Dynamic Heat Research Articles

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.

Numerical Simulation of Unsteady Turbulent Flow and Heat Transfer of Dynamic Thermal Flow Sensor

Improving energy efficiency in the building’s design is a priority area. To avoid unnecessary energy consumption, electronic control (intelligent) systems can be used to measure and monitor heat exchange between building walls and the surrounding environment, as (Calorimetric Sensor, Heat Flux Sensor ...). They are ideally suited for research in rationalizing and improving thermal efficiency. The aim of this study was a computational fluid dynamics investigation of unsteady turbulent flow and heat transfer of dynamic heat flux sensor for quantitative description of the heat transfer between the building's walls and the surrounding environment.Using CFD software, we numerically simulated the wind tunnel where the sensor was installed; we used six different air speeds (Vinlet=2m/s to 12m/s) in the inlet. To improve the standard features of the CFD code, the User-Defined Function (UDF) was written in the C language program and integrated into the solver of ANSYS Fluent, in order to determine the thermal flow file applied to the surface of the sensor. Heat transfer coefficient (h0) values are obtained according to each speed. The results obtained were compared to results in previous experimental and theoretical literature. There is a good compatibility of all results that allows dependence on numerical simulations in the future as a way of stewardship when studying energy rationalization.

Hybrid-timescale dispatch of heat and electricity integrated system considering dynamic heat flow

In the electricity and heat integrated energy system, the transmission speed of heat energy is much slower than that of electricity. While the ignorance of the dynamic characteristic of heat system during the dispatch process often fails to satisfy the heat load. To address this issue and further improve the flexibility of the system, a dynamic linear model of heat pipeline is proposed, and a hybrid-timescale optimal dispatch strategy is established in this paper. Firstly, based on the finite difference method, the partial differential equation of heat pipeline is converted into a linear equality constraint. Then, a hybrid-timescale optimal dispatch model is established. By considering different dynamic characteristics of heat and power system, the calculation of dynamic linear model and dispatching of devices of power and heat system are realized under three different timescales. Finally, by using MATLAB, the effectiveness of the proposed dynamic model is validated compared with the conventional steady-state model and measured data. A series of simulation results verify that the proposed hybrid-timescale optimal dispatch strategy considering dynamic model helps the system to increase the supply rate of the heat load by 100% and decrease the economic cost,CO2andNOxemission by 0.79%, 0.2%, and 18.9%, respectively.

Why Does a Stronger El Niño Favor Developing towards the Eastern Pacific while a Stronger La Niña Favors Developing towards the Central Pacific?

By decomposing observed El Niño and La Niña events into a strong group and a weak group, respectively, we discovered that the strong La Niña group has its peak center more towards the west compared to the weak La Niña group, whereas the strong El Niño group has its peak center more towards the east compared to the weak El Niño group. The cause of this structure asymmetry is investigated through an ocean mixed-layer heat budget analysis. It was found that the asymmetry is closely linked to the longitudinal distribution of SST anomaly (SSTA) skewness along the equator, and is fundamentally caused by nonlinear dynamic heating, especially nonlinear horizontal temperature advection. It was demonstrated that near the equatorial central Pacific, the anomalous zonal and meridional currents generate negative nonlinear zonal and meridional temperature advection anomalies for both the El Niño and La Niña events, thus favoring a stronger La Niña and a weaker El Niño. Over the eastern Pacific, due to the dominant geostrophic zonal current anomalies and the southward shift of SSTA centers, nonlinear horizontal temperature advection anomalies tend to be positive for both the El Niño and La Niña, thus favoring a stronger growth of El Niño than La Niña. Nonlinear vertical temperature advection anomalies play minor roles in the central Pacific and tend to partially offset the nonlinear horizontal advection effect in the equatorial eastern Pacific.

Signal-processing-based characterization of thermoacoustic coupling in a lean premix swirling gas turbine combustor

This study investigates the strength of the thermoacoustic feedback coupling between the acoustic field and the thermal field in a combustor with the coherence function between dynamic pressure (DP) and heat release rate (HR) signals. The time domain signals of DP and HR - which are measured synchronously from a lean premix combustor experiencing combustion instability (CI) - were used. The coherence function between DP and HR signals in the time-frequency domain reflects the degree of linear interdependence and the mutual causality of signals from the two fields. The results of the coherence analysis revealed the following: (i) the coherences are far from unity due to random properties in both signals during stable combustion, thus implying decoupling of the two fields; (ii) they are close to unity around the acoustic eigenfrequencies of the combustor during unstable combustion, thus demonstrating the linear interdependence and mutual causality between the two signals frequency-wise; and (iii) the formation of nearly linear interdependence between the two signals at the first eigenfrequency precedes the onset of limit cycle oscillation. Based on these findings, we propose an equivalent harmonic oscillator model for a combustion process under severe instability and formulate the damping ratio expression accordingly.

