prompted geothermal research in Norway recently. These studies confirmed rocks with high heat-generation rates in the Oslo Region, covered locally by sediments. Although the geology appeared favourable to the operation of deep geothermal resources in the most densely populated area of Norway, no attempt was made to estimate underground temperatures. In the present work, subsurface temperatures were computed for the Oslo-Asker area by means of 3D numerical modelling. We conclude that deep temperatures are too low to be of economic use with present-day technology. Shallow temperatures (i.e. < 500 m depth below ground level) appear high enough for direct use and heating. There is, however, a crucial need for new data from deep boreholes in order to better constrain the predictions of the models.

Experimental investigations on the correlations between the structure and thermal‐electrochemical properties of over‐discharged ternary/ Si‐C power batteries

The thermal safety of power lithium-ion batteries (LIBs) has seriously affected the booming development of electric vehicles (EVs). Especially, owing to the requirement of high energy density, thermal runaway (TR) easily occurs in LIBs, resulting in a higher heat generation rate. Over-discharging is recognized as a common cause for TR. In the present research, the correlations between the structure and thermal-electrochemical properties of an over-discharged ternary/Si-C battery at room and high temperatures were investigated. The heat generation mechanisms of the batteries due to the maximum surface temperature and peak temperature difference variations during fast charging and discharging processes were investigated. Moreover, the electrochemical performances parameters of the batteries, such as voltage changing trend, discharge time, discharge capacity, internal resistance, electrochemical impedance spectroscopy (EIS) spectra, were analyzed. When the battery was discharged at 2.0C and 55°C, its maximum temperature and highest temperature difference reached 91.34°C and 13.24°C, respectively, finally resulting in a sharp decline in electrochemical performance. Furthermore, the root reasons for performance degradation and heat generation intensification of the over-discharged battery were analyzed by scanning electron microscopy and X-ray diffraction. The cause of the aforementioned phenomenon is due to irreversible damage to the electrode materials. This research not only reveals the relevant relationship between the thermal behavior and the microscopic structure of the over-discharged ternary/Si-C battery under various temperature conditions but also provides valuable insights for improving the safety of LIBs modules even packs.

Sensor based in-operando lithium-ion battery monitoring in dynamic service environment

In this work, a dynamic testing platform to analyze lithium-ion battery (LIB) performance degradation and safety during in-service vibration and impacts is presented. The LIBs are cycled until end of life (EOL) under various dynamic conditions, providing in-operando battery performance examination. A sensor network constructed consisting of a resistance temperature detector (RTD), an accelerometer, an eddy current sensor and a shunt resistor is incorporated into the setup. Mechanisms of LIB capacity fade, temperature rise, and deformation from cycling in representative dynamic environments are analyzed and compared with results from theoretical analyses as well as with electrode structure evaluation. The sensor network identifies critical periods with high heat generation and stress accumulation rates. By comparing single cell and battery pack performances, complex effects of examined boundary conditions on LIB heat generation are analyzed. Using the sensor network, an approach to identify critical cell(s) with the highest risk of safety hazards without the need for electrochemical modeling is presented. Raman spectroscopy analyses, SEM imaging, and electrochemical impedance spectroscopy (EIS) analyses are also applied to support the observations.

Assessment of a possibility to use 232U in radioisotope thermoelectric generators

The paper analyzes advantages and drawbacks of the radioisotope thermoelectric generators (RTG) based on application of 238Pu and 232U. Currently, the RTG on 238Pu are widely used for long-term autonomous power supply of spaceships due to the following positive properties of 238Pu: high specific heat generation rate, long half-life, weak emission of neutrons and γ-rays. Isotope 238Pu may be produced by neutron irradiation of 237Np (main component of transuranium radioactive wastes) in nuclear reactors. The paper considers application of 232U for the same purpose because of the following positive properties of 232U: power elevation during initial 10 years of the RTG operation (effect of α and β-emitters in 232U decay chain), long half-life (comparable with 238Pu half-life). Unfortunately, 232U decay chain includes also intense emitters of high-energy γ-rays. As a compromise, a possibility is considered to create the RTG based on mixture of 238Pu with small (below 5%) additive of 232U. Such RTG will be able to keep long-term stable operation at high power level. The following two-step technology is proposed to produce 232U: generation of 231Pa in thorium blanket of hybrid thermonuclear reactors and subsequent neutron irradiation of 231Pa in nuclear reactors till accumulation of significant 232U quantities.

