The use of mixed refrigerants offers several advantages in low-temperature applications. In mixed-refrigerant cycles, an optimized composition can significantly reduce the overall energy demand of the process. One critical property is the freezing point of the fluid, which defines the lowest temperature at which the mixture remains completely liquid and therefore usable in refrigeration processes. Due to freezing-point depression, the freezing point of eutectic mixtures lies below that of its pure components, allowing lower temperatures to be reached depending on the composition.  Accurate knowledge of this property is essential to prevent blockages in piping and the associated operational and safety risks. Furthermore, freezing-point data are essential for determining activity coefficients, which are a prerequisite for the accurate modeling of the real fluid behavior of mixtures.

In the future, three different methods for determining the freezing points of mixed refrigerants will be tested at the cryogenic phase equilibrium test stand CryoPHAEQTS. Two of these methods (visual observation and cooling‑curve analysis) are already well established. In addition, a promising new approach based on particle detection through light diffraction will be investigated and compared with the existing techniques.

To enable these measurements, the current equilibrium cell must be upgraded. The new cell will be manufactured from pure sapphire glass, allowing detection of diffracted light in both the forward and 90° directions. A magnetic stirrer will be integrated to reduce temperature gradients within the cell, thereby ensuring more homogeneous measurement conditions.