From the appearance to distinguish the inlet and outlet of the cooling fan can be judged by the following aspects:

1. Viewing mesh or filter: Air intakes are usually designed with mesh or filter to prevent dust and debris from entering the fan. These grids or filters are usually located on the front or side of the fan.

2. Observe the direction of the fan blades: The direction of the fan blades determines the air inlet and outlet directions of the fan. In general, the side of the blade facing the air inlet indicates that the side is the air inlet, and the side of the blade facing the air outlet indicates that the side is the air outlet.

3. Observe the logo or logo of the fan: Some cooling fans are marked with the corresponding logo or logo at the intake or outlet to indicate their function. For example, an INTAKE vent might be marked "IN" or "INTAKE", while an EXHAUST vent might be marked "OUT" or "EXHAUST".。

4. Observe the location and layout of the fan: Typically, the air inlet of the cooling fan is located on the front or side of the fan, while the air outlet is located on the back or top of the fan. By observing the positions and layout of fans, you can determine which side is the air intake and outlet.

It should be noted that there may be some differences between different brands and models of cooling fans, so the above method is only a general reference, and the specific situation needs to be judged according to the actual situation. If in doubt, refer to the fan's manual or consult the relevant professional.