Temperature and size measurements of cryogenic spray droplets with global rainbow refractometry

In this study, global rainbow refractometry (GRR) is applied to investigate cryogenic spray droplets (i.e., liquid nitrogen, liquid oxygen, and liquid methane). The refractive index and droplet size probability distribution are retrieved from the global rainbow pattern with inversion methods, using the complex angular momentum (CAM) scattering theory. Results show that temperature retrieved from the rainbow signal agrees well with temperature measured by the thermocouple, with discrepancy less than 7.5% for test sprays at temperatures ranging from 80 to 110 K. The temperature measurement uncertainty of GRR is estimated to lie within 1.0 K. The temperature recorded by the thermocouple is corrected by taking account of the heat transfer effect, which causes a temperature deviation of about 10−²K. With Saengkaew's methods, the deduced droplet size distribution shows bimodal or even multimodal characteristics in the measurement volume. The present work demonstrates the application of the GRR technique to the cryogenic sprays.