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168 results on '"Jin, Kaiqiang"'

36. Flame Acceleration and DDT in a Channel with Continuous Triangular Obstacles: Effect of Blockage Ratio.

Author

Li, Xiaoxi, Dong, Jizhou, Jin, Kaiqiang, Duan, Qiangling, Sun, Jinhua, and Xiao, Huahua

Subjects
FLAME, SPEED of sound, HIGH-speed photography, BOUNDARY layer (Aerodynamics), ENERGY dissipation, CELL size
Abstract

Experiments were conducted in a stoichiometric hydrogen-oxygen mixture at initial pressure of 1 atm to study the flame acceleration and deflagration-to-detonation transition (DDT) in a 20 mm high channel equipped with continuous triangular obstacles. Effect of blockage ratio (br) was explored by considering different obstacle heights of 0, 1 mm, 3 mm, 5 mm, and 7 mm, corresponding to br = 0, 0.1, 0.3, 0.5, and 0.7, respectively. High-speed schlieren photography and OH* chemiluminescence recording were used to visualize the processes. Results show that blockage ratio has a significant effect on the scales and velocities of the vortices generated in the gaps between neighboring obstacles and consequently on the subsequent flame-vortex interactions. Higher br leads to faster flame acceleration via stronger flame-vortex interactions. The intricate shock-flame interactions cause successive local explosions in the br = 0.3, 0.5, and 0.7 cases, creating conditions for DDT. An eventual choking regime occurs in the br = 0.7 case due to energy losses by continuous diffractions at the obstacle vertices. It was found that the onset of DDT is triggered when the critical height of the unobstructed passage is approximately greater than three detonation cell sizes. The mechanism of DDT changes as the br decreases. One important feature observed is that the br = 0.1 case has the shortest DDT distance. In addition, the final flame speed (~740 m/s, 1.4 times unburned sound speed) before DDT for br = 0.1 is significantly smaller than those (~1300 m/s, 2.4 times unburned sound speed) for br ≥ 0.3. The reason is that the low obstacles retain the characteristics of the obstacle, while mimicking the wall roughness, resulting in both shock compression of unburned gas and viscous heating in the boundary layer ahead of the flame front. The combined effects promote the occurrence of DDT for the case with br = 0.1. [ABSTRACT FROM AUTHOR]

Published
2024
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40. Investigation of gas diffusion behavior and detection of 86 Ah LiFePO4batteries in energy storage systems during thermal runaway

Author

Jia, Zhuangzhuang, Wang, Shuping, Qin, Peng, Li, Changhao, Jin, Kaiqiang, Sun, Jinhua, and Wang, Qingsong

Abstract

With the widespread use of lithium iron phosphate (LFP) batteries in electrochemical energy storage (EES) systems, gas diffusion and early detection during thermal runaway (TR) are receiving increasing attention. In this work, the gas diffusion behavior and detection of a single 86 Ah LFP battery at two levels of the EES system are systematically investigated by a combination of experiment and simulation during TR. The TR experiment of a single 86 Ah LFP battery is carried out for the battery pack and it is evident that H2diffusion is faster and earlier response than CO. The maximum concentrations of H2and CO outside the battery pack are 1493 and 802 ppm, respectively. The gas diffusion behavior inside the battery energy storage container is simulated, and it is found that the maximum concentrations of H2and CO are 618 and 412 ppm. Within 10 s after the safety venting, the gas diffusion behavior and detection are not affected by ventilation. However, during the later TR, the stable threshold of gas concentration under ventilation is much smaller than that without ventilation. The results can provide a theoretical guide in gas diffusion and detection, which is meaningful to the early warning and safe protection of EES systems.

Published
2024
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43. Ultra-effective room temperature gas discrimination based on monolithic Pd@MOF-derived porous nanocomposites: an exclusive scheme with photoexcitation.

Author

Duan, Peiyu, Wang, Haowen, Peng, Qingkui, Chen, Shiyao, Zhou, Hongmin, Duan, Qiangling, Jin, Kaiqiang, and Sun, Jinhua

Abstract

Chemiresistive sensing materials capable of efficiently identifying specific flammable gases are imperative. Although plenty of high-performance chemiresistive sensors have been developed in related fields, the high selectivity response to a single flammable gas at room temperature is still a great challenge. Conventional single chemiresistive metal oxide semiconductor materials exhibit similar response characteristics to flammable gases at high temperatures, while arrays are limited by high cost and miniaturization. Herein, the unique gas discrimination based on a monolithic MOF-derived chemiresistive sensor is achieved with photoexcitation at room temperature. 5.0Pd@ZnO exhibits a typical p-type semiconductor response (200 ppm, 52.89) to H2, while it displays a typical n-type semiconductor response to other flammable gases (CO, MeOH, EtOH, and H2S response of −25.15, −13.63, −49.92, and −40.36, respectively), which indicates that H2 can be fully identified merely from the original electrical signal. Meanwhile, the as-prepared sensors combined the advantages of MOF and MOS materials, and exhibited high linearity response, favorable repeatability, and long-term stability. The special response characteristics of the sensor to each flammable gas have been explored in detail, and the distinct effects of two different Pd surface states on gas molecules are discovered by DFT calculations. The mechanism of the high-selectivity response behavior at room temperature is systematically analyzed. This work provides a solid reference and feasible solution for the development of high-selectivity room temperature sensors. [ABSTRACT FROM AUTHOR]

Published
2024
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