Abstract
This paper summarizes the direct observation of tagged hydroxyl within 200 µs after its formation in the temperature range of 294 K–891 K. We estimate the time and temperature frame of the coexistence of chemical reactions and diffusion based on analysis of the behavior of the tagging fluorescence spot of photodissociation hydroxyl. The reasons for the existence of chemical reactions and interactions between chemical reactions and diffusion are then analyzed. Theoretical and experimental identification of this frame can be explored for non-contact spectral measurements based on hydroxyl in a general flow field.
Highlights
Velocimetry measurements based on OH-tagging [hydroxy tagging velocimetry (HTV)] and temperature measurements based on OH-PLIF [planar laser-induced fluorescence (PLIF)] in the flow fields have been developed
We report the direct observation of OH photodissociation (OHp) using an intensified charge-coupled device (ICCD) in a special helium flow field with a small amount of water vapor
Our results indicate that the temperature dependence of the diffusion in the OHp-tagging fluorescence spot (TFS) cannot be identified because of chemical reactions
Summary
Hydroxyl (OH), which widely exists in the flow field, has become an important medium[1,2,3] for non-contact spectral measurements[4,5,6,7,8] of flow fields owing to its good fluorescence and tagging characteristics.[9,10,11] For example, velocimetry measurements based on OH-tagging [hydroxy tagging velocimetry (HTV)] and temperature measurements based on OH-PLIF [planar laser-induced fluorescence (PLIF)] in the flow fields have been developed. The concentration of OHp has a direct effect on temperature measurement precision and the diffusion rate of OHp on velocimetry measurement accuracy. It is precisely because OH is a free radical with strong activities and a short life.[14,15] for OHp in flow fields, chemical reactions and physical diffusion may coexist, even interact, unlike stable molecules where only diffusion exits.[16–34] for the research focusing on the diffusion process of OH,[35–37] it is difficult to provide a comprehensive reference for the flow field measurement based on the photodissociation of OH. The characteristic temperature dependence with diffusion was limited by chemical reactions, according to the area variation rate of the TFS
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