"Cooling Fan Manufacturer" outlet appearance is a seemingly "stupid Meng," the great circle. However, the internal structure of a cavity with a special structure, rather than a simple solid metal box. Can be seen from the sectional view, "Cooling Fan Manufacturer" vent "cavity" portion toward the positive direction of the air is thin, and is completely closed. The opposite direction is thick and wrapped with a metal sheet leaving a narrow "gap" after lap, this "gap" is "the downwind." As the "blade less fan" of the "blade" is the horizontal rotation, "Cooling Fan Manufacturer" installed after the "outlet" completely unable to find outside. Over time, it was the people who know the truth falsely called "blade less fan."