Tunable diode laser absorption spectroscopy monitoring of the water vapor condensation process in the high-speed flow

Abstract In this work, non-invasive high-precision quantitative measurements of the water vapor condensation process have been carried out using tunable diode laser absorption spectroscopy at the sub-millisecond level. The high-speed condensation of water vapor is achieved by a self-designed rarefaction wave reflection system. Combined with different sizes of experimental cavities, the condensation process is realized at various time scales of sub-milliseconds (0.2–0.66 ms). The processes of temperature and water vapor content during the high-speed condensation are measured using the water vapor absorption spectra near 7168.437 cm −1 and 7185.597 cm −1 . The experimental results show that the hypervelocity expansion flow field generated by the experimental system demonstrates good uniformity and reaches a cooling rate of 10 5 K·s −1 , which has the same order as that of the supersonic nozzle. The condensation process is similar on different sub-millisecond timescales and the normalized temperature change curves are approximately the same. Moreover, the higher the water vapor content, the shorter the condensation time.