The tests with N 2 did not produce any visual indication of the presence of fluid motion other than the decay of the buoyant flow present before the drop. Since N 2 is not a radiating gas, this is in accordance with the proposal outlined above. Figure 3 shows an interferometer image of the flow in SF 6 at 2 atm taken near the end of the drop test. The large deformation of the fringes in the right half of the frame denote a sharp density gradient and the presence of flow. Interferometer image of radiation-driven flow at g taken near end of drop period.
Fringes are parallel lines when no flow is present.
In fact, CO 2 tests and N 2 tests performed at the same Grashof number were noticeably different. Figures 4 and 5 show interferometer images from CO 2 and N 2 drop tests, respectively, taken near the end of the drop. The CO 2 image shows several regions where fringe deformation is significant, while in the N 2 test only minimal fringe deformation is observed. Interferometer image of radiation-driven flow at g taken near end of drop period. Interferometer image of decaying buoyant flow at g taken near end of drop period.