Thermal Performance of a Micro Heat Pipe Array for Battery Thermal Management Under Special Vehicle-Operating Conditions

The thermal management of battery systems is critical for maintaining the energy storage capacity, life span, and thermal safety of batteries used in electric vehicles, because the operating temperature is a key factor affecting battery performance. Excessive temperature rises and large temperature differences accelerate the degradation rate of such batteries. Currently, the increasing demand for fast charging and special on-vehicle scenarios has increased the heat dissipation requirements of battery thermal management systems. To address this demand, this work proposes a novel micro heat pipe array (MHPA) for thermal management under a broadened research scope, including high heat generation rates, large tilt angles, mild vibration, and distributed heat generation conditions. The experimental results indicate that the temperature difference is maintained 3.44 °C at a large heat generation of 50 W for a limited range of tilt angles. Furthermore, a mild vehicle vibration condition was found to improve temperature uniformity by 3.3 °C at a heat generation of 10 W. However, the use of distributed heat sources results in a temperature variation of 3.88 °C, suggesting that the heat generation distribution needs to be considered in thermal analyses. Understanding the effects of these special battery-operating conditions on the MHPA could significantly contribute to the enhancement of heat transfer capability and temperature uniformity improvement of battery thermal management systems based on heat pipe technologies. This would facilitate the realization of meeting the higher requirements of future battery systems.

Numerical modeling of coupled biochemical and thermal behavior of municipal solid waste in landfills

A coupled bio-thermal (BT) model is proposed and validated for the prediction of long-term biochemical and thermal behavior of municipal solid waste (MSW) in landfills. The biochemical and thermal behavior of the waste was modeled using a two-stage anaerobic degradation model and diffusive heat transport model, respectively. A temperature function that accounts for the inhibitory effect of non-optimum temperatures on the microbial growth was proposed to simulate the coupled effects of biochemical and thermal behavior of waste in landfills. Six numerical simulation cases representing conventional and bioreactor landfill conditions were performed on a typical full-scale landfill cell model to determine the spatial and temporal variation in the long-term biochemical and thermal characteristics of waste in landfills. The results from the numerical analyses show that incorporating the effect of temperature of waste in the modeling of biodegradation of waste in landfills plays a significant role in realistically predicting the long-term biochemical and thermal regime in MSW landfills. The proposed BT model captures the key trends in the landfill gas (LFG) production and waste temperatures typically observed in actual full-scale landfills. Elevated waste temperatures were predicted especially in the bioreactor landfill cases suggesting that rapid decomposition of waste induces high heat generation rates; however, the elevated temperatures were short-lived.

Thermofluidic modeling and temperature monitoring of Li-ion battery energy storage system

The battery energy storage system (BESS) is widely used in the power grid and renewable energy generation. With respect to a lithium-ion battery module of a practical BESS with the air-cooling thermal management system, a thermofluidic model is developed to investigate its thermal behavior. The thermal model for a single battery is established and experimentally validated first, and then the thermofluidic model for this battery module is developed based on the single battery thermal model and validated by experimental data also. Simulations are performed considering the practical frequency regulation condition and some hypothetical situations with unexpectedly high heat generation rates. Thermal behaviors of the battery module under different conditions are carefully analyzed. Results show that the fans-on forced air convection cooling reduces the maximum temperature by 0.4 K and makes the maximum temperature appear in a different battery of the BESS module compared with the natural air convection cooling. Especially, the temperature monitoring strategy is studied. Due to technical and cost constraints, only a limited number of temperature monitoring points can be set and the temperature that can be monitored is the battery surface temperature or some connecting bars’ surface temperature. The rationality of the locations of different temperature monitoring points is analyzed. The obtained results clearly indicate that enough caution must be paid when setting the temperature monitoring points in practical BESSs. The bad temperature-monitoring strategy may largely underestimate the maximum temperature (by as much as 3 K under the normal frequency regulation condition, and probably much larger under harsh working conditions) in the BESS and fails at reflecting the thermal status of the BESS.

