查看更多>>摘要：Excellent thermal management is very significant in preserving lithium-ion battery cell work-performance and extending cell cycle-life. This work presents a method of thermal control for a large-scale pouch cell by using an existing liquid cooling plate with streamline channels. Numerically, influences of mass flow rates, cooling trigger-time, and glycol solution concentration on the cell thermal distribution are analyzed in detail. Experimentally, the simulation effectiveness is validated by a constructed thermal test system. It is shown that the increasing mass flow rate plays a positive role in crippling the cell temperature rise and difference. However, there is a marginal effect in this condition. Effect of postponing cooling trigger-time on promoting the cell thermal homogeneity is negative, when the cooling starts at 31 °C, the final cell temperature and temperature difference beyond 32 °C and 5 °C, respectively. The maximum cell temperature and channel pressure drop increase with increasing glycol solution concentration from 0 to 80%. Experimental validation suggests that the test and simulation results coincide with each other (within 2.5 °C), indicating that a promising availability dwells in present thermal management to manage the cell temperature field under a desirable range. This study would be valuable for one to develop a reliable cooling solution for a battery pack stacked with large-scale pouch cells.
查看更多>>摘要：Thermal runaway and its propagation are the technological barriers for the large-scale promotion of new energy vehicles and energy storage. This paper investigates the temperature characteristics between jelly rolls, influence of heating power on internal propagation time and energy flow during thermal runaway propagation through experiments and models. Results indicated that the maximum temperature between jelly rolls has a maximum temperature difference up to 487℃ compared to the surface temperature during thermal runaway. The distribution of energy flow showed that approximately 60% of total energy was used to self-heated and approximately 31% was emitted through venting. Experimental results and model calculation shows that the time it takes for thermal runaway to propagate within the Cell-to-Pack battery is affected by heating power. This study provides a reference for creating safe cell designs, developing mitigation strategies for addressing thermal runaway propagation in system, and investigating battery-related accidents in new energy vehicles and energy storage.
查看更多>>摘要：Gas turbine is a crucial power equipment around the world. Its inlet temperature increases year by year, bringing great challenges to the temperature resistance of turbine blades. Thus, exploring high-efficiency cooling structure is a must. In this paper, flow and heat transfer characteristics of a rotating rectangular smooth internal U-channel with orientation angles of 90° called Coriolis-utilization rotating rectangular smooth cooling U-channel have been numerically investigated by comparing with non-rotation smooth U-channel and conventional rotating smooth U-channel with Reynolds-Averaging Navier–Stokes (RANS) method. The Reynolds number kept constant at 10000. The Rotation number was between 0 and 0.1. The numerical method has been validated by experiment results. The results demonstrate that the Coriolis-utilization rotating U-channel not only utilizes the Coriolis force merit on the leading and trailing walls to strengthen heat transfer, but also performs lower pressure loss than the conventional rotating U-channel. Therefore, the Coriolis-utilization rotating U-channel is a promising internal cooling structure of rotor blade for higher inlet-temperature turbine in the future.
查看更多>>摘要：Absorption refrigeration can utilize low grade heat, but the application is limited by the huge system size and low energy efficiency. The mass transfer area of absorber occupies more than 50% of the whole system. The improvement absorption effect of the absorber is significant to reduce the system size and improve the energy efficiency ratio. A method to enhance the mass transfer in an ammonia-water falling absorber by implementing ultrasonic oscillators is proposed in this paper. A mathematical model of the absorber with the installing of oscillator is established. The solution of the model shows that the total mass transfer coefficient and the ammonia absorbed rate are increased by 22.53% and 20.25%, respectively, when the sound intensity at the surface of oscillator is 20 W/m2. The enhancement effect increases with oscillation output power, the ammonia absorbed rate increases by 31.2% when the sound intensity at the surface of oscillator is 50 W/m2.
