Study on the thermal characteristics and heat-insulation ability of gel-stabilized foam used for preventing the spontaneous combustion of coal

Gel-stabilized foam serves a critical role in preventing spontaneous combustion of coal by impeding heat transfer from the coal-fire area to adjacent safe areas. To elucidate the thermal characteristics of gel-stabilized foam, the microstructure and heat-transfer characteristics were investigated. The results revealed that gel-stabilized foam was an accumulation system of many stable and closed bubbles, and there was a layer of gel structure on the bubble surface. This gel layer endows the bubbles with exceptional heat-insulation capability by effectively encapsulating air. To further analyze the relationship of heat-transfer characteristics and foam structure parameters, a theoretical thermal-conductivity model was established to revel the thermal characteristics of gel-stabilized foam. Moreover, the experimental tests were conducted to verify the accuracy of theoretical model, and found that the fitting errors were around 8 %, affirming the model's suitability for gel-stabilized foam. Notably, the theoretical model demonstrated that foam's thermal-conductivity was only monotonically related to foam expansion ratios in theory. In addition, the heat-insulation experiments indicated that the heat-transfer rate of foam depended not only on the thermal-conductivity but also on the foam's stability, both of which were affected by the expansion ratio. Hence, the effective heat-insulation time (EHT) was proposed to assess gel-stabilized foam's heat-insulation characteristics. The heat-insulation ability tests results showed that EHT values initially increased and then decreased with rising foam expansion ratios, primarily influenced by the volume of air encapsulated within the foam. Particularly noteworthy were the test results indicating that gel-stabilized foam with an expansion ratio of 10 times and a stacking thickness of at least 15 cm exhibited excellent heat-insulation capability against heat transfer from the spontaneous combustion zones. The research may provide a theoretical foundation and offer guidance for the prospective utilization of gel-stabilized foam in coal mines.