The sample temperature and supersaturation are determined by the wall temperatures and the velocity profile. The plot shows contours of temperature (yellow) and SSw (red = water saturation, blue above, and green below). Thus, with the cold wall at -20C and the warm wall -7.5C, the sample is -15C and 0% supersaturation. Because the walls are vertical, there is a convective circulation, and the sample is slightly closer to the cold wall. The exact location is calculated by the data system computer in real time.
Note that at any one instant, the CFD is sampling at one temperature and one supersaturation. To cover a range of T or SS conditions, the wall temperatures are changed.
A similar plot for sampling at colder temperatures.