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针对研制的基于非对称椭球聚光镜/气室的红外甲烷(CH4)检测系统,利用菲克第一定律,建立了用于分析仪器响应时间的数学模型,在CH4气体由椭球气室内向气室外扩散和由气室外向气室内扩散两种情况下,推导得到了气室中实时CH4浓度与响应时间的关系表达式,计算并分析了响应时间与气室结构参数、初始浓度以及目标浓度的关系。计算结果显示,仪器的10~90%的响应时间与气室的结构参数有关,而与气室内的初始浓度和目标浓度均无关。当长轴取为7.6cm、开孔直径分别为0.50cm和2.24cm时,计算得到的仪器响应时间约为9.42s。利用所制作的非对称椭球聚光镜/气室和CH4检测仪,分别测量了仪器的响应时间,仪器所处容器的浓度在0~10-4间变化时,其上升和下降时间分别为7.25s和9.00s;仪器所处容器的浓度在10-3~10-2间变化时,其上升和下降时间均约8.25s。由于实验条件未能较好满足菲克定律要求,实验结果和理论计算结果存在一定的差异。尽管如此,本文给出的分析理论和相关模型,在估算具有类似气室结构的检测仪响应时间方面具有应用价值。
Aiming at the infrared methane (CH4) detection system based on asymmetric ellipsoidal condenser / air chamber, a mathematical model for analyzing the response time of the instrument is established by using Fick’s first law. In the CH4 gas from the ellipsoidal chamber to the gas Outdoor diffusion and diffusion from the gas chamber to the gas chamber, the expression of the relationship between the real-time CH4 concentration and the response time in the gas chamber was deduced. The response time and the parameters of the gas chamber structure, the initial concentration and the target concentration were calculated and analyzed relationship. The calculation results show that the response time of 10 ~ 90% of the instrument is related to the structural parameters of the gas chamber, but not to the initial concentration and the target concentration in the gas chamber. When the long axis is taken as 7.6cm and the hole diameter is 0.50cm and 2.24cm respectively, the calculated instrument response time is about 9.42s. The asymmetric ellipsoidal condenser / gas chamber and CH4 detector were used to measure the response time of the instrument. The concentration of the vessel in the instrument varied from 0 to 10-4, and the rise and fall times were 7.25s And 9.00s; when the concentration of container in the instrument changes between 10-3 ~ 10-2, the rising and falling times are about 8.25s. Due to the experimental conditions failed to better meet the Fick’s law requirements, the experimental results and theoretical calculations there are some differences. Nevertheless, the analytical theory and related models presented in this paper have applications in estimating detector response times with similar gas cell structures.