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Thermal runaway propagation of the power battery pack is an essential factor affecting the safety of electric vehicles. The commonly adopted propagation inhibition methods mainly include adding heat insulation materials and enlarging battery spacing, which could cause problematic heat dissipation and lower the system energy density. Herein, an innovative battery thermal management system composed of non-uniform thermal conductivity phase change materials and assisted liquid cooling is proposed. Combining the phase change materials with high and low thermal conductivity balances heat transfer and heat insulation requirements. The cooling performance and the ability of thermal runaway propagation mitigation of the proposed schemes are numerically studied. The results show that the proposed strategy can meet the heat dissipation requirements under normal operation and control the thermal runaway in a safe range by transferring the heat generated from the battery thermal runaway in the set direction. The maximum battery temperature and the temperature difference are 38.1 °C and 2.1 °C, respectively, under 3C discharge. Under thermal runaway conditions, the strategy successful confines the thermal runaway propagation within the middle row. The maximum battery temperature in other rows can be controlled under the irreversible thermal runaway reaction temperature of 200 °C. Further study found that increased thermal conductivity benefits the battery heat dissipation and reduces the risk of thermal runaway. However, it propagates faster and broader once the thermal runaway is triggered. In comparison, the decrease of thermal conductivity is beneficial to the mitigation of propagation but may reduce the overall heat dissipation of the battery module. This study can provide a new way to solve the contradiction between battery temperature control and thermal runaway spread suppression. • An innovative strategy is proposed to mitigate thermal runaway propagation. • Non-uniform phase change materials with different thermal conductivity are adopted. • The thermal runaway generated heat can be limited to transfer in a specific direction. • A suitable combination of high and low thermal conductivity for PCM is necessary. • Temperature control and thermal runaway suppression can be achieved simultaneously. [ABSTRACT FROM AUTHOR]

The demand for high energy density in lithium-ion battery packs for electric vehicles poses a challenge to maintaining its optimum operating temperature while reducing the risk of thermal runaway (TR) propagation. This study proposes a novel hybrid TR propagation mitigation system that balances heat transfer and thermal insulation requirements using low and high thermal conductivity phase change materials (PCM), heat pipes (HP), and air-cooling. The design and optimization of such a mitigation system are complex due to the many design parameters involved. The Adaptive-Kriging-High dimensional model representation (Adaptive-Kriging-HDMR) is used to establish a surrogate model of the system, and the sensitivity of the system's design parameters is evaluated with the maximum battery temperature and the system weight as the targets, thereby improving the efficiency of model calculation and reducing the dimension of optimization parameters. Then, the design of the sensitive parameters is optimized using an extended elitist non‐dominated sorting genetic algorithm (E-NSGA-II) multi-objective optimization algorithm. The results show that the modeling difficulty and optimization calculation time are significantly reduced by using a surrogate model. The calculation time for a single surrogate model only takes a few seconds instead of several hours for the original three-dimensional heat transfer and flow calculation. The thermal conductivity of high thermal conductivity-PCM, the distance between battery and low thermal conductivity-PCM, the battery spacing, and the HP length significantly affect the system. The optimized system substantially reduces the overall weight of the battery system while ensuring its good heat dissipation capability. In the case of TR in a single battery, the system succeeds in limiting the TR propagation to the same row, with the maximum battery temperature in the second row being only 64.3 °C, well below the battery TR trigger point. Under more severe conditions, such as TR occurring in two batteries simultaneously, the maximum battery temperature in the second row is 155.5 °C, and no TR spreads to the adjacent row. This study provides a rapid and effective method for designing a TR propagation mitigation system. It can serve as a reference for the engineering design and optimization of battery thermal management systems. [ABSTRACT FROM AUTHOR]

