"24V DC Cooling Fan", the fan has a long history. China in BC for many years had been to create a simple wooden windmill hulling, its action principle is basically the same with modern centrifugal fan. In 1862, "24V DC Cooling Fan" centrifugal fan British Guyana Bell invented, its impeller, housing concentric type chassis with brick, wood backward straight blade impeller, the efficiency is only about 40%, mainly for mine ventilation. In 1880, it devised volute casing "24V DC Cooling Fan" for mine blast in row, and backward curved centrifugal fan blades, the structure has been more perfect.