An immersive multisensory virtual reality approach to the study of human-built environment interactions: Technical workflows

Virtual Reality technology has gained increased attention due to its capacity to provide immersive and interactive experiences to its users. Although increasing evidence has suggested that incorporating multisensory components in VR can promote the sense of presence and improve user performance, most of the current VR applications are limited to visual and auditory senses. In this article, a novel method of integrating thermal-related devices (heat lamps and fans) into Virtual Reality was developed. Automated interaction with the thermal-related devices was achieved using Arduino-based control module with its program embedded into the VR platform-Unity. The functions, hardware and software requirements of the multisensory Virtual Reality system as well as the step-by-step procedures are detailed to provide a reproducible workflow for future applications.•A practical workflow to integrate thermal apparatus into Virtual Reality.•Dynamic airflow and radiative heating incorporated into Virtual Reality.•Automated process to allow user interaction with the thermal components in Virtual Reality.

Injection parameter design to improve the high-speed gear heat dissipation: CFD simulation and regression orthogonal experiment

A heat dissipation model of high-speed helical gears based on Computational Fluid Dynamics (CFD) is proposed under injection lubrication. Gear heat dissipation is investigated by static and dynamic heat flow coupling. The oil injection lubrication test is designed to measure tooth temperature by an infrared thermal imager. The results show that owing to the gear centrifugal force, the oil splash, and the blocking effect of the high-speed airflow, the average temperature first decreases and then increases, and the temperature difference increases first and then decreases with the increase in injection angle, distance, and velocity. The average temperature and temperature difference are remarkably affected by the injection velocity and distance, respectively. The optimal injection angle, distance, and velocity predicted by the regression orthogonal method are 9.212°, 54.514 mm and 35.561 m/s, respectively. Infrared thermometry experiments show that the optimal injection parameters enhance the gear heat emission by 6.93%. These findings provide support for the heat dissipation study and injection system design for aerospace gears.

Numerical investigation of the effect of carotid bifurcation stenosis degree on pulsatility characteristics.

Arterial bifurcations are regions that are susceptible to hemodynamic effects and thrombus formation. In the current study, the hemodynamic effects of a simplified 3D model of an arterial bifurcation were simulated using the commercial computational fluid dynamics software FLUENT. The non-Newtonian properties of blood were modeled using the Carreau model, and the pulsation dynamics and heat transfer characteristics of blood at different degrees of stenosis in the arterial bifurcation were analyzed. The results indicate that arterial stenosis caused by a thrombus when the pulsation velocity reaches its peak has an essential impact on blood transport. The stenosis of the bifurcation increases the peak pulsatile flow pressure drop, and each 0.5mm stenosis of the arterial bifurcation increases the mean wall shear stress of the bifurcated segment by approximately 0.25Pa. From the heat transfer perspective, arterial stenosis has little effect on the heat transfer coefficient. The heat transfer coefficient measured inside the bifurcation is much larger than that measured outside the bifurcation. The stenosis of the arterial bifurcation causes an increase in the mean velocity of the arterial cross-section, and the volume-averaged absolute vorticity is introduced to quantify the secondary flow effect during the pulsation cycle, where the arterial stenosis causes an increase in the mean absolute vorticity at pulsation velocity and accelerates the decay of the vorticity at uniform velocity. In this paper, the hemodynamics of carotid bifurcation pulsation is analyzed in conjunction with flow field properties to reveal the flow field dynamics factors and heat transfer characteristics of local stenosis of the carotid bifurcation and to conduct an exploratory study for the diagnosis and treatment of carotid bifurcation thrombosis.

Dynamic thermal demand analysis of residential buildings based on IoT air conditioner

With the development of communication technology and artificial intelligence, the application of IoT (Internet of Things) has driven the development of smart cities. Real-time and non-intrusive IoT air-conditioning data as a supporting source provides new possibilities for studying dynamic heat demand in residential buildings. However, the data structure of IoT is very different from that of traditional sources. Therefore, this study conducts a dynamic thermal demand analysis of residential buildings at a regional scale based on IoT air conditioners. Firstly, the data preprocessing paradigm for the IoT air conditioner was constructed. Next, the change of dynamic thermal demand was comparatively analyzed through the coupling regulation of the air conditioner set temperature and wind velocity, as well as the frequency adjustment of active functions in two functional rooms and three demand groups. There were two further findings, by evaluating the PMV fluctuation performance under different operating conditions, the retaliatory and economic thermal demand in different groups were found to exist. Meanwhile, another finding was that there were seasonal adaptive adjustments and delayed compensatory adjustments for air conditioners. Moreover, the energy-saving potential of air conditioner operation under energy-saving awareness was quantified. From lower to upper class, 0.90%, 0.94%, and 0.38% of the accumulative time spent by bedroom users have thermal demand energy-saving potential of 75%, and 0.31%, 0.44%, and 0.33% have thermal demand energy-saving potential of 6%.

