Preliminary investigation of the capillary adsorption for a hollow waveguide based laser ammonia analyzer

摘要

Hollow Waveguide (HWG) is usually used as gas cell in a infrared gas sensor feathered with low-volume and high-sensitivity. However, the measured concentration is often distorted by the interference of the adsorption of gas molecules on the inner wall surface of the HWG This adsorption is a type of physical absorption called capillary adsorption, In order to correct this distortion, the characteristics of HWG adsorption of ammonia were investigated by using the laser analyzer itself under HWG heating-cooling process and various ammonia flow rate in the HWG The results showed that the readout of ammonia concentration increased by 17.8% when heating the HWG for no-flowing ammonia in the HWG, and the readout undergone a process of increase to fast decrease to slow increase when heating the HWG for flowing ammonia in the HWG at various flow rate. These surely come from the adsorption and desorption of ammonia on the inner wall surface of the HWG The preliminary investigation provides a quantitative readout distortion and a creditable evidence for further study about the adsorption of HWG.