The density wave stability boundary has been experimentally determined for super critical helium flowing in a long (L = 185 m), heated channel of high aspect ratio (L/d = 46 (10)4). A pressure drop ratio and the fluid expansion ratio correlate the oscillation inception point data. The growth of enthalpy (temperature) perturbations in a heated channel has been experimentally verified. During the density wave oscillation, the channel exit temperature and inlet mass flow were observed to be in phase, and the oscillation period was close to twice the fluid transit time. All three observations agree with a simple incompressible flow model. Oscillation amplitudes as great as 11 K and 100 percent of inlet flow were observed.

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