Summary: With the increasing demand for the driving range of new energy vehicles, the energy of power battery is increasing. As a temperature‐sensitive component, the life, safety, and charge–discharge performance of lithium‐ion power battery will be affected by the working temperature, which makes the battery thermal management system particularly important. Concerning the fact that the thermal contact resistance between the power battery and the heat transfer components has become the bottleneck of battery thermal management system, this study firstly establishes a traditional sandwich structure of phase change material–based thermal management system and then try to reduce the thermal contact resistance of the system by increasing the thermal conductivity of the cooling part and filling the interface with high thermal conductivity material. The thermal contact resistance and the heat flux between the power battery and the thermal management module are experimentally tested and calculated. Based on the external and internal temperature of battery, the effect of contact resistance on the performance of a thermal management system is discussed. The results show that when increasing the thermal conductivity of the cooling part, the battery external and internal temperatures under 3C, 4C, and 5C discharge are reduced by 8.3%, 8.1%, 7.6% and 5.2%, 9.3%, 6.3%, respectively, as compared to the traditional sandwich structure of phase change material–based thermal management system. And the temperatures are further reduced by 6.5%, 7.7%, 6.3% and 7.8%, 6.1%, 7.3% when the interface between the battery and the thermal management module are filled with graphene with high thermal conductivity. Furthermore, the power battery can work within the optimum operating temperature range for a long period and can ensure battery safety by reducing the thermal contact resistance. [ABSTRACT FROM AUTHOR]

Plant roots release various organic materials that may modify soil structure and affect heat and mass transfer processes. The objective of this study was to determine the effects of a synthetic root exudate (SRE) on penetrometer resistance (PR), thermal conductivity (λ), hydraulic conductivity (k) and evaporation of water in a sandy soil. Soil samples, mixed with either distilled water or the SRE, were packed into columns at a designated bulk density and water content, and incubated for 7 days at 18°C. Soil PR, λ, k and evaporation rate were monitored during drying processes. Compared with those incubated with water, samples incubated with SRE had visible hyphae, greater PR (0.7–5.5 MPa in the water content range of 0.11 to 0.22 m3 m−3) and λ (0.2–0.7 W m−1 K−1 from 0.05 to 0.22 m3 m−3), and increased k in the wet region but decreased k in the dry region. SRE treatment also reduced the overall soil water evaporation rate and cumulative water loss. Analysis of X‐ray computed tomography (CT) scanning showed that the SRE‐treated samples had a greater proportion of small pores (<60 μm). These changes were attributed mainly to SRE‐stimulated microbial activities. Highlights: The effects of incubating a sandy soil with a synthetic root exudate (SRE) on soil physical properties and evaporation are examined.SRE incubation increased the fraction of small pores.SRE incubation increased soil penetrometer resistance and thermal conductivity.Soil hydraulic conductivity was increased in the wet region but was reduced in the dry region.SRE incubation reduced the overall evaporation rate and cumulative water loss. [ABSTRACT FROM AUTHOR]

• A simple model for penetrometer resistance is developed. • Input variables can be estimated from heat pulse and shear wave measurements. • Matric potential does not need to be measured to estimate penetrometer resistance. • Combined effects of compaction and drying are taken into account by the small strain shear modulus. • A method that could be used in the field is proposed. Continuous estimates of penetrometer resistance (Q) would be useful in root elongation and in soil management studies. However, penetrometers produce estimates of penetration resistance at discrete time points. In this paper, a method with the potential to provide continuous estimates of penetrometer resistance is developed. We use measurements of soil water content, shear wave velocity (V s) determined from piezo electric devices, and bulk density (ρ b) determined with the heat pulse (HP) method, to estimate penetrometer resistance. Soil samples of a loamy sand were packed into cylinders with axial pressures of 50, 100, and 200 kPa, and allowed to equilibrate at matric potentials of −2, −6, −10, −30, −100, −300, and −500 kPa. Thermal conductivity (λ), V s and Q were measured after equilibration. A λ -based approach was applied to estimate ρ b , and small strain shear modulus (G) was calculated from ρ b and V s. Our results confirmed a linear relationship between Q and G (where G = V s 2 ρ b), which provides a basis to estimate penetrometer data in the field using buried sensors and a physically based model. [ABSTRACT FROM AUTHOR]