The ornamental design for a portablefan, as shown and described.
FIG. 1 is a left side front perspective view of a portable fan showing my new design;
FIG. 2 is a left side rear perspective view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a rear elevation view thereof; and,
FIG. 7 is a top plan view thereof.
The broken line showing of a front grill, right and left side grills, left side controls and left side electrical outlets are included for the purpose of illustrating environmental structure and forms no part of the claimed design.