Detection of gaseous halocarbon refrigerants and extinguishing agent based on photoacoustic spectroscopy

Abstract

A photoacoustic (PA) gaseous halocarbon refrigerants and extinguishing agent detector based on a mid-infrared broadband source was developed. H1301 (extinguishing agent), R134a and R410A (refrigerants) were the target gases. A mid-infrared thermal radiation source radiated along the longitudinal direction of the cylindrical PA cell and was reflected by a gold-plated mirror to excite PA signals. The concentrations of CO2 and H2O were measured to reduce their interference. The PA signals of H1301, R134a, R410A, CO2 and H2O were excited by using a thermal radiation source with five different optical filters, respectively. The fundamental-frequency intensity modulation (1f-IM) technique was used to measure the generated PA signals. The detection limits (1σ) of H1301, R134a and R410A were 49 ppb, 80 ppb and 211 ppb with an average time of 100 s, respectively. According to the absorption spectrum of the three target gases, there are strong cross interference around the wavelength of 8.5 µm. By using the proposed calculation method to obtain the concentrations of the target gases, the high cross interference among these gases is reduced to less than 2 %.