Cavity "Waterproof Cooling Fan" box toward the positive direction of the thin air, completely closed in the opposite direction thick sheet metal wrapped after leaving a narrow gap in a circle, this gap is the outlet. Blade less fan out of the wind box airflow outlet slit from the base up, spread out the cavity filled "Waterproof Cooling Fan" wind box, it will accumulate to a certain extent than normal atmospheric pressure chamber in vitro, thus forming the wind. The rear end of the front end of a narrow cavity generous experience forced airflow inside the cavity toward the rear end of the broader movement, constantly "mutual squeeze" the air last only from a small slit in the "leak" out, "Waterproof Cooling Fan" continued after running for some time, this structure can gradually strengthen air pressure, resorted to vent air gap more quickly.