"Cross Flow Fan", also known as through-flow fan, the 1892 French engineer Mortes (Mortier) first proposed multi-leaf impeller, long cylindrical shape, having a forward multi-wing blade. When the 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, non-steady gas flow velocity in the impeller there is a vortex, located near the center of the volute tongue. The existence of the vortex, the output of the impeller creates a circulating flow in the vortex, the air flow within the impeller line circular arc. Therefore, the impeller outer circumference of the flow rate at each point is inconsistent, closer to the vortex center, the greater the speed, the more close to the volute, the speed is smaller. Fan in the outlet air flow rate and pressure is not uniform, and thus the fan flow coefficient and pressure coefficient is an average value. Vortex position on the cross-flow fan performance is large, the vortex center close to the circumference of the volute tongue and close to the impeller, fan performance is better; from the center of the vortex vortex tongue far, the zone recycle stream is increased, reducing the efficiency of the fan, the flow is not increase the degree of stability.