Evaluation of favourable hot dry rock areas in the east of the Yishu fault zone in China

Hot dry rock (HDR) geothermal resources have great development potential and prospects, owing to their wide distribution and high thermal storage temperature. HDR resources are abundant in China, but their exploration and exploitation remain in the early stages. The Yishu fault zone in Shandong Province in eastern China is in a high-temperature geothermal zone of the Pacific Rim. Three craters and 15 hot springs are in this area, which possesses abundant geothermal resources and favourable conditions for the occurrence of HDR resources. Nevertheless, HDR resources in this area have not been studied in detail, and the index-evaluation system for HDR is still imperfect. In this paper, five index layers are selected, including: the gravity and magnetic fields, geothermal field, tectonic activity, reservoir and cover characteristics, and remotely sensed features. Thirteen index elements were also selected as evaluation factors. In combination, these index layers and index elements have established a favourable evaluation index system for HDR resources in this region, and the analytic hierarchy process has been used to determine the weight of each factor. Then, the GIS spatial analysis function is used to carry out spatial superposition analyses for each index element, and finally the distribution characteristics of HDR resources east of the Yishu fault zone were determined, with four favourable selection areas being delineated. The occurrence conditions of HDR resources are analysed in detail with evaluation indexes. It is believed that HDR resources are closely related to neotectonic movement, volcanism and rocks with high heat-generation rates. Searching for areas with geothermal anomalies is indispensable for the evaluation of HDR resources. This study provides a basis for the exploration and development of HDR resources in the region, and it can also provide a reference for similar work in other parts of the country. KEY POINTS A set of evaluation indexes to determine favourable areas for HDR resources, including gravity, geothermal field, geological structure and crustal stability, heat storage and heat cover and features on remotely sensed images, is established. East of Yishu fault zone, there is a great potential of HDR resources, with an area of 19 399 km2 of favourable and more favourable areas, accounting for approximately 38.8% of the total area. HDR resources are likely closely associated with neotectonics, igneous activity, geothermal anomalies and rocks with a high heat-generation rate such as granites.

Experimental and simulation study on thermal characteristics of 18,650 lithium–iron–phosphate battery with and without spot–welding tabs

Thermal condition is crucial to the safety and performance of battery and battery pack. In this work, a two–dimensional, axisymmetric, electrochemical–thermal coupled model of 18,650 lithium–iron–phosphate battery is established and validated by our own experimental results. The model is used to investigate the effect of ambient temperature on battery performance and heat generation. The results show that the temperature rise in the battery increases with decreasing ambient temperature, which is mainly due to the increase in heat generated from Ohmic loss and polarization with decreased ambient temperature. While considering the welded structure, in which the cylindrical batteries are assembled into a battery pack, the effect of spot–welded nickel strip on battery performance under different discharge rates is experimentally studied at the ambient temperature of 298.15 K. It is found that the battery with the spot-welded nickel strip has a lower discharge plateau and a higher heat generation rate. The nickel strip has a greater impact on battery performance and temperature if the discharge C-rate increases.

Aging investigation of an echelon internal heating method on a three-electrode lithium ion cell at low temperatures

Abstract An echelon internal heating method based on alternating current has exhibited many advantages of high heat generation rate and thermal uniformity for fast battery heating at low temperatures. However, inappropriate parameter settings for the echelon internal heating method are prone to risk battery health due to side reactions. To address this problem, a three-electrode cell is fabricated to investigate the effect of the echelon internal heating method on cell health at low temperatures. A fractional order circuit model is used to determine the optimal current amplitude and frequency of alternating current at different temperatures for preheating the cell. After many cycles of preheating the cell, capacity calibration results and incremental capacity curves show no apparent detrimental effect of the proposed heating method on cell health.