Obtaining Li2CO3 from β-LiAlSi2O6 by solid state reaction with NaOH

Li2CO3 was obtained by the solid-state reaction between β-LiAlSi2O6 (β-spodumene) and NaOH under dynamic and static thermal conditions in the temperature range between 300 °C and 800 °C followed by washing and drying stages. Prior to the reaction, the reagents have been mixed by mechanical milling 1 h under air atmosphere at room temperature. The ball-milled mixture of β-LiAlSi2O6:NaOH has been studied after heating to determine its morphological, microstructural, structural and thermal stability characteristics. The results indicate that sodium from NaOH replaces lithium in the aluminosilicate structure by heating under air. Different crystalline phases have been observed depending on temperature: NaAlSi2O6 near 300 °C and non-stoichiometric sodium aluminosilicates over 500 °C. The only lithium-containing product formed has been Li2CO3 obtained at 350 °C and 300 °C under dynamic and static heating conditions, respectively. Additional experiments at different β-LiAlSi2O6:NaOH molar ratios have shown that a major amount of NaAlSi2O6 phase is obtained for the 1:1 M ratio. Lithium recovery experiments (as Li2CO3) combining washing and drying stages have given 91.2 wt% of Li2CO3 in the recovered solid residue.

Dynamic regulation of the thermal performance of the S–CO2 minichannel using a piezoelectric oscillating fin

It is difficult to alter the thermal performance of a minichannel heat sink with a fixed structure under constant operating conditions. In particular, if the local heat transfer of the substrate cannot be regulated in real time, the dynamic heat dissipation needs of high-power electronic components cannot be met in the electrical servo systems of flight vehicles. In this paper, a new minichannel heat sink structure based on the classical rectangular channel is proposed and a piezoelectric oscillating fin (POF) is introduced to replace the fixed fin. The thermal performance of the heat sink can then be regulated using the swing of the POF, with supercritical carbon dioxide (S–CO2) as the coolant. Transient numerical simulations are applied to investigate the influence of various POF operating parameters on the heat transfer of the channel, such as the oscillation amplitude and frequency. The results demonstrate that a channel with a POF can allow for dynamic and rapid adjustment of the thermal performance through control of the oscillation frequency and amplitude of the POF, with a constant channel configuration, coolant, and operating conditions. The heat transfer can be enhanced significantly by the swing of the POF, with the local Nusselt number growing up to 8.3 times and the overall one up to 1.14 times. Both the oscillation frequency and amplitude have a positive correlation with the intensity of heat transfer. The POF also contributes to a greater pressure drop and fluctuation in pumping power. A comprehensive evaluation coefficient shows that the POF is effective at improving the overall thermal performance with a low-frequency swing, while high-frequency operation enhances the local heat transfer and decreases the local temperature near the tail end of the POF. Finally, considering the effects of the frequency and amplitude of the POF, as well as the variable thermophysical properties of the supercritical coolant, a heat transfer correlation based on the Dittus–Boelter equation is established to predict the thermal performance of the channel with a POF. This prediction has a maximum error of ±0.56%.

A numerical study on performance efficiency of a low-temperature horizontal ground-source heat pump system

