This study aims to investigate the non-ideal rupture mechanism of burst discs within an explosion shock tube and its impact on the propagation characteristics of shock waves within the tube. Gaining a comprehensive understanding of the complex dynamics involved in burst disc rupture and its effect on shock-wave propagation is essential for enhancing the safety and reliability of explosion simulation devices, such as explosion shock tubes. These devices are vital tools in explosion damage research.

This study was conducted using a 13-meter-long explosion shock tube under varying explosion intensity conditions. High-speed strain and dynamic pressure acquisition methods were employed to determine the rupture time and pressure peak values corresponding to different burst disc opening ratios. High-speed photography and the Schlieren method were employed to observe the impact of varying opening ratios on downstream shock-wave propagation. A theoretical analysis of shock-wave flows was performed to develop a semi-empirical model that captured the differences in the Mach number within the downstream pipeline for various burst disc opening ratios. Furthermore, the attenuation rate of the incident shock wave was analyzed. By integrating rigid body fixed-axis deflection theory with the Drewry model, a high-precision prediction model was established to accurately determine the burst disc rupture angle under instantaneous explosion loads.

The high-speed strain and overpressure measurements reveal that the burst disc rupture process unfolds in three distinct stages: the crack tip formation stage, petal evolution stage, and plastic completion stage. The crack tip formation stage plays a crucial role in affecting the pressure rise rate in the driving section. Meanwhile, the petal evolution and plastic completion stages determine the overpressure peak throughout the rest of the shock tube. Furthermore, a theoretical analysis of shock-wave flows leads to the development of a semi-empirical model describing the Mach number variations in the downstream pipeline corresponding to various burst disc opening ratios. By examining the attenuation rate of the incident shock in the experimental section, the propagation characteristics of shock waves are elucidated, leading to the construction of a quantitative model. The shock-wave attenuation rate transitions through three distinct phases. Initially, it increases gradually as the burst disc's petal evolution stage impedes the flow, affecting both shock-wave generation and propagation. Subsequently, when A_ratio surpasses 0.2, the attenuation rate rises sharply, owing to reduced obstruction from the disc and increased dynamic loads in the driver section, leading to intensified shock-wave decay. Furthermore, once A_ratio exceeds 0.5, the attenuation rate stabilizes, indicating a dynamic equilibrium in shock-wave attenuation, which remains unaffected by further changes in A_ratio. Finally, by integrating rigid body fixed-axis deflection theory with the Drewry model, a high-precision prediction model for the burst disc rupture angle under instantaneous explosion loads is established, considerably reducing the model's prediction error rate from 32.59% to 6.31%.

Overall, this study provides a robust experimental and theoretical framework for understanding the flow field evolution within a shock tube influenced by the non-ideal rupture effects of a burst disc. The findings substantially enhance the safety and reliability of explosion simulation devices, such as explosion shock tubes. The findings of this study have the potential to advance the structural design of explosion simulation devices and provide valuable insights into the evolution of flow fields influenced by non-ideal burst disc ruptures.

Firefighting suits worn by firefighters in high-temperature radiation environments, coupled with moderate physical exertion, can lead to body heat accumulation and increased microenvironment temperature inside the suits, which triggers adverse physiological reactions due to severe heat stress, resulting in decreased work efficiency, heat cramps, and other harms. Hence, cooling vests are widely used by firefighters to effectively alleviate heat stress in firefighting scenarios. However, most contemporary cooling vests encounter issues such as severe cold stress, short cooling duration, and poor comfort. Therefore, it is necessary to conduct research on the cooling performance of these vests.

The cooling effectiveness of three types of firefighter cooling vests was assessed using a thermal manikin system in an environmental chamber under the following conditions: temperatures of 35 ℃, 40 ℃, and 45 ℃ and directed thermal radiation of 1.5 and 2.5 kW/m², with low, moderate, and high levels of physical exertion. D1922L temperature sensors were deployed on the thermal manikin system to measure the temperatures of the outer, insulation, comfort, and inner layers of the cooling vest as well as the temperatures of the inner and outer layers of the firefighting suit.

The experiments reveal that the cooling vests effectively reduce the microenvironmental temperature inside the firefighting suit, with a temperature difference of 6.6 ℃ between the inner and outer layers of the firefighting suit after 200 min of exposure. The cooling effect is most pronounced in the abdominal area with direct radiation. Among the three types of cooling vests assessed, Cooling Vest 1 exhibits the best performance, achieving a cooling power of 4.097 W and a cooling duration exceeding 2 h. Meanwhile, Cooling Vest 3 has a relatively poor cooling performance, with a cooling power of 0.753 W and a cooling duration of 90 min. As the physical exertion levels increase, the cooling effect of the vests is less pronounced. The linear fitting slopes of the temperature variation curves for the manikin's abdominal areas at 65, 110, and 165 W/m² are 0.106 8, 0.273 4, and 0.508 6, respectively. Furthermore, the cooling performance of the vests diminishes with increasing environmental temperatures. At an environmental temperature of 45 ℃, the temperature gradients in the manikin's chest, shoulders, abdomen, and back areas increase by 50.0%, 40.6%, 60.0%, and 50.0%, respectively. Moreover, the directed thermal radiation has a significant impact on the cooling performance of the vests. The temperature of the manikin's chest area reaches 35.69 ℃ within only 7 min with a directed thermal radiation of 2.5 kW/m².

These research findings are anticipated to serve as the preliminary data to enable the determination of rational work durations and intensity. In real fire rescue scenarios, the distribution of phase change materials for heat storage over the chest area and the duration of high-intensity work should be carefully considered. Additionally, these findings provide technical support for the development, testing, and evaluation of personal thermal protective equipment.