微重力下热薄材料燃烧特性的窄通道实验研究

A Narrow Channel Experimental Study on Flammability Characteristics of Thermally Thin Fuels under Simulated Microgravity Conditions

利用高度分别为10mm,12mm和14mm的水平窄通道对微重力环境下热薄材料表面的火焰传播、材料的可燃极限进行了地面实验模拟研究。在环境氧气浓度为18%和21%,气流速度为0-50cm/s条件下,窄通道模拟实验结果与已有微重力实验结果的对比分析表明:气流速度小于15-20cm/s时,高度为12mm和14mm的窄通道能较好模拟微重力条件下材料表面的火焰传播,气流速度大于15-20cm/s时,高度为10mm的通道能较好模拟;高度为12mm和14mm的窄通道能够模拟热薄材料的可燃极限曲线,而高度为10mm的通道模拟的可燃极限曲线则出现一定偏差。分析认为,窄通道能够有效地限制浮力对流,进而提供模拟微重力条件下材料燃烧特性的实验环境,通道内的剩余浮力对流和通道壁面热损失可能是造成材料燃烧特性定量差别的主要原因。

The flame spread over thermally thin solid material surfaces and the flammability limits of such material have been experimentally investigated in narrow channels with height of 10 mm,12 mm and 14 mm,which are used to produce simulated microgravity conditions in laboratory. The experimental results under conditions of flow velocity of 0-50 cm/s and oxygen concentration of 18% and 21% are compared with those from previous tests conducted under the microgravity condition. For flow velocities less than 15-20 cm/s,flame spread characteristics under microgravity condition can be effectively reproduced in narrow channels of 12 mm and 14 mm height,moreover,for flow velocities greater than 15-20 cm/s,flame spread rates under the microgravity can well be simulated by flames spreading in the 10-mm-height channel. In narrow channels with height of 12 mm and 14 mm,the measured flammability map is found close to that obtained at microgravity,whereas the flammability boundary obtained in the 10-mm-height channel deviate from the microgravity case. The experiments show that the buoyant convection is suppressed to a great degree in narrow channels,consequently in which a simulated microgravity environment can be produced. The results also indicate some quantitative differences between observations under simulated and actual microgravity conditions,and these diversities in quantities may be attributed to the effects of residual buoyant convection in narrow channels and heat loss on channel walls.