查看更多>>摘要：Driving range has become one of the primary issues restricting the electric vehicle development, which requires more battery energy to be filled in the pack volume. However, it is challenging to continuously to enhance the specific energy of battery. Compact pack structure can further enhance the specific energy of the pack, such as the cell-to-pack (CTP) design. Compared with the traditional design structure, the CTP battery system omitted the small module components, which directly increased the volume energy density by 15%-20%, making an essential breakthrough in pack specific energy. The thermal performance of the CTP battery pack gradually emerged in applications. Thermal performance analysis for the CTP battery system has become a critical factor restricting the large-scale application. This paper carries out the primary work is for the digital twin modeling of the CTP battery system. An accurate thermal model of cells and the battery pack with a liquid plate structure is established based on measuring the heating characteristics and thermo-physical parameters. After calibration, the thermal model can not only predict the temperature response of CTP system under fast charging and cooling conditions, but also further guide the development of other battery systems. The calculation error of the CTP thermal model is controlled within ± 15% under various operations compared with the experimental results. The proposed thermal model synchronizes with the battery pack test, significantly enhances the efficiency of battery system design, providing guidance for the thermal characteristics analysis, design, and optimization of CTP pack thermal management systems.
查看更多>>摘要：The load tracking performance of combined cooling, heating and power multi-energy system (CCHP-MES) is greatly dependent on the system design, including system structure optimization and equipment capacity configuration. Conventional CCHP-MES design approach only considers the economic, environmental and efficiency performance, while the dynamic load tracking performance is underestimated. For this reason, this paper proposes a novel tracking ability index in the capacity configuration optimization of the CCHP-MES by comparing the closed-loop dynamic differences of the involved adjustable equipment. The rise time and overshoot of the equipment output are selected as dynamic characteristics evaluation parameters, and their product can reflect the load following performance quality of the CCHP-IES. The tracking ability index is then embedded into the capacity configuration optimization objective of the CCHP-MES, and a novel MES configuration model is proposed with integrated consideration of the economic benefits and transient load tracking ability. Case studies using typical electrical, thermal, cooling loads and renewable power data verify the efficacy of the optimization model in the planning and design of the CCHP-MES. Considering the load tracking ability of the MES in the configuration will significantly improve the load following performance of the CCHP-MES at the expense of the increased capital investment.
查看更多>>摘要：In this study, the Exergy analysis of the shell and helically coiled tube heat exchanger (SHCTHX) were investigated. The heat transfer Exergy loss of the SHCTHX implemented by MATLAB software was developed, where the dimensionless number named heat transfer Exergy loss number (ξHT) was proposed. The effect of parameters (core tube diameter (DC), space between the shell and the core tube (ΔDBC), inner diameter of coiled tube (di), thickness of the coiled tube (dt) and mass flow rate (Mshell)) on the effectiveness (ε), heat transfer Exergy loss number (ξHT) and number of transfer unit (NTU) were investigated. Moreover, the optimization of the SHCTHX was studied. When the design parameters are set as DC, ΔDBC, di, and dt, there is coincidently opposite variation trend for ξHT and ε, the optimization results of which are identical. When the design parameters are set as DC, ΔDBC, di, dt and Mshell, the effectiveness (ε) of optimization results with ξHT is 30% larger than that without ξHT; while the heat transfer area, the overall heat transfer coefficient, the needed mass flow rate and the heat transfer irreversible loss of optimization results with ξHT have reduction of 30%, 15%, 30% and 10% than those without ξHT.
