Through-flow fan known as "Cross Flow Fan", so refer to the same thing, just a different name! This through-flow fan is a 1892 French engineer Mortes (Mortier) first proposed multi-leaf impeller, long cylindrical shape, having a forward multi-wing blade. The structure as shown at right. "Cross Flow Fan" impeller rotates, air enters the open from the impeller cascade through the interior of the impeller, volute discharged from the other side of the cascade, forming working air flow. Air flow in the impeller flow situation is very complicated, "Cross Flow Fan" airflow velocity field is non-stable, in the impeller there is a vortex, located near the center of the volute tongue.