The ornamental design for a fan, as shown and described.
The design is for a fan used in a heat exchanger such as a radiator or an air conditioner capacitor.
FIG. 1 is a front view of the fan showing our new design:
FIG. 2 is a rear view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a top(plan) view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a front perspective view thereof.
The portion indicated by solid lines is the portion for which design registration as a partial design is requested.
The broken line showing of a heat exchanger is included for the purpose of illustrating environmental structure and forms no part of the claimed design.