Fast lithium growth and short circuit induced by localized-temperature hotspots in lithium batteries

Fast-charging and high-energy-density batteries pose significant safety concerns due to high rates of heat generation. Understanding how localized high temperatures affect the battery is critical but remains challenging, mainly due to the difficulty of probing battery internal temperature with high spatial resolution. Here we introduce a method to induce and sense localized high temperature inside a lithium battery using micro-Raman spectroscopy. We discover that temperature hotspots can induce significant lithium metal growth as compared to the surrounding lower temperature area due to the locally enhanced surface exchange current density. More importantly, localized high temperature can be one of the factors to cause battery internal shorting, which further elevates the temperature and increases the risk of thermal runaway. This work provides important insights on the effects of heterogeneous temperatures within batteries and aids the development of safer batteries, thermal management schemes, and diagnostic tools.

Thermomechanical Safety Analyses for a 238Pu Production Target at the HFIR

Safety analyses at the high flux isotope reactor (HFIR) are required to qualify irradiation of production targets containing neptunium dioxide/aluminum cermet (NpO2/Al) pellets for the production of plutonium-238 (238Pu). High heat generation rates (HGRs) due to a fertile starting material (237Np), low melting temperatures, and previously unstudied material irradiation behavior (i.e., swelling/densification, fission gas release) require a sophisticated set of steady-state thermal simulations in order to ensure sufficient safety margins. Experience gained from previous models for preliminary target designs is incorporated into a more comprehensive production target model designed to qualify a target for three cycles of irradiation and illuminate potential in-reactor behavior of the target.

Numerical analysis of forced convective heat transfer of nanofluids in microchannel for cooling electronic equipment

Abstract Electronic components depend on the passage of electric current to perform their duties, and they become potential sites for excessive heating, since the current flow through a resistance is accompanied by heat generation. The heat generated must be removed by designing a suitable thermal management system for reliable operation of the electronic device. Also the size of electronic systems used in industries such as microelectronics, telecommunications, aerospace, biomedical, robotics and similar other areas are rapidly decreasing. Unless properly designed and controlled, high rates of heat generation result in high operating temperatures for electronic equipment, which jeopardizes its safety and reliability. With the advent of micro-manufacturing technology, multiple micro channels are machined on the back of the substrates of electronic components in integrated circuits. The heat generated by the electronic component is transferred to the coolant by forced convection. In the present study analysis on a rectangular microchannel heat sink was done by using water, Al2O3-water, and TiO2-water nanofluids as working fluids. The nanofluid properties were evaluated with correlations available in the literature. The hydrodynamic and thermal behavior of a microchannel was studied in the present work. The variation wall temperature, pressure drop in the channel and the heat transfer rate was calculated. The effect of Reynolds number on heat transfer in the microchannel was also studied. A significant improvement in the heat transfer was found with microchannel heat sink due to decrease in convective heat transfer resistance as the size of the thermal boundary layer decreased with microscopic size of the channels. It was also found from the simulation results that there was no extra pressure drop at low volume fractions of nanoparticles in the base fluid. The simulation results generated were compared with the analytical data available in the literature and found good agreement.

Thermo-Mechanical Safety Analyses of Preliminary Design Experiments for 238Pu Production

Safety analyses at the high flux isotope reactor (HFIR) are required to qualify experiment targets for the production of plutonium-238 (238Pu) from neptunium dioxide/aluminum cermet (NpO2/Al) pellets. High heat generation rates (HGRs) due to fissile material and low melting temperatures require a sophisticated set of steady-state thermal simulations in order to ensure sufficient safety margins. These simulations are achieved in a fully coupled thermo-mechanical analysis using comsolmultiphysics for four different preliminary target designs using an evolving set of pre- and postirradiation data inputs, and subsequently evolving solution scopes, from the unique pellet and target designs. A new comprehensive presentation of these preliminary analyses is given and revisited analyses of the first prototypical target designs are presented to reveal the effectiveness of evolving methods and input data.