A Fresnel-reflection based fiber-optic sensor to study the low-temperature thermodynamics in fluidic mixtures

Abstract

Understanding the behaviour of electrolytic solutions at sub-zero temperatures reveals certain exotic processes. Fluid inclusions which reveal dissolution of two phases, that is ice and salt-hydrates, can only be interpreted in ternary water-salt system. We have developed a fiber-optic sensor based on Fresnel reflection phenomenon to study the phase changes in the mixture of H2O-NaCl-CaCl2 ternary system by cooling them using liquid nitrogen. This fluidic mixture exhibited the separation of antarcticite phase of CaCl2.6H2O at the eutectic temperature of about -51 °C and remained as an unfrozen metastable brine at -200 °C for few minutes before it consolidated into a dense solid. The sensor proved efficient in measuring accurate response which correspond to thermodynamic models in literature and the sensor offers multipoint measurements from remote locations.