Exploitation of shallow ground and its low-grade heat potential is fundamental to designing 5th generation district heating and cooling (DHC) networks. Horizontal ground-source heat pump (HGSHP) systems are a common way to utilize shallow geothermal energy. Realistic estimation and prediction of performance of a HGSHP system and shallow ground thermal behaviour should consider the whole system including building heating and cooling load, heat pump and ground heat exchanger, and the ground. This should be accompanied by realistic atmospheric and ground conditions. In this paper, a three-dimensional coupled thermal–hydraulic model with realistic boundary conditions adopting a whole system approach is presented. Dynamic heat pump coefficient of performance (COP) that depends on seasonal variation of heating/cooling demand and ground conditions are also considered. Model validations are conducted against experimental and analytical results in literatures. The model is applied for evaluating a HGSHP system to support development of a 5th generation DHC network on a potential site in the UK. Several influencing factors, such as ground moisture transfer, building thermal load mode, buried depth of ground loops, and initial ground temperature profile are studied to assess performance efficiency of the HGSHP system and evolution of ground thermal behaviour in response to heat extraction or rejection into the ground. The results show that 5% of the monthly total heat demand of the site could be met by the designed HGSHP system, consisting of 200 U-shaped ground loops buried at the depth of 3 m and pure water as the heat carrier. Overlooking the ground moisture transfer or hyperbolizing the ground saturation would overestimate the load-carrying capacity of the HGSHP system. The HGSHP system is more efficient with a higher heat pump COP under the heating and cooling mode than under the heating-only mode. Predicted performance of the HGSHP system improves with buried depth of the ground loops. The results also show that a 1 ℃ increase in the undisturbed ground temperature could suffice up to 8% of the monthly total heat demand of the site.

Математическая модель теплоснабжения помещения как объекта динамического управления температурой

Energy saving issue in the process of administrative buildings heating is an important one. Dynamic control of room temperature depending on the schedule of its usage gives great opportunities. Dynamic control should meet the criteria of energy efficiency and ensure air temperature in the rooms at time intervals of their usage at the required level in terms of external impact on the building. Obviously, such control can only be implemented by an automatic system. To synthesize such a system, we need mathematical models of room heating as control objects. Consequently, the problem under consideration is relevant. Experimental data and numerical simulation methods are used to obtain mathematical models. Mathematical models are obtained in the state space and in the form of transfer functions for controlling and disturbing influences based on the equations of the dynamic heat balance of the room. Two types of mathematical model of the room are defined. They make it possible to synthesize the laws of qualitative and quantitative control of the heat supply of the building with a given accuracy and to determine schedules of temperature changes depending on the schedule of its use, optimal in terms of minimum energy consumption.

Coupled characteristics and performance of heat pipe cooled reactor with closed Brayton cycle

Heat pipe cooled reactors with closed Brayton cycle (CBC) have the potential of achieving both high efficiency and high safety. However, the coupled characteristics and performance of CBC coupled with heat pipe reactors have not been well studied. Few works consider both the neutron dynamics in heat pipe cooled reactors and the dynamic heat and mass transfer in CBC. In this paper, a novel nuclear power system configuration, heat pipe cooled reactor with CBC, is proposed and comprehensively analyzed. A dynamic model is built based on the modular modeling idea, and verified using a Brayton cycle test bench. The proposed system has load following capability within certain motor speed, and its maximum thermal-electric energy conversion efficiency exceeds 20%. The dynamic charge amount control strategy is further proposed to improve efficiency. The maximum efficiency improvement is about 5% at 2kWe. The self-power-regulation and inherent passive safety of the reactor are verified through dynamic simulation. The power and temperature overshoots of the dynamic responses are selected as quantitative indicators of system dynamic performance. MAPs of the temperature and power overshoots for unit changes in output power are obtained, and can be used to evaluate the system safety during dynamic operations.

Transient temperature distribution in a multilayer semiconductor device with dynamic thermal load and non-uniform thermal contact resistance between layers

The thermal management challenge in microelectronic chips is exacerbated by their multilayer architecture and manufacturing processes that introduce non-uniform thermal contact resistance between adjacent layers. Most of the past work on development of thermal models to predict temperature distribution in microelectronic chips either does not account for such thermal contact resistance at all, or simply assumes it to be spatially uniform. This work presents an exact analytical solution for the transient temperature distribution in a multilayer chip with non-uniform thermal contact resistance between layers as well as dynamic, non-uniform heat generation. The problem is solved by first carrying out a Laplace transformation and then implementing a series solution, the coefficients of which are determined by solving a set of algebraic equations derived from the non-uniform thermal contact resistances between adjacent layers. While the problem is solved for a general M-layered chip, the solution for the practical case of a two-layer chip is also provided. Results indicate that the temperature distribution and its evolution over time is determined by the nature of the non-linear thermal contact resistance, and its overlap with the dynamic heat loads imposed on the chip. The impact of these and other relevant parameters is examined in detail. Results presented here improve the fundamental understanding of thermal transport modeling in multilayer semiconductor chips, with possible applications in other multilayer engineering systems as well.

