Double ball "Axial Flow Fan", with the fan running conditions of heat and changed to slow speed operation, the fan will have less noise and consumes less energy. In most of the design requirements, the operating hours of the fan speed is lower than the air temperature is generally the maximum design temperature value. Under normal circumstances, low-speed operation "Axial Flow Fan" can be enough to complete its work. However, in the selection and installation should also be considered: first, the selected fan must be able to provide a sufficient amount of exhaust (rpm), under the high temperature conditions inside the hot-air cooling apparatus; when the hot gas temperature is relatively low and the comparison less time is to do the opposite of work. Secondly, the choice of the location of the sensor installation should pay attention to the sensor in the proper position, try to make the sensor can be clamped directly to the surface to be cooled. In operation, a temperature-controlled fan will operate at a faster rate if the temperature of the therm at a higher feeling; while at lower temperatures, will be running at a lower speed; these upper and lower middle, "Axial Flow Fan" speed is hardly changed with temperature. Fan slow temperature change, change the fan speed is slower, the speed of the fan will not suddenly change and noise. The reaction time depends mainly on the length of its heat-sensitive sensor sensitivity.