Cyclone or other element with spiral strip round central axis

摘要

The element has a spiral strip running round a central axis. This strip has upper and lower boundary surfaces which lie between inner and outer shell curves, the latter co-axial with the central axis. The boundary surfaces (20, 22) run on a spiral surface which is bounded by theoretical straight lines (30, 34). These lines are tangential to the shell curves (14, 24) and parallel to a plane (32) perpendicular to the central axis (32). The shell curves may be formed from cylindrical lateral areas. The imaginary straight lines of the upper boundary surface run anti-clockwise about the shell curves.