Experimental study of performance enhancement strategies for hydrogen production-purification systems in packed-bed reactors under power fluctuations

Methanol reforming for hydrogen production and purification is a key technology in current fuel cell hydrogen source systems. The packed-bed reactor has a simple structure and is widely used, yet it has disadvantages such as slow dynamic response and limited heat and mass transfer. In this paper, an experimental approach is used to simulate the reaction characteristics of the packed bed during power fluctuation and start-up phase. It is found that the combined catalysts are the best in terms of both economical and purification effects, especially the precious metal combined copper-based catalysts. Meanwhile, the methanol conversion rate can seriously affect CO-PROX during the fuel cell start-up phase, and the use of combined catalysts can mitigate the impact of power fluctuation on the system and reduce the CO concentration. The combination of catalysts in such a way that the noble metal should be ensured in the front section, the optimal reaction temperature of copper-based combination noble metal-based catalysts is explored, with reforming temperature of 200 °C and CO-PROX temperature of 180–200 °C, and optimal O2/CO ratio between 0.5 and 1.5, when methanol conversion reaches more than 70%, CO concentration as low as 0.42% and hydrogen concentration higher than 40%.

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.

Differential heat transfer characteristics of coal macerals and their control mechanism: At the mesoscale

The dynamic heat transfer process of coal with different macroscopic types was characterized by a thermal imaging acquisition system, and the differential control mechanism of maceral composition and distribution on coal heat transfer was revealed. The results show that the temperature distribution in bright and dull coal samples are unimodal compared with the bimodal temperature distribution in semibright and semidull coal. With the extension of the heating time, the difference of the temperature distribution in the samples are first decreased, then increased and finally decreased. According to the evolutionary characteristics of the temperature difference, the heat transfer process can be divided into four stages: rapid temperature rise, slow down, fluctuating temperature rise and dynamic equilibrium. Inertinite is heated up faster, forming a high-temperature region, and vitrinite is heated slowly resulting in a low-temperature region. The temperature rise rate and equilibrium temperature in the low-temperature region are inversely proportional to the distance from the high-temperature region. It is difficult for vitrinite to heat up as vitrinite has the largest specific heat capacity and the smallest thermal conductivity and thermal diffusion coefficient. Therefore, the heat transfer capacity of vitrinite is generally weak, featured by a lower rate of temperature transfer disturbance.

Heating efficiency enhanced by combination of phase change materials and activated carbon for dry floor heating system

Phase change materials (PCMs) have diverse applications in energy storage, buildings, cooling, and heat exchangers. In this study, n-docosane and activated carbon (AC) were combined using the vacuum impregnation method to form an aggregate, which was then injected into a Poly vinyl chloride container and applied to a dry floor heating system. Thermal storage, gravimetric, conductivity, and specific heat analyses were performed to evaluate the thermal performance of n-docosane and AC-based heat-storage aggregate (D-HSA). The dynamic heat transfer performance and power consumption of the dry floor heating system after D-HSA application were then evaluated. Pure n-docosane and D-HSA showed latent heat capacities of 242.7 J/g and 235.1 J/g and 92.10 J/g and 92.66 J/g during heating and cooling. In terms of thermal durability, D-HSA was more stable than pure n-docosane. Thermal conductivity analysis revealed that D-HSA had a high thermal conductivity (approximately 597 %) in the liquid state. In the field-based dynamic heat transfer analysis experiment, the PCM dry floor heating system filled with D-HSA had the advantages of both dry and wet floor heating systems, namely, a fast surface temperature increase rate and the time-lag effect, respectively. Therefore, the PCM dry floor heating system can compensate for the disadvantages of the dry and wet floor heating systems and can be considered an efficient heating system in terms of energy savings.

Temporal design of flow intermittency in grooved channel for advanced heat transfer enhancement

The present numerical work is a continuing exploration of heat transfer enhancement by flow intermittency in grooved channels based on the energy buffer mechanism elucidated in our previous study, and aims to quantitatively optimize the time domain design of the intermittency pattern. The open-source computational fluid dynamics code OpenFOAM is employed to resolve the intermittent channel flow with triangular surface grooves. The main conclusion is that the optimal thermal performance is achieved when the time duration of each intermittency stage (acceleration, pulse-on, and deceleration) matches the characteristic time of flow dynamics (vortex development and heat transportation). The averaged surface Nusselt number is increased by 120% under the optimized intermittency pattern with the thermal performance factor reaching 1.9. The pulse-off stage of the flow intermittency expands further flexibility to meet diverse prerequisites in practical applications (constant coolant consumption, energy cost, or cooling capacity). By revealing the characteristic flow physics that governs the thermal performance of intermittent flow in grooved channels, the present work novelly proposes quantitative guidance on the temporal design of flow intermittency to achieve effective heat transfer enhancement.