Piston effect in supercritical nitrogen around the pseudo-critical line

The combination of very high thermal compressibility and small thermal diffusion near the critical points of fluids affects thermal energy propagation, leading to the formation of weak acoustic waves as carriers of thermal energy. This heat transfer phenomenon is called the piston effect. It has been reported that the piston effect appears near the critical point. In this study, the piston effect in supercritical nitrogen was investigated by use of a laser holography interferometer. Since natural convection due to gravity interferes with the piston effect under terrestrial conditions, we attempted to suppress the generation of natural convection by adding heat from the top of the experimental cell and successfully observed the typical temperature profiles formed by the piston effect around the pseudo-critical line. The pressure and the temperature are relatively higher than the critical pressure and the critical temperature.