Ceramic Fiber-Reinforced Polyimide Aerogel Composites with Improved Shape Stability against Shrinkage.

Polyimide (PI) aerogels, renowned for their nano-porous structure and exceptional performance across a spectrum of applications, often encounter significant challenges during fabrication, primarily due to severe shrinkage. In this study, we innovatively incorporated ceramic fibers of varying diameters into the PI aerogel matrix to enhance the shape stability against shrinkage. The structure of the resulting ceramic fiber-reinforced PI (CF-PI) aerogel composites as well as their performance in thermal decomposition, thermal insulation, and compression resistance were characterized. The results revealed that the CF-PI aerogel composites dried by supercritical ethanol achieved greatly reduced shrinkage as low as 5.0 vol.% and low thermal conductivity ranging from 31.2 mW·m-1·K-1 to 35.3 mW·m-1·K-1, showcasing their excellent performance in shape stability and thermal insulation. These composites also inherited the superior residue-forming ability of ceramic fibers and the robust mechanical attributes of PI, thereby exhibiting enhanced thermal stability and compression resistance. Besides, the effects of different drying conditions on the structure and properties of CF-PI aerogels were also discussed. The coupling use of supercritical ethanol drying with the addition of ceramic fibers is preferred. This preferred condition gives birth to low-shrinkage CF-PI aerogel composites, which also stand out for their integrated advantages include high thermal stability, low thermal conductivity, and high mechanical strength. These advantages attribute to CF-PI aerogel composites substantial potential for a wide range of applications, particularly as high-performance thermal insulation materials for extreme conditions.

Effects of liquid cooling garment on physiological and psychological strain of firefighter in hot and warm environments.

This study aimed to explore the effects of a liquid cooling garment on the physiological and psychological strains of firefighters. Twelve participants wearing firefighting protective equipment with the liquid cooling garment (LCG group) and without the liquid cooling garment (CON group) were recruited to conduct human trials in a climate chamber. During the trials, physiological parameters (mean skin temperature (Tsk), core temperature (Tc), and heart rate (HR)) and psychological parameters (thermal sensation vote (TSV), thermal comfort vote (TCV), and rating of perceived exertion (RPE)) were measured continuously. The heat storage, sweating loss, physiological strain index (PSI), and perceptual strain index (PeSI) were calculated. The results indicated that the liquid cooling garment decreased the mean skin temperature (maximum value of 0.62 °C), scapula skin temperature (maximum value of 1.90 °C), sweating loss (26%), and PSI (0.95 scales) with a significant difference (p < 0.05) at some time points when compared with the CON group. Moreover, the liquid cooling garment had little influence (p > 0.05) on core temperature, heart rate, TSV, TCV, RPE, and PeSI. The association analysis indicated that psychological strain had the potential to predict physiological heat strain with an R2 value of 0.86 between the PeSI and PSI. This study offers insights into the evaluation of cooling system performance, the design of next-generation cooling systems, and the improvement of firefighters' benefits.

Thermal insulation fibers with a Kevlar aerogel core and a porous Nomex shell.

Kevlar aerogel fibers which inherit the aerogel's brilliant properties of low density, high porosity and large surface area are promising candidates for thermal insulation applications in textiles. To enhance the mechanical strength of Kevlar aerogel fibers, an extra Nomex shell was introduced by a simple coaxial-wet-spinning approach. The resultant coaxial fibers were observed to have a Kevlar aerogel core and a porous Nomex shell. Besides, there also formed an air gap between the core and the shell. This multi-layered coaxial structure with numerous pores inside contributes to the excellent thermal insulation performance of the fibers and their fabrics. The temperature differences between the hot plate and the outer surface of the fabrics were measured to be as high as 80 °C when exposed to a temperature of 300 °C. In addition, these fibers also performed well in thermal stability, and almost did not decompose before 380 °C. Not only that, the breaking strength of the Nomex shell can be up to twice that of the Kevlar core, resulting in a significant improvement in the fiber's mechanical strength. It can be envisaged that the developed coaxial fibers with excellent thermal insulation and endurance properties as well as improved mechanical strength may have broad prospects for thermal insulation at high temperatures.

A novel microbial electrolysis cell-A/O system treating cotton dyeing pretreatment wastewater: performance and microbial diversity analysis.

The textile industry is developing rapidly in China. It generates large volumes of cotton dyeing pretreatment wastewater (CDPW). CDPW contains high concentrations of pollutants characterized by their strongly alkaline and recalcitrant nature for microbial degradation. This project aimed to evaluate the performance of a microbial electrolysis cell (MEC) coupled with anoxic/oxic (A/O) system (MEC-A/O) in treating CDPW, as well as analyze changes in microbial diversity. The results indicated that the effect of biological treatment in an electrolytic cell to treat CDPW was optimal at the voltage of 0.6V. The chemical oxygen demand (COD) removal efficiency under optimum conditions was 69.13%, higher than that of the A/O system alone (48.93%). Within a certain range, applied voltage was able to enhance microbial activity, increase the sludge concentration and enlarge the sludge particle size. At the same time, the applied voltage could effectively increase the abundance and the diversity of Bacteria and Archaea, as well as accelerate the degradation of pollutants.

Review on modeling heat transfer and thermoregulatory responses in human body.

Several mathematical models of human thermoregulation have been developed, contributing to a deep understanding of thermal responses in different thermal conditions and applications. In these models, the human body is represented by two interacting systems of thermoregulation: the controlling active system and the controlled passive system. This paper reviews the recent research of human thermoregulation models. The accuracy and scope of the thermal models are improved, for the consideration of individual differences, integration to clothing models, exposure to cold and hot conditions, and the changes of physiological responses for the elders. The experimental validated methods for human subjects and manikin are compared. The coupled method is provided for the manikin, controlled by the thermal model as an active system. Computational Fluid Dynamics (CFD) is also used along with the manikin or/and the thermal model, to evaluate the thermal responses of human body in various applications, such as evaluation of thermal comfort to increase the energy efficiency, prediction of tolerance limits and thermal acceptability exposed to hostile environments, indoor air quality assessment in the car and aerospace industry, and design protective equipment to improve function of the human activities.

Theoretical and experimental studies on the atmospheric degradation of 2-bromo-3,3,3-trifluoropropene.

As a new kind of Halon replacement, 2-bromo-3,3,3-trifluoropropene (2-BTP) is finding application as a fire extinguishing agent in confined spaces. For assessing its environmental impact, it is necessary to perform kinetic and product studies of its degradation in the atmospheric environment. In this sense, five possible reaction pathways between 2-BTP and OH radicals are found by Gaussian 03. Detailed analysis shows that the main product is the CF3CBrCH2OH radical, which may produce a series of compounds by further reaction with O2, NO, etc. In order to further prove the validity of the theoretical calculations and investigate the atmospheric transformation process of 2-BTP, atmospheric degradation of 2-BTP is then studied experimentally under controlled radiation conditions. Based on the theoretical analyses and experimental results, the atmospheric degradation mechanism of 2-BTP is finally proposed and detailed information on the atmospheric chemistry of 2-BTP is provided.