Numerical Simulation of Interaction between Large-Scale Congestion and Vent during the Natural Gas Explosion in a Kitchen

The influence of large-scale congestion on a confined natural gas explosion in a typical Chinese kitchen was studied using the computational fluid dynamics technology. It was found that opening the explosion venting surface promotes the development of turbulence, flame propagation velocity, and multipeak overpressure in the explosion flow field. Large-scale congestion can significantly strengthen the influence of the explosion venting surface on the flow field; the congestion and the explosion venting surface have a synergistic effect on the explosion flow field. At the moment of gas explosion, the flow fields in each area of the kitchen exhibit different distribution characteristics. A flow field near small-scale congestion is more likely to produce greater turbulence, combustion rate, and flame speed. The obstruction effect of large-scale congestion perpendicular to the flame propagation direction is dominant. The indoor flame propagation speed and overpressure development speed increase and the peak combustion rate and indoor peak overpressure decrease with an increase in obstacle blockage. Increases in the large-scale volume congestion rate and volume blockage in the kitchen induce changes in the indoor flame propagation mode and increase the external explosion overpressure. This paper investigated the correlation behavior between large-scale congestion and vent surface in a typical Chinese civil kitchen during natural gas explosion process and provided important support for understanding the mechanism of congestion on gas explosion process and the distribution of explosion hazards in a kitchen.

Microcrystalline cellulose treated by steam explosion and used for thermo-mechanical improvement of polypropylene

The use of cellulose fibers derived from renewable resources as reinforcement in polymeric composites provides positive environmental benefits with respect to disposal and raw material savings. Microcrystalline cellulose is a regenerated cellulose material that is free of lignin and hemicellulose, widely used in various applications. Recently, there has been enormous interest in producing polymer nanocomposites using cellulose nanofibers as reinforcement. Moreover, the steam explosion process is an ecofriendly method to modify cellulose fibers by inducing fibrillation, allowing the production of nanofibers. Fibrillation of microcrystalline cellulose using steam explosion process as the only cellulose treatment process was not yet studied in the literature. In the present work, steam explosion process was applied to commercial microcrystalline cellulose and the obtained fibers were characterized and employed in composites with polypropylene for evaluation of the thermal, mechanical, and morphological properties in relation to the matrix. The results showed that this process promoted partial fibrillation to nanosized diameter, and an increase in crystalline degree and thermal stability of the original fiber. As for the polypropylene/cellulose composites in the absence of compatibilizer, there was an increase of thermal degradation temperature and mechanical properties measured by dynamic-mechanical analysis in comparison with pure polypropylene.