查看更多>>摘要：The influence of heating equipment with low thermal conductivity, such as vacuum drying equipment and electric heating atomization systems, on the temperature distribution of heated objects is vital for structure design. The transient temperature of small heating equipment is difficult to obtain, particularly when the geometric size of the equipment is less than 0.1 m. Based on Fourier's law, a heat transfer model for a multilayer composite cylinder with porous media is established to solve this problem. The heat transfer of the porous media is simplified by the local heat balance assumption. An experiment is designed to validate the reliability of the model. The results of this study indicated that the temperature difference between the inner and outer parts of the composite cylinder with thermal conductivity is noticeable when heated by a centralized heat source. When the temperature of the centralized heat source is approximately 190 °C, the temperature difference between the inner and outer parts of the porous medium layer in the composite cylinder is approximately 50 °C. Moreover, when the temperature of the outer part of the porous medium layer in the composite cylinder is approximately 50 ℃, the temperature increased by approximately 1 °C for every 10 % decrease in the porosity. The centralized heat source cannot be used to uniformly heat a material with low heat transfer performance. Increasing the equivalent thermal conductivity of porous media materials or changing the heating structure can effectively improve this problem. Furthermore, the temperature distribution of the composite cylinder can be easily controlled by adjusting the temperatures of the surrounding and centralized heat sources. This study proposes a simple and accurate unsteady temperature prediction method for composite cylinders containing porous media. The temperature of the heating structure and the surrounding environment of the composite cylinder are obtained through simple experiments, and a theoretical model is used to predict the transient temperature of the composite cylinder during the heating process. Moreover, the influence of various factors affecting the heat source and heated object on the unsteady temperature of the composite cylinder with porous media is clarified. This new technology can solve the difficulty in measuring the temperature field of heating structures and heated objects in small heating equipment. This work can aid in the heat source design of small heating equipment.
查看更多>>摘要：A horizontal-well deep borehole closed-loop heat exchanger (DBHE) is presented in this paper, enlarging the heat transfer area by the horizontal section compared with the vertical well. Previous studies about DBHEs focused on vertical wells and few of them concerned horizontal wells and system efficiency. Then, a new 3D transient flow and heat transfer model is established. Temperature characteristics of the working fluid and formation are analyzed. System efficiency is introduced, and finally a comparison with vertical wells is carried out. The results show that under conditions in this paper, the temperature rising degree of the working fluid in the horizontal section is 2.67 times of that in the vertical. Geothermal water flow velocity can enhance heat convection obviously when it beyond a critical value. Horizontal length and flow rate are the vital factors of heat extraction. The outlet temperature rises about 2 °C by every 500 m horizontal length longer. Increasing horizontal length and flow rate have significant promotion in system efficiency and economy compared with the vertical well in a certain extent. The key results can provide guiding significance for design and retrofit of DBHEs.
查看更多>>摘要：Aimed at improving the combustion and thermal performance of micro combustor to increase energy output, a Y-shaped fin is designed to enhance the heat transfer. Firstly, the combustion and thermal performance of conventional micro combustor (MC), micro combustor embedded with straight fin (MCESF) and micro combustor embedded with Y-shaped fin (MCEYF) are compared. The results show that the embedding of Y-shaped fin improves the combustion and thermal performance obviously, especially MCEYF has the best comprehensive performance, meanwhile the mean outer wall temperature and the combustion efficiency are up to 1213.3 K and 99.14% at 5 m/s, which are significantly higher than MC and MCESF. Besides, a larger Y-shaped fin length is beneficial to fully enhance the heat transfer, but it directly destroys the temperature uniformity and consumes huge power due to the huge inlet pressure. Although the fin length of 12 mm brings an exergy up to 19.11 W, but the outer wall maximum temperature difference and inlet pressure have reached 181.38 K and 246.38 Pa, and Y-shaped fin with length of 8 mm maintains best comprehensive performance at 5 m/s. In addition, increasing the inlet velocity is conducive to improving the energy conversion, resulting in greater radiation energy and exergy, but it reduces the radiation efficiency and the exergy efficiency, meanwhile bring a huge pressure drop. Exergy increases from 13.68 W to 18.39 W with an inlet velocity from 3 m/s to 8 m/s, but the corresponding exergy efficiency decreases from 50.42% to 25.42%, and the low efficiency causes a large amount of energy to be lost as exhaust gas. Based on the analysis of the combustor material, high thermal conductivity material is beneficial to MTPV system energy conversion, and the combined use of multiple materials is worth considering. This study obtained the combustion and thermal characteristics under the action of Y-shaped fin, providing reference value for the energy conversion improvement of the micro thermo-photovoltaic system.
NSTL
Elsevier