  Room temperature compressed air was pumped into a short (H/D = 0.18) vortex
chamber. Experiments revealed temperature separation. The highest temperature
of the periphery was 465 degC, and the lowest temperature of the central zone
was -45 degC. During the process, heat was transferred to periphery in the
opposite direction of the powerful vortex flow. This heat transfer cannot be
explained by conventional heat transfer processes. To explain this phenomenon,
the concept of Pressure Gradient Waves (PGW) is proposed in the paper. PGW are
elastic waves which operate in compressible fluids with pressure gradients and
density fluctuations.
